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ACS Photonics

Backward Time-Correlated W-State Triphoton Generation via Atomic Coherence

Feng Zhou, Siqiang Zhang, Rui Zhuang, Guobin Liu, Feng Li, Kangkang Li, Yanpeng Zhang

Published Jul 11, 2025• 4 citations
Publisher

Abstract

Scalability in quantum communication and computation critically relies on the efficient generation of high-quality entangled multiphoton states. Consequently, the ability to prepare multiple entangled particles is critical for advancing quantum technologies. Here, we report a significant advancement in the generation of narrowband, time–energy-entangled W-state triphotons exhibiting backward time correlation, achieved via spontaneous six-wave mixing in a five-level atomic system. By leveraging anomalous dispersion and atomic coherence control in a T-type electromagnetically induced transparency (EIT) configuration, our method markedly enhances the triphoton generation rate, extends the photon correlation time, and suppresses noise photons. With meticulous optimization of system parameters, the correlation time of the generated triphotons exceeds 80 ns, the production rate reaches 175 ± 9 triphotons per minute, and accidental photon counts are suppressed to 8 ± 2 per minute. This work presents an efficient framework for preparing triphotons with long coherence, high production efficiency, and low noise, offering substantial potential for applications in quantum communication and quantum computing.

DOI
10.1021/acsphotonics.5c00579

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Scalability in quantum communication and computation critically relies on the efficient generation of high-quality entangled multiphoton states. Consequently, the ability to prepare multiple entangled particles is critical for advancing quantum technologies. Here, we report a significant advancement in the generation of narrowband, time–energy-entangled W-state triphotons exhibiting backward time correlation, achieved via spontaneous six-wave mixing in a five-level atomic system. By leveraging anomalous dispersion and atomic coherence control in a T-type electromagnetically induced transparency (EIT) configuration, our method markedly enhances the triphoton generation rate, extends the photon correlation time, and suppresses noise photons. With meticulous optimization of system parameters, the correlation time of the generated triphotons exceeds 80 ns, the production rate reaches 175 ± 9 triphotons per minute, and accidental photon counts are suppressed to 8 ± 2 per minute. This work presents an efficient framework for preparing triphotons with long coherence, high production efficiency, and low noise, offering substantial potential for applications in quantum communication and quantum computing.
Abstract Sources of entangled multiphotons are not only essential for fundamental tests of quantum foundations, but are also the cornerstone of a variety of optical quantum technologies today. Over past three decades, tremendous efforts have been devoted to creating multiphoton entanglement by multiplexing existing biphoton sources with linear optics and postselections. Different from all previous protocols, here we report, for the first time, the observation of continuous-mode time-energy-entangled W-class triphotons with an unprecedented generation rate directly through the process of spontaneous six-wave mixing (SSWM) in a four-level triple-Λ atomic vapor cell. Facilitated by electromagnetically induced transparency and coherence control, our SSWM scheme enables versatile narrowband triphoton generation with many intriguing properties including long temporal coherence and controllable waveforms, ideal for implementing long-distance quantum communications, networking, and information processing by interfacing photons and atoms. Most importantly, our work paves a way for the development of a reliable and efficient genuine triphoton source, thus making the research on multiphoton entanglement within easy reach.
Entangled multiphoton sources are essential for both fundamental tests of quantum foundations and building blocks of contemporary optical quantum technologies. While efforts over the past three decades have focused on creating multiphoton entanglement through multiplexing existing biphoton sources with linear optics and postselections, our work presents a groundbreaking approach. We observe genuine continuous-mode time-energy-entangled W-class triphotons with an unprecedented production rate directly generated through spontaneous six-wave mixing (SSWM) in a four-level triple-Λ atomic vapor cell. Using electromagnetically induced transparency and coherence control, our SSWM scheme allows versatile narrowband triphoton generation with advantageous properties, including long temporal coherence and controllable waveforms. This advancement is ideal for applications like long-distance quantum communications and information processing, bridging single photons and neutral atoms. Most importantly, our work establishes a reliable and efficient genuine triphoton source, facilitating accessible research on multiphoton entanglement.
