# API

## Quantum-objects

### Types

- General basis types. Specialized bases can be found in the section API: Quantum-systems.

`QuantumInterface.Basis`

— TypeAbstract base class for all specialized bases.

The Basis class is meant to specify a basis of the Hilbert space of the studied system. Besides basis specific information all subclasses must implement a shape variable which indicates the dimension of the used Hilbert space. For a spin-1/2 Hilbert space this would be the vector `[2]`

. A system composed of two spins would then have a shape vector `[2 2]`

.

Composite systems can be defined with help of the `CompositeBasis`

class.

`QuantumInterface.GenericBasis`

— Type`GenericBasis(N)`

A general purpose basis of dimension N.

Should only be used rarely since it defeats the purpose of checking that the bases of state vectors and operators are correct for algebraic operations. The preferred way is to specify special bases for different systems.

`QuantumInterface.CompositeBasis`

— Type`CompositeBasis(b1, b2...)`

Basis for composite Hilbert spaces.

Stores the subbases in a vector and creates the shape vector directly from the shape vectors of these subbases. Instead of creating a CompositeBasis directly `tensor(b1, b2...)`

or `b1 ⊗ b2 ⊗ …`

can be used.

- States

`QuantumInterface.StateVector`

— TypeAbstract base class for `Bra`

and `Ket`

states.

The state vector class stores the coefficients of an abstract state in respect to a certain basis. These coefficients are stored in the `data`

field and the basis is defined in the `basis`

field.

`QuantumOpticsBase.Bra`

— Type`Bra(b::Basis[, data])`

Bra state defined by coefficients in respect to the basis.

`QuantumOpticsBase.Ket`

— Type`Ket(b::Basis[, data])`

Ket state defined by coefficients in respect to the given basis.

- General purpose operators. A few more specialized operators are implemented in API: Quantum-systems.

`QuantumInterface.AbstractOperator`

— TypeAbstract base class for all operators.

All deriving operator classes have to define the fields `basis_l`

and `basis_r`

defining the left and right side bases.

For fast time evolution also at least the function `mul!(result::Ket,op::AbstractOperator,x::Ket,alpha,beta)`

should be implemented. Many other generic multiplication functions can be defined in terms of this function and are provided automatically.

`QuantumOpticsBase.DataOperator`

— TypeAbstract type for operators with a data field.

This is an abstract type for operators that have a direct matrix representation stored in their `.data`

field.

`QuantumOpticsBase.Operator`

— Type`Operator{BL,BR,T} <: DataOperator{BL,BR}`

Operator type that stores the representation of an operator on the Hilbert spaces given by `BL`

and `BR`

(e.g. a Matrix).

`QuantumOpticsBase.DenseOperator`

— Function`DenseOperator(b1[, b2, data])`

Dense array implementation of Operator. Converts any given data to a dense `Matrix`

.

`QuantumOpticsBase.SparseOperator`

— Function`SparseOperator(b1[, b2, data])`

Sparse array implementation of Operator.

The matrix is stored as the julia built-in type `SparseMatrixCSC`

in the `data`

field.

`QuantumOpticsBase.LazyTensor`

— Type`LazyTensor(b1[, b2], indices, operators[, factor=1])`

Lazy implementation of a tensor product of operators.

The suboperators are stored in the `operators`

field. The `indices`

field specifies in which subsystem the corresponding operator lives. Note that these must be sorted. Additionally, a factor is stored in the `factor`

field which allows for fast multiplication with numbers.

`QuantumOpticsBase.LazySum`

— Type```
LazySum([Tf,] [factors,] operators)
LazySum([Tf,] basis_l, basis_r, [factors,] [operators])
LazySum(::Tuple, x::LazySum)
```

Lazy evaluation of sums of operators.

All operators have to be given in respect to the same bases. The field `factors`

accounts for an additional multiplicative factor for each operator stored in the `operators`

field.

The factor type `Tf`

can be specified to avoid having to infer it from the factors and operators themselves. All `factors`

will be converted to type `Tf`

.

The `operators`

will be kept as is. It can be, for example, a `Tuple`

or a `Vector`

of operators. Using a `Tuple`

is recommended for runtime performance of operator-state operations, such as simulating time evolution. A `Vector`

can reduce compile-time overhead when doing arithmetic on `LazySum`

s, such as summing many `LazySum`

s together.

To convert a vector-based `LazySum`

`x`

to use a tuple for operator storage, use `LazySum(::Tuple, x)`

.

`QuantumOpticsBase.LazyProduct`

— Type```
LazyProduct(operators[, factor=1])
LazyProduct(op1, op2...)
```

Lazy evaluation of products of operators.

The factors of the product are stored in the `operators`

field. Additionally a complex factor is stored in the `factor`

field which allows for fast multiplication with numbers.

- Time-dependent operators. See also Time-dependent operators.

`QuantumOpticsBase.AbstractTimeDependentOperator`

— Type`AbstractTimeDependentOperator{BL,BR} <: AbstractOperator{BL,BR}`

Abstract type providing a time-dependent operator interface. Time-dependent operators have internal "clocks" that can be addressed with `set_time!`

and `current_time`

. A shorthand `op(t)`

, equivalent to `set_time!(copy(op), t)`

, is available for brevity.

A time-dependent operator is always concrete-valued according to the current time of its internal clock.

`QuantumOpticsBase.TimeDependentSum`

— Type```
TimeDependentSum(lazysum, coeffs, init_time)
TimeDependentSum(::Type{Tf}, basis_l, basis_r; init_time=0.0)
TimeDependentSum([::Type{Tf},] [basis_l,] [basis_r,] coeffs, operators; init_time=0.0)
TimeDependentSum([::Type{Tf},] coeff1=>op1, coeff2=>op2, ...; init_time=0.0)
TimeDependentSum(::Tuple, op::TimeDependentSum)
```

Lazy sum of operators with time-dependent coefficients. Wraps a `LazySum`

`lazysum`

, adding a `current_time`

(or operator "clock") and a means of specifying time coefficients as functions of time (or numbers).

The coefficient type `Tf`

may be specified explicitly. Time-dependent coefficients will be converted to this type on evaluation.

- Super operators:

`QuantumOpticsBase.SuperOperator`

— Type`SuperOperator <: AbstractSuperOperator`

SuperOperator stored as representation, e.g. as a Matrix.

`QuantumOpticsBase.DenseSuperOperator`

— Function```
DenseSuperOperator(b1[, b2, data])
DenseSuperOperator([T=ComplexF64,], b1[, b2])
```

SuperOperator stored as dense matrix.

`QuantumOpticsBase.SparseSuperOperator`

— Function```
SparseSuperOperator(b1[, b2, data])
SparseSuperOperator([T=ComplexF64,], b1[, b2])
```

SuperOperator stored as sparse matrix.

### Functions

- Functions to generate general states, operators and super-operators

`QuantumOpticsBase.basisstate`

— Function`basisstate([T=ComplexF64, ]b, index)`

Basis vector specified by `index`

as ket state.

For a composite system `index`

can be a vector which then creates a tensor product state $|i_1⟩⊗|i_2⟩⊗…⊗|i_n⟩$ of the corresponding basis states.

`basisstate([T=ComplexF64,] b::ManyBodyBasis, occupation::Vector)`

Return a ket state where the system is in the state specified by the given occupation numbers.

`QuantumOpticsBase.sparsebasisstate`

— Function`sparsebasisstate([T=ComplexF64, ]b, index)`

Sparse version of `basisstate`

.

`QuantumInterface.identityoperator`

— Function```
identityoperator(a::Basis[, b::Basis])
identityoperator(::Type{<:AbstractOperator}, a::Basis[, b::Basis])
identityoperator(::Type{<:Number}, a::Basis[, b::Basis])
identityoperator(::Type{<:AbstractOperator}, ::Type{<:Number}, a::Basis[, b::Basis])
```

Return an identityoperator in the given bases. One can optionally specify the container type which has to a subtype of `AbstractOperator`

as well as the number type to be used in the identity matrix.

`QuantumOpticsBase.diagonaloperator`

— Function`diagonaloperator(b::Basis)`

Create a diagonal operator of type `SparseOperator`

.

`QuantumOpticsBase.randoperator`

— Function`randoperator([T=ComplexF64,] b1[, b2])`

Calculate a random unnormalized dense operator.

`QuantumOpticsBase.spre`

— Function`spre(op)`

Create a super-operator equivalent for right side operator multiplication.

For operators $A$, $B$ the relation

\[ \mathrm{spre}(A) B = A B\]

holds. `op`

can be a dense or a sparse operator.

`QuantumOpticsBase.spost`

— Function`spost(op)`

Create a super-operator equivalent for left side operator multiplication.

For operators $A$, $B$ the relation

\[ \mathrm{spost}(A) B = B A\]

holds. `op`

can be a dense or a sparse operator.

`QuantumOpticsBase.sprepost`

— Function`sprepost(op)`

Create a super-operator equivalent for left and right side operator multiplication.

For operators $A$, $B$, $C$ the relation

\[ \mathrm{sprepost}(A, B) C = A C B\]

holds. `A`

ond `B`

can be dense or a sparse operators.

`QuantumOpticsBase.liouvillian`

— Function`liouvillian(H, J; rates, Jdagger)`

Create a super-operator equivalent to the master equation so that $\dot ρ = S ρ$.

The super-operator $S$ is defined by

\[S ρ = -\frac{i}{ħ} [H, ρ] + \sum_i J_i ρ J_i^† - \frac{1}{2} J_i^† J_i ρ - \frac{1}{2} ρ J_i^† J_i\]

**Arguments**

`H`

: Hamiltonian.`J`

: Vector containing the jump operators.`rates`

: Vector or matrix specifying the coefficients for the jump operators.`Jdagger`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.

- As far as it makes sense the same functions are implemented for bases, states, operators and superoperators.

`QuantumInterface.samebases`

— Function`samebases(a, b)`

Test if two objects have the same bases.

`QuantumInterface.check_samebases`

— Function`check_samebases(a, b)`

Throw an `IncompatibleBases`

error if the objects don't have the same bases.

`QuantumInterface.@samebases`

— Macro`@samebases`

Macro to skip checks for same bases. Useful for `*`

, `expect`

and similar functions.

