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arXiv:2604.05422

Decoherence-Induced Multiphoton Interference

Yifan Du, Jiuyi Zhang, Daniel López Martínez, Santosh Kumar, Misagh Izadi, Yuping Huang

quant-phphysics.opticsSubmitted Apr 7, 2026• Announced Apr 8, 2026• 0 citations• Revised Oct 28, 2026 (v2)
v1 · Apr 7, 2026v2 · Oct 28, 2026
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Abstract

Decoherence is usually deemed detrimental to quantum information processing. Its control and minimization require significant costs and operating overheads, constituting a major hurdle to the practical deployment of quantum technologies. Yet, quantum mechanics provides for counterintuitive, sometimes surprisingly useful, phenomena and effects associated with decoherence, leading to unusual practical utilities. Here we demonstrate such an example of fundamental interest and practical potential, where quantum interference is created among multiple photons through their dissipative coupling to a shared reservoir. On a thin-film lithium niobate chip, we dissipatively link two spontaneous parametric down-converters through a common, highly lossy channel to create phase-sensitive multiphoton states. Our results show that faithful correlations can be established among two, three, and four photons, and tuned by shifting the relative phase between the driving pumps for the converters. This experiment highlights an under-explored territory in quantum science and technology, where loss and decoherence serve as resources, rather than adversaries, for quantum information processing.

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Decoherence is usually deemed detrimental to quantum information processing. Its control and minimization require significant costs and operating overheads, constituting a major hurdle to the practical deployment of quantum technologies. Yet, quantum mechanics provides for counterintuitive, sometimes surprisingly useful, phenomena and effects associated with decoherence, leading to unusual practical utilities. Here we demonstrate such an example of fundamental interest and practical potential, where quantum interference is created among multiple photons through their dissipative coupling to a shared reservoir. On a thin-film lithium niobate chip, we dissipatively link two spontaneous parametric down-converters through a common, highly lossy channel to create phase-sensitive multiphoton states. Our results show that faithful correlations can be established among two, three, and four photons, and tuned by shifting the relative phase between the driving pumps for the converters. This experiment highlights an under-explored territory in quantum science and technology, where loss and decoherence serve as resources, rather than adversaries, for quantum information processing.
Recent advances in non-Hermitian physical systems have led to numerous novel optical phenomena and applications. Such systems typically involve gain and loss associated with dissipative coupling to the environment, hence interesting quantum phenomena are often washed out, rendering most realizations classical. Here, in contrast, we propose to employ dissipative coupling to enable quantum correlations. In particular, two distant optical channels are judiciously designed to couple to and exchange information with a common reservoir environment, under an anti-parity-time-symmetric setting of hot but coherent atoms. We realize a non-Hermitian nonlinear phase sensitive parametric process, where atomic motion leads to quantum correlations between two distant light beams in the symmetry-unbroken phase. This Letter starts a new route to exploring the non-Hermitian quantum phenomena by bridging the fields of atomic physics, non-Hermitian optics, quantum information, and reservoir engineering. Potential applications include novel quantum light sources, quantum information processing and sensing, and generalization to correlated many-body systems.
The interference of quanta lies at the heart of quantum physics. The multipartite generalization of single-quanta interference creates entanglement, the coherent superposition of states shared by several quanta. Entanglement allows non-local correlations between many quanta and hence is a key resource for quantum information technology. Entanglement is typically considered to be essential for creating non-local quantum interference. Here, we show that this is not the case and demonstrate multiphoton non-local quantum interference that does not require entanglement of any intrinsic properties of the photons. We harness the superposition of the physical origin of a four-photon product state, which leads to constructive and destructive interference with the photons' mere existence. With the intrinsic indistinguishability in the generation process of photons, we realize four-photon frustrated quantum interference. This allows us to observe the following noteworthy difference to quantum entanglement: We control the non-local multipartite quantum interference with a photon that we never detect, which does not require quantum entanglement. These non-local properties pave the way for the studies of foundations of quantum physics and potential applications in quantum technologies.
Thin-film lithium niobate (TFLN) waveguides have emerged as a pivotal platform for on-chip spontaneous parametric down-conversion (SPDC), serving as a crucible for the generation of entangled photon pairs. The periodic poling of TFLN, while capable of generating high-efficiency SPDC, demands intricate fabrication processes that can be onerous in terms of scalability and manufacturability. In this work, we introduce a novel approach to the generation of entangled photon pairs via SPDC within TFLN waveguides, harnessing the principles of modal phase-matching (MPM). To address the challenge of efficiently exciting pump light typically in a higher-order mode, we have engineered a mode converter that couples two asymmetrically dimensioned waveguides. This converter adeptly transforms the fundamental mode into a higher-order mode, demonstrating a conversion loss of 1.55 dB at 785 nm with a 3 dB bandwidth exceeding 30 nm. Subsequently, we have showcased the device's capabilities by characterizing the pair generation rate (PGR), coincidences-to-accidentals ratio (CAR), and spectral profile of the entangled photon source. Our findings present a simplified and versatile method for the on-chip generation of entangled photon sources, which may pave the way for the application in the realms of quantum information processing and communication technologies.
Quantum frequency conversion (QFC) is essential for bridging the spectral gap between stationary qubits and low-loss optical communication channels. Practicable QFC interfaces connecting ultraviolet and telecommunication bands are of great significance but have remained elusive, constrained by the dual challenges of a high-performance frequency converter and effective noise suppression in short-wavelength pumping configurations. We address this by demonstrating the phase-matching mechanism with domain defects and differential-tuning behavior of the spontaneous parametric down-conversion noises. Based on a quantitative analysis of performance degradation induced by domain defects, we propose specific fabrication guidelines and experimentally achieve an ultrahigh normalized conversion efficiency of 839%/(W cm^{2}) for the fundamental guided mode in thin-film lithium niobate waveguides. Meanwhile, we reveal a new noise control mechanism for short-wavelength pumping by utilizing the differential-tuning behaviors of difference-frequency generation and spontaneous parametric down-conversion processes. Then a single-stage QFC from 393 nm to the telecom C band with a record-high external efficiency of 28.8% and an ultralow noise level of 35 counts per second is achieved experimentally. The proposed mechanisms would enable other QFCs with higher efficiency and lower noise, advancing the development of scalable quantum networks. Furthermore, it holds significant potential for driving progress in both classical and integrated nonlinear photonics.