Class ParamCirc

Inheritance Relationships

Base Type

Class Documentation

class ParamCirc : public qb::CircuitBuilder

This class is used to build parametrized quantum circuits for execution as part of quantum machine learning algorithms. It can use any of the standard gates from qb::CircuitBuilder, as well as create input/ variational parameters using the single-parameter gates shown below.

Public Functions

ParamCirc(std::size_t numQubits, qml::DefaultAnsatzes ansatzType, std::size_t numAnsatzRepetitions, qb::VectorString varGates)

Creates a parametrized circuit with a pre-defined ansatz.

Parameters:

  • numQubits – Number of qubits in the parametrised circuit (also currently sets number of input parameters) [size_t]

  • ansatzType – Type of parametric circuit ansatz to be created (currently only query opt. implemented) [qb::qml::DefaultAnsatzes]

  • numAnsatzRepetitions – Number of layers of the ansatz [size_t]

  • varGates – Which gates to be optimised variationally, given as a vector of gate names within {“Rx”,”Ry”,”Rz”} [qb::VectorString]

inline ParamCirc(size_t numQubits)

Constructs an empty parametrized circuit to be used with the circuit builder.

Parameters:

numQubits – Number of qubits in the parametrised circuit

inline void RX(size_t index, char *type)

RX gate.

This method adds an x-axis rotation (RX) gate to the circuit.

The RX gate is defined by its action on the basis states

\[ RX(\theta)\ket{0} \rightarrow \cos(\theta/2)\ket{0} - i\sin(\theta/2)\ket{1} RX(\theta)\ket{1} \rightarrow -i\sin(\theta/2)\ket{0} + \cos(\theta/2)\ket{1} \]

Parameters:

  • index – the index of the qubit being acted on [size_t]

  • type – the type of input parameter (“input” or “variational”) [std::string]

inline void RY(size_t index, char *type)

RY gate.

This method adds a y-axis rotation (RY) gate to the circuit.

The RY gate is defined by its action on the basis states

\[ RY(\theta)\ket{0} \rightarrow \cos(\theta/2)\ket{0} + \sin(\theta/2)\ket{1} RY(\theta)\ket{1} \rightarrow -\sin(\theta/2)\ket{0} + \cos(\theta/2)\ket{1} \]

Parameters:

  • index – the index of the qubit being acted on [size_t]

  • type – the type of input parameter (“input” or “variational”) [std::string]

inline void RZ(size_t index, char *type)

RZ gate.

This method adds a z-axis rotation (RZ) gate to the circuit.

The RZ gate is defined by its action on the basis states

\[ RZ(\theta)\ket{0} \rightarrow e^{-i\theta/2}\ket{0} RZ(\theta)\ket{1} \rightarrow e^{i\theta/2}\ket{1} \]

Parameters:

  • index – the index of the qubit being acted on [size_t]

  • type – the type of input parameter (“input” or “variational”) [std::string]

inline void U1(size_t index, char *type)

U1 gate.

This method adds a phase (U1) gate to the circuit.

The U1 gate is defined by its action on the basis states

\[ U1(\theta)\ket{0} \rightarrow \ket{0} U1(\theta)\ket{1} \rightarrow e^{i\theta}\ket{1} \]

Parameters:

  • index – the index of the qubit being acted on [size_t]

  • type – the type of input parameter (“input” or “variational”) [std::string]

inline void CPhase(size_t ctrl_index, size_t target_index, char *type)

CPhase gate.

This method adds a controlled-U1 (CPhase) gate to the circuit.

The CPHase gate performs a U1 gate on the target qubit conditional on the control qubit being in the \(\ket{1}\) state. That is:

\[ CPhase(\theta)\ket{ab} \rightarrow \ket{a}U1(\theta)^a \ket{b} \]

Parameters:

  • ctrl_index – the index of the control qubit [size_t]

  • target_index – the index of the target qubit [size_t]

  • type – the type of input parameter (“input” or “variational”) [std::string]

inline void reupload()

Function for reuploading within the circuit, allowing for repeating the encoding ansatz.

inline std::size_t getNumInputs()

Return the number of input parameters.

inline std::size_t getNumParams()

Return the number of variational parameters.

inline std::size_t getNumQubits()

Return the number of qubits in the parametrized circuit.

inline std::size_t getNumAnsatzRepetitions()

Return the number of repetitions of the base ansatz (currently only has utility for DefaultAnsatz constructor).

Private Functions

void queryOptAnsatz()
std::vector<std::string> genParamNames()
void processAndAddGate(std::string gateName, std::vector<size_t> qubits, char *type)

Private Members

std::size_t numQubits_ = {0}
std::size_t numInputs_ = {0}
std::size_t numAnsatzRepetitions_{0}
qb::VectorString varGates_
std::size_t numParams_ = {0}
bool reuploading_{false}
std::shared_ptr<xacc::CompositeInstruction> encodingAnsatz_
std::vector<size_t> encParamIndices_
std::vector<size_t> varParamIndices_

Friends

friend class QMLExecutor