`QuantumInterface.multiplicable`

— Function`multiplicable(a, b)`

Check if two objects are multiplicable.

`QuantumInterface.check_multiplicable`

— Function`check_multiplicable(a, b)`

Throw an `IncompatibleBases`

error if the objects are not multiplicable.

`QuantumInterface.basis`

— Function`basis(a)`

Return the basis of an object.

If it's ambiguous, e.g. if an operator has a different left and right basis, an `IncompatibleBases`

error is thrown.

`QuantumInterface.dagger`

— Function`dagger(x)`

Hermitian conjugate.

`QuantumInterface.tensor`

— Function`tensor(x, y, z...)`

Tensor product of the given objects. Alternatively, the unicode symbol ⊗ (\otimes) can be used.

`QuantumInterface.projector`

— Method`projector(a::Ket, b::Bra)`

Projection operator $|a⟩⟨b|$.

`QuantumInterface.projector`

— Method`projector(a::Ket)`

Projection operator $|a⟩⟨a|$.

`QuantumInterface.projector`

— Method`projector(a::Bra)`

Projection operator $|a⟩⟨a|$.

`QuantumInterface.dm`

— Function`dm(a::StateVector)`

Create density matrix $|a⟩⟨a|$. Same as `projector(a)`

.

`LinearAlgebra.norm`

— Method`norm(x::StateVector)`

Norm of the given bra or ket state.

`LinearAlgebra.tr`

— Function`tr(x::AbstractOperator)`

Trace of the given operator.

`QuantumInterface.ptrace`

— Function`ptrace(a, indices)`

Partial trace of the given basis, state or operator.

The `indices`

argument, which can be a single integer or a vector of integers, specifies which subsystems are traced out. The number of indices has to be smaller than the number of subsystems, i.e. it is not allowed to perform a full trace.

`LinearAlgebra.normalize`

— Method`normalize(x::StateVector)`

Return the normalized state so that `norm(x)`

is one.

`LinearAlgebra.normalize`

— Method`normalize(op)`

Return the normalized operator so that its `tr(op)`

is one.

`LinearAlgebra.normalize!`

— Method`normalize!(x::StateVector)`

In-place normalization of the given bra or ket so that `norm(x)`

is one.

`LinearAlgebra.normalize!`

— Method`normalize!(op)`

In-place normalization of the given operator so that its `tr(x)`

is one.

`QuantumInterface.expect`

— Function`expect(index, op, state)`

If an `index`

is given, it assumes that `op`

is defined in the subsystem specified by this number.

`expect(op, state)`

Expectation value of the given operator `op`

for the specified `state`

.

`state`

can either be a (density) operator or a ket.

`QuantumInterface.variance`

— Function`variance(index, op, state)`

If an `index`

is given, it assumes that `op`

is defined in the subsystem specified by this number

`variance(op, state)`

Variance of the given operator `op`

for the specified `state`

.

`state`

can either be a (density) operator or a ket.

`QuantumInterface.embed`

— Function`embed(basis1[, basis2], operators::Dict)`

`operators`

is a dictionary `Dict{Vector{Int}, AbstractOperator}`

. The integer vector specifies in which subsystems the corresponding operator is defined.

`embed(basis1[, basis2], indices::Vector, operators::Vector)`

Tensor product of operators where missing indices are filled up with identity operators.

`embed(basis1[, basis2], indices::Vector, op::AbstractOperator)`

Embed operator acting on a joint Hilbert space where missing indices are filled up with identity operators.

```
embed(basis_l::SumBasis, basis_r::SumBasis,
index::Integer, operator)
```

Embed an operator defined on a single subspace specified by the `index`

into a `SumBasis`

.

```
embed(basis_l::SumBasis, basis_r::SumBasis,
indices, operator)
```

Embed an operator defined on multiple subspaces specified by the `indices`

into a `SumBasis`

.

```
embed(basis_l::SumBasis, basis_r::SumBasis,
indices, operators)
```

Embed a list of operators on subspaces specified by the `indices`

into a `SumBasis`

.

`QuantumInterface.permutesystems`

— Function`permutesystems(a, perm)`

Change the ordering of the subsystems of the given object.

For a permutation vector `[2,1,3]`

and a given object with basis `[b1, b2, b3]`

this function results in `[b2, b1, b3]`

.

`Base.exp`

— Method`exp(op::AbstractOperator)`

Operator exponential.

`LinearAlgebra.mul!`

— Function```
mul!(Y::DataOperator,A::AbstractOperator,B::DataOperator,alpha,beta) -> Y
mul!(Y::StateVector,A::AbstractOperator,B::StateVector,alpha,beta) -> Y
```

Fast in-place multiplication of operators/state vectors. Updates `Y`

as `Y = alpha*A*B + beta*Y`

. In most cases, the call gets forwarded to Julia's 5-arg mul! implementation on the underlying data. See also `LinearAlgebra.mul!`

.

- Conversion of operators

`QuantumOpticsBase.dense`

— Function`dense(op::AbstractOperator)`

Convert an arbitrary Operator into a `DenseOperator`

.

`SparseArrays.sparse`

— Method`sparse(op::AbstractOperator)`

Convert an arbitrary operator into a `SparseOperator`

.

- Time-dependent operators. See also Time-dependent operators.

`QuantumOpticsBase.current_time`

— Function`current_time(op::AbstractOperator)`

Returns the current time of the operator `op`

. If `op`

is not time-dependent, this throws an `ArgumentError`

.

`QuantumOpticsBase.set_time!`

— Function`set_time!(o::AbstractOperator, t::Number)`

Sets the clock of an operator (see `AbstractTimeDependentOperator`

). If `o`

contains other operators (e.g. in case `o`

is a `LazyOperator`

), recursively calls `set_time!`

on those.

This does nothing in case `o`

is not time-dependent.

`QuantumOpticsBase.time_shift`

— Function`time_shift(op::TimeDependentSum, t0)`

Shift (translate) a `TimeDependentSum`

`op`

forward in time (delaying its action) by `t0`

units, so that the coefficient functions of time `f(t)`

become `f(t-t0)`

. Return a new `TimeDependentSum`

.

`QuantumOpticsBase.time_stretch`

— Function`time_stretch(op::TimeDependentSum, Sfactor)`

Stretch (in time) a `TimeDependentSum`

`op`

by a factor of `Sfactor`

(making it 'longer'), so that the coefficient functions of time `f(t)`

become `f(t/Sfactor)`

. Return a new `TimeDependentSum`

.

`QuantumOpticsBase.time_restrict`

— Function```
time_restrict(op::TimeDependentSum, t_from, t_to)
time_restrict(op::TimeDependentSum, t_to)
```

Restrict a `TimeDependentSum`

`op`

to the time window `t_from <= t < t_to`

, forcing it to be exactly zero outside that range of times. If `t_from`

is not provided, it is assumed to be zero. Return a new `TimeDependentSum`

.

### Exceptions

`QuantumInterface.IncompatibleBases`

— TypeException that should be raised for an illegal algebraic operation.

## Quantum systems

### Fock

`QuantumInterface.FockBasis`

— Type`FockBasis(N,offset=0)`

Basis for a Fock space where `N`

specifies a cutoff, i.e. what the highest included fock state is. Similarly, the `offset`

defines the lowest included fock state (default is 0). Note that the dimension of this basis is `N+1-offset`

.

`QuantumOpticsBase.number`

— Method`number([T=ComplexF64,] b::FockBasis)`

Number operator for the specified Fock space with optional data type `T`

.

`QuantumOpticsBase.destroy`

— Method`destroy([T=ComplexF64,] b::FockBasis)`

Annihilation operator for the specified Fock space with optional data type `T`

.

`QuantumOpticsBase.create`

— Method`create([T=ComplexF64,] b::FockBasis)`

Creation operator for the specified Fock space with optional data type `T`

.

`QuantumOpticsBase.displace`

— Function`displace([T=ComplexF64,] b::FockBasis, alpha)`

Displacement operator $D(α)=\exp{\left(α\hat{a}^\dagger-α^*\hat{a}\right)}$ for the specified Fock space with optional data type `T`

, computed as the matrix exponential of finite-dimensional (truncated) creation and annihilation operators.

`QuantumOpticsBase.displace_analytical`

— Function`displace_analytical(alpha::Number, n::Integer, m::Integer)`

Get a specific matrix element of the (analytical) displacement operator in the Fock basis: `Dmn = ⟨n|D̂(α)|m⟩`

. The precision used for computation is based on the type of `alpha`

. If `alpha`

is a Float64, ComplexF64, or Int, the computation will be carried out at double precision.

```
displace_analytical(b::FockBasis, alpha::Number)
displace_analytical(::Type{T}, b::FockBasis, alpha::Number)
```

Get the "analytical" displacement operator, whose matrix elements match (up to numerical imprecision) those of the exact infinite-dimensional displacement operator. This is different to the result of `displace(..., alpha)`

, which computes the matrix exponential `exp(alpha * a' - conj(alpha) * a)`

using finite-dimensional (truncated) creation and annihilation operators `a'`

and `a`

.

`QuantumOpticsBase.displace_analytical!`

— Function`displace_analytical!(op, alpha::Number)`

Overwrite, in place, the matrix elements of the FockBasis operator `op`

, so that it is equal to `displace_analytical(eltype(op), basis(op), alpha)`

`QuantumOpticsBase.fockstate`

— Function`fockstate([T=ComplexF64,] b::FockBasis, n)`

Fock state $|n⟩$ for the specified Fock space.

`QuantumOpticsBase.coherentstate`

— Function`coherentstate([T=ComplexF64,] b::FockBasis, alpha)`

Coherent state $|α⟩$ for the specified Fock space.

`QuantumOpticsBase.coherentstate!`

— Function`coherentstate!(ket::Ket, b::FockBasis, alpha)`

Inplace creation of coherent state $|α⟩$ for the specified Fock space.

`QuantumOpticsBase.squeeze`

— Function`squeeze([T=ComplexF64,] b::FockBasis, z)`

Squeezing operator $S(z)=\exp{\left(\frac{z^*\hat{a}^2-z\hat{a}^{\dagger2}}{2}\right)}$ for the specified Fock space with optional data type `T`

, computed as the matrix exponential of finite-dimensional (truncated) creation and annihilation operators.

