Cooling and Autonomous Feedback in a Bose-Hubbard chain with Attractive Interactions

TL;DR

This paper demonstrates a method to cool and stabilize specific quantum states in a Bose-Hubbard chain with attractive interactions using engineered quantum baths and autonomous feedback, implemented with superconducting qubits.

Contribution

It introduces a novel cooling protocol that preserves particle number and enables autonomous stabilization of eigenstates in a Bose-Hubbard system using superconducting qubits.

Findings

Successful implementation of a quantum bath for entropy exchange.

Preparation of dark states inaccessible by coherent drives.

Continuous microwave radiation achieves autonomous feedback for state stabilization.

Abstract

We engineer a quantum bath that enables entropy and energy exchange with a one-dimensional Bose-Hubbard lattice with attractive on-site interactions. We implement this in an array of three superconducting transmon qubits coupled to a single cavity mode; the transmons represent lattice sites and their excitation quanta embody bosonic particles. Our cooling protocol preserves particle number--realizing a canonical ensemble-- and also affords the efficient preparation of dark states which, due to symmetry, cannot be prepared via coherent drives on the cavity. Furthermore, by applying continuous microwave radiation, we also realize autonomous feedback to indefinitely stabilize particular eigenstates of the array.