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Effective Two-Level Dynamics in Confined Alkali Vapors at Telecom Wavelengths

Golan Ben-Ari, G. W. Orr, Eliran Talker

Published Apr 8, 2026• 0 citations
Publisher

Abstract

Abstract We demonstrate the emergence of an effective two-level atomic system at telecom wavelengths in hot rubidium vapor confined to a sub-micron-thick cell. In this extreme confinement regime, frequent atom–surface collisions reshape the atomic dynamics by selecting a narrow velocity class of atoms moving nearly parallel to the cell walls. This confinement-induced filtering suppresses optical pumping into intermediate and uncoupled states. As a result, a closed cycling transition in the telecom band becomes the dominant interaction channel, thereby giving rise to a robust effective two-level response. Through combined absorption and fluorescence measurements, supported by a theoretical model incorporating wall-induced relaxation, we show that optical behavior is governed by effectively isolated two-level dynamics. Our results reveal a new mechanism for engineering simplified quantum systems from complex atomic media without external state preparation. This approach enables telecom-compatible, compact atomic platforms with intrinsically reduced decoherence pathways, opening a route toward integrated quantum photonics, including chip-scale quantum memories, telecom frequency references, and scalable quantum information processing.

DOI
10.21203/rs.3.rs-9268286/v1

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Abstract We demonstrate the emergence of an effective two-level atomic system at telecom wavelengths in hot rubidium vapor confined to a sub-micron-thick cell. In this extreme confinement regime, frequent atom–surface collisions reshape the atomic dynamics by selecting a narrow velocity class of atoms moving nearly parallel to the cell walls. This confinement-induced filtering suppresses optical pumping into intermediate and uncoupled states. As a result, a closed cycling transition in the telecom band becomes the dominant interaction channel, thereby giving rise to a robust effective two-level response. Through combined absorption and fluorescence measurements, supported by a theoretical model incorporating wall-induced relaxation, we show that optical behavior is governed by effectively isolated two-level dynamics. Our results reveal a new mechanism for engineering simplified quantum systems from complex atomic media without external state preparation. This approach enables telecom-compatible, compact atomic platforms with intrinsically reduced decoherence pathways, opening a route toward integrated quantum photonics, including chip-scale quantum memories, telecom frequency references, and scalable quantum information processing.
We combined experimental and theoretical investigations of an effective two-level atomic system operating in the near-infrared telecom wavelength regime, realized using hot rubidium vapor confined within a sub-micron-thick cell. In this strongly confined geometry, atomic coherence is profoundly influenced by wall-induced relaxation arising from frequent atom-surface collisions. By analyzing both absorption and fluorescence spectra, we demonstrate that the optical response is dominated by a closed cycling transition, which effectively isolates the atomic dynamics to a two-level configuration despite the presence of multiple hyperfine states. This confinement-induced selection suppresses optical pumping into uncoupled states and enables robust, controllable light-matter interaction at telecom wavelengths within a miniature atomic platform. Our results establish a practical route to realizing near-infrared atomic two-level systems in compact vapor-cell devices, opening new opportunities for integrated quantum photonic technologies, including on-chip quantum memories, telecom-band frequency references, and scalable quantum information processing.
Accurate and stable frequency sources can be realized by locking lasers to well-known transitions between energy levels in isolated quantum systems such as alkali atoms. Unfortunately, current implementations of such frequency standards typically involve bulky optical setups and discrete optical components. Furthermore, the common transitions of alkali atoms are in the near-infrared, hindering their use as frequency references in the telecom regime. Our current work is focused on mitigating these deficiencies. In particular, we demonstrate the design, fabrication, and experimental characterization of an on-chip telecom frequency reference that is based on a ladder transition of rubidium atoms integrated with nanoscale optical waveguides. These atomic cladded waveguides are implemented in a serpentine geometry in order to optimize the chip area and maximize the interaction of light with the alkali atoms. Following its fabrication, the device is used to stabilize a telecom laser around a 1.5 μm wavelength to a precision better than 200 kHz at ∼250 s. Moreover, in spite of the fact that the natural lifetime of the excited state of the atom corresponding to only a few megahertz line widths, the nanoscale confinement of the optical mode dictates ultrashort interaction times and extreme photonic energy densities allowing us to demonstrate low power and faster (∼200 MHz) all-optical modulation of a near-infrared light with a telecom light. The results presented in this paper push forward the efforts toward fully integrated chip-scale stabilization system and provide an extremely efficient link between atomic based devices and silicon photonics platform in the telecom.
