Analytical Simulator¶

The analytical simulator computes the expectation value of the cost Hamiltonian, \(H_C\), with respect to the given circuit, using the energy_expectation_analytical function in openqaoa.utilities. The formula can be found in the appendices of [1]. It is mostly used to study QAOAs with a single layer, that is it only works for \(p=1\).

For the curious

Since the expectation value of the quantum state prepared with a p=1 QAOA circuit cna be computed efficiently on a classical computer, \(O(n^4)\), there's no quantum speedup for such circuits. Nevertheless, those are very interesting from research perspective.

Key features:¶

Only works for a single-layer circuits, \(p=1\), standard parametrization, x_mixer_hamiltonian
Preferred choice for large circuits, \(n \geq 20\).
Noiseless simulations

Explicitly create the analytical simulator device¶

If you want to explicitly set the analytical simulator device use the following snippet

from openqaoa import QAOA, create_device

analytical_device = create_device(location='local', name='analytical_simulator')
q.set_device(analytical_device)

Expectation values of RQAOA

Recall that RQAOA requires computing the expectation values of pair and single spins. When using the analytical device, the expectation values will also be computed analytically, using the exp_val_single_analytical and exp_val_pair_analytical functions from the openqaoa.utilities.

References¶

S. Bravyi, A. Kliesch, R. Koenig, and E. Tang, (2022) Quantum 6, 678, https://arxiv.org/abs/2011.13420.