Atomic Vapor Research Articles

Switching, amplifying, and chirping diode lasers with current pulses for high bandwidth quantum technologies.

A series of simple and low-cost devices for switching, amplifying, and chirping diode lasers based on current modulation are presented. Direct modulation of diode laser currents is rarely sufficient to establish precise amplitude and phase control over light, as its effects on these parameters are not independent. These devices overcome this limitation by exploiting amplifier saturation and dramatically outperform commonly used external modulators in key figures of merit for quantum technological applications. Semiconductor optical amplifiers operated on either rubidium D line are recast as intensity switches and shown to achieve ON:OFF ratios >106 in as little as 50ns. Current is switched to a 795nm wavelength (Rb D1) tapered amplifier to produce optical pulses of few nanosecond duration and peak powers of 3 W at a similar extinction ratio. Fast rf pulses are applied directly to a laser diode to shift its emission frequency by up to 300MHz in either direction and at a maximum chirp rate of 150MHzns-1. Finally, the latter components are combined, yielding a system that produces watt-level optical pulses with arbitrary frequency chirps in the given range and <2% residual intensity variation, all within 65ns upon asynchronous demand. Such systems have broad application in atomic, molecular, and optical physics and are of particular interest to fast experiments simultaneously requiring high power and low noise, for example, quantum memory experiments with atomic vapors.

Numerical simulation of CuCr alloys vacuum arc under conditions of arc contraction, deflection, and anode vapor

In practical arc ignition processes of high-current vacuum arcs, despite the calibration effect of the axial magnetic field, the strong magnetic constriction force still causes the arc to contract. Additionally, during the actual electrode opening process, due to the random nature of the arcing position, the center of the arc column is often not located at the center of the electrode. At this point, the behavior of the vacuum arc can be understood as an asymmetric three-dimensional (3D) process under the influence of the spatial magnetic field, affecting the generation of anode vapor and the characteristics of arc species. Therefore, it is useful to conduct simulation studies on multi-species vacuum arc behavior considering arc contraction and arc deflection. In this paper, the spatial magnetic field distribution under different electrode effective areas and different arc center deflection distances have been simulated, and the influence of actual magnetic field-induced by arc contraction and deflection on 3D spatial distribution characteristics of arc plasma has been studied based on a 3D multi-species (CuCr alloys) vacuum arc model with anode vapor. The simulation results show that with the contraction of the arc column, the area occupied by neutral atomic vapor decreases correspondingly, but the ionization and recombination process between the arc column regions becomes more intense. The axial current density and electron temperature distribution around the neutral atomic vapor area become more non-uniform. When the arc column deviates from electrode center, the neutral atomic vapor area shows an asymmetrical distribution on both sides of the arc column center axis, and the axial current density and electron temperature gather and enhance in the opposite direction of the arc deflection, thereby significantly affecting the distribution of arc species.

Study on the influence of shielding effect for plasma cloud on multi-field coupling mechanism during laser cladding

Laser is a kind of electromagnetic wave. During laser cladding, metal vapor will be produced when the temperature reaches the material sublimation point, and plasma clouds will be produced after vapor atoms are ionized by laser. When the laser beam passes through the plasma cloud, it will be absorbed or refracted, resulting in the decrease of laser energy reaching the substrate surface. Plasma cloud shielding effect will directly affect the multi-field coupling behavior during laser cladding. It is significant to quantitatively reveal the influence mechanism of plasma cloud on multi-field coupling during laser cladding for improving the cladding layer quality. In the paper, a multi-field coupled numerical model for laser cladding of Fe60 with ASTM 1045 disk laser was established. The interaction between the waist beam of cladding powder jet, plasma cloud and laser beam was considered in the modeling. The influence of plasma cloud shielding effect on transient evolution for the temperature field, flow field, and stress field during laser cladding was compared and analyzed. The results show that the maximum temperature of molten pool is less than 2700 K, no plasma cloud will be produced during cladding. When the temperature is higher than 2700 K, the plasma cloud initiates. Under the same conditions, the molten pool temperature slightly decreases, the velocity decreases, and the stress increases slightly due to the shielding effect of the plasma cloud. And with the increase of laser power, the shielding effect of plasma cloud is more and more significant.

Review of the Latest Achievements on Atomic Vapor Laser Isotope Separation

Review of the Latest Achievements on Atomic Vapor Laser Isotope Separation

Impact of longitudinal magnetic fields on EIT linewidth and dispersive properties in 87Rb vapor

By employing the density matrix approach, this study systematically examines the impact of a longitudinal magnetic field on electromagnetically induced transparency (EIT) within the context of the effective three-level Zeeman sublevels associated with the D 2 -line of 87Rb atomic vapor. Our investigation reveals that a sufficient enhancement in the longitudinal magnetic field induces a discernible narrowing of the EIT linewidth, accompanied by an enhancement in the peak transmission through a Rubidium (Rb) vapor cell. Related to these, we analyse the effect of magnetic field on the dispersive properties of the system, including group delay and group velocity and observed a slight decrement in the group delay and increment in the group velocity, which specifies the transition from slow to fast light under the application of the magnetic field.

