We propose a component-selective scheme for improving two-photon sources in a cavity-coupled two-atom system, where a single cavity mode interacts with two two-level atoms driven by phase-controlled classical fields of the same frequency. By controlling the atomic detunings and driving phase, the system can be tailored toward optimized cavity-field two-photon blockade or strongly correlated fluorescence photon-pair emission. When the two-cavity-photon component is enhanced, the cavity field exhibits optimized two-photon blockade with simultaneous suppression of unwanted one- and three-photon components at a comparable two-photon population. In another parameter regime, strongly correlated fluorescence photon pairs can also be generated from the two atoms by selecting the double-atomic-excitation component in the same two-excitation manifold. This approach provides a route toward high-quality and versatile two-photon sources, with potential applications in few-photon quantum optics and quantum information processing.
Photon blockade produces antibunched light, but a source also needs a defined output port, nonzero extractable flux, and experimentally accessible controls. We analyze an atom-assisted three-wave-mixing cavity where the driven target mode is monitored directly as the output. A two-level emitter and an auxiliary pair-exchange channel provide coherent paths to the same target-mode Fock states, with their interference controlled by η = (Ω/ F a ) e i Δ ϕ . In the weak-drive limit, canceling the target two-photon amplitude gives high-purity single-photon blockade (1PB), whereas canceling the target three-photon amplitude gives pair-enhanced two-photon blockade (2PB). Full Lindblad calculations yield g a (2) (0)∼10 −4 and P 1 /(1 − P 0 ) > 0.99 over R / κ a = 0.2–5. A representative 2PB point has g a (2) (0)=1.91, g a (3) (0)=1.26×10 −3 , and P n ≥3 / P 2 = 7.55 × 10 −8 . At fixed | η |, changing only the relative phase switches the output from a single-photon-dominated endpoint to a pair-enhanced 2PB endpoint within a few cavity lifetimes. The optimized states remain weakly populated, so the scheme favors purity and reconfigurability over high flux.
A two-level system interacting with a cavity field is an important model for investigating the photon blockade (PB) effect. Most work on this topic has been based on the assumption that the atomic transition frequency is resonant with the fundamental mode frequency of the cavity. We relax this constraint and reexamine PB in a more general atom--cavity system with arbitrary atomic and cavity detunings from a driving field. The results show that when the signs of the atomic and cavity detunings are the same, PB occurs only in the strong-coupling regime, but for opposite signs of the atomic and cavity detunings, strong photon antibunching is observed in both the weak- and strong-coupling regimes and a better PB effect 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 PB and may be help in the construction of single-photon sources with higher purity and better flexibility using atom--cavity systems.
Photon antibunching based on a single two-level atom strongly coupled to a single-mode optical cavity has been demonstrated in experiments. Here, we put forward an improved version of such an antibunching by introducing a pump field and a microwave field in the coupled atom-cavity system to form both a three-level $\mathrm{\ensuremath{\Delta}}$-type transition and closed-loop coupling. Via calculating the zero-time-delay second-order correlation function
g(2)(0) of the single-mode cavity field, we find that a complete photon blockade, namely,
g(2)(0)=0, can be well achieved without detuning the driving and cavity resonance. In addition, it is clearly shown that this strong photon antibunching effect appears in the weak-coupling regime of light-atom interactions. The enhanced photon antibunching is ascribed to quantum interference between the two transition paths from the three-level $\mathrm{\ensuremath{\Delta}}$ atom weakly coupled to the three involved fields (cavity, pump, and microwave). Our proposal is useful for the single-photon generation by photon blockade, which has applications in quantum information processing.
High-purity and bright single-photon sources are important for quantum information processing and precision measurement. We propose a collectively enhanced universal photon-blockade scheme in a multi-emitter two-photon Tavis--Cummings system. Independent coherent drives of the cavity and collective emitter enable destructive interference between two-photon excitation pathways, while collective coupling supplies level anharmonicity. Full-quantum master-equation simulations, the Holstein--Primakoff approximation, and a non-Hermitian probability-amplitude analysis yield the optimal conditions: cavity resonance together with phase and amplitude matching. Compared with a purely collective blockade, the proposed scheme lowers
g(2)(0), and essentially preserves the single-photon population. As the emitter number
N increases, the optimal point remains at
Δc=0, while the minimum correlation follows
gmin(2)(0)∝N−2. By contrast, unconventional photon blockade shifts away from resonance as
N increases, limiting its purity improvement and brightness. In the weak-drive regime, universal blockade obeys
g(2)(0)∝εa2, owing to a higher-order bypass through the three-excitation manifold. The drive strength therefore provides an additional purity--brightness control, although the interference mechanism makes the scheme more sensitive to dissipation-rate mismatch. Our results establish a scalable route to bright, high-purity, and tunable single-photon emission in multi-emitter cavity-QED systems.
Abstract We propose a scheme to enhance photon blockades simultaneously in two microwave cavities connected by a giant atom. In the case that only one cavity is weakly driven, we observe that the enhanced photon blockades occur in both cavities at the same time, which is attributed to the anharmonic eigenenergy spectrum constructed by the resonantly coupled giant atom. When the cavity and the atom are simultaneously driven, the stronger photon blockades in two cavities can be successfully achieved by the destructive quantum interference of two-photon excitation. Interestingly, we find that high single-photon occupations can be obtained in both cases. Moreover, we give the optimal conditions for conventional and unconventional photon blockades through analytical calculations, which are in good agreement with numerical results. Our scheme opens a prospective path to achieve simultaneous photon blockades in two indirectly coupled cavities, and provides a promising method to generate the high-quality and brightness single photon source.
The antibunching effect generated in a cavity containing first a single two-level atomic system and then two identical atoms is explored for off-resonant interactions, in strong- and weak-coupling regimes. The cavity is driven by coherent and squeezed sources. Using the second-order correlation function analytically derived in the weak-excitation regime, we show that squeezed light achieves and improves strong antibunching, leading to a photon blockade. This enhancement is due to a destructive quantum interference mechanism induced by the nonclassical light, creating a supplementary transition pathway. The best effect is obtained for equal frequency detunings in the strong-coupling regime. More interestingly, our investigation reveals that the two-atom-cavity system can further improve the antibunching effect compared to the single-atom cavity. It turns out that the additional couplings appearing in the cavity due to the implementation of the two atoms, combined with the squeezed light, could substantially enhance the photon-blockade effect.