Prain A, Vezzoli S, Westerberg N, Roger T, Faccio D
Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, EH14 7AS Edinburgh, United Kingdom.
Phys Rev Lett. 2017 Mar 31;118(13):133904. doi: 10.1103/PhysRevLett.118.133904. Epub 2017 Mar 29.
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.
量子场论预测，空间均匀但随时间变化的介质会从真空态激发光子对。然而，由于难以在介质中实现所需的非绝热和大幅度变化，这一重要的理论预测缺乏实验验证。最近的研究表明，在近零介电常数（ENZ）材料中，有可能在飞秒时间尺度上光学诱导出折射率变化达到单位量级。通过研究空间均匀、随时间变化的ENZ介质的量子场论，我们从理论上预测，与非ENZ随时间变化的材料相比，光子对产生量要高出几个数量级。我们还发现，在标准材料中，发射光谱取决于微扰的时间尺度，而在ENZ材料中，发射总是在ENZ波长处达到峰值。这些研究为从随时间变化的背景中对光子对发射进行技术上可行的观测铺平了道路，这对凝聚态物质系统之外的量子场论具有重要意义，并且作为一种新的纠缠光源具有潜在应用价值。