### Phase space

`QuantumOpticsBase.qfunc`

— Function```
qfunc(a, α)
qfunc(a, x, y)
qfunc(a, xvec, yvec)
```

Husimi Q representation $⟨α|ρ|α⟩/π$ for the given state or operator `a`

. The function can either be evaluated on one point α or on a grid specified by the vectors `xvec`

and `yvec`

. Note that conversion from `x`

and `y`

to `α`

is done via the relation $α = \frac{1}{\sqrt{2}}(x + i y)$.

`QuantumOpticsBase.wigner`

— Function```
wigner(a, α)
wigner(a, x, y)
wigner(a, xvec, yvec)
```

Wigner function for the given state or operator `a`

. The function can either be evaluated on one point α or on a grid specified by the vectors `xvec`

and `yvec`

. Note that conversion from `x`

and `y`

to `α`

is done via the relation $α = \frac{1}{\sqrt{2}}(x + i y)$.

`QuantumOpticsBase.coherentspinstate`

— Function`coherentspinstate(b::SpinBasis, θ::Real, ϕ::Real)`

A coherent spin state |θ,ϕ⟩ is analogous to the coherent state of the linear harmonic oscillator. Coherent spin states represent a collection of identical two-level systems and can be described by two angles θ and ϕ (although this parametrization is not unique), similarly to a qubit on the Bloch sphere.

`QuantumOpticsBase.qfuncsu2`

— Function```
qfuncsu2(ket,Ntheta;Nphi=2Ntheta)
qfuncsu2(rho,Ntheta;Nphi=2Ntheta)
```

Husimi Q SU(2) representation $⟨θ,ϕ|ρ|θ,ϕ⟩/π$ for the given state.

The function calculates the SU(2) Husimi representation of a state on the generalised bloch sphere (0 < θ < π and 0 < ϕ < 2 π) with a given resolution `(Ntheta, Nphi)`

.

```
qfuncsu2(rho,θ,ϕ)
qfuncsu2(ket,θ,ϕ)
```

This version calculates the Husimi Q SU(2) function at a position given by θ and ϕ.

`QuantumOpticsBase.wignersu2`

— Function```
wignersu2(ket,Ntheta;Nphi=2Ntheta)
wignersu2(rho,Ntheta;Nphi=2Ntheta)
```

Wigner SU(2) representation for the given state with a resolution `(Ntheta, Nphi)`

.

The function calculates the SU(2) Wigner representation of a state on the generalised bloch sphere (0 < θ < π and 0 < ϕ < 2 π) with a given resolution by decomposing the state into the basis of spherical harmonics.

```
wignersu2(rho,θ,ϕ)
wignersu2(ket,θ,ϕ)
```

This version calculates the Wigner SU(2) function at a position given by θ and ϕ

`QuantumOptics.ylm`

— Function`ylm(l::Integer,m::Integer,theta::Real,phi::Real)`

Spherical harmonics Y(l,m)(θ,ϕ) where l ∈ N, m = -l,-l+1,...,l-1,l, θ ∈ [0,π], and ϕ ∈ [0,2π).

This function calculates the value of Y(l,m) spherical harmonic at position θ and ϕ.

### N-level

`QuantumInterface.NLevelBasis`

— Type`NLevelBasis(N)`

Basis for a system consisting of N states.

`QuantumOpticsBase.transition`

— Method`transition([T=ComplexF64,] b::NLevelBasis, to::Integer, from::Integer)`

Transition operator $|\mathrm{to}⟩⟨\mathrm{from}|$.

`QuantumOpticsBase.nlevelstate`

— Function`nlevelstate([T=ComplexF64,] b::NLevelBasis, n::Integer)`

State where the system is completely in the n-th level.

### Spin

`QuantumInterface.SpinBasis`

— Type`SpinBasis(n)`

Basis for spin-n particles.

The basis can be created for arbitrary spinnumbers by using a rational number, e.g. `SpinBasis(3//2)`

. The Pauli operators are defined for all possible spin numbers.

`QuantumOpticsBase.sigmax`

— Function`sigmax([T=ComplexF64,] b::SpinBasis)`

Pauli $σ_x$ operator for the given Spin basis.

`QuantumOpticsBase.sigmay`

— Function`sigmay([T=ComplexF64,] b::SpinBasis)`

Pauli $σ_y$ operator for the given Spin basis.

`QuantumOpticsBase.sigmaz`

— Function`sigmaz([T=ComplexF64,] b::SpinBasis)`

Pauli $σ_z$ operator for the given Spin basis.

`QuantumOpticsBase.sigmap`

— Function`sigmap([T=ComplexF64,] b::SpinBasis)`

Raising operator $σ_+$ for the given Spin basis.

`QuantumOpticsBase.sigmam`

— Function`sigmam([T=ComplexF64,] b::SpinBasis)`

Lowering operator $σ_-$ for the given Spin basis.

`QuantumOpticsBase.spinup`

— Function`spinup([T=ComplexF64,] b::SpinBasis)`

Spin up state for the given Spin basis.

`QuantumOpticsBase.spindown`

— Function`spindown([T=ComplexF64], b::SpinBasis)`

Spin down state for the given Spin basis.

### Particle

`QuantumOpticsBase.PositionBasis`

— Type```
PositionBasis(xmin, xmax, Npoints)
PositionBasis(b::MomentumBasis)
```

Basis for a particle in real space.

For simplicity periodic boundaries are assumed which means that the rightmost point defined by `xmax`

is not included in the basis but is defined to be the same as `xmin`

.

When a `MomentumBasis`

is given as argument the exact values of $x_{min}$ and $x_{max}$ are due to the periodic boundary conditions more or less arbitrary and are chosen to be $-\pi/dp$ and $\pi/dp$ with $dp=(p_{max}-p_{min})/N$.

`QuantumOpticsBase.MomentumBasis`

— Type```
MomentumBasis(pmin, pmax, Npoints)
MomentumBasis(b::PositionBasis)
```

Basis for a particle in momentum space.

For simplicity periodic boundaries are assumed which means that `pmax`

is not included in the basis but is defined to be the same as `pmin`

.

When a `PositionBasis`

is given as argument the exact values of $p_{min}$ and $p_{max}$ are due to the periodic boundary conditions more or less arbitrary and are chosen to be $-\pi/dx$ and $\pi/dx$ with $dx=(x_{max}-x_{min})/N$.

`QuantumOpticsBase.spacing`

— Function`spacing(b::PositionBasis)`

Difference between two adjacent points of the real space basis.

`spacing(b::MomentumBasis)`

Momentum difference between two adjacent points of the momentum basis.

`QuantumOpticsBase.samplepoints`

— Function`samplepoints(b::PositionBasis)`

x values of the real space basis.

`samplepoints(b::MomentumBasis)`

p values of the momentum basis.

`Base.position`

— Method`position([T=ComplexF64,] b::PositionBasis)`

Position operator in real space.

`Base.position`

— Method`position([T=ComplexF64,] b:MomentumBasis)`

Position operator in momentum space.

`QuantumOpticsBase.momentum`

— Method`momentum([T=ComplexF64,] b::PositionBasis)`

Momentum operator in real space.

`QuantumOpticsBase.momentum`

— Method`momentum([T=ComplexF64,] b:MomentumBasis)`

Momentum operator in momentum space.

`QuantumOpticsBase.potentialoperator`

— Function`potentialoperator([T=Float64,] b::PositionBasis, V(x))`

Operator representing a potential $V(x)$ in real space.

`potentialoperator([T=ComplexF64,] b::MomentumBasis, V(x))`

Operator representing a potential $V(x)$ in momentum space.

`potentialoperator([T=Float64,] b::CompositeBasis, V(x, y, z, ...))`

Operator representing a potential $V$ in more than one dimension.

**Arguments**

`b`

: Composite basis consisting purely either of`PositionBasis`

or`MomentumBasis`

. Note, that calling this with a composite basis in momentum space might consume a large amount of memory.`V`

: Function describing the potential. ATTENTION: The number of arguments accepted by`V`

must match the spatial dimension. Furthermore, the order of the arguments has to match that of the order of the tensor product of bases (e.g. if`b=bx⊗by⊗bz`

, then`V(x,y,z)`

).

`QuantumOpticsBase.gaussianstate`

— Function```
gaussianstate([T=ComplexF64,] b::PositionBasis, x0, p0, sigma)
gaussianstate([T=ComplexF64,] b::MomentumBasis, x0, p0, sigma)
```

Create a Gaussian state around `x0`

and`p0`

with width `sigma`

.

In real space the gaussian state is defined as

\[\Psi(x) = \frac{1}{\pi^{1/4}\sqrt{\sigma}} e^{i p_0 (x-\frac{x_0}{2}) - \frac{(x-x_0)^2}{2 \sigma^2}}\]

and is connected to the momentum space definition

\[\Psi(p) = \frac{\sqrt{\sigma}}{\pi^{1/4}} e^{-i x_0 (p-\frac{p_0}{2}) - \frac{1}{2}(p-p_0)^2 \sigma^2}\]

via a Fourier-transformation

\[\Psi(p) = \frac{1}{\sqrt{2\pi}} \int_{-\infty}^{\infty} e^{-ipx}\Psi(x) \mathrm{d}x\]

The state has the properties

- $⟨p⟩ = p_0$
- $⟨x⟩ = x_0$
- $\mathrm{Var}(x) = \frac{σ^2}{2}$
- $\mathrm{Var}(p) = \frac{1}{2 σ^2}$

Due to the numerically necessary discretization additional scaling factors $\sqrt{Δx}$ and $\sqrt{Δp}$ are used so that $\langle x_i|Ψ\rangle = \sqrt{Δ x} Ψ(x_i)$ and $\langle p_i|Ψ\rangle = \sqrt{Δ p} Ψ(p_i)$ so that the resulting Ket state is normalized.

`QuantumOpticsBase.FFTOperator`

— Type`FFTOperator`

Abstract type for all implementations of FFT operators.

`QuantumOpticsBase.FFTOperators`

— Type`FFTOperators`

Operator performing a fast fourier transformation when multiplied with a state that is a Ket or an Operator.

`QuantumOpticsBase.FFTKets`

— Type`FFTKets`

Operator that can only perform fast fourier transformations on Kets. This is much more memory efficient when only working with Kets.

`QuantumOpticsBase.transform`

— Function```
transform(b1::MomentumBasis, b2::PositionBasis)
transform(b1::PositionBasis, b2::MomentumBasis)
```

Transformation operator between position basis and momentum basis.

