Quantum non-demolition measurements of moving target states

TL;DR

This paper introduces a protocol for quantum non-demolition measurements that uses entanglement and continuous monitoring to infer the state and dynamics of a quantum system, with applications in quantum metrology and computing.

Contribution

It extends quantum non-demolition measurement techniques to moving target states via resonant coupling and entanglement with a meter system.

Findings

Photon number in a cavity can be resolved through continuous measurement.

The protocol enables non-destructive inference of quantum state evolution.

Potential applications include enhanced quantum measurement and information processing.

Abstract

We present a protocol for probing the state of a quantum system by its resonant coupling and entanglement with a meter system. By continuous measurement of a time evolving meter observable, we infer the evolution of the entangled systems and, ultimately, the state and dynamics of the system of interest. The photon number in a cavity field is thus resolved by simulated monitoring of the time dependent excited state population of a resonantly coupled two-level system, and we propose to regard this as an extension of quantum non-demolition measurements with potential applications in quantum metrology and quantum computing.