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Advanced Quantum Technologies

Photon–Photon Interaction Mediated by an Inverted Y ‐type Four‐Level Atom

Ya Yang, YunLan Zuo, ShiYang Zhang, Lan Xu, Lan Zhou

Published Dec 26, 2025• 0 citations
Publisher

Abstract

ABSTRACT We investigate the transport properties of two photons in a system consisting of an inverted Y –type four‐level atom chirally coupled to a 1D dual‐waveguide structure, focusing on the two‐photon antibunching effect. By analyzing the two‐photon scattering states, we identified a range of nonlinear effects, including spatial attraction and repulsion between photons, background fluorescence, and the emergence of two distinct two‐photon bound states. The key parameters for controlling photon antibunching are systematically identified. In both symmetric and chiral coupling scenarios between the atom and the waveguides, suitably designed two‐photon inputs can eliminate correlations between transmitted photons. This mechanism suppresses the fluorescence quenching through destructive interference between the two bound states, thereby enabling precise control of two‐photon antibunching.

DOI
10.1002/qute.202500740

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ABSTRACT We investigate the transport properties of two photons in a system consisting of an inverted Y –type four‐level atom chirally coupled to a 1D dual‐waveguide structure, focusing on the two‐photon antibunching effect. By analyzing the two‐photon scattering states, we identified a range of nonlinear effects, including spatial attraction and repulsion between photons, background fluorescence, and the emergence of two distinct two‐photon bound states. The key parameters for controlling photon antibunching are systematically identified. In both symmetric and chiral coupling scenarios between the atom and the waveguides, suitably designed two‐photon inputs can eliminate correlations between transmitted photons. This mechanism suppresses the fluorescence quenching through destructive interference between the two bound states, thereby enabling precise control of two‐photon antibunching.
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We calculate the one- and two-photon scattering matrices of a pair of collocated nonidentical two-level atoms coupled to a waveguide. We show that by proper choice of a two-photon input, the background fluorescence by the atoms may be completely quenched, as a result of quantum interference, and that when the atoms' detuning is smaller than their linewidths, extremely narrow fluorescence features emerge. Furthermore, the system emits a two-photon bound state which can display spatial oscillations or quantum beats, and can be tuned from bunched to antibunched statistics as the total photon energy is varied.
We investigate the two-photon transport properties inside one-dimensional waveguide side coupled to a cavity. The cavity is doped with a four-level atom. By employing dressed state basis, we show that the atom-cavity molecule produces a nonlinear interaction. The bunching and antibunching of the transmitted and reflected photons can be observed due to the nonlinearity. By tuning the Rabi frequency of the classical field, the transmission and reflection of the correlated photons can be controlled.
We present a theoretical technique for solving the quantum transport problem of a few photons through a one-dimensional, strongly nonlinear waveguide. We specifically consider the situation where the evolution of the optical field is governed by the quantum nonlinear Schr\"odinger equation. Although this kind of nonlinearity is quite general, we focus on a realistic implementation involving cold atoms loaded in a hollow-core optical fiber, where the atomic system provides a tunable nonlinearity that can be large even at a single-photon level. In particular, we show that when the interaction between photons is effectively repulsive, the transmission of multiphoton components of the field is suppressed. This leads to antibunching of the transmitted light and indicates that the system acts as a single-photon switch. On the other hand, in the case of attractive interaction, the system can exhibit either antibunching or bunching, which is in stark contrast to semiclassical calculations. We show that the bunching behavior is related to the resonant excitation of bound states of photons inside the system.
Controlling the interaction between photons is one of the important technologies applied to quantum information processing at the few-photon level. We investigate the two-photon interaction via a Ξ-type atom, where one atomic transition is coupled to a one-dimensional waveguide, and the other transition is coupled to a cavity field. Whether the cavity is initially in the vacuum state or not, determines the effective configuration of the quantum emitter. When the cavity is in the vacuum state, only one bound state appears. We further found that the joint probability of transmitted photons oscillates with their spatial separation due to the coexistence of two bound states, if the cavity is in fock state |n〉 (n ≠ 0). With the incoming wave function consists entirely of plane waves, we present the exact out-state function that exhibit the bunching and antibunching behaviors. And, we discuss in detail with the behaviors of varying both the photon pair energy(E) and the energy difference between the two photons (Δ). Moreover, the spatial attraction and repulsion between the two transmitted photons can be controlled by the parameters of the cavity.
We investigate few-photon scattering properties in two one-dimensional waveguides chirally coupled to a nonlinear cavity. The quantum states of scattered few photons are solved analytically via a real-space approach, and the solution indicates the few-photon reflection and transmission properties. When inputting two photons of equal energy to resonate with the cavity, the propagation characteristics of the two photons will be interesting, which is different from the previous anti-bunching effects with a quantum emitter. More importantly, when the total energy of the two incident photons equals the energy of a nonlinear cavity accommodating two photons, influence of the bound state will become larger to result in disappearance of antibunching effect. However, the bound state has no effect on probability of routing to another waveguide.