Rubidium Atoms Research Articles

N-changing population of Rydberg states by low-energy electron-Rydberg collisions.

Inelastic n-changing collisions play an important role in the evolution of Rydberg atoms into ultracold plasmas. However, for the initially intermediate n (n ∼ 40) Rydberg states, these collisions can hardly be observed due to the low electron temperature in ultracold plasmas. In this work, we designed an experimental scheme to facilitate collisions between free electrons at 1.5eV and intermediate n Rydberg atoms. Using the field ionization technique, we measured the state distributions resulting from the evolution of initially cold rubidium atoms in the 45P3/2 Rydberg state. The experimentally obtained probability of inelastic collisions excitation agrees well with the Monte Carlo simulation results. In addition, our experimental results indicate that the n-changing population induced by hot electrons is significant for lower nP Rydberg states. Our work plays a significant role in calculating the rates of electron-ion three-body recombination in ultracold plasmas.

Use of the 5P3/2→6P3/2 electric dipole forbidden transition in Rb as a non-perturbing probe of atom dynamics in an operating magneto-optical trap

Abstract Results of spectroscopy experiments using the $5P_{3/2} \to 6P_{3/2}$ electric dipole forbidden transition in cold rubidium atoms are presented. Production of this forbidden transition is detected by observing the emission of the $420 $ nm fluorescence photons that result from the decay of the $6P_{3/2} $ state into the ground state. The experiments are performed under the steady state operation conditions of a magneto-optical trap (MOT), and thus provide non-perturbing information on the atom-light system. The hyperfine structure of the $6P_{3/2}$ level is completely resolved, and the fluorescence peaks show the expected Autler-Townes (AT) splitting of the emission lines. This hyperfine structure is used to calibrate the frequency scale of all spectra recorded. A combination of this absolute frequency scale and an expression for the AT profile allows an absolute determination of the effective Rabi frequency and detuning of the MOT. The behavior of these AT doublets is studied as a function of frequency detuning and also as a function of the trapping light intensity.
The experiments also take full advantage of the strong polarization dependence of the relative intensities of the hyperfine fluorescence components.
This study results in a sensitive probe of the relative populations of the magnetic sublevel projections relative to the trapping magnetic field gradient.
An almost isotropic population distribution was found, but small deviations from isotropy could be determined with this electric dipole forbidden probe.

Synchronous achievement of laser frequency stabilization and tunability via modulation transfer spectroscopy on the rubidium D1 line

In the Spin Exchange Relaxation Free (SERF) magnetometer, the laser frequency must be stabilized at the alkali D1 line and tunable within a range of several gigahertz (GHz). We theoretically and experimentally analyzed the modulated sideband and resonant frequencies on the D1 transition line of rubidium (Rb) atoms using a modulation transfer spectroscopy (MTS) frequency stabilization system. The laser's self-estimated frequency stability shows the Allan deviation of 1.5 × 10−12/τ for resonance peak stabilization and 1.4 × 10−12/τ for sideband stabilization. The spectrum of the modulated laser interacting with the rubidium D1 line exhibits several absorption peaks and MTS signals across a 6 GHz scanning frequency range, which can be used to lock and tune the laser. This method enhances the application of distributed feedback semiconductor lasers in Rb atom-based magnetometers.

Rubidium and Cesium Ion-Induced Electron and Ion Signals for Scanning Ion Microscopy Applications.

Scanning ion microscopy applications of novel focused ion beam (FIB) systems based on ultracold rubidium (Rb) and cesium (Cs) atoms were investigated via ion-induced electron and ion yields. Results measured on the Rb+ and Cs+ FIB systems were compared with results from commercially available gallium (Ga+) FIB systems to verify the merits of applying Rb+ and Cs+ for imaging. The comparison shows that Rb+ and Cs+ have higher secondary electron (SE) yields on a variety of pure element targets than Ga+, which implies a higher signal-to-noise ratio can be achieved for the same dose in SE imaging using Rb+/Cs+ than Ga+. In addition, analysis of the ion-induced ion signals reveals that secondary ions dominate Cs+ induced ion signals while the Rb+/Ga+ induced signals contain more backscattered ions.

