BackendEstimatorV2

class qiskit.primitives.BackendEstimatorV2(*, backend, options=None)

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Bases: BaseEstimatorV2

Evaluates expectation values for provided quantum circuit and observable combinations.

The BackendEstimatorV2 class is a generic implementation of the BaseEstimatorV2 interface that is used to wrap a BackendV2 (or BackendV1) object in the BaseEstimatorV2 API. It facilitates using backends that do not provide a native BaseEstimatorV2 implementation in places that work with BaseEstimatorV2. However, if you’re using a provider that has a native implementation of BaseEstimatorV2, it is a better choice to leverage that native implementation as it will likely include additional optimizations and be a more efficient implementation. The generic nature of this class precludes doing any provider- or backend-specific optimizations.

This class does not perform any measurement or gate mitigation, and, presently, is only compatible with Pauli-based observables. More formally, given an observable of the type $O=\sum_{i=1}^Na_iP_i$, where $a_i$ is a complex number and $P_i$ is a Pauli operator, the estimator calculates the expectation $\mathbb{E}(P_i)$ of each $P_i$ and finally calculates the expectation value of $O$ as $\mathbb{E}(O)=\sum_{i=1}^Na_i\mathbb{E}(P_i)$. The reported std is calculated as

$$\frac{\sum_{i=1}^{n}|a_i|\sqrt{\textrm{Var}\big(P_i\big)}}{\sqrt{N}}\:,$$

where $\textrm{Var}(P_i)$ is the variance of $P_i$, $N=O(\epsilon^{-2})$ is the number of shots, and $\epsilon$ is the target precision [1].

Each tuple of (circuit, observables, <optional> parameter values, <optional> precision), called an estimator primitive unified bloc (PUB), produces its own array-based result. The run() method can be given a sequence of pubs to run in one call.

The options for BackendEstimatorV2 consist of the following items.

• default_precision: The default precision to use if none are specified in run(). Default: 0.015625 (1 / sqrt(4096)).
• abelian_grouping: Whether the observables should be grouped into sets of qubit-wise commuting observables. Default: True.
• seed_simulator: The seed to use in the simulator. If None, a random seed will be used. Default: None.

Reference:

[1] O. Crawford, B. van Straaten, D. Wang, T. Parks, E. Campbell, St. Brierley, Efficient quantum measurement of Pauli operators in the presence of finite sampling error. Quantum 5, 385(opens in a new tab)

Parameters

• backend (BackendV1 |BackendV2) – The backend to run the primitive on.
• options (dict(opens in a new tab) | None) – The options to control the default precision (default_precision), the operator grouping (abelian_grouping), and the random seed for the simulator (seed_simulator).

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Attributes

backend

options

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Methods

run