Operators

Projector0(a)

One-qubit operator corresponding to a projection onto $|0\rangle$.

The corresponding matrix

\[\begin{pmatrix} a & 0\\ 0 & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling. Equivalent to DiagonalOp(a,0).

The parameter $a$ is optional and is set to 1 by default.

See also Projector1, DiagonalOp.

Examples

julia> Projector0()
P₀(1)

julia> Projector0(0.5)
P₀(0.5)

julia> push!(Circuit(), ExpectationValue(Projector0()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₀(1)⟩ @ q[1], z[1]

Projector00(a)

Two-qubit operator corresponding to a projection onto $|00\rangle$.

The corresponding matrix

\[\begin{pmatrix} a & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also Projector01, Projector10, Projector11.

Examples

julia> Projector00()
P₀₀(1)

julia> Projector00(0.5)
P₀₀(0.5)

julia> push!(Circuit(), ExpectationValue(Projector00()), 1, 2, 1)
2-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₀₀(1)⟩ @ q[1:2], z[1]

Projector01(a)

Two-qubit operator corresponding to a projection onto $|01\rangle$.

The corresponding matrix

\[\begin{pmatrix} 0 & 0 & 0 & 0\\ 0 & a & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also Projector00, Projector10, Projector11.

Examples

julia> Projector01()
P₀₁(1)

julia> Projector01(0.5)
P₀₁(0.5)

julia> push!(Circuit(), ExpectationValue(Projector01()), 1, 2, 1)
2-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₀₁(1)⟩ @ q[1:2], z[1]

Projector1(a)

One-qubit operator corresponding to a projection onto $|1\rangle$.

The corresponding matrix

\[\begin{pmatrix} 0 & 0\\ 0 & a \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling. Equivalent to DiagonalOp(0,a).

The parameter $a$ is optional and is set to 1 by default.

See also Projector0, DiagonalOp.

Examples

julia> Projector1()
P₁(1)

julia> Projector1(0.5)
P₁(0.5)

julia> push!(Circuit(), ExpectationValue(Projector1()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₁(1)⟩ @ q[1], z[1]

Projector10(a)

Two-qubit operator corresponding to a projection onto $|10\rangle$.

The corresponding matrix

\[\begin{pmatrix} 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & a & 0\\ 0 & 0 & 0 & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also Projector00, Projector01, Projector11.

Examples

julia> Projector10()
P₁₀(1)

julia> Projector10(0.5)
P₁₀(0.5)

julia> push!(Circuit(), ExpectationValue(Projector10()), 1, 2, 1)
2-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₁₀(1)⟩ @ q[1:2], z[1]

Projector11(a)

Two-qubit operator corresponding to a projection onto $|11\rangle$.

The corresponding matrix is

\[\begin{pmatrix} 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 0 & a \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also Projector00, Projector01, Projector10.

Examples

julia> Projector11()
P₁₁(1)

julia> Projector11(0.5)
P₁₁(0.5)

julia> push!(Circuit(), ExpectationValue(Projector11()), 1, 2, 1)
2-qubit, 1-vars circuit with 1 instruction:
└── ⟨P₁₁(1)⟩ @ q[1:2], z[1]

ProjectorX0(a)

One-qubit operator corresponding to a projection onto $|+\rangle$.

The corresponding matrix

\[\frac{a}{2} \begin{pmatrix} 1 & 1\\ 1 & 1 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also ProjectorX1.

Examples

julia> ProjectorX0()
PX₀(1)

julia> ProjectorX0(0.5)
PX₀(0.5)

julia> push!(Circuit(), ExpectationValue(ProjectorX0()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨PX₀(1)⟩ @ q[1], z[1]

ProjectorX1(a)

One-qubit operator corresponding to a projection onto $|-\rangle$.

The corresponding matrix

\[\frac{a}{2} \begin{pmatrix} 1 & -1\\ -1 & 1 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also ProjectorX0.

Examples

julia> ProjectorX1()
PX₁(1)

julia> ProjectorX1(0.5)
PX₁(0.5)

julia> push!(Circuit(), ExpectationValue(ProjectorX1()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨PX₁(1)⟩ @ q[1], z[1]

ProjectorY0(a)

One-qubit operator corresponding to a projection onto $|y+\rangle$.