DFT insight into the phase stability, optoelectronic, elastic, vibrational, and thermodynamic properties of metal chalcogenides RbKM (M = S, Se, Te) for energy harvesting technology

In this manuscript, the structural, optoelectronic, elastic, vibrational, and thermodynamic properties of RbKM (M = S, Se, Te) chalcogenides are explored via first principles approach. The estimated equilibrium lattice parameters a(c) through the TB-mBJ functional are 5.3876 Å (8.2810 Å), 5.2700 Å (8.6550 Å) and 5.2656 Å (8.7707 Å) for RbKS, RbKSe and RbKTe, respectively. The large value of the cohesive (Ecoh) and formation energy (Eform) reveals that all these compounds are stable at 0 K that may be difficult to decompose at ambient conditions. The direct band gap for RbKS, RbKSe and RbKTe is noted as 4.05 eV, 3.71 eV and 3.63 eV, respectively that is sufficient to declare them as semiconducting materials. So far as, the projected density of states (PDOS), pseudo electrons residing in d orbitals of the rubidium atoms contribute in the conduction region and p orbitals of chalcogen elements partake in the valence band. The optical parameters are determined by Kramers-Kronig relations. The elastic constants unveil that all compounds are mechanically stable and hold anisotropic nature. Here the vibrational properties of RbKM (M = S, Se, Te) are examined through Density functional perturbation theory (DFPT) technique. The Harmonic Approximation Method (HAM) is utilized to seek thermodynamic stability that is ensured due to the observance of negative free energy for all cases. Our theoretical outcomes for RbKM (M = S, Se, Te) can contribute significantly to amelioration for future research in devising optoelectronic and energy harvesting like appliances.

Proposed experiment to measure nonlinear optical susceptibilities in the saturated regime.

When an optical beam passes through a thin slice of a homogeneous material, the change of its phase and amplitude is characterized by the material's linear and nonlinear susceptibility, the latter also known as the hyperpolarizability. The standard method for measuring the nonlinear susceptibility is the scan. This widely used method is sometimes applied outside of its range of validity, leading to systematic errors. These errors are illustrated for a two-level system with parameters taken from atomic rubidium. The present paper proposes a method called the phase retrieval of modes to determine the nonlinear susceptibility without an assumption about its functional form, in contrast to both the -scan method and variants intended to apply in cases of saturation. In brief, a Gaussian beam passes through a thin sample and is detected on three planes in a focal scan. Phase retrieval methods are used to find coefficients of the modes which in turn determine the optical nonlinear susceptibility. Nearly exact recovery of the nonlinear susceptibility is shown numerically in the no-noise case. Additionally, two types of noise are considered: shot noise on the detector and intensity fluctuations of the input.

High-performance silicon photonic single-sideband modulators for cold-atom interferometry.

The laser system is the most complex component of a light-pulse atom interferometer (LPAI), controlling frequencies and intensities of multiple laser beams to configure quantum gravity and inertial sensors. Its main functions include cold-atom generation, state preparation, state-selective detection, and generating a coherent two-photon process for the light-pulse sequence. To achieve substantial miniaturization and ruggedization, we integrate key laser system functions onto a photonic integrated circuit. Our study focuses on a high-performance silicon photonic suppressed-carrier single-sideband (SC-SSB) modulator at 1560 nanometers, capable of dynamic frequency shifting within the LPAI. By independently controlling radio frequency (RF) channels, we achieve 30-decibel carrier suppression and unprecedented 47.8-decibel sideband suppression at peak conversion efficiency of -6.846 decibels (20.7%). We investigate imbalances in both amplitudes and phases between the RF signals. Using this modulator, we demonstrate cold-atom generation, state-selective detection, and atom interferometer fringes to estimate gravitational acceleration, g ≈ 9.77 ± 0.01 meters per second squared, in a rubidium (87Rb) atom system.

