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arXiv:2511.22480

Radio-Frequency Hong-Ou-Mandel Interference with Conditionally Built States

A. Sheleg, D. Vovchuk, K. Boiko, P. Ginzburg, G. Slepyan, A. Boag, A. Mikhalychev, A. Ulyanenkov, T. Salgals, P. Kuzhir, D. Mogilevtsev

quant-phSubmitted Nov 27, 2025• Announced Nov 28, 2025• 0 citations
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Abstract

We report an experimental demonstration of room-temperature Hong-Ou-Mandel (HOM) interference at a radio-wave frequency of 120 MHz using conditional build-up of quantum states from classical phase-averaged coherent states. This approach enables observation of quantum effects in spectral regimes where conventional single-photon sources and detectors are unavailable or require cryogenic conditions. By constructing a high-fidelity approximation of a single-photon state with phase-averaged coherent states, we observe the normalized second-order intensity correlation dips significantly below the classical limit of 0.5. The method allows for tunable noise suppression via optimization of the state representation. Our results establish the feasibility of using conditionally prepared classical states to simulate quantum interference phenomena in the radio-frequency domain. This technique opens the door to realizing other quantum protocols, such as Bell inequality tests, in frequency ranges where standard quantum technologies are currently infeasible.

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Structured photons are a crucial resource in both classical and quantum technologies, particularly in spin–orbit hybrid photons, enabling various practical applications ranging from ultra-sensitive metrology techniques to quantum-enhanced information processing tasks. However, the two-photon interference of spin–orbit hybrid photons, which combines polarization modes and complex transverse spatial structures across the beam profile, remains unexplored. Here, we present an experimental observation of Hong–Ou–Mandel (HOM) interference of spin–orbit hybrid photons. The tunable q-plates that work as spin–orbit coupler devices are used to prepare various forms of spin–orbit hybrid entangled photons. By harnessing the match degree in the temporal domain, the coalescence and anti-coalescence effects resulting from the symmetric and anti-symmetric properties of the incident quantum states are observed. Moreover, we demonstrated the feasibility of quantum-enhanced photon polarization gears through HOM interference and theoretically analyze the noise-resilient advantages based on coherent HOM measurements. These results provide an alternative route toward quantum experiments with structured photons that allows for controlling their quantum interference in a compact, stable, and efficient way.

