Squeezing and entanglement in a Bose-Einstein condensate

TL;DR

This paper demonstrates the creation of spin-squeezed, entangled states in a Bose-Einstein condensate, enabling precision measurements surpassing the standard quantum limit by 3.8 dB.

Contribution

It provides an experimental realization of entanglement in a BEC through lattice splitting and site-resolved detection, advancing quantum sensor capabilities.

Findings

Achieved 3.8 dB sensitivity gain over the standard quantum limit.

Demonstrated entanglement via atom number difference and phase fluctuations.

Split condensate into multiple parts using a lattice potential.

Abstract

Entanglement, a key feature of quantum mechanics, is a resource that allows the improvement of precision measurements beyond the conventional bound reachable by classical means. This is known as the standard quantum limit, already defining the accuracy of the best available sensors for various quantities such as time or position. Many of these sensors are interferometers in which the standard quantum limit can be overcome by feeding their two input ports with quantum-entangled states, in particular spin squeezed states. For atomic interferometers, Bose-Einstein condensates of ultracold atoms are considered good candidates to provide such states involving a large number of particles. In this letter, we demonstrate their experimental realization by splitting a condensate in a few parts using a lattice potential. Site resolved detection of the atoms allows the measurement of the conjugated variables atom number difference and relative phase. The observed fluctuations imply entanglement between the particles, a resource that would allow a precision gain of 3.8 dB over the standard quantum limit for interferometric measurements.