Multiphoton entangled states are pivotal resources for implementing optical quantum information protocols. Recently, energy-time-entangled triphotons have been observed in hot atomic ensembles. However, in these protocols, the complex fifth-order nonlinear susceptibility entailed by four- or five-level systems limits our understanding of triphoton generation. Here, to directly capture the generation mechanism of triphotons and their associated optical properties, we investigate the generation of energy-time-entangled triphotons in a six-level cold atomic ensemble. The fifth-order nonlinear susceptibility indicates the existence of two sets of spontaneous six-wave mixing in the system. Notably, triphoton generation in this system is subject to stringent timing constraints. Collectively, these characteristics give rise to threefold coincidence counts, which -- dominated by the fifth-order nonlinear susceptibility -- exhibit asymmetrically damped Rabi oscillations in the two-dimensional time domain. Furthermore, we analytically derive that the temporal correlation properties of conditional two-photon states are preserved -- a unique feature of WWW-class tripartite entanglement. These results not only lay the groundwork for the experimental preparation of triphotons using six-level systems but also provide key support for understanding the generation mechanism of triphotons involving more complex fifth-order nonlinear susceptibilities.
Narrow-band multiphoton entanglement sources serve as a core enabling resource for advanced quantum information technologies. Recently, researchers have directly generated energy-time entangled triphoton W states in a hot atomic medium via spontaneous six-wave mixing for the first time. However, a rigorous theoretical framework for this process remains lacking to date, confining our understanding to a mere extension of the biphoton model. Here, we analytically investigate the generation mechanism of energy-time entangled triphotons and their classically controllable optical properties in an electromagnetically induced transparency-assisted five-level cold atomic system. Notably, triphoton generation follows strict temporal ordering, resulting in asymmetric quantum interference in triple coincidence counts--unreplicable and unexplainable by the inherently symmetric biphoton model. These results establish a rigorous physical framework for spontaneous six-wave mixing-generated triphotons, clarify their distinctions from states produced via cascaded nonlinear models, and substantially advance their utility in quantum information protocols.
Non-Hermitian quantum systems — characterized by parity–time symmetry and the emergence of exceptional points — have attracted increasing interest, particularly in light–matter interaction platforms where dissipation and radiative losses play a fundamental role. In this work, we investigate the modulation of coupling states between atomic energy levels during the generation of backward W-state triphotons via a spontaneous six-wave mixing (SSWM) process. By employing tunable external control beams, we realize dynamic modulation from the weak to the strong coupling regime, accompanied by a qualitative transition in triphoton coincidence statistics from anti-bunching to damped Rabi oscillations. Remarkably, the appearance of single exponential decays in the triphoton coincidence count traces marks the onset of an exceptional point in the non-Hermitian system. Furthermore, triphoton correlations in the τ21 and τ31 directions can be independently modulated by selectively tuning of the coupling state via ED1 and ED2, respectively. These results provide a versatile and coherent platform for the one-step generation of backward entangled triphoton states and offer a promising approach to engineering high-dimensional entanglement, with potential applications in quantum communication and quantum information processing.
In quantum communication and quantum computation, adding each entangled photon leads to an exponential increase in communication and computational capabilities. Utilizing a fifth-order nonlinear process, narrow-band non-Gaussian W-triphotons are experimentally generated through the spontaneous six -wave mixing (SSWM), but the manipulation of such entangled state in the group delay regime is still lacked. For the first time, the observation of optical precursors at the triphoton level is reported through the SSWM process. By appropriately adjusting the optical depth, optical precursors are effectively separated from the main wave through utilizing the slow-light effect to manipulate the triphoton temporal correlations in the group delay regime. In biphoton and conditional two-photon, the intensity ratio between the precursor and the main wave is tunable by adjusting the detuning and power of the laser. These pivotal breakthroughs mark a significant advancement in the study of optical precursors and open new possibilities for their application in quantum technologies.