Influence of the size of the cubic atomic vapor cell on a Rydberg atomic microwave sensor.

This study investigates the enhancement of the microwave (MW) electric (E) field due to the Fabry-Perot (FP) effect in cubic cells of varying sizes, and it is confirmed that the lower limit of MW power can be measured. Theoretical simulations and empirical validations are conducted for three vapor cells of different sizes. At a MW frequency of 23.904GHz, the FP effect in the 10mm cell is found to significantly enhance the MW E-field relative to larger cells (20 and 25mm). The results show that, due to the existence of the FP effect, the lower limit of MW power can be measured in the cubic atomic vapor cells with different sizes. These findings contribute to the advancement of the vapor cell design for quantum accuracy measurements and the development of future atomic MW communication technologies.

Broad Instantaneous Bandwidth Microwave Spectrum Analyzer with a Microfabricated Atomic Vapor Cell

We report on broad instantaneous bandwidth microwave spectrum analysis with hot Rb87 atoms in a microfabricated vapor cell in a large magnetic field gradient. The sensor is a MEMS atomic vapor cell filled with isotopically pure Rb87 and N2 buffer gas to localize the motion of the atoms. The microwave signals of interest are coupled through a coplanar waveguide to the cell, inducing spin-flip transitions between optically pumped ground states of the atoms. A static magnetic field with large gradient maps the frequency spectrum of the input microwave signals to a position-dependent spin-flip pattern on absorption images of the cell recorded with a laser beam onto a camera. In our proof-of-principle experiment, we demonstrate a microwave spectrum analyzer that has ≈1 GHz instantaneous bandwidth centered around 13 GHz, 3 MHz frequency resolution, 2 kHz refresh rate, and a −23 dBm single-tone microwave power detection limit in 1 s measurement time. A theoretical model is constructed to simulate the image signals by considering the processes of optical pumping, microwave interaction, diffusion of Rb87 atoms, and laser absorption. We expect to reach more than 25 GHz instantaneous bandwidth in an optimized setup, limited by the applied magnetic field gradient. Our demonstration offers a practical alternative to conventional microwave spectrum analyzers based on electronic heterodyne detection. Published by the American Physical Society 2024

Room temperature single-photon terahertz detection with thermal Rydberg atoms

Single-photon terahertz (THz) detection is one of the most demanding technologies for a variety of fields and could lead to many breakthroughs. Although significant progress has been made in the past two decades, operating it at room temperature still remains a great challenge. Here, we demonstrate, for the first time, a room temperature THz detector at single-photon levels based on nonlinear wave mixing in thermal Rydberg atomic vapor. The low-energy THz photons are coherently upconverted to high-energy optical photons via a nondegenerate Rydberg state involved in a six-wave mixing process, and therefore, single-photon THz detection is achieved by a conventional optical single-photon counting module. The noise equivalent power of such a detector reaches 9.5 × 10−19 W/Hz1/2, which is more than four orders of magnitude lower than the state-of-the-art room temperature THz detectors. The optimum quantum efficiency of the whole-wave mixing process is about 4.3%, with 40.6 dB dynamic range, and the maximum conversion bandwidth is 172 MHz, which is all-optically controllable. The developed fast and continuous-wave single-photon THz detector at room temperature operation has a great potential for portability and chip-scale integration, and could be revolutionary for a wide range of applications in remote sensing, wireless communication, biomedical diagnostics, and quantum optics.

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 S1/2 and 78 P1/2 is tuned based on AC Stark effect of 70 MHz radio frequency (RF) field that is applied outside the vapor cell. The use of the j=1/2 Rydberg states ensures that only a single mj sublevel is involved. The generated Rydberg Floquet states act to enhance the sensitivity of the AC-Stark-tuned states when the frequency is matched and further extend the bandwidths. We achieve microwave field measurements with over 1.172 GHz continuous frequency tuning and a sensitivity ranging from 280.2 nVcm−1Hz−1/2 to 14.6 μ Vcm−1Hz−1/2. The achieving of continuous frequency and high sensitivity microwave detection will promote the application of Rydberg receivers in the radar technique and wireless communication.

Rydberg electromagnetically induced transparency based laser lock to Zeeman sublevels with 0.6GHz scanning range.

