arXiv subjects

Jingxu Bai

Publications and source records attributed to Jingxu Bai.

At least 19 recordsLinked to original sources

arXiv2026

Doppler-enhanced superheterodyne Rydberg microwave receiver

We report the enhanced sensitivity of the Rydberg microwave (MW) receiver by exploiting the Doppler effect in a vapor cell. A two-photon Rydberg ladder scheme is implemented via the co-propagation of probe and coupling lasers, which enhances the Doppler effect. When an MW field is applied, microwave dressing modifies the velocity-dependent resonance condition, enabling stronger contributions from atoms with non-zero velocities and leading to an enhancement of the EIT transmission. Based on this mechanism, we achieve a sensitivity of $35.1\ \mathrm{nV\ cm^{-1}\ Hz^{-1/2}}$ using the heterodyne technique, which is 1.5 times better than that obtained in the counter-propagating configuration. Meanwhile, the required local oscillator (LO) field is reduced by a factor of 17.6 compared with the counter-propagating configuration, which is advantageous for applications requiring minimal radiation and low power consumption. Moreover, the co-propagating configuration is more amenable to integration or portable sensing platforms because multiple laser fields can be delivered through a single optical fiber.

physics.atom-ph↗

arXiv2026

Recent advances in Ultralong-range Rydberg molecules

Rydberg molecule, formed by one or more Rydberg atoms, exhibits remarkable properties, including an exceptionally large spatial extent, rich rovibrational level structures, permanent electric dipole moments, and a pronounced sensitivity to external fields. Based on the underlying binding mechanisms, Rydberg molecules can be divided into three categories, the ground-Rydberg molecule that is bound via a low-energy electron-atom scattering interaction between ground atom and Rydberg electron, the Rydberg-Rydberg molecule that is bound via a long-range electrostatic interaction between Rydberg atoms, and the ion-Rydberg molecule that is bound via single- or multi-polar interactions between Rydberg atom and ion. This review focuses on recent theoretical and experimental advances in diatomic Rydberg molecules, covering their formation and binding mechanisms, potential energy curves, experimental observations, and spectroscopic properties, with the aim of providing a comprehensive overview of the current state and future prospects of this rapidly developing field.

physics.atom-ph↗

arXiv2025

Observation of multiple time crystals in a driven-dissipative system with Rydberg gas

Time crystals, as temporal analogs of space crystals, manifest as stable and periodic behavior that breaks time translation symmetry. In an open quantum system, many-body interaction subjected to dissipation allows one to develop the time crystalline order in an unprecedented way, as refer to dissipative time crystals. Here we report the observation of multiple time crystals in the continuously driven-dissipative and strongly interacting Rydberg thermal gases, in which continuous time crystals, sub-harmonic time crystals, and high-harmonic time crystals are observed in the same system by manipulating the Rydberg excitation. Our work provides new ways to explore the nonequilibrium phases of matter in open systems. Such time crystals with persistent oscillation rooted in emergent quantum correlations, may emerge as a ubiquitous tool in quantum metrology, for instance, continuous sensing and parameter estimation surpassing the standard quantum limit.

physics.atom-ph↗

arXiv2025

Arbitrary Instantaneous Bandwidth Microwave Receiver via Scalable Rydberg Vapor Cell Array with Stark Comb

Rydberg atoms have great potential for microwave (MW) measurements due to their high sensitivity, broad carrier bandwidth, and traceability. However, the narrow instantaneous bandwidth of the MW receiver limits its applications. Improving the instantaneous bandwidth of the receiver is an ongoing challenge. Here, we report on the achievement of an arbitrary instantaneous bandwidth MW receiver via a linear array of scalable Rydberg vapor cells with Stark comb, where the Stark comb consists of an MW frequency comb (MFC) and a position-dependent Stark field. In the presence of the Stark field, the resonance MW transition frequency between two Rydberg states is position dependent, so that we can make each MFC line act as a local oscillator (LO) field to resonantly couple one Rydberg cell. Thus, each cell receives part of a broadband MW signal within its instantaneous bandwidth using atomic heterodyne detection, achieving the measurements of the broadband MW signal simultaneously. In our proof-of-principle experiment, we demonstrate the MW receiver with 210~MHz instantaneous bandwidth using an MFC field with 21 lines. Meanwhile, we achieve an overall sensitivity of 326.6~nVcm$^{-1}$Hz$^{-1/2}$. In principle, the method allows for achieving an arbitrary instantaneous bandwidth of the receiver, provided we have enough MFC lines with enough power. Our work paves the way to design and develop a scalable MW receiver for applications in radar, communication, and spectrum monitoring.

