Quantum metrology enhanced by effective time reversal

TL;DR

This paper reviews four classes of quantum metrology strategies that leverage effective time reversal techniques, unifying them under the concept of time-reverse metrology and exploring their potential applications.

Contribution

It introduces a unified framework for four quantum metrology strategies based on effective time reversal, highlighting their properties and potential uses.

Findings

Identifies four classes of time-reversal based quantum metrology strategies.

Unifies these strategies under the concept of time-reverse metrology.

Outlines opportunities for applications across various physics fields.

Abstract

Quantum metrology involves the application of quantum resources to enhance measurements. Several communities have developed quantum-metrology strategies that leverage effective time reversals. These strategies, we posit, form four classes. First, echo metrology begins with a preparatory unitary and ends with that unitary's time-reverse. The protocol amplifies the visibility of a small parameter to be sensed. Similarly, weak-value amplification enhances a weak coupling's detectability. The technique exhibits counterintuitive properties captured by a retrocausal model. Using the third strategy, one simulates closed timelike curves, worldlines that loop back on themselves in time. The fourth strategy involves indefinite causal order, which characterises channels applied in a superposition of orderings. We review these four strategies, which we unify under the heading of time-reverse metrology. We also outline opportunities for this toolkit in quantum metrology; quantum information science; quantum foundations; atomic, molecular, and optical physics; and solid-state physics.