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Communications in Theoretical Physics

Dual-field and cross-field nonclassical light generation in a one-133Cs atom cavity QED system

Zhiqiang Wen, Chen Wang, Shougang Zhang

Published Apr 16, 2025• 0 citations
Publisher

Abstract

Abstract Nonclassical light fields exhibit unique quantum characteristics that not only expand the scope of optical research but also provide a solid foundation for advancements in quantum technologies. In this study, we investigate a system consisting of one-133Cs atom placed in a resonant cavity. Pumped by 459 nm laser light, the system generates cavity modes corresponding to the atomic 7S 1/2 → 6P 3/2 (1470 nm) and 7S 1/2 → 6P 1/2 (1359 nm) transitions, which are associated with the clock states of the cesium active optical clock. By analyzing the statistical and dynamical properties of the fields, we systematically explore the nonclassical behavior of the system under varying coupling strengths and cavity decay rates. We identify parameter regions where both individual fields and their cross-correlation exhibit nonclassicality, with the Cauchy–Schwarz (CS) violation coefficient R reaching a maximum of 13.9. This demonstrates the system’s ability to generate highly nonclassical photon pairs, enriching the repertoire of nonclassical light sources.

DOI
10.1088/1572-9494/adcd4e

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Abstract Nonclassical light fields exhibit unique quantum characteristics that not only expand the scope of optical research but also provide a solid foundation for advancements in quantum technologies. In this study, we investigate a system consisting of one-133Cs atom placed in a resonant cavity. Pumped by 459 nm laser light, the system generates cavity modes corresponding to the atomic 7S 1/2 → 6P 3/2 (1470 nm) and 7S 1/2 → 6P 1/2 (1359 nm) transitions, which are associated with the clock states of the cesium active optical clock. By analyzing the statistical and dynamical properties of the fields, we systematically explore the nonclassical behavior of the system under varying coupling strengths and cavity decay rates. We identify parameter regions where both individual fields and their cross-correlation exhibit nonclassicality, with the Cauchy–Schwarz (CS) violation coefficient R reaching a maximum of 13.9. This demonstrates the system’s ability to generate highly nonclassical photon pairs, enriching the repertoire of nonclassical light sources.
We present a proposal to control and improve the nonclassicality of photons in a single-atom cavity-QED system with a strong coupling strength, where the atom is directly driven by external fields. Exploring the eigenvalues and the corresponding eigenstates of the system, we show that the dressed states can be optically manipulated by changing the control field intensity. In particular, tuning the control field frequency to be resonant with the one-photon excitation state, we show that the nonclassicality of cavity photons arising from the two-photon blockade can be actively controlled. We also show that there exists a magic control field Rabi frequency at which the two-photon blockade phenomenon can be significantly improved. The work presented here provides an optical method to control the statistical features of the cavity field that could find utility in nonclassical light generation, photon gateway operation, and exotic quantum-state generation.
Nonclassical light is a critical resource for a broad range of quantum technologies and fundamental science. However, leading platforms such as laser-cooled atoms and solid-state systems both present substantial challenges to scalability due to complexity and spectral drift. Here, we demonstrate a hybrid approach using a chip-scale rubidium beam coupled to a high-finesse cavity-quantum electrodynamics (QED) system. Specifically, we generate nonclassical light and observe optical nonlinearities at the few photon level. This is achieved without degradation of the cavity-QED system. By demonstrating the compatibility of these two technologies, we open a path for distributed sources of nonclassical light and set the stage for using cavity-QED to enhance the performance of chip-scale magnetometers and atomic clocks.
Although conventional lasers operate with a large number of intracavity atoms, the lasing properties of a single atom in a resonant cavity have been theoretically investigated for more than a decade. Here we report the experimental realization of such a one-atom laser operated in a regime of strong coupling. Our experiment exploits recent advances in cavity quantum electrodynamics that allow one atom to be isolated in an optical cavity in a regime for which one photon is sufficient to saturate the atomic transition. In this regime the observed characteristics of the atom-cavity system are qualitatively different from those of the familiar many atom case. Specifically, we present measurements of intracavity photon number versus pump intensity that exhibit "thresholdless" behavior, and infer that the output flux from the cavity mode exceeds that from atomic fluorescence by more than tenfold. Observations of the second-order intensity correlation function demonstrate that our one-atom laser generates manifestly nonclassical light that exhibits both photon antibunching and sub-Poissonian photon statistics.
Alkali atoms are a workhorse in quantum optics, owing to the relative simplicity of their elec- tronic structure, which affords remarkable and reliable control over their behaviour. In particular, the ability to probe and manipulate alkali atoms with electromagnetic fields provides an important resource for studying and harnessing their fundamental properties. This thesis explores interac- tions between alkali atoms and light, to uncover ways of exploiting their properties for a variety of purposes. The main results of the thesis are divided into three main parts, as we detail below. Firstly, we develop theoretical models of effective interactions between alkali atoms in cavity quantum electrodynamics (cavity QED) systems, building on previous work in this area. The models are based on Raman transitions between the Zeeman sublevels of hyperfine ground states in an alkali atom. We show that by coupling light to both D-lines of the atom simultaneously, a versatile effective Hamiltonian can be realised with terms that can be manipulated independently. Additionally, we show that, with careful arrangement of the fields, the effective interactions can persistinsteadystate, continuouslyoutputtinglightthatcarriessignaturesoftheinteraction. These models reveal novel mechanisms for generating nonclassical states of light, with the potential for producing Wigner-negative and quadrature-squeezed light from single-atom sources. We simulate full hyperfine structure models of the interactions, using parameters inspired by modern cavity QED architectures, to demonstrate the robustness of their implementation in a real atom. Secondly, we explore nonclassical photon statistics through specific configurations of single- atom nanofibre cavity QED systems. By coupling an alkali atom to nanofibre cavity modes, we demonstrate antibunching and strong two-mode correlations, showcasing the versatility of these systems for generating nonclassical photon statistics. We consider two schemes for their photon correlations, each based on coupling two cavity modes to a single atom. First, the generation of nonclassical light at telecom-band wavelengths is studied, using cascaded transitions within a caesium atom. The atomic states are chosen such that one of the cavity modes is resonant at a telecom-band frequency. Second, we explore the coupling an adjacent pair of resonances of a long cavity to a strongly-driven atom. The characteristic emission spectrum is matched to the free spectral range of the cavity. In both cases, we consider simplified models to understand the critical behaviour of the systems, and then use full hyperfine structure models to examine the viability of implementing them in modern nanofibre cavity QED systems. Finally, we present a model for the interaction of light with a thermal cloud of Rydberg atoms. The random thermal motion of a room-temperature gas necessitates ensemble averaging in order to predict the absorption spectrum for a probe beam. The effective model that we develop accurately predicts the absorption profile of electromagnetically-induced transparency in the atomic cloud, offering insights for experiments in atom-based sensing of microwave-frequency electromagnetic fields. Overall, this thesis enhances the fundamental understanding of alkali atom-light interactions and adds to the ever-growing quantum-optical toolbox.
We introduce a method for the conditional generation of nonclassical states of light in a cavity. We consider two-level atoms traveling along the transverse direction to the cavity axis and show that by conditioning on one of the output measurements nonclassical field states are generated. The two-level atoms are prepared in the ground state and we conditioned them on the events in which they are also detected in the ground state. Nonclassical properties of the cavity mode are identified and characterized. This includes quadrature squeezing, sub-Poissonian photon-number distributions, and negative Wigner functions. We determine the optimal parameter regions where the corresponding nonclassical features are most distinct.