We propose a technique for frequency locking a laser to the Zeeman sublevel transitions between the 5P3/2 intermediate and 32D5/2 Rydberg states in 87Rb. This method allows for continuous frequency tuning over 0.6GHz by varying an applied external magnetic field. In the presence of the applied field, the electromagnetically induced transparency (EIT) spectrum of an atomic vapor splits via the Zeeman effect according to the strength of the magnetic field and the polarization of the pump and probe lasers. We show that the 480nm pump laser, responsible for transitions between the Zeeman sublevels of the intermediate state and the Rydberg state, can be locked to the Zeeman-split EIT peaks. The short-term frequency stability of the laser lock is 0.15MHz, and the long-term stability is within 0.5MHz. The linewidth of the laser lock is ∼0.8 and ∼1.8MHz in the presence and absence of the external magnetic field, respectively. In addition, we show that in the absence of an applied magnetic field and adequate shielding, the frequency shift of the lock point has a peak-to-peak variation of 1.6MHz depending on the polarization of the pump field, while when locked to Zeeman sublevels, this variation is reduced to 0.6MHz. The proposed technique is useful for research involving Rydberg atoms, where large continuous tuning of the laser frequency with stable locking is required.

Additive manufacturing of functionalised atomic vapour cells for next-generation quantum technologies

Abstract Atomic vapour cells are an indispensable tool for quantum technologies (QT), but potential improvements are limited by the capacities of conventional manufacturing techniques. Using an additive manufacturing (AM) technique – vat polymerisation by digital light processing - we demonstrate, for the first time, a 3D-printed glass vapour cell. The exploitation of AM capacities allows intricate internal architectures, overprinting of 2D optoelectronical materials to create integrated sensors and surface functionalisation, while also showing the ability to tailor the optical properties of the AM glass by in-situ growth of gold nanoparticles. The produced cells achieve ultra-high vacuum of 2 x 10-9 mbar and enable Doppler-free spectroscopy; we demonstrate laser frequency stabilisation as a QT application. These results highlight the transformative role that AM can play for QT in enabling compact, optimised and integrated multi-material components and devices.

Graphene reinforced magnesium metal matrix composites by infiltrating coated-graphene preform with melt

Graphene’s exceptional mechanical, electrical, and thermal conductivity capabilities make it an ideal reinforcement for metal matrix composites. However, graphene is hard to be dispersed in the melt metal due to its high surface energy, non-wetting nature, and strong van der Waals interactions between graphene sheets, which weaken the reinforcing efficiency of composites. A novel process by infiltrating the coated-graphene preform with melt magnesium was proposed to improve the dispersion of graphene in the magnesium matrix. Graphene preforms with oriented pores were prepared by a directional freeze-drying method. Magnesium oxide coatings were deposited on the surface of graphene inside the graphene preform using the evaporation of magnesium atoms to enhance the strength as well as the wettability between the preform and magnesium matrix. Magnesium matrix composites were fabricated by liquid-solid pressure infiltrating coated-graphene preform with molten magnesium. The microstructure of graphene preforms and composites and mechanical properties of the composites were characterized. The results show that graphene is uniformly dispersed in the matrix and presents a reticular structure, and the hardness, elastic modulus, and compressive strength of the composite were improved apparently compared to the matrix. This study suggests that the method of preparing composites by infiltration provides a novel strategy for fabricating nano-material reinforced magnesium matrix composites.

Publisher Correction: Rydberg states of alkali atoms in atomic vapour as SI-traceable field probes and communications receivers

Publisher Correction: Rydberg states of alkali atoms in atomic vapour as SI-traceable field probes and communications receivers

Phase-modulation-induced reconfigurable rotating photonic lattices in atomic vapors.

We propose a method to prepare optically induced rotating hexagonal and honey-comb photonic lattices by employing the phase modulated three-beam interference in atomic vapors with electromagnetically induced transparency. The phase differences among the three beams are dynamically elaborated to synthesize the circular motion (in transverse dimensions) of waveguides in the photonic lattices. Further, we verify this model experimentally in the case of low-speed modulation. A weak Gaussian probe field is sent into the constructed helical photonic lattices to image their structures under electromagnetically induced transparency (EIT). The motion trajectories of the sites on the discretized output patterns exhibit repeated circles, advocating the formation of rotating lattices. By introducing phase modulations to involved beams, we provide a continent way for producing transverse motions in waveguide arrays with reconfigurability in rotational direction, radius, and speed. This work looks forward to promising applications in topological photonics with great popularity.

