# Quantum Virtual Cooling

## TL;DR

This paper introduces a quantum virtual cooling protocol that uses collective measurements on multiple copies of a quantum system to effectively lower its temperature, enabling access to regimes beyond conventional cooling methods.

## Contribution

The authors propose and experimentally demonstrate a quantum information-based scheme for virtual cooling of many-body systems, achieving lower effective temperatures than physical cooling.

## Key findings

- Successfully implemented on a Bose-Hubbard model with up to 12 sites.
- Extracted observables at half the physical temperature.
- Demonstrated techniques for directly accessing zero-temperature states.

## Abstract

We propose a quantum information based scheme to reduce the temperature of quantum many-body systems, and access regimes beyond the current capability of conventional cooling techniques. We show that collective measurements on multiple copies of a system at finite temperature can simulate measurements of the same system at a lower temperature. This idea is illustrated for the example of ultracold atoms in optical lattices, where controlled tunnel coupling and quantum gas microscopy can be naturally combined to realize the required collective measurements to access a lower, virtual temperature. Our protocol is experimentally implemented for a Bose-Hubbard model on up to 12 sites, and we successfully extract expectation values of observables at half the temperature of the physical system. Additionally, we present related techniques that enable the extraction of zero-temperature states directly.