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Physical Review A

Photon-pair generation on resonance via a dark state

Hui-Min Zhao, Xiaojun Zhang, M. Artoni, Giuseppe Carlo La Rocca, Jin‐Hui Wu

Published Aug 17, 2022• 10 citations
Publisher

Abstract

We present a scheme to generate photon-pair states through resonant spontaneous four-wave mixing (SFWM) in a five-level double-bowtie $(\ensuremath{\bowtie})$ configuration subject to two pumping fields and one coupling field when a quasidark state is created between two of three ground levels. The quasidark state is used here to largely suppress linear resonant absorption (gain) of the generated photon pairs while supporting strong SFWM nonlinearities and nonclassical cross-correlation. Numerical results for cold atomic samples show that the generation efficiency may be comparable to or even larger than that obtained in the off-resonance four-level single-bowtie configuration with only one pumping field. This scheme is robust to fluctuations of atomic populations and enables one to easily control the ratio of two rates with which distinct SFWM processes generate photon-pair states.

DOI
10.1103/physreva.106.023711

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We present a scheme to generate photon-pair states through resonant spontaneous four-wave mixing (SFWM) in a five-level double-bowtie (\ensuremath⋈)(\ensuremath{\bowtie})(\ensuremath⋈) configuration subject to two pumping fields and one coupling field when a quasidark state is created between two of three ground levels. The quasidark state is used here to largely suppress linear resonant absorption (gain) of the generated photon pairs while supporting strong SFWM nonlinearities and nonclassical cross-correlation. Numerical results for cold atomic samples show that the generation efficiency may be comparable to or even larger than that obtained in the off-resonance four-level single-bowtie configuration with only one pumping field. This scheme is robust to fluctuations of atomic populations and enables one to easily control the ratio of two rates with which distinct SFWM processes generate photon-pair states.
Tunable Rydberg interactions in cold atoms can be used to generate strongly correlated photon pairs through a spontaneous four-wave-mixing process in which all driving fields are allowed to work on resonance. The scheme relies on electromagnetically induced transparency and an imbalanced dark state with most atoms trapped in a ground state and a weakly populated Rydberg state. We show in particular that the combination of these two effects results in negligible linear absorption and Raman gain at the Stokes and anti-Stokes frequencies of generated photon pairs, while the nonlocal (Rydberg) nonlinearities contribute significantly to the enhancement of photon-pair generation rates and cross correlations at very low pump strengths and optical depths.
We model the generation of multiple photon pairs (biphotons) through engineering of two coexisting nearly resonant spontaneous four-wave-mixing (SFWM) processes in five-level atoms driven to a quasi-dark state trapping regime. This is achieved through a suitable choice of two pump beams and one coupling beam whose spectral profiles are taken into account both to provide realistic estimates for the effects of their linewidths on atomic populations, coherences, and photon correlations and to engineer the joint spectral amplitude (JSA) distributions of generated biphotons directly by tuning the beams' parameters. We specifically leverage this tunability to control the degree of spectral indistinguishability of two biphotons with ultranarrow linewidths. The large degree of indistinguishability achievable in our model can be harnessed for advanced applications in quantum communication and information processing and potentially adapted to compatible solid-state interfaces.
We present a detailed study of the generation of photon pairs by spontaneous four-wave mixing in a structure composed of two linearly uncoupled resonators, where energy can be transferred from one resonator to another only through a nonlinear interaction. Specifically, we consider the case of two racetrack-shaped resonators connected by a coupler designed to guarantee that the resonance comb of each resonator can be tuned independently and to allow the nonlinear interaction between modes that belong to different combs. We show that such a coupler can be realized in at least two ways: A directional coupler or a Mach-Zehnder interferometer. For these two scenarios, we derive analytic expressions for the pair-generation rate via single-pump spontaneous four-wave mixing and compare these results with that achievable in a single-ring resonator.
We show that narrowband two-color entangled single Stokes photons can be generated in a ultra-cold atoms sample via selective excitation of two spontaneous four-wave mixing (SFWM) processes. Under certain circumstances, the generation, heralded by the respective common anti-Stokes photon, is robust against losses and phase-mismatching and is remarkably efficient owing to balanced resonant enhancement of the two four-wave mixing processes in a regime of combined induced transparency. Maximally color-entangled states can be easily attained by adjusting the detunings of the external couplings and driving fields, even when these are quite weak.
In this thesis, quantum coherent control of dynamic properties of double-dark-resonance atomic systems is pursued in detail. First we show our scheme for creating atomic coherent superposition states via the technique of stimulated Raman adiabatic passage in a Lambda-type four-level system. With the application of a control field, it is found that the presence of double dark states leads to two arbitrary coherent superposition states with equal amplitude but inverse relative phases, even though the condition of multiphoton resonance is not met. The suitable manipulation of the control field and detunings enables the proposed scheme to create any coherent superposition states one desired. Then, in the above mentioned double-dark-resonant system, a scheme for giant enhancement of the Kerr nonlinearity is put forward. Compared with that generated in a single-dark-resonance system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. We attribute this dramatic enhancement to the interaction of dark resonances. As another possible means for enhancement of Kerr nonlinearity, spontaneously generated coherence is proposed. Meanwhile, a theoretical investigation is carried out in a five-level tripod system for obtaining a high efficiency double-channel four-wave-mixing process. By manipulating the intensity of the two coupling fields, the conversion efficiency of four-wave-mixing can be controlled.