Macroscopic superpositions of Bose-Einstein condensates

TL;DR

This paper demonstrates that measurements of scattered photons can induce macroscopic superpositions and entanglement between two Bose-Einstein condensates, revealing quantum coherence effects in large atomic systems.

Contribution

It introduces a method to generate superpositions of Bose-Einstein condensates via photon scattering and detection, highlighting the role of quantum statistics and measurement in macroscopic quantum states.

Findings

Superpositions can be established in the thermodynamic limit.

Photon measurements lead to entangled superpositions of number states.

Scattering is enhanced into already occupied states due to Bose-Einstein statistics.

Abstract

We consider two dilute gas Bose-Einstein condensates with opposite velocities from which a monochromatic light field detuned far from the resonance of the optical transition is coherently scattered. In the thermodynamic limit, when the relative fluctuations of the atom number difference between the two condensates vanish, the relative phase between the Bose-Einstein condensates may be established in a superposition state by detections of spontaneously scattered photons, even though the condensates have initially well-defined atom numbers. For a finite system, stochastic simulations show that the measurements of the scattered photons lead to a randomly drifting relative phase and drive the condensates into entangled superpositions of number states. This is because according to Bose-Einstein statistics the scattering to an already occupied state is enhanced.