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Laser & Photonics Review

Direct Manipulation of Biphoton Generation From the non‐Hermitian Nature of Light‐matter Interaction

Kangkang Li, Yin Cai, Jin Yan, Zhou Feng, Liu Fu, Lei Zhang, Feng Li, Yanpeng Zhang

Published Feb 27, 2025• 8 citations
Publisher

Abstract

Abstract While biphoton generation holds significant importance in quantum entanglement and quantum technology, its dynamics involving non‐Hermitian characteristics have experimentally been untouched so far. Nevertheless, it is found that the non‐Hermitian features induced by the atomic coherence can be well employed for the direct control of biphoton generation and entanglement. By harnessing such natural non‐Hermitian interaction, a method is devised to expand a non‐Hermitian Hao biphoton generation processes. It is experimentally demonstrated such biphoton correlation can be adjusted within an unprecedentedly wide range, ranging from Rabi oscillation to antibunching‐exponential‐decay. Typically, the exceptional point at the transition boundary between the two regimes is distinctly observed.

DOI
10.1002/lpor.202402149

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Abstract While biphoton generation holds significant importance in quantum entanglement and quantum technology, its dynamics involving non‐Hermitian characteristics have experimentally been untouched so far. Nevertheless, it is found that the non‐Hermitian features induced by the atomic coherence can be well employed for the direct control of biphoton generation and entanglement. By harnessing such natural non‐Hermitian interaction, a method is devised to expand a non‐Hermitian Hao biphoton generation processes. It is experimentally demonstrated such biphoton correlation can be adjusted within an unprecedentedly wide range, ranging from Rabi oscillation to antibunching‐exponential‐decay. Typically, the exceptional point at the transition boundary between the two regimes is distinctly observed.
Biphoton process is an essential benchmark for quantum information science and technologies, while great efforts have been made to improve the coherence of the system for better quantum correlations. Nevertheless, we find that the non-Hermitian features induced by the atomic quantum interference could be well employed for the direct control of entanglement. We report the demonstration of exceptional point (EP) in biphotons by measuring the light-atom interaction as a natural non-Hermitian system, in which the electromagnetically induced transparency regime provides a powerful mechanism to precisely tune the non-Hermitian coupling strength. Such biphoton correlation is tuned within an unprecedented large range from Rabi oscillation to antibunching-exponential-decay, also indicating high-dimensional entanglement within the strong and weak light-matter coupling regimes. The EP at the transition point between the two regimes is clearly observed with the biphoton quantum correlation measurements, exhibiting a single exponential decay and manifesting the coalesced single eigenstate. Our results provide a unique method to realize the controllability of natural non-Hermitian processes without the assistance of artificial photonic structures, and paves the way for quantum control by manipulating the non-Hermitian features of the light-matter interaction.
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Multipartite entanglement has emerged as a valuable quantum resource for constructing large-scale quantum networks. However, the presence of non-Hermitian features induced by natural microscopic quantum systems significantly modifies the overall response of nonlinear parametric processes, thereby enabling direct manipulation of multipartite entanglement properties. In this study, we demonstrate the generation of multimode entanglement through atomic four-wave mixing (FWM) and analyze the properties of exceptional points (EP) under dressing control in non-Hermitian systems. By leveraging dressing-controlled atomic nonlinearity, we achieve versatile EPs and higher-order EPs by carefully tuning the atomic multi-parameter in the cascading FWM system. Additionally, we investigate the entanglement properties of various permutations of the output signal modes using the positive partial transpose (PPT) criterion. Notably, under non-Hermitian control, the application of single-, double-, and N-dressing splits leads to coherent multichannel control and further extends the scale of quantum entanglement. The outcomes of our research offer a novel approach to actively control non-Hermitian quantum phenomena without relying on artificial photonic structures. Furthermore, this paves the way for the realization of complex quantum information tasks by exploiting the non-Hermitian characteristics of the light-matter interaction.
Abstract The non‐classical states of light serve as a potential candidate for emerging quantum information process. A processing trend to enhance its scalability is to integrate multiple nonlinear processes with the dressed‐state picture into a single device, and therefore, are useful for quantum computations. Here, a novel method is proposed to experimentally achieve the generation of coexisting two pairs of narrow‐band biphotons by two four‐wave mixing processes in a single hot rubidium vapor cell. Based on the photon‐atom nonlinear interfaces, the generated biphotons exhibits genuine entanglement in time–energy. Meanwhile, the nonlinear susceptibility with the dressed‐state picture decides the temporal correlation of the biphotons wave packet as a damped periodic Rabi oscillation, suggesting the property of the high‐dimensional time–energy entangled state. Such a high‐dimensional entangled state also is an efficient way to enhance information carrying capacity. By alternating two nonlinear susceptibilities in a single device, respectively, there exists a competition of the generation rate between such two pairs of biphotons. Moreover, both generated two pairs of biphotons that violate the Cauchy–Schwarz inequality and show their non‐classical behavior.