Single photons behaviour in optical resonators and its applications

Adam Liebendorfer

Optical resonator made with photonic wire and mirrors performs with excellent single-photon purity, pointing to potential for nanopost designs in scalable quantum applications.

Mikhail D. Lukin

Axel Kuhn, Daniel Ljunggren

We introduce the basic concepts and characteristic properties of single-photon emitters based on resonator effects in optical cavities, and provide a review of the most prominent implementations. First we discuss the elementary principles of cavity quantum electrodynamics, which determine how single quantum systems couple to the quantised field modes of optical resonators, and then show how to exploit these principles in order to generate single photons on demand. Furthermore, we elucidate how to study the properties of the photons, namely their singleness and their spectral characteristics. In particular, it is explained how to use a Hanbury-Brown and Twiss interferometer to determine whether the photons arrive one-by-one, and how to probe their mutual indistinguishability with two-photon interference experiments of the Hong–Ou–Mandel type. Finally, we present a classification scheme applicable to most cavity-based photon emitters realised to date. This scheme allows us to assess the pros and cons of the most significant approaches – in particular with regard to photonic quantum computing and quantum communication, which are among the most promising applications to date.

Ping Koy Lam, B. C. Buchler

Shengwang Du, Chang Liu, Yuan Sun +3 more

Jian Tang, Yunlan Zuo, Xun‐Wei Xu +4 more

Backscattering losses (BSL), arising from intrinsic imperfections or unavoidable external perturbations in optical resonators, can severely impact photonic devices. In single-photon systems, robust quantum correlations against BSL remain largely unexplored despite their significance for various applications. Here, we demonstrate that single-photon blockade (SPB), a purely quantum effect, can be preserved against BSL by introducing a nanotip near a Kerr nonlinear resonator with intrinsic defects. Without the tip, BSL disrupts SPB, but tuning the tip's position restores robustness even under strong BSL. Notably, quantum correlations emerge while the classical mean photon number remains suppressed due to the interplay between resonator nonlinearity and tip-induced optical coupling. Our findings highlight nanoscale engineering as a powerful tool to protect and harness fragile quantum correlations, paving the way for robust single-photon sources and backscattering-immune quantum devices.