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Physical Review A

Distinct single-photon blockades based on topological edge states and bulk states in a dimer chain

Wei Zhang, Shutian Liu, Wen‐Xue Cui, Shou Zhang, Hong‐Fu Wang

Published Nov 6, 2025• 2 citations
Publisher

Abstract

Topological photonics, combining the advantages of topological properties with those of optical systems, is anticipated to be significant for various applications. However, how to leverage its benefits for realizing single-photon blockade (PB) remains rarely studied. Here, we propose schemes to generate single PBs in a dimer chain featuring multiple qubits and a two-photon Jaynes-Cummings interaction. We demonstrate that with specific intracell and intercell hopping amplitudes of the lattice, the quantum level lattices are characterized by the form of a one-dimensional array with topological edge states in both two-excitation and three-excitation spaces, resulting in suppressed two-photon excitations and enhanced single-photon excited states. This further leads to a remarkable single PB effect under the resonance-driven case. Interestingly, single PBs can be observed in the off-resonance scenario under coupling strengths with opposite trends, while satisfying that two-excitation and three-excitation transitions are resonant whereas single-photon transition is detuned. We refer to this as an abnormal mechanism compared to previous regimes. Moreover, we show the superiority of the multiqubit-cavity topological chain by comparing with scenarios with different numbers of qubits. Our study not only sheds light on the generation of the single PB effect based on an abnormal mechanism but also establishes a pathway for realizing quantum blockade in topological optical systems, with potential applications in quantum information processing and quantum communication.