The corresponding matrix

\[\frac{a}{2} \begin{pmatrix} 1 & -i\\ i & 1 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also ProjectorY1.

Examples

julia> ProjectorY0()
PY₀(1)

julia> ProjectorY0(0.5)
PY₀(0.5)

julia> push!(Circuit(), ExpectationValue(ProjectorY0()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨PY₀(1)⟩ @ q[1], z[1]

ProjectorY1(a)

One-qubit operator corresponding to a projection onto $|y-\rangle$.

The corresponding matrix

\[\frac{a}{2} \begin{pmatrix} 1 & i\\ -i & 1 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also ProjectorY0.

Examples

julia> ProjectorY1()
PY₁(1)

julia> ProjectorY1(0.5)
PY₁(0.5)

julia> push!(Circuit(), ExpectationValue(ProjectorY1()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨PY₁(1)⟩ @ q[1], z[1]

ProjectorZ0(a)

See Projector0.

ProjectorZ1(a)

See Projector1.

ExpectationValue(op)

Operation to compute and store expectation value of an Operator in a z-register.

An expectation value for a pure state $| \psi \rangle$ is defined as

\[\langle O \rangle = \langle \psi | O | \psi \rangle\]

where $O$ is an operator. With respect to a density matrix $\rho$ it's given by

\[\langle O \rangle = \mathrm{Tr}(\rho O).\]

However, when using quantum trajectories to solve noisy circuits, the expectation value is computed with respect to the pure state of each trajectory.

The argument op can be any gate or non-unitary operator.

See also AbstractOperator, AbstractGate.

Examples

In push! the first argument corresponds to the qubit, and the second to the z-register

julia> ExpectationValue(GateX())
⟨X⟩

julia> c = push!(Circuit(), ExpectationValue(GateX()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨X⟩ @ q[1], z[1]

julia> c = push!(Circuit(), ExpectationValue(SigmaPlus()), 1, 2)
1-qubit, 2-vars circuit with 1 instruction:
└── ⟨SigmaPlus(1)⟩ @ q[1], z[2]

SigmaMinus(a)

One-qubit operator corresponding to $|0 \rangle\langle 1|$.

The corresponding matrix

\[\begin{pmatrix} 0 & a\\ 0 & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also SigmaPlus.

Examples

julia> SigmaMinus()
SigmaMinus(1)

julia> SigmaMinus(0.5)
SigmaMinus(0.5)

julia> push!(Circuit(), ExpectationValue(SigmaMinus()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨SigmaMinus(1)⟩ @ q[1], z[1]

SigmaPlus(a)

One-qubit operator corresponding to $|1 \rangle\langle 0|$.

The corresponding matrix

\[\begin{pmatrix} 0 & 0\\ a & 0 \end{pmatrix}\]

is parametrized by $a$ to allow for phases/rescaling.

The parameter $a$ is optional and is set to 1 by default.

See also SigmaMinus.

Examples

julia> SigmaPlus()
SigmaPlus(1)

julia> SigmaPlus(0.5)
SigmaPlus(0.5)

julia> push!(Circuit(), ExpectationValue(SigmaPlus()), 1, 1)
1-qubit, 1-vars circuit with 1 instruction:
└── ⟨SigmaPlus(1)⟩ @ q[1], z[1]

Delay(t)

1-qubit delay gate

This gate is equivalent to a GateID gate, except that it is parametrized by a time parameter t. The parameter does not affect the action of the gate. The only purpose of this gate is to act as a placeholder to indicate idle noise, in which case the parameter t can later be used to further specify the noise properties.

The gate can be created by calling Delay(t) where t is a number.

See also GateID.

Matrix representation

\[\operatorname{Delay}(t) = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}\]

Examples

julia> c = push!(Circuit(), Delay(0.1), 1)
1-qubit circuit with 1 instruction:
└── Delay(0.1) @ q[1]

Decomposition

julia> decompose(Delay(0.2))
1-qubit circuit with 1 instruction:
└── Delay(0.2) @ q[1]

BondDim()

Operation to get the bond dimension between two halves of the system and store in a z-register.

