High Fidelity Quantum Gates in the Presence of Dispersion

TL;DR

This paper demonstrates high-fidelity quantum gate control in an ensemble of neutral atoms within an optical lattice, effectively managing inhomogeneous and spectral variations caused by dispersion through an ensemble-averaged optimal control approach.

Contribution

It introduces an ensemble-averaged optimal control method that achieves robust, high-fidelity quantum gates despite dispersion and inhomogeneity in the system.

Findings

Achieved average fidelities above 98% for quantum gates.

Developed control pulses with broadband spectra effective across quasimomentum variations.

Demonstrated robustness of control in a model system with up to 13.2% dispersion.

Abstract

We numerically demonstrate the control of motional degrees of freedom of an ensemble of neutral atoms in an optical lattice with a shallow trapping potential. Taking into account the range of quasimomenta across different Brillouin zones results in an ensemble whose members effectively have inhomogeneous control fields as well as spectrally distinct control Hamiltonians. We present an ensemble-averaged optimal control technique that yields high fidelity control pulses, irrespective of quasimomentum, with average fidelities above 98%. The resulting controls show a broadband spectrum with gate times in the order of several free oscillations to optimize gates with up to 13.2% dispersion in the energies from the band structure. This can be seen as a model system for the prospects of robust quantum control. This result explores the limits of discretizing a continuous ensemble for control theory.