Atomic Vapor Research Articles

Key Technologies in Developing Chip-Scale Hot Atomic Devices for Precision Quantum Metrology.

Chip-scale devices harnessing the interaction between hot atomic ensembles and light are pushing the boundaries of precision measurement techniques into unprecedented territory. These advancements enable the realization of super-sensitive, miniaturized sensing instruments for measuring various physical parameters. The evolution of this field is propelled by a suite of sophisticated components, including miniaturized single-mode lasers, microfabricated alkali atom vapor cells, compact coil systems, scaled-down heating systems, and the application of cutting-edge micro-electro-mechanical system (MEMS) technologies. This review delves into the essential technologies needed to develop chip-scale hot atomic devices for quantum metrology, providing a comparative analysis of each technology's features. Concluding with a forward-looking perspective, this review discusses the future potential of chip-scale hot atomic devices and the critical technologies that will drive their advancement.

Radio-Frequency Magnetometry Based on Parametric Resonances.

We propose and demonstrate a radio-frequency (rf) atomic magnetometer based on parametric resonances. Previously, most rf atomic magnetometers are based on magnetic resonances and their sensitivities are often limited by spin-exchange relaxation. Here, we introduce a novel scheme for an rf magnetometer where the rf magnetic field is measured by exciting the parametric resonances instead of magnetic resonances using parametric modulation fields. In this way, the spin-exchange relaxation is almost eliminated. Benefiting from the low spin relaxation rate, the parametric resonance scheme exhibits a narrower linewidth and stronger signal, which results in a higher sensitivity. With a 6×6×3 mm^{3} Rb atomic vapor cell, we developed an rf atomic magnetometer with a noise floor of 2 fT/Hz^{1/2}, which is about one order of magnitude higher than the sensitivity achieved in the magnetic-resonance-based scheme. The presented rf detection scheme holds promise in advancing rf atomic magnetometers and brings new insight into their various applications.

On the reduction of gas permeation through the glass windows of micromachined vapor cells using Al2O3 coatings

Stability and precision of atomic devices are closely tied to the quality and stability of the internal atmosphere of the atomic vapor cells on which they rely. Such an atmosphere can be stabilized by building the cell with low permeation materials such as sapphire or aluminosilicate glass in microfabricated devices. Recently, we have shown that permeation barriers made of Al2O3 thin-film coatings deposited on standard borosilicate glass could be an alternative for buffer gas pressure stabilization. In this study, we, hence, investigate how helium permeation is influenced by the thickness, ranging from 5 to 40 nm, of such Al2O3 thin films coated by atomic layer deposition. Permeation rates are derived from long-term measurements of the pressure-shifted transition frequency of a coherent population trapping (CPT) atomic clock. From thicknesses of 20 nm onward, a significant enhancement of the cell hermeticity is experienced, corresponding to two orders of magnitude lower helium permeation rate. In addition, we test cesium vapor cells filled with neon as a buffer gas and whose windows are coated with 20 nm of Al2O3. As for helium, the permeation rate of neon is significantly reduced, thanks to alumina coatings, leading to a fractional frequency stability of 4×10−12 at 1 day when the cell is used in a CPT clock. These features outperform the typical performances of uncoated Cs–Ne borosilicate cells and highlight the significance of Al2O3 coatings for buffer gas pressure stabilization.

Transformation of optical speckles by atomic vapors: From Rayleigh to Weibull intensity statistics

Transformation of optical speckles by atomic vapors: From Rayleigh to Weibull intensity statistics

Asymmetric diffraction in anti-parity-time symmetry of non-Hermitian photonic lattice

Non-Hermitian systems based on anti-parity-time (PT) symmetry reveal rich physics beyond the Hermitian regime. Here, the anti-PT-symmetric photonic lattice is effectively achieved in a four-level inverted Y-type 85Rb atomic vapor. Such instantaneously reconfigurable anti-PT-symmetric photonic lattice possessing susceptibility of χ(x)=−χ∗(−x), is established by a one-dimensional standing-wave coupling field under the assist of a standing-wave driving field. The input probe beam experiences a periodic refractive index modulation when traveling through the photonic lattice, the evolution of output diffraction patterns with symmetric, asymmetric, and lopsided intensity distribution is obtained by adjusting the relevant parameters of constructed non-Hermitian system. Moreover, the anti-PT symmetry in two-dimensional case of both square and hexagonal lattices are correspondingly realized. Our work promotes the development of non-Hermitian devices, and also has some important applications in quantum simulation.

