AdaptVQE¶

class AdaptVQE(solver, *, threshold=1e-05, max_iterations=None)[source]¶

Bases: qiskit.algorithms.variational_algorithm.VariationalAlgorithm, qiskit.algorithms.minimum_eigensolvers.minimum_eigensolver.MinimumEigensolver

The Adaptive Variational Quantum Eigensolver algorithm.

AdaptVQE is a quantum algorithm which creates a compact ansatz from a set of evolution operators. It iteratively extends the ansatz circuit, by selecting the building block that leads to the largest gradient from a set of candidates. In chemistry, this is usually a list of orbital excitations. Thus, a common choice of ansatz to be used with this algorithm is the Unitary Coupled Cluster ansatz implemented in Qiskit Nature. This results in a wavefunction ansatz which is uniquely adapted to the operator whose minimum eigenvalue is being determined. This class relies on a supplied instance of VQE to find the minimum eigenvalue. The performance of AdaptVQE significantly depends on the minimization routine.

from qiskit.algorithms.minimum_eigensolvers import AdaptVQE, VQE
from qiskit.algorithms.optimizers import SLSQP
from qiskit.primitives import Estimator
from qiskit.circuit.library import EvolvedOperatorAnsatz

# get your Hamiltonian
hamiltonian = ...

# construct your ansatz
ansatz = EvolvedOperatorAnsatz(...)

vqe = VQE(Estimator(), ansatz, SLSQP())

adapt_vqe = AdaptVQE(vqe)

eigenvalue, _ = adapt_vqe.compute_minimum_eigenvalue(hamiltonian)

The following attributes can be set via the initializer but can also be read and updated once the AdaptVQE object has been constructed.

solver¶: a VQE instance used internally to compute the minimum eigenvalues. It is a requirement that the ansatz of this solver is of type qiskit.circuit.library.EvolvedOperatorAnsatz.

threshold¶: the convergence threshold for the algorithm. Once all gradients have an absolute value smaller than this threshold, the algorithm terminates.

max_iterations¶: the maximum number of iterations for the adaptive loop. If None, the algorithm is not bound in its number of iterations.

Parameters

solver (VQE) – a VQE instance used internally to compute the minimum eigenvalues. It is a requirement that the ansatz of this solver is of type qiskit.circuit.library.EvolvedOperatorAnsatz.
threshold (float) – the convergence threshold for the algorithm. Once all gradients have an absolute value smaller than this threshold, the algorithm terminates.
max_iterations (int | None) – the maximum number of iterations for the adaptive loop. If None, the algorithm is not bound in its number of iterations.

Methods

`compute_minimum_eigenvalue`	Computes the minimum eigenvalue.
`supports_aux_operators`	Whether computing the expectation value of auxiliary operators is supported.

Attributes

initial_point¶

Returns the initial point of the internal VQE solver.

Return type: Sequence[float] | None