29 August 2022

ICTS faculty member Sthitadhi Roy’s publication (in collaboration with Max McGinley and S.A. Parameswaran from Oxford University), titled “Absolutely Stable Spatiotemporal Order in Noisy Quantum Systems,” was highlighted as Editors’ Suggestion in Physical Review Letters.

Ordinary crystals, familiar from everyday life, have a periodic structure in space. Out-of-equilibirum quantum systems can host a phase of matter known as a “time crystal” which show regular patterns in both space and time and can be identified from their spatiotemporal order. Unfortunately, there are fundamental obstacles to creating such time crystals in a laboratory or realising it on quantum computers due to the presence of noise and imperfections in real quantum systems, which melt the time crystal. In this work, Sthitadhi and collaborators propose a new way overcoming these obstacles so as to stabilise such a time crystal. To counteract noise, they make regular measurements of the qubits, and use the information gained from these measurements as a feedback in a way that restores the periodic ordering in space-time. This “quantum interactive dynamics” approach to controlling quantum systems, combining measurements and feedback, holds great promise as a means of stabilising other new phases of matter in the rich setting afforded by present-day noisy quantum computing devices.