The bond dimension is only defined for a matrix-product state (MPS), which can be written as (with $i_1=i_{N+1}=1$)

\[|\psi \rangle = \sum_{s_1,s_2,\ldots=1}^2 \sum_{i_2}^{\chi_2} \sum_{i_3}^{\chi_3} \ldots \sum_{i_N}^{\chi_N} A^{(s_1)}_{i_1i_2} A^{(s_2)}_{i_2 i_3} A^{(s_3)}_{i_3 i_4} \ldots A^{(s_N)}_{i_{N}i_{N+1}} | s_1, s_2, s_3, \ldots, s_N \rangle .\]

Here, $\chi_k$ is the bond dimension, i.e. the dimension of the index $i_k$. The first and last bond dimensions are dummies, $chi_0=chi_N=1$. A bond dimension of 1 means there is no entanglement between the two halves of the system.

See also VonNeumannEntropy, SchmidtRank.

Examples

When pushing to a circuit, the qubit index $k$ that we give will get back the bond dimension $i_{k}$ in the above notation, i.e. the bond dimension between qubit $k-1$ and qubit $k$. For $k=1$ the bond dimension returned will always be 1.

julia> k = 5;

julia> c = push!(Circuit(), BondDim(), k, 1)
5-qubit, 1-vars circuit with 1 instruction:
└── BondDim @ q[5], z[1]

SchmidtRank()

Operation to get the Schmidt rank of a bipartition and store in a z-register.

A Schmidt decomposition for a bipartition into subsystems $A$ and $B$ is defined for a pure state as

\[|\psi\rangle = \sum_{i=1}^{r} s_i |\alpha_i\rangle \otimes |\beta_i\rangle,\]

where $|\alpha_i\rangle$ ($|\beta_i\rangle$) are orthonormal states acting on $A$ ($B$). The Schmidt rank is the number of terms $r$ in the sum. A product state gives $r=1$ and $r>1$ signals entanglement.

We only consider bipartitions where $A=\{1,\ldots,k-1\}$ and $B=\{k,\ldots,N\}$, for some $k$ and where $N$ is the total number of qubits.

In MPS, when the state is optimally compressed, the Schmidt rank should be equal to the bond dimension BondDim.

See also VonNeumannEntropy.

Examples

When pushing to a circuit, the qubit index $k$ takes the role of the above bipartition into $A$ and $B$. For $k=1$, $A$ is empty and the Schmidt rank will always return 1.

julia> k = 5;

julia> c = push!(Circuit(), SchmidtRank(), k, 1)
5-qubit, 1-vars circuit with 1 instruction:
└── SchmidtRank @ q[5], z[1]

VonNeumannEntropy()

Operation to get the bipartite Von Neumann entanglement entropy and store in a z-register.

The entanglement entropy for a bipartition into subsystems $A$ and $B$ is defined for a pure state $\rho = | \psi \rangle\langle \psi |$ as

\[\mathcal{S}(\rho_A) = - \mathrm{Tr}(\rho_A \log_2 \rho_A) = - \mathrm{Tr}(\rho_B \log_2 \rho_B) = \mathcal{S}(\rho_A)\]

where $\rho_A = \mathrm{Tr}_B(\rho)$ is the reduced density matrix. A product state has $\mathcal{S}(\rho_A)=0$ and a maximally entangled state between $A$ and $B$ gives $\mathcal{S}(\rho_A)=1$.

We only consider bipartitions where $A=\{1,\ldots,k-1\}$ and $B=\{k,\ldots,N\}$, for some $k$ and where $N$ is the total number of qubits.

When the system is open (i.e. with noise) and we are using quantum trajectories, the entanglement entropy of each trajectory is returned during execution.

See also BondDim, SchmidtRank.

Examples

When pushing to a circuit, the qubit index $k$ takes the role of the above bipartition into $A$ and $B$. For $k=1$, $A$ is empty and the entanglement entropy will always return 0.

julia> k = 5;

julia> c = push!(Circuit(), VonNeumannEntropy(), k, 1)
5-qubit, 1-vars circuit with 1 instruction:
└── VonNeumannEntropy @ q[5], z[1]