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Physical Review Letters

Loss-Assisted Anomalous Hong-Ou-Mandel Interference Based on Nonunitary Multilayer Graphene

Ling Hong, Yuning Zhang, Yuanyuan Chen, Lixiang Chen

Published Jul 8, 2024• 14 citations
Publisher

Abstract

Hong-Ou-Mandel interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables numerous applications in quantum information science. While the photon-photon interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, we present that a nonunitary material provides an alternative degree of freedom to control the two-photon quantum interference, even revealing anomalous quantum interference paths that do not exist in a unitary configuration. An elaborate lossy multilayer graphene that can work as a nonunitary beam splitter is used to explore its tunability over the effective photon-photon interaction in spatial modes, and to verify the particle exchange statistics by its experimental implementation in quantum state filter. This scheme is further extended to observe four-dimensional quantum interference patterns on the lossless and lossy beam splitters, and thus show its applicability even in higher-dimensional Hilbert space.

DOI
10.1103/physrevlett.133.023601

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Hong-Ou-Mandel interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables numerous applications in quantum information science. While the photon-photon interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, we present that a nonunitary material provides an alternative degree of freedom to control the two-photon quantum interference, even revealing anomalous quantum interference paths that do not exist in a unitary configuration. An elaborate lossy multilayer graphene that can work as a nonunitary beam splitter is used to explore its tunability over the effective photon-photon interaction in spatial modes, and to verify the particle exchange statistics by its experimental implementation in quantum state filter. This scheme is further extended to observe four-dimensional quantum interference patterns on the lossless and lossy beam splitters, and thus show its applicability even in higher-dimensional Hilbert space.
Quantum entanglement is essential for various quantum information technologies that are beyond the possibilities of classical physics. However, it is susceptible to decoherence that may arise from noisy channels and environmental noise. While this deleterious problem has been explored by using filtering techniques, such as photon ancillas and Rydberg atom blockade, a concise yet efficient approach to entanglement retrieval is still a formidable challenge. Here, we present that nonunitary material provides an alternative tool to flexibly control the anomalous Hong–Ou–Mandel (HOM) interference and enables the selective entanglement filter with coherent perfect absorption of anti-symmetric quantum states. An elaborate Cr–SiN–Cr film is prepared as a nonunitary beam splitter such that its tunability over the effective photon–photon interaction in frequency modes can be readily explored in the experiment, which may introduce sophisticated nonunitary realization into integrated optical platforms. In addition, we confirm its ability for selective filtering of high-dimensional frequency entanglement by observing the output quantum state of the conventional HOM interference with a unitary beam splitter and the anomalous HOM interference with a nonunitary beam splitter. These results may offer new insights into investigating the quantum light–matter interaction and facilitating the use of two-photon interference for addressing central challenges in quantum technologies.
Quantum interferometry provides a pivotal method for investigating complex photon-photon interaction, enabling various quantum information technologies that beyond the possibilities of classical physics. While such an effective interaction is mostly studied in N × N unitary transformation, m × n nonunitary transformation that relates to lossy multiport quantum interferometry requires a different approach. Here, we experimentally demonstrate a concise yet powerful tool to unravel fundamental features of multiport quantum interferometry with universal nonunitary transformations. To confirm their intriguing unitary and nonunitary properties, Hong-Ou-Mandel (HOM) interference is observed to reveal its nontrivial particle exchange phase, wherein the conventional HOM interference based on unitary transformation and the anomalous HOM interference based on nonunitary transformation can be readily harnessed. These results provide an alternative approach to investigate the quantum light-matter interaction, facilitating the use of complex multiport quantum interference for large-scale quantum information processing tasks such as quantum simulation and quantum computation.
Quantum interference can produce pivotal effective photon-photon interactions, enabling the exploration of various quantum information technologies that are beyond the possibilities of classical physics. While this effective interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, loss-induced nonunitary operations provide an alternative degree of freedom to control quantum interference. Here, we propose and experimentally demonstrate a concise yet powerful tool to unravel the essential features of quantum interference based on the phase change material vanadium dioxide. Since the insulator-metal transition in an elaborate vanadium dioxide thin film can create any desired particle exchange phase response, harnessing its phase transition would allow the dynamical control of photon-photon interaction such that the conventional coalescence and the anomalous anti-coalescence of photons can be continuously tuned. These results highlight an alternative approach for investigating quantum light-matter interactions, and facilitate nonunitary quantum interference for various quantum information processing tasks.
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.
Quantum interference between identical single particles reveals the intrinsic quantum statistic nature of particles, which could not be interpreted through classical physics. Here, we demonstrate quantum interference between nonidentical bosons using a generalized beam splitter based on a quantum memory. The Hong-Ou-Mandel type interference between single photons and single magnons with high visibility is demonstrated, and the crossover from the bosonic to fermionic quantum statistics is observed by tuning the beam splitter to be non-Hermitian. Moreover, multiparticle interference that simulates the behavior of three fermions by three input photons is realized. Our work extends the understanding of the quantum interference effects and demonstrates a versatile experimental platform for studying and engineering quantum statistics of particles.
Two-photon interference is a fundamental quantum optics effect with numerous applications in quantum information science. Here, we study two-photon interference in multiple transverse-spatial modes along a single beam-path. Besides implementing the analog of the Hong-Ou-Mandel interference using a two-dimensional spatial-mode splitter, we extend the scheme to observe coalescence and anticoalescence in different three- and four-dimensional spatial-mode multiports. The operation within spatial modes, along a single beam path, lifts the requirement for interferometric stability and opens up new pathways of implementing linear optical networks for complex quantum information tasks.