Observation of Quasiparticle Pair Production and Quantum Entanglement in Atomic Quantum Gases Quenched to an Attractive Interaction

We report observations of quasiparticle pair production by a modulational instability in an atomic superfluid and present a measurement technique that enables direct characterization of quasiparticle quantum entanglement. By quenching the atomic interaction to attractive and then back to weakly repulsive, we produce correlated quasiparticles and monitor their evolution in a superfluid through evaluating the in situ density noise power spectrum, which essentially measures a homodyne interference between ground-state atoms and quasiparticles of opposite momenta. We observe large amplitude growth in the power spectrum and subsequent coherent oscillations in a wide spatial frequency band within our resolution limit, demonstrating coherent quasiparticle generation and evolution. The spectrum is observed to oscillate below a quantum limit set by the Peres-Horodecki separability criterion of continuous-variable states, thereby confirming quantum entanglement between interaction quench-induced quasiparticles.

Automated summary

In this study, quasiparticle pair production in an atomic superfluid was observed, and a measurement technique was presented to directly characterize quasiparticle quantum entanglement. By monitoring the evolution of correlated quasiparticles in the superfluid, the coherent generation and evolution of quasiparticles was demonstrated. Additionally, quantum entanglement between interaction quench-induced quasiparticles was confirmed by observing oscillations below a quantum limit.