An Approach to Probing Particles and Quasi-particles in the Condensed Bose-Hubbard Model

TL;DR

This paper explores how measurement techniques, specifically phase contrast imaging, influence the dynamics and creation of quasiparticles in a Bose-Einstein condensate array, affecting both observation and system evolution.

Contribution

It demonstrates how measurement parameters can be tuned to probe or control quasiparticle modes and their diffusion in a condensed Bose-Hubbard system.

Findings

Measurement parameters determine whether particle or quasiparticle dynamics are probed.

Selective measurement of quasiparticle modes is achievable.

Measurement can induce and control quasiparticle creation and diffusion.

Abstract

Measurement plays a crucial role in a quantum system beyond just learning about the system state: it changes the post-measurement state and hence influences the subsequent time evolution; further, measurement can even create entanglement in the post-measurement conditional state. In this work, we study how careful choice of parameters for a typical measurement process on cold atoms systems -- phase contrast imaging -- has a strong impact on both what the experimentalist observes but also on the backaction the measurement has on the system, including the creation and diffusion of quasiparticles emerging from the quantum many-body dynamics. We focus on the case of a Bose-Einstein-condensate array, in the low-temperature and low-momentum limit. Our theoretical investigation reveals regimes where the imaging light probes either the bare particle or quasiparticle dynamics. Moreover, we find a path to selectively measuring quasiparticle modes directly, as well as controlling over the measurement-induced creation and diffusion of quasiparticles into different momentum states. This lays a foundation for understanding the effects of both experimental approaches for probing many-body systems, but also more speculative directions such as observable consequences of `spontaneous collapse' predictions from novel models of quantum gravity on aspects of the Standard Model.