A spin based heat engine: demonstration of multiple rounds of algorithmic cooling

TL;DR

This paper demonstrates multiple rounds of heat-bath algorithmic cooling in a solid-state NMR quantum processor, achieving qubit polarization beyond the Shannon bound through advanced quantum control techniques.

Contribution

First experimental demonstration of multiple rounds of heat-bath algorithmic cooling surpassing Shannon bound in a solid-state NMR system.

Findings

Achieved qubit polarization 1.69 times the heat-bath polarization

Demonstrated purification of a single qubit beyond Shannon limit

Showed feasibility of nearly pure qubits with advanced quantum control

Abstract

We show experimental results demonstrating multiple rounds of heat-bath algorithmic cooling in a 3 qubit solid-state nuclear magnetic resonance quantum information processor. By dynamically pumping entropy out of the system of interest and into the heat-bath, we are able show purification of a single qubit to a polarization 1.69 times that of the heat-bath and thus go beyond the Shannon bound for closed system cooling. The cooling algorithm implemented requires both high fidelity coherent control and a deliberate controlled interaction with the environment. We discuss the improvements in control that allowed this demonstration. This experimental work shows that given this level of quantum control in systems with sufficiently large polarizations, nearly pure qubits should be achievable.