Atom-light interactions in nano-scale systems hold great promise for novel technologies based on integrated emitters and optical modes. We present the design architecture, construction method, and characterization of an all-glass alkali-metal vapor cell with nanometer-scale internal structure. Our cell has a glue-free design which allows versatile optical access, in particular with high numerical aperture optics. By performing spectroscopy in different illumination and detection schemes, we investigate atomic densities and velocity distributions in various nanoscopic landscapes. We apply a two-photon excitation scheme to atoms confined in one dimension within our cells, achieving a resonance line-width of 32 MHz in a counter-propagating geometry, and 57.5 MHz in a co-propagating geometry. Both of these are considerably narrower than the Doppler width (GHz), and are limited by transit time broadening and velocity selection. We also demonstrate sub-Doppler line-widths for atoms confined in two dimensions to micron-sized channels. Furthermore, we illustrate control over vapor density within our cells through nano-scale confinement alone, which could offer a scalable route towards room-temperature devices with single atoms within an interaction volume. Our design offers a robust platform for miniaturized devices that could easily be combined with integrated photonic circuits.
Doppler broadening presents a major limitation for high-resolution spectroscopy and nonlinear optics in room-temperature atomic vapors. Here, we demonstrate the suppression of Doppler broadening accompanied by pronounced absorption on the upper transition of a three-level ladder system, achieved by dressing the intermediate state with a strong control field. As a concrete realization, we study a hot vapor of 87^{87}87Rb where the lower transition is driven by a strong control field resonant with the D2 line at a wavelength of 780 nm, while a weak counter-propagating probe field at the telecom C-band wavelength of 1529 nm (5P(3/2)↔4D(5/2)5P_{(3/2)}\leftrightarrow 4D_{(5/2)}5P(3/2)​↔4D(5/2)​) interrogates the dressed states. We observe absorption features with a resonant optical depth of approximately 4 and a full width at half maximum of about 17 MHz. Remarkably, this corresponds to an order-of-magnitude reduction relative to the Doppler width, while the optical depth on the upper transition of the ladder scheme exceeds that of the Doppler-broadened lower transition. The measured spectra are in good agreement with theoretical modeling. Combining high optical density with sub-Doppler-width absorption lines typically requires laser-cooled atoms, while our approach profits from the experimental simplicity of a hot-vapor platform.
Alkali vapors confined in nano-scale cells are promising tools for future integrated atom-based sensor. In this thesis, we investigate the interaction between light and an ensemble of atoms confined in a nano-geometry. We focus on the different processes that can modify the optical response of the atomic ensemble and possibly affect the sensitivity of a sensor based on that technology. First, we study the non-local response of atoms to a light excitation due the atomic motion in thermal vapors. When the distance over which the atoms relaxes is larger than the size of the cell, the optical response depends on the size of the system. We have observed that for transmission spectroscopy, this leads to a periodic modification of the optical response with a period equal to the wavelength of the optical transition. Subsequently we showed that when the density of atom increases, the atomic response becomes local again. In this dense regime, the resonant dipole-dipole interaction in a sub-wavelength geometry leads to collective frequency shifts of the spectral lines. We demonstrate that these shifts were induced by the cavity formed by the cell walls, hence clarifying a long-standing issue. We developed a model to extract the density shifts deconvolved from the cavity effects. Close to a surface, the optical response is also affected by the van der Waals atom-surface interaction. We introduced a new method to extract precisely the strength of this interaction. We also developed a new generation of super-polished glass nano-cells and we presented promising spectroscopic signals. Finally, using these cells, we have compared transmission and off-axis spectroscopic techniques.
We experimentally demonstrate hyperfine optical pumping of rubidium atoms probed by an evanescent electromagnetic field at a dielectric-vapor interface. This light-atom interaction at the nanoscale is investigated using a right angle prism integrated with a vapor cell and excited by evanescent wave under total internal reflection. An efficient hyperfine optical pumping, leading to almost complete suppression of absorption on the probed evanescent signal, is observed when a pump laser beam is sent at normal incidence to the interface. In contrast, when the pump and probe beams are co-propagating in the integrated prism-vapor cell, no clear evidence of optical pumping is observed. The experimental results are supported by a detailed model based on the optical Bloch equation of a four atomic-level structure, which also includes a treatment of transit relaxation and wall collision with relaxation rates that were obtained directly from the thermal velocities of the atoms and the penetration depth of the evanescent wave. The obtained highly efficient optical pumping at the nanoscale is regarded as an important step in the quest for applications such as optical switching, magnetometry, and quantum memory.