# CircuitSampler¶

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

Bases: qiskit.aqua.operators.converters.converter_base.ConverterBase

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.

Methods

 convert Converts the Operator to one in which the CircuitStateFns are replaced by DictStateFns or VectorStateFns. sample_circuits Samples the CircuitStateFns and returns a dict associating their id() values to their replacement DictStateFn or VectorStateFn. set_backend Sets backend with configuration.

Attributes

backend

Returns the backend.

Return type

Union[Backend, BaseBackend]

Returns

The backend used by the CircuitSampler

quantum_instance

Returns the quantum instance.

Return type

QuantumInstance`

Returns

The QuantumInstance used by the CircuitSampler