quant-ph↗

arXiv2025

Direction switchable single-photon emitter using a Rydberg polariton

All-optical redirection or routing of single photons is essential for quantum networks. Although studied in various systems both in theory and experiment, the redirection of single photons with many output ports, compatible with large-scale photonic circuits, still needs to be explored. Here, we demonstrate a direction switchable single-photon emitter using a Rydberg polariton. The Rydberg component of the stored photon is changed using a stimulated Raman transition with a specific intermediate state. By adjusting the direction of the retrieval laser, we can redirect the emitted photon into a rich variety of alternative modes. Building upon this scheme, we propose a quantum routing of single photons with \textit{N} output channels and unity routing efficiency. In addition, the protocol reduces the effect of motional dephasing increasing the photon lifetime to $>10~μ$s ($>20$ times photon processing time), enabling functional quantum devices based on Rydberg polaritons.

quant-ph↗

arXiv2025

Thermal resonance-enhanced transparency in room temperature Rydberg gases

We report the enhanced optical transmission in the coherent, off-resonant excitation of Rydberg atom gases at room temperature via a two-photon process. Here thermal resonance-enhanced transparency (TRET) is induced when the detuning of the two lasers is adjusted to compensate the atomic thermal-motion-induced energy shifts, i.e. single and two-photon Doppler shifts. We show that the atomic velocity is mapped into the transmission of the probe fields, which can be altered by independently and selectively exciting different velocity groups through sweeping the detuning. The maximal transmission in TRET is about 8 times higher than that under the electromagnetically induced transparency (EIT). Utilizing the TRET effect, we enhance the sensitivity of a Rydberg microwave receiver to be 28.7~nVcm$^{-1}$Hz$^{-1/2}$, ultimately reaching a factor of 2.1 of the EIT case. When atoms of separate velocity groups are excited simultaneously by multiple sets of detuned lasers, the receiver sensitivity further increases, which is linearly proportional to the number of the velocity groups. Our study paves a way to exploit light-matter interaction via the TRET, and contributes to current efforts in developing quantum sensing, primary gas thermometry, and wireless communication with room-temperature atomic gases.

physics.atom-ph↗

arXiv2025

Suppression of motional dephasing using state mapping

Rydberg-mediated quantum optics is a useful route toward deterministic quantum information processing based on single photons and quantum networks, but is bottlenecked by the fast motional dephasing of Rydberg atoms. Here, we propose and experimentally demonstrate suppressing the motional dephasing by creating an {\it a priori} unknown but correct phase to each Rydberg atom in an atomic ensemble. The phase created is exactly proportional to the unknown velocity of the thermal motion, resulting in a condition as if no thermal motion occurs to the Rydberg atom upon the retrieval of the signal photon. Our experiments, though hampered by the noise of lasers and the environment, demonstrate more than one order of magnitude enhancement of the coherence time. The feasibility of realizing long-lived storage of single photons in strongly interacting Rydberg media sheds new light on Rydberg-mediated quantum nonlinear optics.

quant-ph↗

arXiv2024

Many-body nonequilibrium dynamics in a self-induced Floquet system

Floquet systems are periodically driven systems. In this framework, the system Hamiltonian and associated spectra of interest are modified, giving rise to new quantum phases of matter and nonequilibrium dynamics without static counterparts. Here we experimentally demonstrate a self-induced Floquet system in the interacting Rydberg gas. This originates from the photoionization of thermal Rydberg gases in a static magnetic field. Importantly, by leveraging the Rydberg electromagnetically induced transparency spectrum, we probe the nonequilibrium dynamics in the bistable regime and identify the emergence of a discrete time crystalline phase. Our work fills the experimental gap in the understanding the relation of multistability and dissipative discrete time crystalline phase. In this regard, it constitutes a highly controlled platform for exploring exotic nonequilibrium physics in dissipative interacting systems.

quant-ph↗

arXiv2024

Observation of electric field induced superradiance slowdown in ultracold Rydberg atomic gases

