cirq.SimulatesExpectationValues

Simulator that computes exact expectation values of observables.

Given a circuit and an observable map, computes exact (to float precision) expectation values for each observable at the end of the circuit.

Implementors of this interface should implement the simulate_expectation_values_sweep_iter method.

Methods

`simulate_expectation_values`

View source

simulate_expectation_values(
    program: 'cirq.AbstractCircuit',
    observables: Union['cirq.PauliSumLike', List['cirq.PauliSumLike']],
    param_resolver: 'cirq.ParamResolverOrSimilarType' = None,
    qubit_order: 'cirq.QubitOrderOrList' = cirq.QubitOrder.DEFAULT,
    initial_state: Any = None,
    permit_terminal_measurements: bool = False
) -> List[float]

Simulates the supplied circuit and calculates exact expectation values for the given observables on its final state.

This method has no perfect analogy in hardware. Instead compare with Sampler.sample_expectation_values, which calculates estimated expectation values by sampling multiple times.

Args
`program`	The circuit to simulate.
`observables`	An observable or list of observables.
`param_resolver`	Parameters to run with the program.
`qubit_order`	Determines the canonical ordering of the qubits. This is often used in specifying the initial state, i.e. the ordering of the computational basis states.
`initial_state`	The initial state for the simulation. The form of this state depends on the simulation implementation. See documentation of the implementing class for details.
`permit_terminal_measurements`	If the provided circuit ends with measurement(s), this method will generate an error unless this is set to True. This is meant to prevent measurements from ruining expectation value calculations.

Returns
A list of expectation values, with the value at index `n` corresponding to `observables[n]` from the input.

Raises
ValueError if 'program' has terminal measurement(s) and 'permit_terminal_measurements' is False.

`simulate_expectation_values_sweep`

View source

simulate_expectation_values_sweep(
    program: 'cirq.AbstractCircuit',
    observables: Union['cirq.PauliSumLike', List['cirq.PauliSumLike']],
    params: 'cirq.Sweepable',
    qubit_order: 'cirq.QubitOrderOrList' = cirq.QubitOrder.DEFAULT,
    initial_state: Any = None,
    permit_terminal_measurements: bool = False
) -> List[List[float]]

Wraps computed expectation values in a list.

Prefer overriding simulate_expectation_values_sweep_iter.

`simulate_expectation_values_sweep_iter`

View source

simulate_expectation_values_sweep_iter(
    program: 'cirq.AbstractCircuit',
    observables: Union['cirq.PauliSumLike', List['cirq.PauliSumLike']],
    params: 'cirq.Sweepable',
    qubit_order: 'cirq.QubitOrderOrList' = cirq.QubitOrder.DEFAULT,
    initial_state: Any = None,
    permit_terminal_measurements: bool = False
) -> Iterator[List[float]]

Simulates the supplied circuit and calculates exact expectation values for the given observables on its final state, sweeping over the given params.

This method has no perfect analogy in hardware. Instead compare with Sampler.sample_expectation_values, which calculates estimated expectation values by sampling multiple times.

Args
`program`	The circuit to simulate.
`observables`	An observable or list of observables.
`params`	Parameters to run with the program.
`qubit_order`	Determines the canonical ordering of the qubits. This is often used in specifying the initial state, i.e. the ordering of the computational basis states.
`initial_state`	The initial state for the simulation. The form of this state depends on the simulation implementation. See documentation of the implementing class for details.
`permit_terminal_measurements`	If the provided circuit ends in a measurement, this method will generate an error unless this is set to True. This is meant to prevent measurements from ruining expectation value calculations.

Returns
An Iterator over expectation-value lists. The outer index determines the sweep, and the inner index determines the observable. For instance, results[1][3] would select the fourth observable measured in the second sweep.

Raises
ValueError if 'program' has terminal measurement(s) and 'permit_terminal_measurements' is False.