Spontaneous Photon Production in Time-Dependent Epsilon-Near-Zero Materials.

A Prain,S Vezzoli,D Faccio,N Westerberg,T Roger

doi:10.1103/physrevlett.118.133904

Abstract

Quantum field theory predicts that a spatially homogeneous but temporally varying medium will excite photon pairs out of the vacuum state. However, this important theoretical prediction lacks experimental verification due to the difficulty in attaining the required nonadiabatic and large amplitude changes in the medium. Recent work has shown that in epsilon-near-zero (ENZ) materials it is possible to optically induce changes of the refractive index of the order of unity, in femtosecond time scales. By studying the quantum field theory of a spatially homogeneous, time-varying ENZ medium, we theoretically predict photon-pair production that is up to several orders of magnitude larger than in non-ENZ time-varying materials. We also find that while in standard materials the emission spectrum depends on the time scale of the perturbation, in ENZ materials the emission is always peaked at the ENZ wavelength. These studies pave the way to technologically feasible observation of photon-pair emission from a time-varying background with implications for quantum field theories beyond condensed matter systems and with potential applications as a new source of entangled light.

Highlights

Quantum field theory predicts that a spatially homogeneous but temporally varying medium will excite photon pairs out of the vacuum state
Introduction.—Epsilon-near-zero (ENZ) materials are characterised by relative dielectric permittivity, whose real part, εr, attains near-zero values around a given frequency ωENZ [1,2]
Recent work pioneered by Engheta et al has started to focus on the quantum properties of these materials, including quantum emission in ENZ cavities and limitation or even complete suppression of vacuum modes [11,12]

Summary

Introduction

Quantum field theory predicts that a spatially homogeneous but temporally varying medium will excite photon pairs out of the vacuum state. For materials such as ITO and AZO that exhibit a small imaginary part of the permittivity, εi, the real part of the refractive index n0 is close ( never equal) to 0 around ωENZ; Δn=n0 can attain values of the order of unity, compared to the modest 10−4 − 10−3 values of non-ENZ materials [20,21].

Results

Conclusion