Anti-Zeno purification of spin baths by quantum probe measurements

TL;DR

This paper introduces a method to purify spin baths using selective measurements on a coupled qubit, enhancing quantum memory and sensing capabilities by creating long-lived, low-entropy bath states.

Contribution

It presents a novel approach to control and purify the environment (spin bath) via measurement sequences, extending quantum Zeno and anti-Zeno paradigms.

Findings

Measurement sequences can significantly increase bath purity.

Purified bath states remain stable after measurements.

Experiment demonstrated bath purification in diamond defect centers.

Abstract

The quantum Zeno and anti-Zeno paradigms have thus far addressed the evolution control of a quantum system coupled to an immutable bath via non-selective measurements performed at appropriate intervals. We fundamentally modify these paradigms by introducing, theoretically and experimentally, the concept of controlling the bath state via selective measurements of the system (a qubit). We show that at intervals corresponding to the anti-Zeno regime of the system-bath exchange, a sequence of measurements has strongly correlated outcomes. These correlations can dramatically enhance the bath-state purity and yield a low-entropy steady state of the bath. The purified bath state persists long after the measurements are completed. Such purification enables the exploitation of spin baths as long-lived quantum memories or as quantum-enhanced sensors. The experiment involved a repeatedly probed defect center dephased by a nuclear spin bath in a diamond at low-temperature.