Development of a novel four-channel atomic gradiometric magnetometer for magnetocardiography: Advancing non-invasive cardiac research with enhanced sensitivity and spatial resolution

The field of magnetocardiography (MCG) has witnessed significant advancements with the use of atomic magnetometers (AMs) and gradiometers, offering numerous advantages over traditional superconducting quantum interference devices (SQUIDs). This study focuses on the development of a highly sensitive four-channel atomic gradiometer specifically designed for measuring the biomagnetic fields of a rat’s heart. By utilizing gradiometric detection and monitoring deviations in the Larmor frequency of rubidium (Rb) atoms, this gradiometer captures cardiac signals with exceptional sensitivity and spatial resolution. One of the key challenges in utilizing AMs as gradiometers lies in minimizing cross-talk effects among the sensors to ensure accurate measurements. In this study, we successfully address this challenge, leading to precise and reliable data acquisition. Furthermore, our gradiometer demonstrates a linear response across a wide range of frequencies, enhancing its versatility and applicability in various experimental setups. The achieved sensitivity of 350 fT/√Hz by our atomic gradiometer showcases its potential in assessing MCG measurements for studying cardiac electrical activities. The non-invasive nature of the technique, combined with the elimination of cryogenic cooling requirements, opens up new avenues for cardiac research and diagnostics. The enhanced spatial and spatiotemporal resolution offered by optically pumped magnetometers (OPMs) further enhances our ability to understand and analyze complex cardiac phenomena.

Modeling interactions between rubidium atom and magnetometer cell wall molecules

Magnetometer cell wall coat molecules play an important role in preserving the lifetime of pumped alkali metal atoms for use in magnetometers that are capable of measuring very small magnetic fields. The goal of this study is to help rationalize the design of the cell coat molecules. Rubidium-87 is studied in terms of its interaction with three template cell coat molecules: ethane, ethene, and methyltrichlorosilane (MeTS). Ab initio electronic structure methods are applied to investigate the effect that the coat molecules have on the 2S ground state and 2P excited state of 87Rb. We find that, from the ab initio results, the three template molecules have differing effects, with MeTS having the largest effect on the ground state and ethane or ethene having the largest effect on the non-degenerate excited states.

Temporal coherences of atomic chaotic light sources: The Siegert relation and its generalisation to higher-order correlation functions

Light is characterized by its electric field, yet quantum optics has revealed the importance of monitoring photon-photon correlations at all orders. We here present a comparative study of two experimental setups, composed of cold and warm rubidium atoms, respectively, which allow us to probe and compare photon correlations. The former operates in the quantum regime where spontaneous emission dominates, whereas the latter exhibits a temperature-limited coherence time. We demonstrate our capability to measure photon correlations up to the fourth order which could be useful to better characterize light scattered by cold atoms beyond the chaotic statistics.

Interplay of electromagnetically induced transparency and Doppler broadening in hot atomic vapors

For multi-level systems in hot atomic vapors the interplay between the Doppler shift due to atomic motion and the wavenumber mismatch between driving laser fields strongly influences transmission and absorption properties of the atomic medium. In a three-level atomic ladder-system, Doppler broadening limits the visibility of electromagnetically-induced transparency (EIT) when the probe and control fields are co-propagating, while EIT is recovered under the opposite condition of counter-propagating geometry and kp<kc , with kp and kc being the wavenumbers of the probe and control fields, respectively. This effect has been studied and experimentally demonstrated as an efficient mechanism to realize non-reciprocal probe light transmission, which may enable applications as magnetic-field free optical isolators. Here, we describe the basics of this effect and discuss a simple picture for the underlying mechanism. We illustrate how the non-reciprocity scales with wavelength mismatch and show how to experimentally demonstrate the effect in a simple Rydberg-EIT system using thermal Rubidium atoms.

