Autonomous coherence protection of a two-level system in a fluctuating environment

TL;DR

This paper demonstrates a generalized coherence protection scheme for two-level quantum systems that effectively mitigates inhomogeneous broadening and environmental noise, significantly enhancing qubit coherence times and uniformity for quantum technologies.

Contribution

The study extends a previous Doppler broadening compensation scheme to protect qubits from time- and space-dependent noise, enabling simultaneous stabilization of multiple qubits.

Findings

Achieves three orders of magnitude increase in qubit coherence time.

Effectively refocuses drifting qubit frequencies in fluctuating environments.

Enables parallel stabilization of multiple qubits for quantum computing and sensing.

Abstract

We re-examine a scheme generalized by [R. Finkelstein et al, Phys. Rev. X 11, 011008 (2021)], whose original purpose was to remove the effects of static Doppler broadening from an ensemble of non-interacting two-level systems (qubits). This scheme involves the simultaneous application of red and blue detuned drives between a qubit level and an auxiliary level, and by carefully choosing the drive amplitudes and detunings, the drive-induced energy shifts can exactly compensate the inhomogeneous static Doppler-induced frequency shifts - effectively removing the inhomogeneous Doppler broadening. We demonstrate that this scheme is far more powerful and can also protect a single (or even an ensemble), qubit's energy levels from noise which depends on both time and space: the same scheme can greatly reduce the effects of dephasing noise induced by a time-fluctuating environment. As examples we study protection against two types of non-Markovian environments that appear in many physical systems: Gaussian noise and non-Gaussian noise - Random Telegraph Noise. Through numerical simulations we demonstrate the enhancement of the spin coherence time $T_2^*$, of a qubit in a fluctuating environment by three orders of magnitude as well as the refocusing of its initially drifting frequency. This same scheme, using only two drives, can operate on an collection of qubits, providing temporal and spatial stabilization simultaneously and in parallel yielding a collection of high quality near-identical qubits which can be useful for many quantum technologies such as quantum computing and sensing, with the potential to achieve fault tolerant quantum computation much sooner.