Coherent Splitting of Single Photons by an Ideal Beam Splitter

Ray LaPierre

J. D. Franson

It is shown that an ideal beam splitter has a small probability of splitting a single photon into a pair of secondary photons, conserving energy in the process. These nonlinear effects are a fundamental consequence of the quantization of the field and are analogous to other nonlinear effects in QED, such as the scattering of one photon by another. \textcopyright{} 1996 The American Physical Society.

Xianxin Guo, Yefeng Mei, Shengwang Du

We report the demonstration of a configurable coherent quantum-memory-based beam splitter (BS) for a single-photon wave packet making use of laser-cooled $^{85}\mathrm{Rb}$ atoms and electromagnetically induced transparency. The single-photon wave packet is converted (stored) into a collective atomic spin state and later retrieved (split) into two nearly opposing directions. The storage time, beam-splitting ratio, and relative phase are configurable and can be dynamically controlled. We experimentally confirm that such a BS preserves the quantum particle nature of the single photon and the coherence between the two split wave packets of the single photon.

Shengwang Du

Gholamreza Honarasa, Alireza Bagheri, Abdolrasoul Gharaati

Jingyuan Guo

The indivisibility of photons is the cornerstone of quantum optics, whose classic experimental evidence comes from the single-photon beam splitting coincidence experiment proposed by Grangier, Roger and Aspect in 1986. This paper points out that there is a systematic loophole in this experiment that has not been strictly excluded: all photodetectors have an energy response threshold. If a single photon is split into sub-pulses with energy below the threshold by the beam splitter, the experiment will be unable to distinguish between the two physical pictures of "the photon is truly indivisible" and "the photon is divisible but its split energy is below the detection threshold", and its conclusion relies on untested implicit assumptions. To address this loophole, this paper proposes an improved experimental scheme of two-stage cascaded beam splitting + four-channel coincidence measurement: the incident light is evenly distributed to four detectors through two stages of 50/50 beam splitters, and a step-by-step photon accumulation injection process is adopted, with the core verdict criterion that "the number of newly triggered detectors after a single photon injection is greater than 1". This criterion is a pure logical constraint, which does not require pre-calibration of the detector threshold and is not affected by non-ideal errors of the splitting ratio. It can serve as a strict verdict experiment on whether photons are divisible. (本文采用中英交替双语排版:每段英文后紧跟对应中文翻译,确保双语言内容完全一致。)