`transform(b1::CompositeBasis, b2::CompositeBasis)`

Transformation operator between two composite bases. Each of the bases has to contain bases of type PositionBasis and the other one a corresponding MomentumBasis.

```
transform([S=ComplexF64, ]b1::PositionBasis, b2::FockBasis; x0=1)
transform([S=ComplexF64, ]b1::FockBasis, b2::PositionBasis; x0=1)
```

Transformation operator between position basis and fock basis.

The coefficients are connected via the relation

\[ψ(x_i) = \sum_{n=0}^N ⟨x_i|n⟩ ψ_n\]

where $⟨x_i|n⟩$ is the value of the n-th eigenstate of a particle in a harmonic trap potential at position $x$, i.e.:

\[⟨x_i|n⟩ = π^{-\frac{1}{4}} \frac{e^{-\frac{1}{2}\left(\frac{x}{x_0}\right)^2}}{\sqrt{x_0}} \frac{1}{\sqrt{2^n n!}} H_n\left(\frac{x}{x_0}\right)\]

### Subspace bases

`QuantumOpticsBase.SubspaceBasis`

— Type`SubspaceBasis(basisstates)`

A basis describing a subspace embedded a higher dimensional Hilbert space.

`QuantumOpticsBase.orthonormalize`

— Function`orthonormalize(b::SubspaceBasis)`

Orthonormalize the basis states of the given `SubspaceBasis`

A modified Gram-Schmidt process is used.

`QuantumInterface.projector`

— Method`projector([T,] b1, b2)`

Projection operator between subspaces and superspaces or between two subspaces.

`QuantumOpticsBase.sparseprojector`

— Function`sparseprojector([T,] b1, b2)`

Sparse version of `projector`

.

### Many-body

`QuantumOpticsBase.ManyBodyBasis`

— Type`ManyBodyBasis(b, occupations)`

Basis for a many body system.

The basis has to know the associated one-body basis `b`

and which occupation states should be included. The occupations_hash is used to speed up checking if two many-body bases are equal.

`QuantumOpticsBase.fermionstates`

— Function```
fermionstates(Nmodes, Nparticles)
fermionstates(b, Nparticles)
```

Generate all fermionic occupation states for N-particles in M-modes. `Nparticles`

can be a vector to define a Hilbert space with variable particle number.

`QuantumOpticsBase.bosonstates`

— Function```
bosonstates(Nmodes, Nparticles)
bosonstates(b, Nparticles)
```

Generate all bosonic occupation states for N-particles in M-modes. `Nparticles`

can be a vector to define a Hilbert space with variable particle number.

`QuantumOpticsBase.number`

— Method`number([T=ComplexF64,] b::ManyBodyBasis, index)`

Particle number operator for the i-th mode of the many-body basis `b`

.

`QuantumOpticsBase.number`

— Method`number([T=ComplexF64,] b::ManyBodyBasis)`

Total particle number operator.

`QuantumOpticsBase.destroy`

— Method`destroy([T=ComplexF64,] b::ManyBodyBasis, index)`

Annihilation operator for the i-th mode of the many-body basis `b`

.

`QuantumOpticsBase.create`

— Method`create([T=ComplexF64,] b::ManyBodyBasis, index)`

Creation operator for the i-th mode of the many-body basis `b`

.

`QuantumOpticsBase.transition`

— Method`transition([T=ComplexF64,] b::ManyBodyBasis, to, from)`

Operator $|\mathrm{to}⟩⟨\mathrm{from}|$ transferring particles between modes.

`QuantumOpticsBase.manybodyoperator`

— Function`manybodyoperator(b::ManyBodyBasis, op)`

Create the many-body operator from the given one-body operator `op`

.

The given operator can either be a one-body operator or a two-body interaction. Higher order interactions are at the moment not implemented.

The mathematical formalism for the one-body case is described by

\[X = \sum_{ij} a_i^† a_j ⟨u_i| x | u_j⟩\]

and for the interaction case by

\[X = \sum_{ijkl} a_i^† a_j^† a_k a_l ⟨u_i|⟨u_j| x |u_k⟩|u_l⟩\]

where $X$ is the N-particle operator, $x$ is the one-body operator and $|u⟩$ are the one-body states associated to the different modes of the N-particle basis.

`QuantumOpticsBase.onebodyexpect`

— Function`onebodyexpect(op, state)`

Expectation value of the one-body operator `op`

in respect to the many-body `state`

.

## Direct sum

`QuantumInterface.SumBasis`

— Type`SumBasis(b1, b2...)`

Similar to `CompositeBasis`

but for the `directsum`

(⊕)

`QuantumInterface.directsum`

— Function`directsum(b1::Basis, b2::Basis)`

Construct the `SumBasis`

out of two sub-bases.

`directsum(x::DataOperator, y::DataOperator)`

Compute the direct sum of two operators. The result is an operator on the corresponding `SumBasis`

.

`QuantumOpticsBase.LazyDirectSum`

— Type`LazyDirectSum <: AbstractOperator`

Lazy implementation of `directsum`

`QuantumOpticsBase.getblock`

— Function`getblock(op::Operator{<:SumBasis,<:SumBasis}, i, j)`

Get the sub-basis operator corresponding to the block `(i,j)`

of `op`

.

`QuantumOpticsBase.setblock!`

— Function`setblock!(x::Ket{<:SumBasis}, val::Ket, i)`

Set the data of `x`

on the ith sub-basis equal to the data of `val`

.

`setblock!(op::DataOperator{<:SumBasis,<:SumBasis}, val::DataOperator, i, j)`

Set the data of `op`

corresponding to the block `(i,j)`

equal to the data of `val`

.

## Metrics

`QuantumOpticsBase.tracenorm`

— Function`tracenorm(rho)`

Trace norm of `rho`

.

It is defined as

\[T(ρ) = Tr\{\sqrt{ρ^† ρ}\}.\]

Depending if `rho`

is hermitian either `tracenorm_h`

or `tracenorm_nh`

is called.

`QuantumOpticsBase.tracenorm_h`

— Function`tracenorm_h(rho)`

Trace norm of `rho`

.

It uses the identity

\[T(ρ) = Tr\{\sqrt{ρ^† ρ}\} = \sum_i |λ_i|\]

where $λ_i$ are the eigenvalues of `rho`

.

`QuantumOpticsBase.tracenorm_nh`

— Function`tracenorm_nh(rho)`

Trace norm of `rho`

.

Note that in this case `rho`

doesn't have to be represented by a square matrix (i.e. it can have different left-hand and right-hand bases).

It uses the identity

\[ T(ρ) = Tr\{\sqrt{ρ^† ρ}\} = \sum_i σ_i\]

where $σ_i$ are the singular values of `rho`

.

`QuantumOpticsBase.tracedistance`

— Function`tracedistance(rho, sigma)`

Trace distance between `rho`

and `sigma`

.

It is defined as

\[T(ρ,σ) = \frac{1}{2} Tr\{\sqrt{(ρ - σ)^† (ρ - σ)}\}.\]

It calls `tracenorm`

which in turn either uses `tracenorm_h`

or `tracenorm_nh`

depending if $ρ-σ$ is hermitian or not.

`QuantumOpticsBase.tracedistance_h`

— Function`tracedistance_h(rho, sigma)`

Trace distance between `rho`

and `sigma`

.

It uses the identity

\[T(ρ,σ) = \frac{1}{2} Tr\{\sqrt{(ρ - σ)^† (ρ - σ)}\} = \frac{1}{2} \sum_i |λ_i|\]

where $λ_i$ are the eigenvalues of `rho`

- `sigma`

.

`QuantumOpticsBase.tracedistance_nh`

— Function`tracedistance_nh(rho, sigma)`

Trace distance between `rho`

and `sigma`

.

Note that in this case `rho`

and `sigma`

don't have to be represented by square matrices (i.e. they can have different left-hand and right-hand bases).

It uses the identity

\[ T(ρ,σ) = \frac{1}{2} Tr\{\sqrt{(ρ - σ)^† (ρ - σ)}\} = \frac{1}{2} \sum_i σ_i\]

where $σ_i$ are the singular values of `rho`

- `sigma`

.

`QuantumOpticsBase.entropy_vn`

— Function`entropy_vn(rho)`

Von Neumann entropy of a density matrix.

The Von Neumann entropy of a density operator is defined as

\[S(ρ) = -Tr(ρ \log(ρ)) = -\sum_n λ_n\log(λ_n)\]

where $λ_n$ are the eigenvalues of the density matrix $ρ$, $\log$ is the natural logarithm and $0\log(0) ≡ 0$.

**Arguments**

`rho`

: Density operator of which to calculate Von Neumann entropy.`tol=1e-15`

: Tolerance for rounding errors in the computed eigenvalues.

`QuantumOpticsBase.entropy_renyi`

— Function`entropy_renyi(rho, α::Integer=2)`

Renyi α-entropy of a density matrix, where r α≥0, α≂̸1.

The Renyi α-entropy of a density operator is defined as

\[S_α(ρ) = 1/(1-α) \log(Tr(ρ^α))\]

`QuantumOpticsBase.fidelity`

— Function`fidelity(rho, sigma)`

Fidelity of two density operators.

The fidelity of two density operators $ρ$ and $σ$ is defined by

\[F(ρ, σ) = Tr\left(\sqrt{\sqrt{ρ}σ\sqrt{ρ}}\right),\]

where $\sqrt{ρ}=\sum_n\sqrt{λ_n}|ψ⟩⟨ψ|$.

`QuantumOpticsBase.ptranspose`

— Function`ptranspose(rho, indices)`

Partial transpose of rho with respect to subsystem specified by indices.

The `indices`

argument can be a single integer or a collection of integers.

`QuantumOpticsBase.PPT`

— Function`PPT(rho, index)`

Peres-Horodecki criterion of partial transpose.

