Eur. Phys. J. D (2016) 70: 45
https://doi.org/10.1140/epjd/e2016-60590-2

Regular Article

Prethermalization in a quenched one-dimensional quantum fluid of light

Intrinsic limits to the coherent propagation of a light beam in a nonlinear optical fiber

INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123 Povo, Italy

^a e-mail: pierre.larre@unitn.it
^b e-mail: carusott@science.unitn.it

Received: 19 October 2015
Received in final form: 11 January 2016
Published online: 3 March 2016

Abstract

We study the coherence properties of a laser beam after propagation along a one-dimensional lossless nonlinear optical waveguide. Within the paraxial, slowly-varying-envelope, and single-transverse-mode approximations, the quantum propagation of the light field in the nonlinear medium is mapped onto a quantum Gross-Pitaevskii-type evolution of a closed one-dimensional system of many interacting photons. Upon crossing the entrance and the back faces of the waveguide, the photon-photon interaction parameter undergoes two sudden jumps, resulting in a pair of quantum quenches of the system’s Hamiltonian. In the weak-interaction regime, we use the modulus-phase Bogoliubov theory of dilute Bose gases to describe the quantum fluctuations of the fluid of light and predict that correlations typical of a prethermalized state emerge locally in their final form and propagate in a light-cone way at the Bogoliubov speed of sound in the photon fluid. This peculiar relaxation dynamics, visible in the light exiting the waveguide, results in a loss of long-lived coherence in the beam of light.