Breaking the limits of purification: Postselection enhances heat-bath algorithmic cooling

TL;DR

This paper introduces a novel quantum cooling protocol that surpasses traditional heat-bath algorithmic cooling by using a quantum switch and postselection, enabling the creation of multiple pure quantum states without residual mixedness.

Contribution

It demonstrates how to exceed the limits of heat-bath algorithmic cooling through measurement-based protocols utilizing quantum switches and postselection.

Findings

Achieved complete purification of quantum states beyond previous limits

Utilized quantum switch to put operations in superposition

Enabled creation of arbitrary numbers of pure states

Abstract

Quantum technologies require pure states, which are often generated by extreme refrigeration. Heat-bath algorithmic cooling is the theoretically optimal refrigeration technique: it shuttles entropy from a multiparticle system to a thermal bath, thereby generating a quantum state with a high degree of purity. Here, we show how to surpass this hitherto-optimal technique by taking advantage of a single binary-outcome measurement. Our protocols can create arbitrary numbers of pure quantum states without any residual mixedness by using a recently discovered device known as a quantum switch to put two operations in superposition, with postselection certifying the complete purification.