`QuantumOpticsBase.negativity`

— Function`negativity(rho, index)`

Negativity of rho with respect to subsystem index.

The negativity of a density matrix ρ is defined as

\[N(ρ) = \frac{\|ρᵀ\|-1}{2},\]

where `ρᵀ`

is the partial transpose.

`QuantumOpticsBase.logarithmic_negativity`

— Function`logarithmic_negativity(rho, index)`

The logarithmic negativity of a density matrix ρ is defined as

\[N(ρ) = \log₂\|ρᵀ\|,\]

where `ρᵀ`

is the partial transpose.

`QuantumOpticsBase.entanglement_entropy`

— Function`entanglement_entropy(state, partition, [entropy_fun=entropy_vn])`

Computes the entanglement entropy of `state`

between the list of sites `partition`

and the rest of the system. The state must be defined in a composite basis.

If `state isa AbstractOperator`

the operator-space entanglement entropy is computed, which has the property

`entanglement_entropy(dm(ket)) = 2 * entanglement_entropy(ket)`

By default the computed entropy is the Von-Neumann entropy, but a different function can be provided (for example to compute the entanglement-renyi entropy).

`QuantumOpticsBase.avg_gate_fidelity`

— Function`avg_gate_fidelity(x, y)`

The average gate fidelity between two superoperators x and y.

## Time-evolution

`QuantumOptics.timeevolution.recast!`

— Function### Schroedinger

`QuantumOptics.timeevolution.schroedinger`

— Function`timeevolution.schroedinger(tspan, psi0, H; fout)`

Integrate Schroedinger equation to evolve states or compute propagators.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`psi0`

: Initial state vector (can be a bra or a ket) or an Operator from some basis to the basis of the Hamiltonian (psi0.basis_l == basis(H)).`H`

: Arbitrary operator specifying the Hamiltonian.`fout=nothing`

: If given, this function`fout(t, psi)`

is called every time an output should be displayed. ATTENTION: The state`psi`

is neither normalized nor permanent! It is still in use by the ode solver and therefore must not be changed.

`QuantumOptics.timeevolution.schroedinger_dynamic`

— Function`timeevolution.schroedinger_dynamic(tspan, psi0, f; fout)`

Integrate time-dependent Schroedinger equation to evolve states or compute propagators.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`psi0`

: Initial state vector (can be a bra or a ket) or an Operator from some basis to the basis of the Hamiltonian (psi0.basis_l == basis(H)).`f`

: Function`f(t, psi) -> H`

returning the time and or state dependent Hamiltonian.`fout=nothing`

: If given, this function`fout(t, psi)`

is called every time an output should be displayed. ATTENTION: The state`psi`

is neither normalized nor permanent! It is still in use by the ode solver and therefore must not be changed.timeevolution.schroedinger_dynamic(tspan, psi0, H::AbstractTimeDependentOperator; fout)

Instead of a function `f`

, this takes a time-dependent operator `H`

.

`QuantumOptics.timeevolution.dschroedinger!`

— Function`dschroedinger!(dpsi, H, psi)`

Update the increment `dpsi`

in-place according to a Schrödinger equation as `-im*H*psi`

.

See also: `dschroedinger_dynamic!`

`QuantumOptics.timeevolution.dschroedinger_dynamic!`

— Function`dschroedinger_dynamic!(dpsi, f, psi, t)`

Compute the Hamiltonian as `H=f(t, psi)`

and update `dpsi`

according to a Schrödinger equation as `-im*H*psi`

.

See also: `dschroedinger!`

### Master

`QuantumOptics.timeevolution.master`

— Function`timeevolution.master(tspan, rho0, H, J; <keyword arguments>)`

Time-evolution according to a master equation.

There are two implementations for integrating the master equation:

`master_h`

: Usual formulation of the master equation.`master_nh`

: Variant with non-hermitian Hamiltonian.

For dense arguments the `master`

function calculates the non-hermitian Hamiltonian and then calls master_nh which is slightly faster.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`H`

: Arbitrary operator specifying the Hamiltonian.`J`

: Vector containing all jump operators which can be of any arbitrary operator type.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.

`timeevolution.master(tspan, rho0, L; <keyword arguments>)`

Time-evolution according to a master equation with a Liouvillian superoperator `L`

.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`L`

: Superoperator defining the right-hand-side of the master equation.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.timeevolution.master_h`

— Function`timeevolution.master_h(tspan, rho0, H, J; <keyword arguments>)`

Integrate the master equation with dmaster_h as derivative function.

Further information can be found at `master`

.

`QuantumOptics.timeevolution.master_nh`

— Function`timeevolution.master_nh(tspan, rho0, H, J; <keyword arguments>)`

Integrate the master equation with dmaster_nh as derivative function.

In this case the given Hamiltonian is assumed to be the non-hermitian version:

\[H_{nh} = H - \frac{i}{2} \sum_k J^†_k J_k\]

Further information can be found at `master`

.

`QuantumOptics.timeevolution.master_dynamic`

— Function`timeevolution.master_dynamic(tspan, rho0, f; <keyword arguments>)`

Time-evolution according to a master equation with a dynamic Hamiltonian and J.

There are two implementations for integrating the master equation with dynamic operators:

`master_dynamic`

: Usual formulation of the master equation.`master_nh_dynamic`

: Variant with non-hermitian Hamiltonian.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`f`

: Function`f(t, rho) -> (H, J, Jdagger)`

or`f(t, rho) -> (H, J, Jdagger, rates)`

`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.timeevolution.master_dynamic(tspan, rho0, H::AbstractTimeDependentOperator, J; <keyword arguments>)

This version takes the Hamiltonian `H`

and jump operators `J`

as time-dependent operators. The jump operators may be `<: AbstractTimeDependentOperator`

or other types of operator.

`QuantumOptics.timeevolution.master_nh_dynamic`

— Function`timeevolution.master_dynamic(tspan, rho0, f; <keyword arguments>)`

Time-evolution according to a master equation with a dynamic non-hermitian Hamiltonian and J.

In this case the given Hamiltonian is assumed to be the non-hermitian version.

\[H_{nh} = H - \frac{i}{2} \sum_k J^†_k J_k\]

The given function can either be of the form `f(t, rho) -> (Hnh, Hnhdagger, J, Jdagger)`

or `f(t, rho) -> (Hnh, Hnhdagger, J, Jdagger, rates)`

For further information look at `master_dynamic`

.

`timeevolution.master_dynamic(tspan, rho0, Hnh::AbstractTimeDependentOperator, J; <keyword arguments>)`

This version takes the non-hermitian Hamiltonian `Hnh`

and jump operators `J`

as time-dependent operators. The jump operators may be `<: AbstractTimeDependentOperator`

or other types of operator.

`QuantumOptics.timeevolution.dmaster_h!`

— Function`dmaster_h!(drho, H, J, Jdagger, rates, rho, drho_cache)`

Update `drho`

according to a master equation given in standard Lindblad form. A cached copy `drho_cache`

of `drho`

is used as a temporary saving step.

See also: `master`

, `dmaster_nh!`

, `dmaster_h_dynamic!`

, `dmaster_nh_dynamic!`

, `dmaster_liouville!`

`QuantumOptics.timeevolution.dmaster_nh!`

— Function`dmaster_nh!(drho, Hnh, Hnh_dagger, J, Jdagger, rates, rho, drho_cache)`

Updates `drho`

according to a master equation given in standard Lindblad form. The part of the Liuovillian which can be written as a commutator should be contained in `Hnh`

and `Hnh_dagger`

. This allows to skip a number of matrix multiplications making it slightly faster than `dmaster_h!`

.

See also: `master`

, `dmaster_h!`

, `dmaster_h_dynamic!`

, `dmaster_nh_dynamic!`

, `dmaster_liouville!`

`QuantumOptics.timeevolution.dmaster_liouville!`

— Function`dmaster_liouville!(drho,L,rho)`

Update `drho`

according to a master equation as `L*rho`

, where `L`

is an arbitrary (super-)operator.

See also: `master`

, `dmaster_h!`

, `dmaster_nh!`

, `dmaster_h_dynamic!`

, `dmaster_nh_dynamic!`

`QuantumOptics.timeevolution.dmaster_h_dynamic!`

— Function`dmaster_h_dynamic!(drho, f, rates, rho, drho_cache, t)`

Computes the Hamiltonian and jump operators as `H,J,Jdagger=f(t,rho)`

and update `drho`

according to a master equation. Optionally, rates can also be returned from `f`

.

See also: `master_dynamic`

, `dmaster_h!`

, `dmaster_nh!`

, `dmaster_nh_dynamic!`

`QuantumOptics.timeevolution.dmaster_nh_dynamic!`

— Function`dmaster_nh_dynamic!(drho, f, rates, rho, drho_cache, t)`

Computes the non-hermitian Hamiltonian and jump operators as `Hnh,Hnh_dagger,J,Jdagger=f(t,rho)`

and update `drho`

according to a master equation. Optionally, rates can also be returned from `f`

.

See also: `master_dynamic`

, `dmaster_h!`

, `dmaster_nh!`

, `dmaster_h_dynamic!`

`QuantumOptics.timeevolution.@skiptimechecks`

— Macro`@skiptimechecks`

Macro to skip checks during time-dependent problems. Useful for `timeevolution.master_dynamic`

and similar functions.

### Monte Carlo wave function

`QuantumOptics.timeevolution.mcwf`

— Function`mcwf(tspan, psi0, H, J; <keyword arguments>)`

Integrate the master equation using the MCWF method.

There are two implementations for integrating the non-hermitian schroedinger equation:

`mcwf_h`

: Usual formulation with Hamiltonian + jump operators

separately.

`mcwf_nh`

: Variant with non-hermitian Hamiltonian.

The `mcwf`

function takes a normal Hamiltonian, calculates the non-hermitian Hamiltonian and then calls `mcwf_nh`

which is slightly faster.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should

be displayed.

`psi0`

: Initial state vector.`H`

: Arbitrary Operator specifying the Hamiltonian.`J`

: Vector containing all jump operators which can be of any arbitrary

operator type.

