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arXiv:2005.07219 · Physical Review Letters

Local Versus Global Two-Photon Interference in Quantum Networks

Thomas Nitsche, Syamsundar De, Sonja Barkhofen, Evan Meyer-Scott, Johannes Tiedau, Jan Sperling, A. Gábris, Igor Jex, Christine Silberhorn

Published Nov 20, 2020• 13 citations
arXivHTMLPDF

Abstract

We devise an approach to characterizing the intricate interplay between classical and quantum interference of two-photon states in a network, which comprises multiple time-bin modes. By controlling the phases of delocalized single photons, we manipulate the global mode structure, resulting in distinct two-photon interference phenomena for time-bin resolved (local) and time-bucket (global) coincidence detection. This coherent control over the photons' mode structure allows for synthesizing two-photon interference patterns, where local measurements yield standard Hong-Ou-Mandel dips while the global two-photon visibility is governed by the overlap of the delocalized single-photon states. Thus, our experiment introduces a method for engineering distributed quantum interferences in networks.

DOI
10.1103/physrevlett.125.213604

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We devise an approach to characterizing the intricate interplay between classical and quantum interference of two-photon states in a network, which comprises multiple time-bin modes. By controlling the phases of delocalized single photons, we manipulate the global mode structure, resulting in distinct two-photon interference phenomena for time-bin resolved (local) and time-bucket (global) coincidence detection. This coherent control over the photons' mode structure allows for synthesizing two-photon interference patterns, where local measurements yield standard Hong-Ou-Mandel dips while the global two-photon visibility is governed by the overlap of the delocalized single-photon states. Thus, our experiment introduces a method for engineering distributed quantum interferences in networks.
We report two-photon interference with continuous-wave multi-mode coherent light. We show that the two-photon interference, in terms of the detection time difference, reveals two-photon beating fringes with the visibility V = 0.5. While scanning the optical delay of the interferometer, Hong-Ou-Mandel dips or peaks are measured depending on the chosen detection time difference. The HOM dips/peaks are repeated when the optical delay and the first-order coherence revival period of the multi-mode coherent light are the same. These results help to understand the nature of two-photon interference and also can be useful for quantum information science.
Hong-Ou-Mandel interference underpins many photonic quantum information protocols and is commonly characterized by a single visibility parameter. This quantity is typically obtained by averaging over a fixed coincidence window, thereby discarding details of the underlying temporal structure that are critical in continuous-wave processes. Four-photon interference with continuous-wave sources furthermore requires photon pairs with long coherence times, which we generate in microring resonators and measure with ultrafast time-resolved detection. Here, we model and resolve their interference and temporal structure by recording all four photon arrival times and mapping their relative delays onto a three-dimensional coincidence histogram relative to a trigger detection. The resulting structure preserves relative arrival-time correlations that are usually discarded and enables post-processed optimization of coincidence windows to trade off visibility against count rate. This method provides a general benchmark for continuous-wave sources in interference-based quantum network protocols.
We report on two-photon quantum interference experiments in the standard telecommunication band. Two identical photons in the 1.5 mm wavelength band were generated in spatially separated modes by a type-I spontaneous parametric down-conversion process, and injected into a fiber-optic Hong-Ou-Mandel interferometer. Two-photon interference patterns of dip and spatial beating in the coincidence counting rate were observed by varying the difference in optical path lengths. The visibilities obtained in the net coincidences were close to the theoretical value of 100%. The raw visibilities were also well above the classical limit.
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.
We demonstrate quantum interference of three photons that are distinguishable in time by resolving them in the conjugate parameter frequency. We show that the multiphoton interference pattern in our setup can be manipulated by tuning the relative delays between the photons, without the need for reconfiguring the optical network. Furthermore, we observe that the symmetries of our optical network and the spectral amplitude of the input photons are manifested in the interference pattern. We also demonstrate time-reversed Hong-Ou-Mandel-like interference in the spectral correlations using time-bin entangled photon pairs. By adding a time-varying dispersion using a phase modulator, our setup can be used to realize dynamically reconfigurable and scalable boson sampling in the time domain as well as frequency-resolved multiboson correlation sampling.