Atoms excited to electronically high-lying Rydberg states decay to low-energy states through spontaneous emission processes. We investigate the impact of a static electric field on the superradiant emission process between Rydberg $|60D_{5/2}\rangle$ and $|61P_{3/2}\rangle$ states in an ultracold Cesium Rydberg atom ensemble. We report experimental observations of a significant slowdown in superradiance upon applying an electric field. To understand the slowing down dynamics, we employ a discrete truncated Wigner approximation (DTWA) method to solve the corresponding master equation numerically. Our numerical simulations demonstrate that superradiance decoherence is caused by the Stark shifts of the Rydberg level. Our theoretical simulations qualitatively match the experimental observations. Our work provides new insights into controlling quantum critical behaviors, with implications for quantum many-body dynamics, and the study of quantum phase transitions.

physics.atom-ph↗

arXiv2024

Measurements of the hyperfine structure of $nP_J$ Rydberg states by microwave spectroscopy in Cs atoms

We present measurements of hyperfine structure (HFS) of the $nP_J$ Rydberg states for large principal quantum number $n$ range ($n=41-55$) employing the microwave spectroscopy in an ultra-cold cesium Rydberg ensemble. A microwave field with 30-$μ$s duration couples the $ nS \to nP $ transition, yielding a narrow linewidth spectroscopy that approaches the Fourier limit, which allows us to resolve the hyperfine structure of $ nP_J $ states. By analyzing the hyperfine splittings of $nP_J$ states, we determine the magnetic-dipole HFS coupling constant $\bar{A}_{HFS,P_{1/2}}=3.760(26) ~$GHz for $P_{1/2}$ state, $\bar{A}_{HFS,P_{3/2}}= 0.718(27)~$GHz, and $ \bar{B}_{HFS,P_{3/2}}= -0.084(102)~$GHz for $P_{3/2}$ state, respectively. Systematic uncertainties caused by stray electromagnetic field, microwave field power and Rydberg interaction are analyzed. This measurement is significant for the investigation of Rydberg electrometry and quantum simulation with dipole interaction involving $nP_J$ state.

physics.atom-ph↗

arXiv2024

Quantum Lotka-Volterra dynamics

Physical systems that display competitive non-linear dynamics have played a key role in the development of mathematical models of Nature. Important examples include predator-prey models in ecology, biology, consumer-resource models in economics, and reaction-diffusion equations in chemical reactions. However, as real world systems are embedded in complex environments, where it is difficult or even impossible to control external parameters, quantitative comparison between measurements and simple models remains challenging. This motivates the search for competitive dynamics in isolated physical systems, with precise control. An ideal candidate is laser excitation in dilute atomic ensembles. For example, atoms in highly-excited Rydberg states display rich many-body dynamics including ergodicity breaking, synchronisation and time crystals. Here, we demonstrate predator-prey dynamics by laser excitation and ionisation of Rydberg atoms in a room temperature vapour cell. Ionisation of excited atoms produce electric fields that suppress further excitation. This starves the ionisation process of resource, giving rise to predator-prey dynamics. By comparing our results to the Lotka-Volterra model, we demonstrate that as well applications in non-linear dynamics, our experiment has applications in metrology, and remote sensing of localised plasmas.

quant-ph↗

arXiv2024

Exploring quantum sensing for fine-grained liquid recognition

Recent years have witnessed the use of pervasive wireless signals (e.g., Wi-Fi, RFID, and mmWave) for sensing purposes. Due to its non-intrusive characteristic, wireless sensing plays an important role in various intelligent sensing applications. However, limited by the inherent thermal noise of RF transceivers, the sensing granularity of existing wireless sensing systems are still coarse, limiting their adoption for fine-grained sensing applications. In this paper, we introduce the quantum receiver, which does not contain traditional electronic components such as mixers, amplifiers, and analog-to-digital converters (ADCs) to wireless sensing systems, significantly reducing the source of thermal noise. By taking non-intrusive liquid recognition as an application example, we show the superior performance of quantum wireless sensing. By leveraging the unique property of quantum receiver, we propose a novel double-ratio method to address several well-known challenges in liquid recognition, eliminating the effect of liquid volume, device-target distance and container. We implement the quantum sensing prototype and evaluate the liquid recognition performance comprehensively. The results show that our system is able to recognize 17 commonly seen liquids, including very similar ones~(e.g., Pepsi and Coke) at an accuracy higher than 99.9\%. For milk expiration monitoring, our system is able to achieve an accuracy of 99.0\% for pH value measurements at a granularity of 0.1, which is much finer than that required for expiration monitoring.