`seed=rand()`

: Seed used for the random number generator.`rates=ones()`

: Vector of decay rates.`fout`

: If given, this function`fout(t, psi)`

is called every time an

output should be displayed. ATTENTION: The state `psi`

is neither normalized nor permanent! It is still in use by the ode solve and therefore must not be changed.

`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump

operators. If they are not given they are calculated automatically.

`display_beforeevent=false`

:`fout`

is called before every jump.`display_afterevent=false`

:`fout`

is called after every jump.`rng_state=nothing`

: An optional`timeevolution.JumpRNGState`

`, providing the RNG and an initial jump threshold. If provided,`

seed` is ignored.`display_jumps=false`

: If set to true, an additional list of times and indices

is returned. These correspond to the times at which a jump occured and the index of the jump operators with which the jump occured, respectively.

`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.timeevolution.mcwf_h`

— Function`mcwf_h(tspan, rho0, Hnh, J; <keyword arguments>)`

Calculate MCWF trajectory where the Hamiltonian is given in hermitian form.

For more information see: `mcwf`

`QuantumOptics.timeevolution.mcwf_nh`

— Function`mcwf_nh(tspan, rho0, Hnh, J; <keyword arguments>)`

Calculate MCWF trajectory where the Hamiltonian is given in non-hermitian form.

\[H_{nh} = H - \frac{i}{2} \sum_k J^†_k J_k\]

For more information see: `mcwf`

`QuantumOptics.timeevolution.mcwf_dynamic`

— Function`mcwf_dynamic(tspan, psi0, f; <keyword arguments>)`

Integrate the master equation using the MCWF method with dynamic Hamiltonian and Jump operators.

The `mcwf`

function takes a normal Hamiltonian, calculates the non-hermitian Hamiltonian and then calls `mcwf_nh`

which is slightly faster.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should

be displayed.

`psi0`

: Initial state vector.`f`

: Function`f(t, psi) -> (H, J, Jdagger)`

or`f(t, psi) -> (H, J, Jdagger, rates)`

that returns the time-dependent Hamiltonian and Jump operators.`seed=rand()`

: Seed used for the random number generator.`rates=ones()`

: Vector of decay rates.`fout`

: If given, this function`fout(t, psi)`

is called every time an

output should be displayed. ATTENTION: The state `psi`

is neither normalized nor permanent! It is still in use by the ode solve and therefore must not be changed.

`display_beforeevent=false`

:`fout`

is called before every jump.`display_afterevent=false`

:`fout`

is called after every jump.`rng_state=nothing`

: An optional`timeevolution.JumpRNGState`

`, providing the RNG and an initial jump threshold. If provided,`

seed` is ignored.`display_jumps=false`

: If set to true, an additional list of times and indices

is returned. These correspond to the times at which a jump occured and the index of the jump operators with which the jump occured, respectively.

`kwargs...`

: Further arguments are passed on to the ode solver.mcwf_dynamic(tspan, psi0, H::AbstractTimeDependentOperator, J; <keyword arguments>)

This version takes the Hamiltonian `H`

and jump operators `J`

as time-dependent operators. The jump operators may be `<: AbstractTimeDependentOperator`

or other types of operator.

`QuantumOptics.timeevolution.mcwf_nh_dynamic`

— Function```
mcwf_nh_dynamic(tspan, rho0, f; <keyword arguments>)
mcwf_nh_dynamic(tspan, rho0, Hnh::AbstractTimeDependentOperator, J; <keyword arguments>)
```

Calculate MCWF trajectory where the dynamic Hamiltonian is given in non-hermitian form.

For more information see: `mcwf_dynamic`

`QuantumOptics.timeevolution.diagonaljumps`

— Function`diagonaljumps(rates, J)`

Diagonalize jump operators.

The given matrix `rates`

of decay rates is diagonalized and the corresponding set of jump operators is calculated.

**Arguments**

`rates`

: Matrix of decay rates.`J`

: Vector of jump operators.

### Bloch-Redfield master

`QuantumOptics.timeevolution.bloch_redfield_tensor`

— Function`bloch_redfield_tensor(H, a_ops; J=[], use_secular=true, secular_cutoff=0.1)`

Create the super-operator for the Bloch-Redfield master equation such that $\dot ρ = R ρ$ based on the QuTiP implementation.

See QuTiP's documentation (http://qutip.org/docs/latest/guide/dynamics/dynamics-bloch-redfield.html) for more information and a brief derivation.

**Arguments**

`H`

: Hamiltonian.`a_ops`

: Nested list of [interaction operator, callback function] pairs for the Bloch-Redfield type processes where the callback function describes the environment spectrum for the corresponding interaction operator. The spectral functions must take the angular frequency as their only argument.`J=[]`

: Vector containing the jump operators for the Linblad type processes (optional).`use_secular=true`

: Specify whether or not to use the secular approximation.`secular_cutoff=0.1`

: Cutoff to allow a degree of partial secularization. Terms are discarded if they are greater than (dw_min * secular cutoff) where dw_min is the smallest (non-zero) difference between any two eigenenergies of H. This argument is only taken into account if use_secular=true.

`QuantumOptics.timeevolution.master_bloch_redfield`

— Function`timeevolution.master_bloch_redfield(tspan, rho0, R, H; <keyword arguments>)`

Time-evolution according to a Bloch-Redfield master equation.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`H`

: Arbitrary operator specifying the Hamiltonian.`R`

: Bloch-Redfield tensor describing the time-evolution $\dot ρ = R ρ$ (see timeevolution.bloch_redfield_tensor).`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.

## Spectral analysis

`QuantumOptics.eigenstates`

— Function`eigenstates(op::Operator[, n::Int; warning=true, kw...])`

Calculate the lowest n eigenvalues and their corresponding eigenstates. By default `n`

is equal to the matrix size for dense matrices; for sparse matrices the default value is 6.

This is just a thin wrapper around julia's `LinearArgebra.eigen`

and `KrylovKit.eigsolve`

functions. Which of them is used depends on the type of the given operator. If more control about the way the calculation is done is needed, use the method instance with `DiagStrategy`

(see below).

NOTE: Especially for small systems full diagonalization with Julia's `eigen`

function is often more desirable. You can convert a sparse operator `A`

to a dense one using `dense(A)`

.

If the given operator is non-hermitian a warning is given. This behavior can be turned off using the keyword `warning=false`

.

**Optional arguments**

`n`

: It can be a keyword argument too!`v0`

: The starting vector for Arnoldi-like iterative methods.`krylovdim`

: The upper bound for dimenstion count of the emerging Krylov space.

`eigenstates(op::Operator, ds::DiagStrategy[; warning=true, kw...])`

Calculate the lowest eigenvalues and their corresponding eigenstates of the `op`

operator using the `ds`

diagonalization strategy. The `kw...`

arguments can be passed to the exact function that does the diagonalization (like `KrylovKit.eigsolve`

).

`QuantumOptics.eigenenergies`

— Function`eigenenergies(op::AbstractOperator[, n::Int; warning=true, kwargs...])`

Calculate the lowest n eigenvalues of given operator.

If the given operator is non-hermitian a warning is given. This behavior can be turned off using the keyword `warning=false`

.

See `eigenstates`

for more info.

`QuantumOptics.simdiag`

— Function`simdiag(ops; atol, rtol)`

Simultaneously diagonalize commuting Hermitian operators specified in `ops`

.

This is done by diagonalizing the sum of the operators. The eigenvalues are computed by $a = ⟨ψ|A|ψ⟩$ and it is checked whether the eigenvectors fulfill the equation $A|ψ⟩ = a|ψ⟩$.

**Arguments**

`ops`

: Vector of sparse or dense operators.`atol=1e-14`

: kwarg of Base.isapprox specifying the tolerance of the approximate check`rtol=1e-14`

: kwarg of Base.isapprox specifying the tolerance of the approximate check

**Returns**

`evals_sorted`

: Vector containing all vectors of the eigenvalues sorted by the eigenvalues of the first operator.`v`

: Common eigenvectors.

## Steady-states

`QuantumOptics.steadystate.master`

— Function`steadystate.master(H, J; <keyword arguments>)`

Calculate steady state using long time master equation evolution.

**Arguments**

`H`

: Arbitrary operator specifying the Hamiltonian.`J`

: Vector containing all jump operators which can be of any arbitrary operator type.`rho0=dm(basisstate(b))`

: Initial density operator. If not given the $|0⟩⟨0|$ state in respect to the choosen basis is used.`tol=1e-3`

: Tracedistance used as termination criterion.`hmin=1e-7`

: Minimal time step used in the time evolution.`rates=ones(N)`

: Vector or matrix specifying the coefficients for the jump operators.`Jdagger=dagger.(Jdagger)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`fout=nothing`

: If given this function`fout(t, rho)`

is called every time an output should be displayed. To limit copying to a minimum the given density operator`rho`

is further used and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.steadystate.eigenvector`

— Function```
steadystate.eigenvector(L)
steadystate.eigenvector(H, J)
```

Find steady state by calculating the eigenstate with eigenvalue 0 of the Liouvillian matrix `L`

, if it exists.

**Keyword arguments:**

`tol = 1e-9`

: Check`abs(eigenvalue) < tol`

to determine zero eigenvalue.`nev = 2`

: Number of calculated eigenvalues. If`nev > 1`

it is checked if there is only one eigenvalue with real part 0. No checks for`nev = 1`

: use if faster or for avoiding convergence errors of`eigs`

. Changing`nev`

thus only makes sense when using SparseSuperOperator.`which = :LR`

: Find eigenvalues with largest real part. Keyword for`eigs`

function (ineffective for DenseSuperOperator).`kwargs...`

: Keyword arguments for the Julia`eigen`

or`eigs`

function.

