Zero-point excitation of a circularly moving detector in an atomic condensate and phonon laser dynamical instabilities

Jamir Marino,Iacopo Carusotto,Gabriel Menezes

doi:10.1103/physrevresearch.2.042009

Abstract

We study a circularly moving impurity in an atomic condensate for the realisation of superradiance phenomena in tabletop experiments. The impurity is coupled to the density fluctuations of the condensate and, in a quantum field theory language, it serves as an analog of a detector for the quantum phonon field. For sufficiently large rotation speeds, the zero-point fluctuations of the phonon field induce a sizeable excitation rate of the detector even when the condensate is initially at rest in its ground state. For spatially confined condensates and harmonic detectors, such a superradiant emission of sound waves provides a dynamical instability mechanism leading to a new concept of phonon lasing. Following an analogy with the theory of rotating black holes, our results suggest a promising avenue to quantum simulate basic interaction processes involving fast moving detectors in curved space-times.

Highlights

Since Unruh’s pioneering proposal in 1981 [1], the last decades of research activities have witnessed a surge of a field where concepts of general relativity and quantum field theories in curved backgrounds are investigated in the socalled analog models of gravity [2]
As a most celebrated example, acoustic analogs of black holes have been studied in trans-sonically flowing atomic Bose-Einstein condensates: The acoustic black-hole horizon corresponds to the interface between regions of, respectively, sub- and supersonic flows, and was anticipated to emit a thermal radiation of phonons via Hawking processes [3]
The first experimental observations of such phenomena [4] were instrumental in triggering the ongoing explosion of the field, with a revived interest in using analog models to investigate a variety of different effects of quantum field theories in curved space-times, from the dynamical Casimir effect [5] to acceleration radiation [6] to vacuum friction and Casimir forces [7,8]

Summary

INTRODUCTION

Since Unruh’s pioneering proposal in 1981 [1], the last decades of research activities have witnessed a surge of a field where concepts of general relativity and quantum field theories in curved backgrounds are investigated in the socalled analog models of gravity [2]. Much less studied are the quantum features when superradiant processes are triggered by zero-point fluctuations and the even more intriguing quantum friction effects that result from back-reaction of superradiance on the rotational motion [19,20]. In this Rapid Communication, we investigate superradiant phenomena that can occur in ultracold atomic systems. [6,8], the neutral impurity plays the role of a two-level detector in a canonical quantum field theory setup, and it allows us to explore superradiant phenomena beyond the usual amplification of incident waves [10,16]. In contrast to the usual laser operation which requires an external pumping of the gain medium, the phonon-lasing mechanism envisioned here is driven by the mechanical motion of a detector that is initially prepared in its ground state

A CIRCULARLY MOVING IMPURITY IN A UNIFORM CONDENSATE

DYNAMICAL INSTABILITIES

PERSPECTIVES