APL Photonics•Dec 1, 2023•11 citations
We report an experimental demonstration of room-temperature Hong-Ou-Mandel (HOM) interference at a radio-wave frequency of 120 MHz using conditional build-up of quantum states from classical phase-averaged coherent states. This approach enables observation of quantum effects in spectral regimes where conventional single-photon sources and detectors are unavailable or require cryogenic conditions. By constructing a high-fidelity approximation of a single-photon state with phase-averaged coherent states, we observe the normalized second-order intensity correlation dips significantly below the classical limit of 0.5. The method allows for tunable noise suppression via optimization of the state representation. Our results establish the feasibility of using conditionally prepared classical states to simulate quantum interference phenomena in the radio-frequency domain. This technique opens the door to realizing other quantum protocols, such as Bell inequality tests, in frequency ranges where standard quantum technologies are currently infeasible.
ABSTRACT We report an experimental demonstration of room‐temperature Hong–Ou–Mandel (HOM) interference at a radio‐wave frequency of 120 MHz using single‐photon states built from phase‐averaged coherent states by the emulation procedure proposed in the recent work. This emulation approach enables observation of quantum effects in spectral regimes where conventional single‐photon sources and detectors are unavailable or require cryogenic conditions. By constructing a high‐fidelity approximation of a single‐photon state with phase‐averaged coherent states, we observe the normalized second‐order intensity correlation dips significantly below the classical limit of 0.5. The method allows for tunable noise suppression via optimization of the state representation. Our results establish the feasibility of using conditionally prepared classical states to simulate quantum interference phenomena in the radio‐frequency domain.
In the context of Fock states, demonstrating multiphoton quantum interference, e.g., the generalized Hong-Ou-Mandel (HOM) interference, is at the core of many applications of quantum technologies. However, it is difficult to demonstrate high-visibility quantum interference for a large number of photons. Here, we introduce an experimentally feasible proposal to achieve this goal using phase-randomized weak coherent states and practical photon-number-resolving detectors. Our method can be used to obtain analytically tight bounds of the generalized HOM dip in a beam splitter, and it is robust against practical errors. The simulation shows that for an ideal detector that can resolve any number of photons without an upper bound, the proposed method can bound the generalize HOM interference for a large number of photons, e.g., 100 photons; for a practical detector that can resolve up to 29 photons, the proposed method can bound the generalized HOM interference for 56 photons with visibility 99.499.4%99.4. Our proposal is a general approach for multiphoton quantum interference in optical networks with multiple inputs and outputs.
The frequency degree-of-freedom, being compatible with well-developed omnipresent optical telecommunication infrastructure, allows for stable, controllable and scalable encoding of quantum information [1] . The HOM effect between independent photons, as a central building block to, e.g., quantum key distribution (QKD), quantum teleportation and entanglement swapping, has been mainly employed within the spatial domain [2] . A key element yet missing to enable scalable and thus real-world frequency-based implementation of quantum computation and non-classical communication, is the demonstration of Hong-Ou-Mandel (HOM) interference between independently created photons of different frequencies. To date, spectral bosonic HOM interference between single photons, produced out of the same continuous-wave (cw)-excited spontaneous parametric down conversion (SPDC) process has been demonstrated [3] , which however does not allow scalability due to the spectral impurity inherent to the proposed approach.
Hong-Ou-Mandel (HOM) interference is a compelling quantum phenomenon that demonstrates the nonclassical nature of single photons. In this study, we investigate an electromagnetically induced transparency-based double-$\mathrm{\ensuremath{\Lambda}}$ four-wave mixing system from the perspective of quantized light fields. The system can be used to realize efficient HOM interference in the frequency domain. By using the reduced density operator theory, we demonstrate that although the double-$\mathrm{\ensuremath{\Lambda}}$ medium does not exhibit phase-dependent properties for the closed-loop case of two incident single photons, frequency-domain HOM two-photon interference occurs. For experimentally achievable optical depth conditions, our theory indicates that this double-$\mathrm{\ensuremath{\Lambda}}$ scheme can perform high-fidelity Hadamard gate operations on frequency-encoded single-photon qubits, and thereby generate HOM two-photon NOON states with a fidelity greater than 0.99. Furthermore, we demonstrate that this scheme can be used to realize arbitrary single-qubit gates and two-qubit SWAP gates by simply controlling the laser detuning and phase, exhibiting its multifunctional properties and providing a different route to scalable optical quantum computing.
Interference between two completely independent photons lies at the heart of many photonic quantum information applications such as quantum repeaters, teleportation, and quantum key distribution. Here, we report the observation of Hong–Ou–Mandel (HOM) interference with two independent continuous-wave coherent light sources that are neither synchronized nor share any common reference. To prepare indistinguishable photons from two independent laser sources, we employ high-precision frequency-stabilization techniques using the 5 S 1 / 2 ( F = 3 ) − 5 P 1 / 2 ( F ′ = 3 ) transition line of Rb 85 atoms. We successfully observe an HOM interference fringe with two independent continuous-wave coherent photons originating from either the frequency-locked or the frequency-modulated lasers. An interference fringe involving two-photon beating is also observed when the frequency difference between the two interfering photons is beyond the spectral bandwidth of the individual coherent photons. We carry out further experiments to verify the robustness of the source preparation regardless of the separation distance between the two independent photon sources.
Structured photons are a crucial resource in both classical and quantum technologies, particularly in spin–orbit hybrid photons, enabling various practical applications ranging from ultra-sensitive metrology techniques to quantum-enhanced information processing tasks. However, the two-photon interference of spin–orbit hybrid photons, which combines polarization modes and complex transverse spatial structures across the beam profile, remains unexplored. Here, we present an experimental observation of Hong–Ou–Mandel (HOM) interference of spin–orbit hybrid photons. The tunable q-plates that work as spin–orbit coupler devices are used to prepare various forms of spin–orbit hybrid entangled photons. By harnessing the match degree in the temporal domain, the coalescence and anti-coalescence effects resulting from the symmetric and anti-symmetric properties of the incident quantum states are observed. Moreover, we demonstrated the feasibility of quantum-enhanced photon polarization gears through HOM interference and theoretically analyze the noise-resilient advantages based on coherent HOM measurements. These results provide an alternative route toward quantum experiments with structured photons that allows for controlling their quantum interference in a compact, stable, and efficient way.