`QuantumOptics.steadystate.liouvillianspectrum`

— Function```
steadystate.liouvillianspectrum(L)
steadystate.liouvillianspectrum(H, J)
```

Calculate eigenspectrum of the Liouvillian matrix `L`

. The eigenvalues and -states are sorted according to the absolute value of the eigenvalues.

**Keyword arguments:**

`nev = min(10, length(L.basis_r[1])*length(L.basis_r[2]))`

: Number of eigenvalues.`which = :LR`

: Find eigenvalues with largest real part. Keyword for`eigs`

function (ineffective for DenseSuperOperator).`kwargs...`

: Keyword arguments for the Julia`eigen`

or`eigens`

function.

`QuantumOptics.steadystate.iterative`

— Function`iterative(H, J, [method!], args...; [log=false], kwargs...) -> rho[, log]`

Compute the steady state density matrix of master equation defined by a Hamiltonian and a set of jump operators by solving `L rho = 0`

via an iterative method provided as argument.

**Arguments**

`rho0`

: Initial density matrix. Note that this gets mutated in-place.`H`

: Operator specifying the Hamiltonian.`J`

: Vector containing all jump operators.`method!`

: The iterative method to be used. Defaults to`IterativeSolvers.bicgstabl!`

.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`rho0=nothing`

: Initial density operator.`args...`

: Further arguments are passed on to the iterative solver.`kwargs...`

: Further keyword arguments are passed on to the iterative solver.

See also: `iterative!`

Credit for this implementation goes to Z. Denis and F. Vicentini. See also https://github.com/Z-Denis/SteadyState.jl

`QuantumOptics.steadystate.iterative!`

— Function`iterative!(rho0, H, J, [method!], args...; [log=false], kwargs...) -> rho[, log]`

Compute the steady state density matrix of master equation defined by a Hamiltonian and a set of jump operators by solving `L rho = 0`

via an iterative method provided as argument.

**Arguments**

`rho0`

: Initial density matrix. Note that this gets mutated in-place.`H`

: Operator specifying the Hamiltonian.`J`

: Vector containing all jump operators.`method!`

: The iterative method to be used. Defaults to`IterativeSolvers.bicgstabl!`

.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`args...`

: Further arguments are passed on to the iterative solver.`kwargs...`

: Further keyword arguments are passed on to the iterative solver.

See also: `iterative`

Credit for this implementation goes to Z. Denis and F. Vicentini. See also https://github.com/Z-Denis/SteadyState.jl

## Time correlations

`QuantumOptics.timecorrelations.correlation`

— Function`timecorrelations.correlation([tspan, ]rho0, H, J, A, B; <keyword arguments>)`

Calculate two time correlation values $⟨A(t)B(0)⟩$.

The calculation is done by multiplying the initial density operator with $B$ performing a time evolution according to a master equation and then calculating the expectation value $\mathrm{Tr} \{A ρ\}$

Without the `tspan`

argument the points in time are chosen automatically from the ode solver and the final time is determined by the steady state termination criterion specified in `steadystate.master`

.

**Arguments**

`tspan`

: Points of time at which the correlation should be calculated.`rho0`

: Initial density operator.`H`

: Operator specifying the Hamiltonian.`J`

: Vector of jump operators.`A`

: Operator at time`t`

.`B`

: Operator at time`t=0`

.`rates=ones(N)`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.timecorrelations.spectrum`

— Function`timecorrelations.spectrum([omega_samplepoints,] H, J, op; <keyword arguments>)`

Calculate spectrum as Fourier transform of a correlation function

This is done with the Wiener-Khinchin theorem

\[S(ω, t) = 2\Re\left\{\int_0^{∞} dτ e^{-iωτ}⟨A^†(t+τ)A(t)⟩\right\}\]

The argument `omega_samplepoints`

gives the list of frequencies where $S(ω)$ is caclulated. A corresponding list of times is calculated internally by means of a inverse discrete frequency fourier transform. If not given, the steady-state is computed before calculating the auto-correlation function.

Without the `omega_samplepoints`

arguments the frequencies are chosen automatically.

**Arguments**

`omega_samplepoints`

: List of frequency points at which the spectrum is calculated.`H`

: Operator specifying the Hamiltonian.`J`

: Vector of jump operators.`op`

: Operator for which the auto-correlation function is calculated.`rho0`

: Initial density operator.`tol=1e-4`

: Tracedistance used as termination criterion.`rates=ones(N)`

: Vector or matrix specifying the coefficients for the jump operators.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.timecorrelations.correlation2spectrum`

— Function`timecorrelations.correlation2spectrum(tspan, corr; normalize_spec)`

Calculate spectrum as Fourier transform of a correlation function with a given correlation function.

**Arguments**

`tspan`

: List of time points corresponding to the correlation function.`corr`

: Correlation function of which the Fourier transform is to be calculated.`normalize_spec`

: Specify if spectrum should be normalized to its maximum.

`QuantumOptics.timecorrelations.correlation_dynamic`

— Function`timecorrelations.correlation_dynamic(tspan, rho0, f, A, B; <keyword arguments>)`

Calculate two time correlation values $⟨A(t)B(0)⟩$ for time-dependent Liouvillian

The calculation is done by multiplying the initial density operator with $B$ performing a time evolution according to a master equation and then calculating the expectation value $\mathrm{Tr} \{A ρ\}$

**Arguments**

`tspan`

: Points of time at which the correlation should be calculated.`rho0`

: Initial density operator.`f`

: Function`f(t, rho) -> (H, J, Jdagger)`

or`f(t, rho) -> (H, J, Jdagger, rates)`

`A`

: Operator at time`t`

.`B`

: Operator at time`t=0`

.`rates=ones(N)`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators.`kwargs...`

: Further arguments are passed on to the ode solver.

## Semi-classical

`QuantumOptics.semiclassical.State`

— TypeSemi-classical state.

It consists of a quantum part, which is either a `Ket`

or a `DenseOperator`

and a classical part that is specified as a complex vector of arbitrary length.

`QuantumOptics.semiclassical.schroedinger_dynamic`

— Function`semiclassical.schroedinger_dynamic(tspan, state0, fquantum, fclassical[; fout, ...])`

Integrate time-dependent Schrödinger equation coupled to a classical system.

**Arguments**

`tspan`

: Vector specifying the points of time for which the output should be displayed.`psi0`

: Initial semi-classical state`semiclassical.State`

.`fquantum`

: Function`f(t, psi, u) -> H`

returning the time and or state dependent Hamiltonian.`fclassical!`

: Function`f!(du, u, psi, t)`

calculating the possibly time and state dependent derivative of the classical equations and storing it in the vector`du`

.`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is neither normalized nor permanent!`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.semiclassical.dschroedinger_dynamic!`

— Function`dschroedinger_dynamic!(dstate, fquantum, fclassical!, state)`

Update the semiclassical state `dstate`

according to a time-dependent, semiclassical Schrödinger equation.

See also: `semiclassical.schroedinger_dynamic`

`QuantumOptics.semiclassical.master_dynamic`

— Function`semiclassical.master_dynamic(tspan, state0, fquantum, fclassical!; <keyword arguments>)`

Integrate time-dependent master equation coupled to a classical system.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial semi-classical state`semiclassical.State`

.`fquantum`

: Function`f(t, rho, u) -> (H, J, Jdagger)`

returning the time and/or state dependent Hamiltonian and Jump operators.`fclassical!`

: Function`f!(du, u, rho, t)`

calculating the possibly time and state dependent derivative of the classical equations and storing it in the complex vector`du`

.`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is not permanent!`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.semiclassical.dmaster_h_dynamic!`

— Function`dmaster_h_dynamic!(dstate, fquantum, fclassical!, rates, state, tmp, t)`

Update the semiclassical state `dstate`

according to a time-dependent, semiclassical master eqaution.

See also: `semiclassical.master_dynamic`

`QuantumOptics.semiclassical.mcwf_dynamic`

— Function`semiclassical.mcwf_dynamic(tspan, psi0, fquantum, fclassical!, fjump_classical!; <keyword arguments>)`

Calculate MCWF trajectories coupled to a classical system. **NOTE**: The quantum state with which `fquantum`

and `fclassical!`

are called is NOT NORMALIZED. Make sure to take this into account when computing expectation values!

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`psi0`

: Initial semi-classical state`semiclassical.State`

featuring a`Ket`

(@ref).`fquantum`

: Function`f(t, psi, u) -> (H, J, Jdagger)`

returning the time and/or state dependent Hamiltonian and Jump operators.`fclassical!`

: Function`f!(du, u, psi, t)`

calculating the possibly time and state dependent derivative of the classical equations and storing it in the complex vector`du`

.`fjump_classical!`

: Function`f(t, psi, u, i)`

performing a classical jump when a quantum jump of the i-th jump operator occurs.`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is not permanent!`display_beforeevent`

: Choose whether or not an additional point should be saved before a jump occurs. Default is false.`display_afterevent`

: Choose whether or not an additional point should be saved after a jump occurs. Default is false.`display_jumps=false`

: If set to true, an additional list of times and indices is returned. These correspond to the times at which a jump occured and the index of the jump operators with which the jump occured, respectively.`kwargs...`

: Further arguments are passed on to the ode solver.

## Stochastics

`QuantumOptics.stochastic.schroedinger`

— Function`stochastic.schroedinger(tspan, state0, H, Hs[; fout, ...])`

Integrate stochastic Schrödinger equation.

**Arguments**

`tspan`

: Vector specifying the points of time for which the output should be displayed.`psi0`

: Initial state as Ket.`H`

: Deterministic part of the Hamiltonian.`Hs`

: Stochastic part(s) of the Hamiltonian (either an operator or a vector of operators).`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is neither normalized nor permanent!`normalize_state=false`

: Specify whether or not to normalize the state after each time step taken by the solver.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.stochastic.schroedinger_dynamic`

— Function`stochastic.schroedinger_dynamic(tspan, state0, fdeterm, fstoch[; fout, ...])`

Integrate stochastic Schrödinger equation with dynamic Hamiltonian.

**Arguments**

`tspan`

: Vector specifying the points of time for which the output should be displayed.`psi0`

: Initial state.`fdeterm`

: Function`f(t, psi, u) -> H`

returning the deterministic (time- or state-dependent) part of the Hamiltonian.`fstoch`

: Function`f(t, psi, u, du) -> Hs`

