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arXiv:1708.09436 · Journal of Physics B Atomic Molecular and Optical Physics

Entanglement generation and manipulation in the Hong-Ou-Mandel experiment: a hidden scenario beyond two-photon interference

Li-Kai Yang, Han Cai, Tao Peng, Da-Wei Wang

Published May 1, 2018• 2 citations
arXivHTMLPDF

Abstract

Abstract The Hong−Ou−Mandel (HOM) effect was long believed to be a two-photon interference phenomenon. It describes the fact that two indistinguishable photons mixed at a beam splitter will bunch together to one of the two output modes. Considering the two single-photon emitters such as trapped ions, we explore a hidden scenario of the HOM effect, where entanglement can be generated between the two ions when a single photon is detected by one of the detectors. A second photon emitted by the entangled photon sources will be subsequently detected by the same detector. However, we can also control the fate of the second photon by manipulating the entangled state. Instead of two-photon interference, the phase of the entangled state is responsible for the photon’s path in our proposal. Toward a feasible experimental realization, we conduct a quantum jump simulation on the system to show its robustness against experimental errors.

DOI
10.1088/1361-6455/aac184

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Abstract The Hong−Ou−Mandel (HOM) effect was long believed to be a two-photon interference phenomenon. It describes the fact that two indistinguishable photons mixed at a beam splitter will bunch together to one of the two output modes. Considering the two single-photon emitters such as trapped ions, we explore a hidden scenario of the HOM effect, where entanglement can be generated between the two ions when a single photon is detected by one of the detectors. A second photon emitted by the entangled photon sources will be subsequently detected by the same detector. However, we can also control the fate of the second photon by manipulating the entangled state. Instead of two-photon interference, the phase of the entangled state is responsible for the photon’s path in our proposal. Toward a feasible experimental realization, we conduct a quantum jump simulation on the system to show its robustness against experimental errors.
Two-photon interference effects arise because photons are indistinguishable particles. In the wellknown Hong-Ou-Mandel (HOM) effect, the transmission of two photons at a beam splitter interferes destructively with the reflection of both photons, requiring both photons to "bunch up" by leaving the beam splitter on the same side. Here, we show that the interference between locally propagating photons and photons exchanged by a mode swap can be implemented by post-selecting spatially separated photon outputs of a four-path interferometer. Even though the photons detected at spatially separated locations must have travelled along paths that never met up at the same beam splitter, the Hong-Ou-Mandel effect can be observed in correlations between the output ports that originate from the association of detection events with non-local output modes defined by the two single photon inputs. Local phase shifts can be used to map out non-classical correlations between the photons detected at different output locations, clarifying the role of linear optics in generating entanglement between spatially separated photons. Our work thus establishes a fundamental relation between multiphoton interference and entanglement, opening the door to new possibilities in optical quantum technologies.
Controlling light at the level of individual photons has led to advances in fields ranging from quantum information and precision sensing to fundamental tests of quantum mechanics. A central development that followed the advent of single-photon sources was the observation of the Hong–Ou–Mandel (HOM) effect, a novel two-photon path interference phenomenon experienced by indistinguishable photons. The effect is now a central technique in the field of quantum optics, harnessed for a variety of applications such as diagnosing single-photon sources and creating probabilistic entanglement in linear quantum computing. Recently, several distinct experiments using atomic sources have realized the requisite control to observe and exploit Hong–Ou–Mandel interference of atoms. This chapter provides a summary of this phenomenon and discusses some of its implications for atomic systems. Transitioning from the domain of photons to atoms opens new perspectives on fundamental concepts, such as the classification of entanglement of identical particles. It aids in the design of novel probes of quantities such as entanglement entropy by combining well-established tools of AMO physics—unity single-atom detection, tunable interactions, and scalability—with the Hong–Ou–Mandel interference. Furthermore, it is now possible for established protocols in the photon community, such as measurement-induced entanglement, to be employed in atomic experiments that possess deterministic single-particle production and detection. Hence, the realization of the HOM effect with atoms represents a productive union of central ideas in quantum control of atoms and photons.
In the original formulation of the Hong–Ou–Mandel (HOM) experiment, when two otherwise indistinguishable photons are incident upon the two input ports of a balanced beam splitter, they coalesce, always leaving via the same output port. It is often interpreted that this interference arises due to the indistinguishability of the single photons at the beam splitter; the situation, however, is often more nuanced. Here, we demonstrate an analog of HOM interference between two photons of completely different color. To do so, we utilize a quantum frequency converter based on sum- and difference-frequency generation as an “active” beam splitter—coupling frequency-entangled red and telecom single photons with an octave-spanning energy difference of 282 THz. We achieve an uncorrected two-photon interference visibility beyond 90%. This work presents the first demonstration of HOM interference between two single photons of distinctly different color, deepening our understanding of what underlies quantum interference. It also suggests a novel approach to interfacing photonic qubits in heterogeneous quantum systems where frequency conversion and quantum interference are unified.
We present a quantum jump/trajectory analysis of the two-photon interference phenomenon in the context of the Hong–Ou–Mandel (HOM) effect. In particular, we consider the standard setup of the HOM effect, which consists of two-photon sources firing single photons from opposite sides of a 50/50 beam splitter and two perfect detectors placed at the output ports to record photodetection events. For single-photon sources, we consider two special cases: (1) two excited two-level atoms and (2) two atom–cavity setups with initially present single photons in both cavities. For both cases, we report analytic results as well as quantum jump-based Monte Carlo simulations to demonstrate the signatures of these single-photon sources on the HOM effect under different working conditions (e.g., strong- and weak-coupling regimes of cavity quantum electrodynamics). The HOM effect offers applications in the areas of linear optics quantum computing, as well as in protocols that test the indistinguishability of single-photon sources.
The two-photon Hong-Ou-Mandel (HOM) interference is a pure quantum effect which indicates the degree of indistinguishability of photons. The four-photon HOM interference exhibits richer dynamics in comparison to the two-photon interference and simultaneously is more sensitive to the input photon states. We demonstrate theoretically and experimentally an explicit dependency of the four-photon interference on the number of temporal modes, created in the process of parametric down-conversion. Moreover, we exploit the splitting ratio of the beam splitter to manipulate the interference between bunching and antibunching. Our results reveal that the temporal mode structure (multimodeness) of the quantum states shapes many-particle interference.
The Hong-Ou-Mandel (HOM) interference is one of the most fundamental quantum-mechanical effects that reveal a nonclassical behavior of single photons. Two identical photons that are incident on the input ports of an unbiased beam splitter always exit the beam splitter together from the same output port, an effect referred to as photon bunching. In this Letter, we utilize a single electro-optic phase modulator as a probabilistic frequency beam splitter, which we exploit to observe HOM interference between two photons that are in different spectral modes, yet are identical in other characteristics. Our approach enables linear optical quantum information processing protocols using the frequency degree of freedom in photons such as quantum computing techniques with linear optics.