Metasurface optical trap array for single atoms

Metasurfaces made of subwavelength silicon nanopillars provide unparalleled capacity to manipulate light, and have emerged as one of the leading platforms for developing integrated photonic devices. In this study, we report on a compact, passive approach based on planar metasurface optics to generate large optical trap arrays. The unique configuration is achieved with a meta-hologram to convert a single incident laser beam into an array of individual beams, followed up with a metalens to form multiple laser foci for single rubidium atom trapping. We experimentally demonstrate two-dimensional arrays of 5 × 5 and 25 × 25 at the wavelength of 830 nm, validating the capability and scalability of our metasurface design. Beam waists ∼1.5 µm, spacings (about 15 µm), and low trap depth variations (8%) of relevance to quantum control for an atomic array are achieved in a robust and efficient fashion. The presented work highlights a compact, stable, and scalable trap array platform well-suitable for Rydberg-state mediated quantum gate operations, which will further facilitate advances in neutral atom quantum computing.

Spontaneously Sliding Multipole Spin Density Waves in Cold Atoms.

We report on the observation of spontaneously drifting coupled spin and quadrupolar density waves in the ground state of laser driven Rubidium atoms. These laser-cooled atomic ensembles exhibit spontaneous magnetism via light mediated interactions when submitted to optical feedback by a retroreflecting mirror. Drift direction and chirality of the waves arise from spontaneous symmetry breaking. The observations demonstrate a novel transport process in out-of-equilibrium magnetic systems.

Research on the Frequency Stabilization System of an External Cavity Diode Laser Based on Rubidium Atomic Modulation Transfer Spectroscopy Technology

To achieve high-frequency stability on the external cavity diode laser (ECDL), a 780 nm ECDL serves as the seed light source, and its frequency is precisely locked to the saturated absorption peak of rubidium (Rb) atoms using modulation transfer spectroscopy (MTS) technology. For improving the performance of frequency locking, the scheme is designed to find the optimal operating conditions. Correlations between the frequency discrimination signal (FDS) and critical parameters, such as the temperature of the Rb cell, the power ratio of the probe and pump light, and the frequency and amplitude of the modulation and demodulation signals, are observed to attain the optimal conditions for frequency locking. To evaluate the performance of the frequency-stabilized 780 nm ECDL, a dual-beam heterodyne setup was constructed. Through this arrangement, the laser linewidth, approximately 65.4 kHz, is measured. Then, the frequency stability of the laser, quantified as low as 4.886 × 10−12 @32 s, is determined by measuring the beat-frequency signal with a frequency counter and calculating the Allan variance. Furthermore, using the realized frequency locking technology, the 780 nm ECDL can achieve long-term stabilization even after 25 h. The test results show the exceptional performance of the implemented frequency stabilization system for the 780 nm ECDL.

Loading atoms from a large magnetic trap to a small intra-cavity optical lattice

We show that an optimized loading of a cold ensemble of rubidium-87 atoms from a magnetic trap into an optical lattice sustained by a single, far-red-detuned mode of a high-Q optical cavity can be efficient despite the large volume mismatch of the traps. The magnetically trapped atoms are magnetically transported to the vicinity of the cavity mode and released from the magnetic trap in a controlled way meanwhile undergoing an evaporation period. Large number of atoms get trapped in the dipole potential of the cavity mode for several hundreds of milliseconds. We monitor the number of atoms in the mode volume by a second tone of the cavity close to the atomic resonance. While this probe tone can pump atoms to another ground state uncoupled to the probe, we demonstrate state-independent trapping by applying a repumper laser.

Tailoring Sub‐Doppler Spectra of Thermal Atoms with a Dielectric Optical Metasurface Chip

AbstractCompact and robust structures to precisely control and acquire atomic spectra are increasingly important for the pursuit of widespread applications. Sub‐Doppler responses of thermal atoms are critical in constructing high‐precision devices and systems. In this study, a nanograting metasurface specifically is designed for atomic rubidium vapor and integrated it into a miniature vapor cell. Using the metasurface with built‐in multifunctional controls for light, pump‐probe atomic spectroscopy is established and sub‐Doppler responses are experimentally observed at low incident power. Moreover, the sub‐Doppler lineshape can be tailored by varying the incident polarization state. The spectrum transformation from absorption to transparency is observed. Using one of the sharp responses, laser stabilization with a stability of at 2 s can be achieved. This work reveals the effective control of atomic spectra with optical metasurface chips, which may have great potential for future developments in fundamental optics and novel optical applications.