DOI
10.1103/dg6g-7z9p

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Topological photonics, combining the advantages of topological properties with those of optical systems, is anticipated to be significant for various applications. However, how to leverage its benefits for realizing single-photon blockade (PB) remains rarely studied. Here, we propose schemes to generate single PBs in a dimer chain featuring multiple qubits and a two-photon Jaynes-Cummings interaction. We demonstrate that with specific intracell and intercell hopping amplitudes of the lattice, the quantum level lattices are characterized by the form of a one-dimensional array with topological edge states in both two-excitation and three-excitation spaces, resulting in suppressed two-photon excitations and enhanced single-photon excited states. This further leads to a remarkable single PB effect under the resonance-driven case. Interestingly, single PBs can be observed in the off-resonance scenario under coupling strengths with opposite trends, while satisfying that two-excitation and three-excitation transitions are resonant whereas single-photon transition is detuned. We refer to this as an abnormal mechanism compared to previous regimes. Moreover, we show the superiority of the multiqubit-cavity topological chain by comparing with scenarios with different numbers of qubits. Our study not only sheds light on the generation of the single PB effect based on an abnormal mechanism but also establishes a pathway for realizing quantum blockade in topological optical systems, with potential applications in quantum information processing and quantum communication.
Quantum technologies, holding the promise of exponentially superior performance in comparison to their classical counterparts for certain tasks, have consistently encountered challenges, including instability in quantum light sources, quantum decoherence, and vulnerability to losses that topological photonics happens to adeptly address. Here, we theoretically put forth a quantum Su-Schrieffer-Heeger-type chain designed to greatly enhance single-photon blockade (single PB) effect with topological protection. By designing the deliberate coupling strengths, the quantum level lattices take the form of a one-dimensional array with a topological edge state in single-excitation space and a two-dimensional square breathing lattice with topological corner states in two-excitation space, resulting in enhanced single-photon excitation and the suppression of two-photon transitions. Therefore, the second-order correlation function is diminished by up to 2 orders of magnitude at the cavity resonance frequency, accompanied by stronger brightness. Furthermore, the PB effect is robust to local perturbations in cavity-qubit coupling and qubit frequency, benefitting from topological protection.
We explore a method for achieving photon blockade (PB) through a two-photon Jaynes-Cummings (JC) model that includes both cavity and atom drivings. Analytical expressions for the steady state are derived to calculate photon-number distribution and correlation functions. Based on this analysis, we establish the theoretical conditions required for generating PB by controlling both drivings and propose a scheme to identify conventional photon blockade (CPB) and unconventional photon blockade (UPB) by analyzing the second- and third-order correlation functions. We validate our findings through numerical simulations conducted in an artificial atom system. We discuss two cases, one in which the transition frequency of the two-level atom is in two-photon resonance with the cavity frequency and the other in which it is off-resonance. We observe a significant interplay between CPB and UPB effects in the resonant case. In the off-resonance case, we demonstrate that UPB can be achieved by manipulating the strengths of atom driving and cavity driving to satisfy a specific relationship while meeting the requirements for optimal detuning relations. This work provides essential insights into controlling the PB effect using the two-photon JC model with both the atom and cavity drivings.
The dipole blockade phenomenon is a direct consequence of strong dipole-dipole interaction, where only single atom can be excited because the doubly excited state is shifted out of resonance. The corresponding two-body entanglement with non-zero concurrence induced by the dipole blockade effect is an important resource for quantum information processing. Here, we propose a novel physical mechanism for realizing dipole blockade without the dipole-dipole interaction, where two qubits coupled to a cavity, are driven by a coherent field. By suitably chosen placements of the qubits in the cavity and by adjusting the relative decay strengths of the qubits and cavity field, we kill many unwanted excitation pathways. This leads to dipole blockade. In addition, we show that these two qubits are strongly entangled over a broad regime of the system parameters. We show that a strong signature of this dipole blockade is the bunching property of the cavity photons which thus provides a possible measurement of the dipole blockade. We present dynamical features of the dipole blockade without dipole-dipole interaction. The proposal presented in this work can be realized not only in traditional cavity QED, but also in non-cavity topological photonics involving edge modes.
Abstract Quantum information processing, a key component of quantum information science, has attracted considerable attention. Its realization requires physical platforms and resources, among which optical systems and single-photon sources based on photon blockade (PB) have been widely employed. Here we investigate PB behaviors in a coupled optical cavity system driven by both single- and two-photon fields. The optimal conditions for PB are obtained with respect to the two-photon driving strength and cavity-laser detuning via analytical calculations. Using these optimal solutions, we show that a significant PB effect is achievable even with weak Kerr nonlinearity, and confirm that this behavior corresponds to unconventional PB (UPB) through a comparison of the second- and third-order correlation functions. Furthermore, our analysis reveals that UPB can be enhanced by two-photon dissipation. These results provide theoretical strategies for enhancing UPB, and offer insight into its fundamental mechanism.
Single-photon sources with high single-photon purity and high brightness are key elements of many future quantum technologies. While photon blockade (PB) is widely exploited in the development of such sources, achieving the coexistence of high purity and high brightness remains a long-standing challenge. Here, we identify a novel mechanism for high-brightness PB and demonstrate that near-ideal purity and near-ideal brightness can be simultaneously achieved in an extended nondegenerate two-photon Jaynes-Cummings model with two-body and three-body interactions. This mechanism is underpinned by a distinctive energy-level structure arising from the combined action of the two interactions. The energy levels in the multi-excitation manifold essentially retain a harmonic ladder of degenerate doublets, whereas in the single-excitation subspace the doublet degeneracy is lifted, with a finite splitting between the two levels. Consequently, when one bosonic mode is driven by a coherent continuous-wave pump, the former degeneracy enables the other bosonic mode to exhibit near-perfect PB even in the strong driving regime, while the latter splitting allows the mean photon number of that mode to approach unity. Our proposed scheme overcomes the outstanding challenge and offers a promising pathway toward realizing ideal single-photon sources.
A two-level quantum emitter interacting with a cavity field is an important model for investigating the photon blockade (PB) effect. Most work on this topic relies on the assumption that the emitter transition frequency is resonant with the fundamental mode frequency of the cavity. In this work we relax this constraint and reexamine the PB effect in a more general emitter-cavity system with arbitrary emitter and cavity detunings from a driving field. The results show that when the signs of the emitter and cavity detunings are the same, a PB occurs only in the strong-coupling regime, but for opposite signs of the emitter and cavity detunings, strong photon antibunching is observed in both the weak- and strong-coupling regimes, and better antibunching is achieved compared with the case when the signs are the same. More interestingly, we find that this PB arises from quantum interference for both weak and strong nonlinearities. These results deepen our understanding of the underlying mechanism of PBs and may contribute to the construction of single-photon sources with higher purity and better flexibility using two-level emitter-cavity systems.