qml.operation

Warning

Unless you are a PennyLane or plugin developer, you likely do not need to use these classes directly.

See the main operations page for details on available operations and observables.

This module contains the abstract base classes for defining PennyLane operations and observables.

Description

Qubit Operations

The Operator class serves as a base class for operators, and is inherited by both the Observable class and the Operation class. These classes are subclassed to implement quantum operations and measure observables in PennyLane.

  • Each Operator subclass represents a general type of map between physical states. Each instance of these subclasses represents either

    • an application of the operator or

    • an instruction to measure and return the respective result.

    Operators act on a sequence of wires (subsystems) using given parameter values.

  • Each Operation subclass represents a type of quantum operation, for example a unitary quantum gate. Each instance of these subclasses represents an application of the operation with given parameter values to a given sequence of wires (subsystems).

  • Each Observable subclass represents a type of physical observable. Each instance of these subclasses represents an instruction to measure and return the respective result for the given parameter values on a sequence of wires (subsystems).

Differentiation

In general, an Operation is differentiable (at least using the finite-difference method) with respect to a parameter iff

  • the domain of that parameter is continuous.

For an Operation to be differentiable with respect to a parameter using the analytic method of differentiation, it must satisfy an additional constraint:

  • the parameter domain must be real.

Note

These conditions are not sufficient for analytic differentiation. For example, CV gates must also define a matrix representing their Heisenberg linear transformation on the quadrature operators.

CV Operation base classes

Due to additional requirements, continuous-variable (CV) operations must subclass the CVOperation or CVObservable classes instead of Operation and Observable.

Differentiation

To enable gradient computation using the analytic method for Gaussian CV operations, in addition, you need to provide the static class method _heisenberg_rep() that returns the Heisenberg representation of the operation given its list of parameters, namely:

  • For Gaussian CV Operations this method should return the matrix of the linear transformation carried out by the operation on the vector of quadrature operators \(\mathbf{r}\) for the given parameter values.

  • For Gaussian CV Observables this method should return a real vector (first-order observables) or symmetric matrix (second-order observables) of coefficients of the quadrature operators \(\x\) and \(\p\).

PennyLane uses the convention \(\mathbf{r} = (\I, \x, \p)\) for single-mode operations and observables and \(\mathbf{r} = (\I, \x_0, \p_0, \x_1, \p_1, \ldots)\) for multi-mode operations and observables.

Note

Non-Gaussian CV operations and observables are currently only supported via the finite-difference method of gradient computation.

Functions

classproperty(func)

The class property decorator

operation_derivative(operation)

Calculate the derivative of an operation.

Classes

AdjointUndefinedError

Raised when an Operator’s adjoint version is undefined.

CV()

A mixin base class denoting a continuous-variable operation.

CVObservable(*params[, wires, do_queue, id])

Base class representing continuous-variable observables.

CVOperation(*params[, wires, do_queue, id])

Base class representing continuous-variable quantum gates.

Channel(*params[, wires, do_queue, id])

Base class for quantum channels.

DecompositionUndefinedError

Raised when an Operator’s representation as a decomposition is undefined.

DiagGatesUndefinedError

Raised when an Operator’s diagonalizing gates are undefined.

EigvalsUndefinedError

Raised when an Operator’s eigenvalues are undefined.

GeneratorUndefinedError

Exception used to indicate that an operator does not have a generator

MatrixUndefinedError

Raised when an Operator’s matrix representation is undefined.

Observable(*params[, wires, do_queue, id])

Base class representing observables.

Operation(*params[, wires, do_queue, id])

Base class representing quantum gates or channels applied to quantum states.

Operator(*params[, wires, do_queue, id])

Base class representing quantum operators.

OperatorPropertyUndefined

Generic exception to be used for undefined Operator properties or methods.

ParameterFrequenciesUndefinedError

Exception used to indicate that an operator does not have parameter_frequencies

PowUndefinedError

Raised when an Operator’s power is undefined.

SparseMatrixUndefinedError

Raised when an Operator’s sparse matrix representation is undefined.

Tensor(*args)

Container class representing tensor products of observables.

TermsUndefinedError

Raised when an Operator’s representation as a linear combination is undefined.

WiresEnum(value)

Integer enumeration class to represent the number of wires an operation acts on

Variables

AllWires

An enumeration which represents all wires in the subsystem.

AnyWires

An enumeration which represents any wires in the subsystem.

List

The central part of internal API.

defines_diagonalizing_gates

Returns True if an operator defines the diagonalizing gates are defined.

gen_is_multi_term_hamiltonian

Returns True if an operator has a generator defined and it is a Hamiltonian with more than one term.

has_gen

Returns True if an operator has a generator defined.

has_grad_method

Returns True if an operator has a grad_method defined.

has_multipar

Returns True if an operator has more than one parameter according to num_params.

has_nopar

Returns True if an operator has no parameters according to num_params.

has_unitary_gen

Returns True if an operator has a unitary_generator according to the has_unitary_generator flag.

is_measurement

Returns True if an operator is a MeasurementProcess instance.

is_trainable

Returns True if any of the parameters of an operator is trainable according to qml.math.requires_grad.

not_tape

Returns True if the object is not a quantum tape

Class Inheritance Diagram

Inheritance diagram of pennylane.operation.AdjointUndefinedError, pennylane.operation.CV, pennylane.operation.CVObservable, pennylane.operation.CVOperation, pennylane.operation.Channel, pennylane.operation.DecompositionUndefinedError, pennylane.operation.DiagGatesUndefinedError, pennylane.operation.EigvalsUndefinedError, pennylane.operation.GeneratorUndefinedError, pennylane.operation.MatrixUndefinedError, pennylane.operation.Observable, pennylane.operation.Operation, pennylane.operation.Operator, pennylane.operation.OperatorPropertyUndefined, pennylane.operation.ParameterFrequenciesUndefinedError, pennylane.operation.PowUndefinedError, pennylane.operation.SparseMatrixUndefinedError, pennylane.operation.Tensor, pennylane.operation.TermsUndefinedError, pennylane.operation.WiresEnum

Operation attributes

PennyLane contains a mechanism for storing lists of operations with similar attributes and behaviour (for example, those that are their own inverses). The attributes below are already included, and are used primarily for the purpose of compilation transforms. New attributes can be added by instantiating new Attribute objects.

Attribute

Class to represent a set of operators with a certain attribute.

composable_rotations

Operations for which composing multiple copies of the operation results in an addition (or alternative accumulation) of parameters.

diagonal_in_z_basis

Operations that are diagonal in the computational basis.

has_unitary_generator

Operations that are generated by a unitary operator.

self_inverses

Operations that are their own inverses.

supports_broadcasting

Operations that support parameter broadcasting.

symmetric_over_all_wires

Operations that are the same if you exchange the order of wires.

symmetric_over_control_wires

Controlled operations that are the same if you exchange the order of all but the last (target) wire.