Extracting double-quantum coherence in two-dimensional electronic spectroscopy under pump-probe geometry.

Two-dimensional electronic spectroscopy (2DES) can be implemented with different geometries, e.g., BOXCARS, collinear, and pump-probe geometries. The pump-probe geometry has the advantage of overlapping only two beams and reducing phase cycling steps. However, its applications are typically limited to observing the dynamics with single-quantum coherence and population, leaving the challenge to measure the dynamics of the double-quantum (2Q) coherence, which reflects the many-body interactions. We demonstrate an experimental technique in 2DES under pump-probe geometry with a designed pulse sequence and the signal processing method to extract 2Q coherence. In the designed pulse sequence, with the probe pulse arriving earlier than the pump pulses, our measured signal includes the 2Q signal as well as the zero-quantum signal. With phase cycling and data processing using causality enforcement, we extract the 2Q signal. The proposal is demonstrated with rubidium atoms. We observe the collective resonances of two-body dipole-dipole interactions in both the D1 and D2 lines.

Indication of critical scaling in time during the relaxation of an open quantum system

Near continuous phase transitions, universal power-law scaling, characterized by critical exponents, emerges. This behavior reflects the singular responses of physical systems to continuous control parameters like temperature or external fields. Universal scaling extends to non-equilibrium dynamics in isolated quantum systems after a quench, where time takes the role of the control parameter. Our research unveils critical scaling in time also during the relaxation dynamics of an open quantum system. Here we experimentally realize such a system by the spin of individual Cesium atoms dissipatively coupled through spin-exchange processes to a bath of ultracold Rubidium atoms. Through a finite-size scaling analysis of the entropy dynamics via numerical simulations, we identify a critical point in time in the thermodynamic limit. This critical point is accompanied by the divergence of a characteristic length, which is described by critical exponents that turn out to be unaffected by system specifics.

Coherent control of photonic band gaps through the relative phase using modified superradiance lattice.

We report photonic band gaps based on a modified superradiance lattice having reflectivity close to 100% for both the low and high-frequency ranges. We observe that tuning the relative phase between the coupling fields provides additional control over photonic band gaps. We notice that the relative phase can control three input channels of the probe field simultaneously and efficiently. This feature of relative phase over photonic band gaps provides potential in the field of quantum optics. Further, this scheme is experimentally more viable. Rubidium atoms 87Rb can obtain low-frequency (infrared) photonic band gaps. On the other hand, rubidium atoms 85Rb and beryllium ions Be2+ can form high-frequency ultraviolet and soft X-ray photonic band gaps, achieving reflectivities of 80% and 96%, respectively. This scheme holds promise for constructing highly efficient optical switches and beam splitters.

Numerical analysis of on-chip acousto-optic modulators for visible wavelengths.

On-chip acousto-optic modulators that operate at an optical wavelength of 780nm and a microwave frequency of 6.835GHz are proposed. The modulators are based on a lithium-niobate-on-sapphire platform and efficiently excite surface acoustic waves and exhibit strong interactions with tightly confined optical modes in waveguides. In particular, a high-efficiency phase modulator and single-sideband mode converter are designed. We found that for both microwave and optical wavelengths below 1µm, the interactions at the cross-sections of photonic waveguides are sensitive to the waveguide width and are significantly different from those in previous studies. Our designed devices have small footprints and high efficiencies, making them suitable for controlling rubidium atoms and realizing hybrid photonic-atomic chips. Furthermore, our devices have the potential to extend the acousto-optic modulators to other visible wavelengths for other atom transitions and for visible light applications, including imaging and sensing.