qiskit.aqua.operators.converters.CircuitSampler

class CircuitSampler(backend, statevector=None, param_qobj=False, attach_results=False)

The CircuitSampler traverses an Operator and converts any CircuitStateFns into approximations of the state function by a DictStateFn or VectorStateFn using a quantum backend. Note that in order to approximate the value of the CircuitStateFn, it must 1) send state function through a depolarizing channel, which will destroy all phase information and 2) replace the sampled frequencies with square roots of the frequency, rather than the raw probability of sampling (which would be the equivalent of sampling the square of the state function, per the Born rule.

The CircuitSampler aggressively caches transpiled circuits to handle re-parameterization of the same circuit efficiently. If you are converting multiple different Operators, you are better off using a different CircuitSampler for each Operator to avoid cache thrashing.

Parameters

backend (Union[Backend, BaseBackend, QuantumInstance]) – The quantum backend or QuantumInstance to use to sample the circuits.
statevector (Optional[bool]) – If backend is a statevector backend, whether to replace the CircuitStateFns with DictStateFns (from the counts) or VectorStateFns (from the statevector). None will set this argument automatically based on the backend.
attach_results (bool) – Whether to attach the data from the backend Results object for a given CircuitStateFn` to an execution_results field added the converted DictStateFn or VectorStateFn.
param_qobj (bool) – Whether to use Aer’s parameterized Qobj capability to avoid re-assembling the circuits.

Raises

ValueError – Set statevector or param_qobj True when not supported by backend.

init

__init__(backend, statevector=None, param_qobj=False, attach_results=False)

Parameters

backend (Union[Backend, BaseBackend, QuantumInstance]) – The quantum backend or QuantumInstance to use to sample the circuits.
statevector (Optional[bool]) – If backend is a statevector backend, whether to replace the CircuitStateFns with DictStateFns (from the counts) or VectorStateFns (from the statevector). None will set this argument automatically based on the backend.
attach_results (bool) – Whether to attach the data from the backend Results object for a given CircuitStateFn` to an execution_results field added the converted DictStateFn or VectorStateFn.
param_qobj (bool) – Whether to use Aer’s parameterized Qobj capability to avoid re-assembling the circuits.

Raises

ValueError – Set statevector or param_qobj True when not supported by backend.

Methods


`__init__`(backend[, statevector, param_qobj, …])	type backend`Union`[`Backend`, `BaseBackend`, `QuantumInstance`]
`convert`(operator[, params])	Converts the Operator to one in which the CircuitStateFns are replaced by DictStateFns or VectorStateFns.
`sample_circuits`([circuit_sfns, param_bindings])	Samples the CircuitStateFns and returns a dict associating their `id()` values to their replacement DictStateFn or VectorStateFn.
`set_backend`(backend, **kwargs)	Sets backend with configuration.

Attributes


`backend`	Returns the backend.
`quantum_instance`	Returns the quantum instance.

backend

Returns the backend.

Return type

Union[Backend, BaseBackend]

Returns

The backend used by the CircuitSampler

convert

convert(operator, params=None)

Converts the Operator to one in which the CircuitStateFns are replaced by DictStateFns or VectorStateFns. Extracts the CircuitStateFns out of the Operator, caches them, calls sample_circuits below to get their converted replacements, and replaces the CircuitStateFns in operator with the replacement StateFns.

Parameters

operator (OperatorBase) – The Operator to convert
params (Optional[Dict[Parameter, Union[float, List[float], List[List[float]]]]]) – A dictionary mapping parameters to either single binding values or lists of binding values.

Return type

OperatorBase

Returns

The converted Operator with CircuitStateFns replaced by DictStateFns or VectorStateFns.

Raises

AquaError – if extracted circuits are empty.

quantum_instance

Returns the quantum instance.

Return type

QuantumInstance

Returns

The QuantumInstance used by the CircuitSampler

sample_circuits

sample_circuits(circuit_sfns=None, param_bindings=None)

Samples the CircuitStateFns and returns a dict associating their id() values to their replacement DictStateFn or VectorStateFn. If param_bindings is provided, the CircuitStateFns are broken into their parameterizations, and a list of StateFns is returned in the dict for each circuit id(). Note that param_bindings is provided here in a different format than in convert, and lists of parameters within the dict is not supported, and only binding dicts which are valid to be passed into Terra can be included in this list.

Parameters

circuit_sfns (Optional[List[CircuitStateFn]]) – The list of CircuitStateFns to sample.
param_bindings (Optional[List[Dict[Parameter, List[float]]]]) – The parameterizations to bind to each CircuitStateFn.

Return type

Dict[int, Union[StateFn, List[StateFn]]]

Returns

The dictionary mapping ids of the CircuitStateFns to their replacement StateFns.

Raises

AquaError – if extracted circuits are empty.

set_backend

set_backend(backend, **kwargs)

Sets backend with configuration.

Raises

ValueError – statevector or param_qobj are True when not supported by backend.

Return type

None

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