Tutorial on laser locking techniques and the manufacturing of vapor cells for spectroscopy

Abstract This tutorial provides a hands-on entry point about laser locking for atomic vapor research and related research such as laser cooling. We furthermore introduce common materials and methods for the fabrication of vapor cells as a tool for this research. Its aim is not to be exhaustive, but rather to provide an overview about the possible techniques that are actively employed in labs today. Some critical parameters of locked laser system for use with thermal atomic vapors are introduced and discussed. To exemplify this, we describe a versatile locking system that caters for many of the needs we found during our research with thermal atomic vapors. We also emphasize the compromises we took during our decision-making process.

Simultaneously measuring microwave electric fields at different frequencies by Rydberg-atom-based electrometry with Zeeman-resolved Autler–Townes splitting

We provide the simultaneous traceable measurements of microwave electric fields at two different frequencies by the electromagnetically induced transparency (EIT) and Autler–Townes (AT) splitting. A static magnetic field working together with a linearly polarized probe and coupling light prepares Rydberg atoms in Zeeman sublevels with maximal |mJ| in an atomic vapor cell. Using the EIT-AT splitting of these two maximal |mJ| states, the microwave electric fields at two different frequencies are simultaneously measured, in which their frequency difference can be adjustable within the linear range of magnetic field-induced level shifts. The proposed method provides a promising prospect for calibrating multiple microwave frequencies simultaneously in the future.

A Method of Laser Frequency Stabilization Based on the Effect of Linear Dichroism in Alkali Metal Vapors in a Modulated Transverse Magnetic Field

We present a method of laser frequency stabilization based on the linear dichroism signal in a transverse magnetic field. This method is similar to the DAVLL (Dichroic Atomic Vapor Laser Lock) method. It differs from DAVLL and from its existing modifications primarily by the fact that it uses signals of linearly polarized light caused by alignment, rather than circular refraction caused by orientation, and therefore allows us to obtain error signals at the magnetic field modulation frequency (or its second harmonic) by extremely simple means. The method allows the laser frequency to be stabilized in the vicinity of the low-frequency transition in the D1 line of Cs; it does not require strong magnetic fields or careful shielding of cells containing cesium atoms. Although the absorption line in a gas-filled cell is typically gigahertz wide, the achievable resolution, limited by the signal-to-noise ratio of photon shot noise, can reach units or tens of kilohertz in a one hertz bandwidth.

Strong interactions between integrated microresonators and alkali atomic vapors: towards single-atom, single-photon operation

Cavity quantum electrodynamics (cQED), the interaction of a two-level system with a high quality factor (Q) cavity, is a foundational building block in different architectures for quantum computation, communication, and metrology. The strong interaction between the atom and the cavity enables single-photon operation, which is required for quantum gates and sources. Cold atoms, quantum dots, and color centers in crystals are among the systems that have shown single-photon operations, but they require significant physical infrastructure. Atomic vapors, on the other hand, require limited experimental infrastructure and are hence much easier to deploy outside a laboratory, but they consist of an ensemble of moving atoms that results in short interaction times involving multiple atoms, which can hamper quantum operations. A solution to this issue can be found in nanophotonic cavities, where the optical mode is confined to a small volume and light-matter interaction is enhanced, so that fast single-atom, single-photon operations are enabled. In this work, we study the interaction of an atomically clad microring resonator (ACMRR) with different-sized ensembles of Rb atoms. We demonstrate strong coupling between an ensemble of ≈50 atoms interacting with a high quality factor (Q=4.3×105) ACMRR, yielding a many-atom cooperativity C=(5.5±0.3). We continue to observe signatures of atom-photon interaction for a few (&lt;3) atoms, for which we observe saturation at the level of a few intracavity photons. Further development of our platform, which includes integrated thermo-optic heaters to enable cavity tuning and stabilization, should enable the observation of interactions between single photons and single atoms.

Electromagnetically induced transparency using selective reflection radiation from a thin Rb vapor cell

We have investigated electromagnetically induced transparency (EIT) in the spectrum of selective reflection at the interface between Rb atomic vapor and a dielectric nanocell window made of technical sapphire. Two types of spectroscopic cells were used: a nanocell with atomic vapor column thicknesses ranging from 150 to 1200 nm, and a 50μm-thick microcell. We have compared electromagnetically induced transparency resonances in a Λ-type atomic system observed using selective reflection as the probe radiation and/or transmission radiation. It was demonstrated that for thicknesses below 1000 nm, the selective reflection technique is more advantageous. Notably, at a thickness of ∼150nm, electromagnetically induced transparency resonance is clearly observed using selective reflection, while it is nearly absent when using transmission radiation. This enables the realization of ∼150nm spatial resolution in mapping a strongly inhomogeneous magnetic field of 3.3 G/μm.

Rydberg states of alkali atoms in atomic vapour as SI-traceable field probes and communications receivers

Rydberg states of alkali atoms in atomic vapour as SI-traceable field probes and communications receivers