The generation and control of quantum entangled states hold significant importance for quantum information processing. Non-Hermitian systems, characterized by parity-time symmetry and exceptional points, provide a powerful framework for controlling quantum states. Although both the non-Hermitian nature and triphoton generation have been demonstrated in light–matter interaction processes, achieving non-Hermitian control of triphoton states remains challenging because of the lack of active adjustment within a wide range of coupling strengths. We realize the non-Hermitian control of reconfigurable backward time-energy-entangled W triphotons through atomic coherence, transiting the different eigenstates of the triphoton by employing external control beams. These different triphoton eigenstates are experimentally demonstrated by the triphoton temporal correlations, ranging from Rabi oscillation to antibunching exponential decay. Furthermore, both the generation rate and the violation of the Cauchy–Schwarz inequality of triphotons confirm the highly nonclassical performance. Our results establish a versatile platform for reconfigurable multipartite entanglement and provide new opportunities for complex quantum information processing based on non-Hermitian light–matter interactions.
The generation and control of quantum entangled states hold significant importance for quantum information processing. Non-Hermitian systems, characterized by parity-time symmetry and exceptional points, provide a powerful framework for controlling quantum states. Although both the non-Hermitian nature and triphoton generation have been demonstrated in light–matter interaction processes, achieving non-Hermitian control of triphoton states remains challenging because of the lack of active adjustment within a wide range of coupling strengths. We realize the non-Hermitian control of reconfigurable backward time-energy-entangled W triphotons through atomic coherence, transiting the different eigenstates of the triphoton by employing external control beams. These different triphoton eigenstates are experimentally demonstrated by the triphoton temporal correlations, ranging from Rabi oscillation to antibunching exponential decay. Furthermore, both the generation rate and the violation of the Cauchy–Schwarz inequality of triphotons confirm the highly nonclassical performance. Our results establish a versatile platform for reconfigurable multipartite entanglement and provide new opportunities for complex quantum information processing based on non-Hermitian light–matter interactions.
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.
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.
The exploration of the effect of non-Hermitian (NH) in quantum systems is gaining renewed momentum as a result of the recent progress in experiments. It has been indicated that the ability to engineer the orders of exceptional points (EPs) can be fundamental to its applications in quantum control, such as accelerating entanglement generation; however, an initial survey of the interactions between different orders of EPs is still missing. In this work, we try to partially address this issue by employing a non-reciprocally coupled cavity system which can be experimentally realizable with a two-dimensional reconfigurable NH gauged laser array. With deliberate design, our systems display both second and third orders of EPs. The sign of a novel, purely quantum continuous entanglement phase transition is observed, which reveals how multi-EP interactions alter entanglement dynamics across different regimes while maintaining accelerated generation. Our findings reveil the genuinely quantum NH physics of higher-order EPs, which has opened up a new avenue for future investigations of the higher-order degeneracy application and the dynamic phase transitions of quantum systems.
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.
Abstract Non-Hermitian quantum systems showcase many distinct and intriguing features with no Hermitian counterparts. One of them is the exceptional point which marks the PT (parity and time) symmetry phase transition, where an enhanced spectral sensitivity arises and leads to novel quantum engineering. Here we theoretically study the multipartite entanglement properties in non-Hermitian superconducting qubits, where high-fidelity entangled states can be created under strong driving fields or strong couplings among the qubits. Under an interplay between driving fields, couplings, and non-Hermiticity, we focus on generations of GHZ states or GHZ classes in three and four qubits with all-to-all couplings, which allows a fidelity approaching unity when relatively low non-Hermitian decay rates are considered. This presents an ultimate capability of non-Hermitian qubits to host a genuine and maximal multipartite entanglement. Our results can shed light on novel quantum engineering of multipartite entanglement generations in non-Hermitian qubit systems.
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.