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Advanced Quantum Technologies

PT‐Symmetry‐Enhanced Simultaneous Photon Blockade in a Dual‐Cavity QED System

Y ch Wang, Zhong Ding, Yong Zhang

Published Feb 1, 2026• 2 citations
Publisher

Abstract

ABSTRACT We investigate how parity‐time () symmetry influences photon blockade in an atom‐coupled dual‐cavity quantum electrodynamics (QED) system, with a focus on distinguishing the underlying mechanisms. Statistical analysis demonstrates that photon blockade exhibits qualitatively distinct behaviors in the ‐symmetric and symmetry‐broken phases, thereby providing a clear signature of the phase transition. In this ‐symmetric structure, the two‐level atom provides the required nonlinearity, while cavity‐cavity coupling under ‐symmetric control cooperatively enhances photon antibunching, leading to simultaneous photon blockade in both the passive and the active cavities. These phenomena are comprehensively analyzed using both analytical solutions of the Schrödinger equation and numerical simulations of the master equation. Comparisons with non‐‐symmetric configurations reveal that symmetry significantly enhances photon antibunching, mean photon number and promotes cooperative blockade behavior across both cavities. In contrast to conventional photon blockade schemes, our approach remains effective under weak coupling and weak nonlinearity conditions, offering a robust and tunable pathway toward realizing high‐performance single‐photon sources in non‐Hermitian quantum systems.

DOI
10.1002/qute.202500689

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ABSTRACT We investigate how parity‐time () symmetry influences photon blockade in an atom‐coupled dual‐cavity quantum electrodynamics (QED) system, with a focus on distinguishing the underlying mechanisms. Statistical analysis demonstrates that photon blockade exhibits qualitatively distinct behaviors in the ‐symmetric and symmetry‐broken phases, thereby providing a clear signature of the phase transition. In this ‐symmetric structure, the two‐level atom provides the required nonlinearity, while cavity‐cavity coupling under ‐symmetric control cooperatively enhances photon antibunching, leading to simultaneous photon blockade in both the passive and the active cavities. These phenomena are comprehensively analyzed using both analytical solutions of the Schrödinger equation and numerical simulations of the master equation. Comparisons with non‐‐symmetric configurations reveal that symmetry significantly enhances photon antibunching, mean photon number and promotes cooperative blockade behavior across both cavities. In contrast to conventional photon blockade schemes, our approach remains effective under weak coupling and weak nonlinearity conditions, offering a robust and tunable pathway toward realizing high‐performance single‐photon sources in non‐Hermitian quantum systems.
We study the effects of parity-time (PT\mathcal{PT}PT) symmetry on the photon blockade and distinguish the different blockade mechanisms in a double-cavity optomechanical system. By studying the light statistics of the system, we find the completely different photon blockade behaviors when the PT\mathcal{PT}PT symmetry is broken or unbroken, which is related to the PT\mathcal{PT}PT phase transition. Furthermore, an interesting phenomenon that the two cavities are blocked at the same time is found with the appropriate system parameters. Those statistical phenomena are all analyzed in detail and demonstrated by analytically solving the Schr\"odinger equation and numerically simulating the master equation, respectively. Finally, we also consider the non-PT\mathcal{PT}PT-symmetric situations which further reveal the physical essence of the photon blockade by comparing those results. Different from the usual photon blockade, our proposal is feasible even with weak parameter mechanism, i.e., the proposal neither requires the strong optomechanical coupling nor the large tunneling coupling between cavities.
We investigate theoretically the model of a cavity-quantum-electrodynamics (QED) system that consists of two two-level atoms coupled to a single-mode cavity in the weak coupling regime, where the system is driven by quantum light. The dynamics behavior of the entire system is tackled in the framework of a cascaded quantum system. We find that the two-photon blockade with two-photon bunching and three-photon antibunching can be obtained even when the strong system dissipation is included. This result shows that our work has potential for realizing entangled photon pairs in a weakly coupled cavity. Moreover, we also analyze the photon statistics of the system in the case of out-of-resonance coupling between cavity and two nonidentical atoms. Here, an unconventional photon blockade effect with suppression of two-photon correlation and enhancement of three-photon correlation can be realized, which shows many quantum statistical characteristics of a cavity QED system in weak coupling.
We theoretically investigate the quantum-interference-induced photon blockade effect in a single two-level atom-cavity quantum electrodynamics (QED) system with degenerate parametric amplification. The analytical calculations reveal the optimal parametric gain and phase parameters for achieving optimum unconventional photon blockade conditions. Under the optimal parameter regime, the numerical results of the second-order correlation function demonstrate strong photon antibunching consistent with the analytical results. Furthermore, the numerical results corroborate that coherently driving the atom leads to a stronger photon blockade than a coherently driven cavity with the optimal parameters. We numerically demonstrate that the UPB effect is compromised by a non-zero cavity-atom coupling in the cavity-driven configuration. However, stronger photon antibunching can be attained with a non-zero cavity-atom coupling in the atom-driven configuration. This work may be suitable for experimentally realising a strongly antibunched single-photon source for applications in quantum technology.
We present an all-fiber emitter-cavity quantum electrodynamics (QED) scheme which makes it possible to realize the strong photon blockade phenomenon in the strong coupling regime. To begin with, we study the emitter-cavity system where the two-level emitter and cavity are driven by a laser field under different driving strengths, respectively. Then, we theoretically derive that through driving the single-mode nanofiber cavity and a single two-level emitter simultaneously with two classical fields, the photon antibunching effect and the intracavity mean photon number will be tremendously enhanced. Compared with the systems driving an emitter or the cavity, respectively, the second-order correlation function at zero time decay g(2)(0){g}^{(2)}(0)g(2)(0) in our system can reach the minimum value as 0.0003, which is much smaller than a single-emitter-cavity QED system of emitter drive or cavity drive. In particular, under the condition of quantum interference model, the strong phenomenon of photon antibunching can be flexibly reached by controlling of the intensity relationship between the dual-pumping fields in the strong coupling regime. Our proposal can be achieved in the near future and has great potential applications in high-quality single-photon sources and quantum communication processing.
Photon blockade (PB) is generally classified into conventional and unconventional types based on their distinct physical mechanisms. Recent studies have aimed to bridge the two regimes to realize a universal photon blockade (universal PB) that combines their respective advantages. Here, we propose a scheme for achieving universal PB based on second-order nonlinearity. The second-order nonlinear coupling between two cavity modes mediates the fundamental interaction, while an optical parametric amplifier embedded in one cavity introduces additional quantum interference pathways. We analytically derive the optimal conditions for universal PB, and the analytical results show excellent agreement with numerical simulations. By comparing universal PB with conventional PB, we highlight its unique performance advantages: the scheme operates effectively in both strong and weak coupling regimes, relaxes experimental constraints, and achieves an ultra-low equal-time second-order correlation function g (2) (0) down to 10 −7 , while maintaining a moderate mean photon number N a ∼ 10 −2 . This work provides a feasible and tunable platform for realizing high-purity single-photon sources and exploring quantum statistical properties in nonlinear cavity systems.
Photon blockade (PB) is an important quantum phenomenon in cavity quantum electrodynamics (QED). Here, we investigate the PB effect in the simplest cavity QED systems (one cavity containing first a single atom and then two atoms), where only the atoms are weakly driven. Via the analytical calculation and numerical simulation, we show that the strong PB can be generated even with the weak-coupling regime at the total resonance. This blockade is ascribed to the two-photon absorption, which is fundamentally different from the conventional and unconventional blockade mechanisms. Therefore, our study provides an alternative approach to produce the PB in the atom-driven cavity QED system.