physics.app-ph↗

arXiv2024

Continuous broadband Rydberg receiver using AC Stark shifts and Floquet States

We demonstrate the continuous broadband microwave receivers based on AC Stark shifts and Floquet States of Rydberg levels in a cesium atomic vapor cell. The resonant transition frequency of two adjacent Rydberg states 78$S_{1/2}$ and 78$P_{1/2}$ is tuned based on AC Stark effect of 70~MHz Radio frequency (RF) field that is applied outside the vapor cell. Meanwhile, the Rydberg states also exhibit Floquet even-order sidebands that are used to extend the bandwidths further. We achieve microwave electric field measurements over 1.172~GHz of continuous frequency range. The sensitivity of the Rydberg receiver with heterodyne technique in the absence of RF field is 280.2~nVcm$^{-1}$Hz$^{-1/2}$, while it is dramatically decreased with tuning the resonant transition frequency in the presence of RF field. Surprisingly, the sensitivity can be greatly improved if the microwave field couples the Floquet sideband transition. The achieving of continuous frequency and high sensitivity microwave detection will promote the application of Rydberg receiver in the radar technique and wireless communication.

physics.atom-ph↗

arXiv2023

Microwave photo-association of fine-structure-induced Rydberg $(n+2)D_{5/2}nF_{J}$ macro-dimer molecules of cesium

Long-range $(n+2)D_{5/2} \, nF_J$ Rydberg macro-dimers are observed in an ultracold cesium Rydberg gas for $39\leq n\leq48$. Strong dipolar "flip" ($\langle D_{5/2} F_{5/2} \vert \hat{V}_{dd} \vert F_{5/2} D_{5/2} \rangle$, $\langle D_{5/2} F_{7/2} \vert \hat{V}_{dd} \vert F_{7/2} D_{5/2} \rangle$) and "cross" ($\langle D_{5/2} F_{7/2} \vert \hat{V}_{dd} \vert F_{5/2} D_{5/2} \rangle$) couplings lead to bound, fine-structure-mixed $(n+2)D_{5/2}nF_J$ macro-dimers at energies between the $F_J$ fine-structure levels. The $DF$ macro-dimers are measured by microwave photo-association from optically prepared $[(n+2)D_{5/2}]_2$ Rydberg pair states. Calculated adiabatic potential curves are used to elucidate the underlying physics and to model the $DF$ macro-dimer spectra, with good overall agreement. Microwave photo-association allows Franck-Condon tuning, which we have studied by varying the detuning of a Rydberg-atom excitation laser. Further, in Stark spectroscopy we have measured molecular DC electric polarizabilities that are considerably larger than those of the atomic states. The large molecular polarizabilities may be caused by high-$\ell$ mixing. The observed linewidths of the Stark-shifted molecular lines provide initial evidence for intra-molecular induced-dipole-dipole interaction.

physics.atom-ph↗

arXiv2023

Microwave spectroscopy and Zeeman effect of cesium $(n+2)D_{5/2}\rightarrow nF_{J}$ Rydberg transitions

We report on high-resolution microwave spectroscopy of cesium Rydberg $(n+2)D_{5/2}\rightarrow nF_{J}$ transitions in a cold atomic gas. Atoms laser-cooled and trapped in a magnetic-optical trap are prepared in the $D$ Rydberg state using a two-photon laser excitation scheme. A microwave field transmitted into the chamber with a microwave horn drives the Rydberg transitions, which are probed via state selective field ionization. Varying duration and power of the microwave pulse, we observe Fourier side-band spectra as well as damped, on-resonant Rabi oscillations with pulse areas up to $\gtrsim 3 π$. Furthermore, we investigate the Zeeman effect of the clearly resolved $nF_J$ fine-structure levels in fields up to 120~mG, where the transition into $nF_{7/2}$ displays a thee-peak Zeeman pattern, while $nF_{5/2}$ shows a two-peak pattern. Our theoretical models explain all observed spectral characteristics, showing good agreement with the experiment. Our measurements provide a pathway for the study of high-angular-momentum Rydberg states, initialization and coherent manipulation of such states, Rydberg-atom macrodimers, and other Rydberg-atom interactions. Furthermore, the presented methods are suitable for calibration of microwave radiation as well as for nulling and calibration of DC magnetic fields in experimental chambers for cold atoms.

