Quantum measurements of atoms using cavity QED

TL;DR

This paper demonstrates how to implement two non-standard quantum measurements using cavity QED with atoms, including state discrimination and superadditive quantum coding, highlighting potential for scalable quantum information processing.

Contribution

It introduces methods to realize two advanced quantum measurements with atoms in cavity QED, expanding beyond photon-based implementations.

Findings

Optimal state discrimination achieved despite experimental imperfections.

Superadditive quantum coding gain persists with high detection error levels.

Potential for scalable atomic quantum measurement implementations.

Abstract

Generalized quantum measurements are an important extension of projective or von Neumann measurements, in that they can be used to describe any measurement that can be implemented on a quantum system. We describe how to realize two non-standard quantum measurements using cavity quantum electrodynamics (QED). The first measurement optimally and unabmiguously distinguishes between two non-orthogonal quantum states. The second example is a measurement that demonstrates superadditive quantum coding gain. The experimental tools used are single-atom unitary operations effected by Ramsey pulses and two-atom Tavis-Cummings interactions. We show how the superadditive quantum coding gain is affected by errors in the field-ionisation detection of atoms, and that even with rather high levels of experimental imperfections, a reasonable amount of superadditivity can still be seen. To date, these types of measurement have only been realized on photons. It would be of great interest to have realizations using other physical systems. This is for fundamental reasons, but also since quantum coding gain in general increases with code word length, and a realization using atoms could be more easily scaled than existing realizations using photons.