Atomic homodyne detection of continuous variable entangled twin-atom states

TL;DR

This paper demonstrates an atomic analog of homodyne detection for matter-wave quadratures, revealing continuous variable entanglement in twin-atom states produced by spin-changing collisions in a Bose-Einstein condensate, advancing quantum measurement techniques for massive particles.

Contribution

It introduces a novel atomic homodyne detection method for matter waves, enabling direct measurement of atomic quadratures and the demonstration of continuous variable entanglement in massive particles.

Findings

Revealed continuous variable entanglement in twin-atom states.

Demonstrated atomic homodyne detection for matter waves.

Showed potential for quantum measurements in many-body systems.

Abstract

Historically, the completeness of quantum theory has been questioned using the concept of bipartite continuous variable entanglement. The non-classical correlations (entanglement) between the two subsystems imply that the observables of one subsystem are determined by the measurement choice on the other, regardless of their distance. Nowadays, continuous variable entanglement is regarded as an essential resource allowing for quantum enhanced measurement resolution, the realization of quantum teleportation and quantum memories, or the demonstration of the Einstein-Podolsky-Rosen paradox. These applications rely on techniques to manipulate and detect coherences of quantum fields, the quadratures. While in optics coherent homodyne detection of quadratures is a standard technique, for massive particles a corresponding method was missing. Here we report on the realization of an atomic analog to homodyne detection for the measurement of matter-wave quadratures. The application of this technique to a quantum state produced by spin-changing collisions in a Bose-Einstein condensate reveals continuous variable entanglement, as well as the twin-atom character of the state. With that we present a new system in which continuous variable entanglement of massive particles is demonstrated. The direct detection of atomic quadratures has applications not only in experimental quantum atom optics but also for the measurement of fields in many-body systems of massive particles.