---
title: CircuitSampler (v0.46)
description: API reference for qiskit.opflow.converters.CircuitSampler in qiskit v0.46
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/0.46/qiskit.opflow.converters.CircuitSampler
---

# CircuitSampler

*class* `qiskit.opflow.converters.CircuitSampler(backend, statevector=None, param_qobj=False, attach_results=False, caching='last')`

[GitHub](https://github.com/qiskit/qiskit/tree/stable/0.46/qiskit/opflow/converters/circuit_sampler.py)

Bases: [`ConverterBase`](/docs/api/qiskit/0.46/qiskit.opflow.converters.ConverterBase "qiskit.opflow.converters.converter_base.ConverterBase")

Deprecated: 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.

> **Deprecated since version 0.24.0**
>
> The class `qiskit.opflow.converters.circuit_sampler.CircuitSampler` is deprecated as of qiskit-terra 0.24.0. It will be removed in the Qiskit 1.0 release. For code migration guidelines, visit [https://qisk.it/opflow\_migration](https://qisk.it/opflow_migration).

**Parameters**

- **backend** ([*Backend*](/docs/api/qiskit/0.46/qiskit.providers.Backend "qiskit.providers.backend.Backend")  *|*[*QuantumInstance*](/docs/api/qiskit/0.46/qiskit.utils.QuantumInstance "qiskit.utils.quantum_instance.QuantumInstance")) – The quantum backend or QuantumInstance to use to sample the circuits.
- **statevector** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *| None*) – 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*](https://docs.python.org/3/library/functions.html#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*](https://docs.python.org/3/library/functions.html#bool)) – Whether to use Aer’s parameterized Qobj capability to avoid re-assembling the circuits.
- **caching** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – The caching strategy. Can be ‘last’ (default) to store the last operator that was converted, set to ‘all’ to cache all processed operators.

**Raises**

[**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError) – Set statevector or param\_qobj True when not supported by backend.

## Attributes

### quantum\_instance

Returns the quantum instance.

**Returns**

The QuantumInstance used by the CircuitSampler

## Methods

### clear\_cache

`clear_cache()`

Clear the cache of sampled operator expressions.

### 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*](/docs/api/qiskit/0.46/qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")) – The Operator to convert
- **params** ([*Dict*](https://docs.python.org/3/library/typing.html#typing.Dict)*\[*[*Parameter*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.parameter.Parameter")*,* [*float*](https://docs.python.org/3/library/functions.html#float)  *|*[*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*float*](https://docs.python.org/3/library/functions.html#float)*] |* [*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*float*](https://docs.python.org/3/library/functions.html#float)*]]] | None*) – A dictionary mapping parameters to either single binding values or lists of binding values.

**Returns**

The converted Operator with CircuitStateFns replaced by DictStateFns or VectorStateFns.

**Raises**

[**OpflowError**](/docs/api/qiskit/0.46/opflow#qiskit.opflow.OpflowError "qiskit.opflow.OpflowError") – if extracted circuits are empty.

**Return type**

[*OperatorBase*](/docs/api/qiskit/0.46/qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")

### 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** ([*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*CircuitStateFn*](/docs/api/qiskit/0.46/qiskit.opflow.state_fns.CircuitStateFn "qiskit.opflow.state_fns.circuit_state_fn.CircuitStateFn")*] | None*) – The list of CircuitStateFns to sample.
- **param\_bindings** ([*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*Dict*](https://docs.python.org/3/library/typing.html#typing.Dict)*\[*[*Parameter*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.parameter.Parameter")*,* [*float*](https://docs.python.org/3/library/functions.html#float)*]] | None*) – The parameterizations to bind to each CircuitStateFn.

**Returns**

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

**Raises**

[**OpflowError**](/docs/api/qiskit/0.46/opflow#qiskit.opflow.OpflowError "qiskit.opflow.OpflowError") – if extracted circuits are empty.

**Return type**

[*Dict*](https://docs.python.org/3/library/typing.html#typing.Dict)\[[int](https://docs.python.org/3/library/functions.html#int), [*List*](https://docs.python.org/3/library/typing.html#typing.List)\[[*StateFn*](/docs/api/qiskit/0.46/qiskit.opflow.state_fns.StateFn "qiskit.opflow.state_fns.state_fn.StateFn")]]