returning a vector that contains the stochastic terms of the Hamiltonian.`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is neither normalized nor permanent!`noise_processes=0`

: Number of distinct white-noise processes in the equation. This number has to be equal to the total number of noise operators returned by`fstoch`

. If unset, the number is calculated automatically from the function output. NOTE: Set this number if you want to avoid an initial calculation of the function output!`normalize_state=false`

: Specify whether or not to normalize the state after each time step taken by the solver.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.stochastic.homodyne_carmichael`

— Function`stochastic.homodyne_carmichael(H0, C, theta)`

Helper function that defines the functions needed to compute homodyne detection trajectories according to Carmichael with `stochastic.schroedinger_dynamic`

.

**Arguments**

`H0`

: The deterministic, time-independent system Hamiltonian.`C`

: Collapse operator (or vector of operators) of the detected output channel(s).`theta`

: The phase difference between the local oscillator and the signal field. Defines the operator of the measured quadrature as $X_\theta = C e^{-i\theta} + C^\dagger e^{i\theta}$. Needs to be a vector of the same length as`C`

if`C`

is a vector.`normalize_expect=true`

: Specifiy whether or not to normalize the state vector when the expectation value in the nonlinear term is calculated. NOTE: should only be set to`false`

if the state is guaranteed to be normalized, e.g. by setting`normalize_state=true`

in`stochastic.schroedinger_dynamic`

.

Returns `(fdeterm, fstoch)`

, where `fdeterm(t, psi) -> H`

and `fstoch(t, psi) -> Hs`

are functions returning the deterministic and stochastic part of the Hamiltonian required for calling `stochastic.schroedinger_dynamic`

.

The deterministic and stochastic parts of the Hamiltonian are constructed as

\[H_{det} = H_0 + H_{nl},\]

where

\[H_{nl} = iCe^{-i\theta} \langle X_\theta \rangle - \frac{i}{2} C^\dagger C,\]

and

\[H_s = iCe^{-i\theta}.\]

`QuantumOptics.stochastic.master`

— Function`stochastic.master(tspan, rho0, H, J, C; <keyword arguments>)`

Time-evolution according to a stochastic master equation.

For dense arguments the `master`

function calculates the non-hermitian Hamiltonian and then calls master_nh which is slightly faster.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`H`

: Deterministic part of the Hamiltonian.`J`

: Vector containing all deterministic jump operators which can be of any arbitrary operator type.`C`

: Vector containing the stochastic operators for a superoperator of the form`C[i]*rho + rho*Cdagger[i]`

.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`Jdagger=dagger.(J)`

: Vector containing the hermitian conjugates of the jump operators. If they are not given they are calculated automatically.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.stochastic.master_dynamic`

— Function`stochastic.master_dynamic(tspan, rho0, fdeterm, fstoch; <keyword arguments>)`

Time-evolution according to a stochastic master equation with a dynamic Hamiltonian and J.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`fdeterm`

: Function`f(t, rho) -> (H, J, Jdagger)`

or`f(t, rho) -> (H, J, Jdagger, rates)`

giving the deterministic part of the master equation.`fstoch`

: Function`f(t, rho) -> (C, Cdagger)`

giving the stochastic superoperator of the form`C[i]*rho + rho*Cdagger[i]`

.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`noise_processes=0`

: Number of distinct white-noise processes in the equation. This number has to be equal to the total number of noise operators returned by`fstoch`

and all optional functions. If unset, the number is calculated automatically from the function outputs. NOTE: Set this number if you want to avoid an initial calculation of function outputs!`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.stochastic.schroedinger_semiclassical`

— Function`stochastic.schroedinger_semiclassical(tspan, state0, fquantum, fclassical![; fout, ...])`

Integrate time-dependent Schrödinger equation coupled to a classical system.

**Arguments**

`tspan`

: Vector specifying the points of time for which the output should be displayed.`state0`

: Initial semi-classical state`semiclassical.State`

.`fquantum`

: Function`f(t, psi, u) -> H`

returning the time and or state dependent Hamiltonian.`fclassical!`

: Function`f!(du, u, psi ,t)`

calculating the possibly time and state dependent derivative of the classical equations and storing it in the vector`du`

.`fstoch_quantum=nothing`

: Function`f(t, psi, u) -> Hs`

that returns a vector of operators corresponding to the stochastic terms of the Hamiltonian. NOTE: Either this function or`fstoch_classical`

has to be defined.`fstoch_classical=nothing`

: Function`f!(du, u, psi, t)`

that calculates the stochastic terms of the derivative`du`

. NOTE: Either this function or`fstoch_quantum`

has to be defined.`fout=nothing`

: If given, this function`fout(t, state)`

is called every time an output should be displayed. ATTENTION: The given state is neither normalized nor permanent!`noise_processes=0`

: Number of distinct quantum noise processes in the equation. This number has to be equal to the total number of noise operators returned by`fstoch`

. If unset, the number is calculated automatically from the function output. NOTE: Set this number if you want to avoid an initial calculation of the function output!`noise_prototype_classical=nothing`

: The equivalent of the optional argument`noise_rate_prototype`

in`StochasticDiffEq`

for the classical stochastic function`fstoch_classical`

only. Must be set for non-diagonal classical noise or combinations of quantum and classical noise. See the documentation for details.`normalize_state=false`

: Specify whether or not to normalize the state after each time step taken by the solver.`kwargs...`

: Further arguments are passed on to the ode solver.

`QuantumOptics.stochastic.master_semiclassical`

— Function`stochastic.master_semiclassical(tspan, rho0, H, Hs, J; <keyword arguments>)`

Time-evolution according to a stochastic master equation. For dense arguments the `master`

function calculates the non-hermitian Hamiltonian and then calls master_nh which is slightly faster.

**Arguments**

`tspan`

: Vector specifying the points of time for which output should be displayed.`rho0`

: Initial density operator. Can also be a state vector which is automatically converted into a density operator.`fquantum`

: Function`f(t, rho, u) -> (H, J, Jdagger)`

or`f(t, rho, u) -> (H, J, Jdagger, rates)`

giving the deterministic part of the master equation.`fclassical!`

: Function`f!(du, u, rho, t)`

that calculates the classical derivatives`du`

.`fstoch_quantum=nothing`

: Function`f(t, rho, u) -> C, Cdagger`

that returns the stochastic operator for the superoperator of the form`C[i]*rho + rho*Cdagger[i]`

.`fstoch_classical=nothing`

: Function`f!(du, u, rho, t)`

that calculates the stochastic terms of the derivative`du`

.`rates=nothing`

: Vector or matrix specifying the coefficients (decay rates) for the jump operators. If nothing is specified all rates are assumed to be 1.`fout=nothing`

: If given, this function`fout(t, rho)`

is called every time an output should be displayed. ATTENTION: The given state rho is not permanent! It is still in use by the ode solver and therefore must not be changed.`noise_processes=0`

: Number of distinct quantum noise processes in the equation. This number has to be equal to the total number of noise operators returned by`fstoch`

. If unset, the number is calculated automatically from the function output. NOTE: Set this number if you want to avoid an initial calculation of the function output!`noise_prototype_classical=nothing`

: The equivalent of the optional argument`noise_rate_prototype`

in`StochasticDiffEq`

for the classical stochastic function`fstoch_classical`

only. Must be set for non-diagonal classical noise or combinations of quantum and classical noise. See the documentation for details.`kwargs...`

: Further arguments are passed on to the ode solver.

## State definitions

`QuantumOpticsBase.randstate`

— Function`randstate([T=ComplexF64,] basis)`

Calculate a random normalized ket state.

`QuantumOpticsBase.thermalstate`

— Function`thermalstate(H,T)`

Thermal state $exp(-H/T)/Tr[exp(-H/T)]$.

`QuantumOpticsBase.coherentthermalstate`

— Function`coherentthermalstate([C=ComplexF64,] basis::FockBasis,H,T,alpha)`

Coherent thermal state $D(α)exp(-H/T)/Tr[exp(-H/T)]D^†(α)$.

`QuantumOpticsBase.phase_average`

— Function`phase_average(rho)`

Returns the phase-average of $ρ$ containing only the diagonal elements.

`QuantumOpticsBase.passive_state`

— Function`passive_state(rho,IncreasingEigenenergies=true)`

Passive state $π$ of $ρ$. IncreasingEigenenergies=true means that higher indices correspond to higher energies.

## Pauli

`QuantumInterface.PauliBasis`

— Type`PauliBasis(num_qubits::Int)`

Basis for an N-qubit space where `num_qubits`

specifies the number of qubits. The dimension of the basis is 2²ᴺ.

`QuantumOpticsBase.PauliTransferMatrix`

— Type`Base class for Pauli transfer matrix classes.`

`QuantumOpticsBase.DensePauliTransferMatrix`

— Type`DensePauliTransferMatrix(B1, B2, data)`

DensePauliTransferMatrix stored as a dense matrix.

`QuantumOpticsBase.ChiMatrix`

— Type`Base class for χ (process) matrix classes.`

`QuantumOpticsBase.DenseChiMatrix`

— Type`DenseChiMatrix(b, b, data)`

DenseChiMatrix stored as a dense matrix.

## Printing

`QuantumOpticsBase.set_printing`

— Function`QuantumOptics.set_printing(; standard_order, rounding_tol)`

Set options for REPL output.

**Arguments**

`standard_order=false`

: For performance reasons, the order of the tensor product is inverted, i.e.`tensor(a, b)=kron(b, a)`

. When changing this to`true`

, the output shown in the REPL will exhibit the correct order.`rounding_tol=1e-17`

: Tolerance for floating point errors shown in the output.

## LazyTensor functions

`QuantumOpticsBase.lazytensor_enable_cache`

— Function`lazytensor_enable_cache(; maxsize::Int = ..., maxrelsize::Real = ...)`

(Re)-enable the cache for further use; set the maximal size `maxsize`

(as number of bytes) or relative size `maxrelsize`

, as a fraction between 0 and 1, resulting in `maxsize = floor(Int, maxrelsize * Sys.total_memory())`

. Default value is `maxsize = 2^32`

bytes, which amounts to 4 gigabytes of memory.

`QuantumOpticsBase.lazytensor_disable_cache`

— Function`lazytensor_disable_cache()`

Disable the cache for further use but does not clear its current contents. Also see `lazytensor_clear_cache()`

`QuantumOpticsBase.lazytensor_cachesize`

— Function`lazytensor_cachesize()`

Return the current memory size (in bytes) of all the objects in the cache.

`QuantumOpticsBase.lazytensor_clear_cache`

— Function`lazytensor_clear_cache()`

Clear the current contents of the cache.