physics.atom-ph↗

arXiv2023

Quantum defects of $n$F$_J$ levels of Cs Rydberg atoms

We present precise measurements of the quantum defects of cesium $n$F$_J$ Rydberg levels. We employ high-precision microwave spectroscopy of $(n+2)\mathrm{D}_{5/2}\rightarrow n\mathrm{F}_{5/2,7/2}$ transitions for $n=45$ to 50 in a cold-atom setup. Cold cesium $(n+2)$D$_{5/2}$ atoms, prepared via two-photon laser excitation, are probed by scanning weak microwave fields interacting with the atoms across the $n\mathrm{F}_{5/2,7/2}$ resonances. Transition spectra are acquired using state-selective electric-field ionization and time-gated ion detection. Transition-frequency intervals are obtained by Lorentzian fits to the measured spectral lines, which have linewidths ranging between 70~kHz and 190~kHz, corresponding to about one to three times the Fourier limit. A comprehensive analysis of relevant line-shift uncertainties and line-broadening effects is conducted. We find quantum defect parameters $δ_{0}(\mathrm{F}_{5/2})=0.03341537(70)$ and $δ_{2}(\mathrm{F}_{5/2})=-0.2014(16)$, as well as $δ_{0}(\mathrm{F}_{7/2})=0.0335646(13)$ and $δ_{2}(\mathrm{F}_{7/2})=-0.2052(29)$, for $J=5/2$ and $J=7/2$, respectively. Fine structure parameters $A_{FS}$ and $B_{FS}$ for Cs $n{\rm{F}}_J$ are also obtained. Results are discussed in context with previous works, and the significance of the results is discussed.

physics.atom-ph↗

arXiv2023

Dephasing of ultracold cesium $80D_{5/2}$-Rydberg Electromagnetically Induced Transparency

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80$D_{5/2}$ state in a strong interaction regime employing a cesium ultracold cloud. In our experiment, a strong coupling laser couples 6$P_{3/2}$ to 80$D_{5/2}$ transition, while a weak probe, driving 6$S_{1/2}$ to 6$P_{3/2}$ transition, probes the coupling induced EIT signal. At the two-photon resonance, we observe that the EIT transmission decreases slowly with time, which is a signature of interaction induced metastability. The dephasing rate $γ_{\rm OD}$ is extracted with optical depth OD = $γ_{\rm OD}t$. We find that the optical depth linearly increases with time at onset for a fixed probe incident photon number $R_{\rm in}$ before saturation. The dephasing rate shows a nonlinear dependence on $R_{\rm in}$. The dephasing mechanism is mainly attributed to the strong dipole-dipole interactions, which leads to state transfer from $nD_{5/2}$ to other Rydberg states. We demonstrate that the typical transfer time $τ_{0(80D)}$ obtained by the state selective field ionization technique is comparable with the decay time of EIT transmission $τ_{0({\rm EIT})}$. The presented experiment provides a useful tool for investigating the strong nonlinear optical effects and metastable state in Rydberg many-body systems.

physics.atom-ph↗

arXiv2022

Continuous-frequency weak electric field measurement with Rydberg atoms

We demonstrate a continuous frequency electric field measurement based on the far off-resonant AC stark effect in a Rydberg atomic vapor cell. In this configuration, a strong far off-resonant field, denoted as a local oscillator (LO) field, acts as a gain shifting the Rydberg level to a high sensitivity region. An incident weak signal field with a few hundreds of kHz difference from the LO field is mixed with the LO field in Rydberg system to generate an intermediate frequency (IF) signal, which is read out by the Rydberg electromagnetically induced transparency (Rydberg-EIT) spectroscopy. Not like resonant EIT-AT spectra, we realize the electric field measurement of the signal frequency from 2 GHz to 5 GHz using a single Rydberg state. A minimum detectable filed strength is down to 2.31~$μ$V/cm and a linear dynamic range is over 65~dB. The minimum detectable filed is comparable with a resonant microwave-dressed Rydberg heterodyne receiver using the same system, which is 1.45~$μ$V/cm. We also show the system has an inherent polarization selectivity feature. Our method can provide a high sensitivity of electric field measurement and be extended to arbitrary frequency measurements.

physics.atom-ph↗