Numerical investigation on direct water injection characteristics under different injection and ambient conditions within oxygen/argon atmosphere

Improving efficiency and reducing emissions are essential to achieve carbon neutrality in transportation sector. The hydrogen-fueled argon power cycle (H2-APC) is a novel power system with high efficiency and zero emission by utilizing argon-oxygen mixture as working fluids. However, knock suppression is a problem within H2-APC engines. Direct water injection (DWI) is an effective method to inhibit detonation. Spray morphology greatly influences the effectiveness of DWI, the investigation of spray characteristics in oxygen/argon atmosphere is critical. This paper established a computational model based on experimental data to investigate DWI characteristics under different injection and ambient conditions within oxygen/argon atmosphere. The results reveal increased jet temperature leads to stronger superheated jet spray collapse, while Sauter mean diameter (SMD) decreases and atomization improves. Increasing jet pressure effectively reduces spray SMD and improves atomization effect and evaporation rate. Higher ambient temperature reduces ambient gas density, spray SMD and penetration are decreased and increased, respectively. Moreover, spray evaporation rate and evaporated mass are dropped with higher ambient pressure for both superheated and subcooled sprays. As ambient density rises, the capacity for jet perturbation and fragmentation is enhanced, and spray SMD decreases. The research results can provide an effective guide for the DWI strategy of H2-APC engines.

Impact of higher-order laguerre-gaussian modes on electromagnetically induced transparency resonances in $$^{87}$$Rb atomic vapor medium

Impact of higher-order laguerre-gaussian modes on electromagnetically induced transparency resonances in $$^{87}$$Rb atomic vapor medium

Precise synthesis of In–Bi alloy nanodroplets through controlled surface reactions on a Si(111) surface at ambient temperature

The synthesis of alloy nanocatalysts with controllable sizes and shapes is a critical prerequisite for vapor–liquid–solid (VLS) growth of one-dimensional nanostructures. In this work, we comprehensively examined surface reactions between evaporated In atoms and a Bi thin film on a Si(111) surface at ambient temperature. InBi2 liquid nanodroplets nucleate and grow during initial vapor–solid (VS) reaction between the In vapor and surface Bi atoms, and the reaction proceeds until a saturation point is reached, following which InBi2 begins to catalyze subsequent VLS growth of various nanocrystals under persistent In-beam flux. The scaled size distribution of individual InBi2 nanodroplets could be explained adequately using the classical capillary nucleation theory, which suggests that the simultaneous homogeneous nucleation of InBi2 nanodroplets occurs during the vapor–solid (VS) reaction of In and Bi.

Polycyclic aromatic hydrocarbons and trace metals contents of Pterocarpus Mildbraedii and Ocimum gratissimum grown near markets within Aba Metropolis, Nigeria: An evaluation of dietary intake risks

Consuming contaminated vegetables is one recognised method that people are exposed to polycyclic aromatic hydrocarbons (PAHs) and trace metals (TMs). For this reason, it is important to constantly keep an eye out for these potentially fatal toxins in vegetables. Eighteen PAHs and TMs were investigated in the leaves of Pterocarpus mildbraedii and Ocimum gratissimum grown near Afule, Ahiaohuru, and Umuocham market locations within Aba metropolis using high-performance liquid chromatography (HPLC) for PAHs while an Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) for trace metals and Hg was analysed using a Cold Vapour Atomic Fluorescence Spectrophotometer (CV-AFS). The results from the study showed that Afule samples gave (mg kg-1 PAHs) 6.84, 8.12; Ahiaohuru samples gave (mg kg-1 PAHs) 11.34, 17.68; and Umuocham samples gave (mg kg-1 PAHs) 0.17, 0.16 for P. mildbraedii and O. gratissimum leaf samples, respectively. As per the estimated data, the concentrations of trace metals in vegetables and soil are found in the range of 0.432–6.03 mg/kg for Al, 0.133–0.867 mg/kg for Cd, 0.003–0.840 mg/kg for Co, 1.400–2.933 mg/kg for Cr, 0.933–4.533 mg/kg for Cu, 132.233–198.197 mg/kg for Fe, BDL–0.0002 mg/kg for Hg, 0.002–0.004 mg/kg for Li, 8.007–19.067 mg/kg for Mn, 0.533–1.633 mg/kg for Pb, 0.300–0.667 mg/kg for V, and 2.050–6.103 mg/kg for Zn. The trace metals observed are compared to the literature reported values. It was discovered that the average metal concentrations were below the FAO/WHO maximum allowable values. Every metal in the study had estimated daily intake (EDI) values that were lower than the reference oral dosage (RfD) for that metal. The health risk index (HRI), target health quotient (THQ) and hazard index (HI) values for both vegetables were much lower than 1 implying that the exposed population is safe from potential toxic metal.

Doppler sensitivity and resonant tuning of Rydberg atom-based antennas

Radio frequency antennas based on Rydberg atom vapor cells can in principle reach sensitivities beyond those of any conventional wire antenna, especially at lower frequencies where very long wires are needed to accommodate the increasing wavelength. They also have other desirable features such as consisting of nonmetallic, hence lower profile, elements. This paper presents a detailed theoretical investigation of Rydberg antenna sensitivity, elucidating parameter regimes that could cumulatively lead to a sensitivity increase 2–3 orders of magnitude beyond that of currently tested configurations. The key insight is to optimally combine the advantages of two well-studied approaches: (i) three laser ‘2D star configuration’ setups that, when enhanced with increased laser power, to some degree compensate for atom motion-induced Doppler broadening, and (ii) resonant coupling between a pair of near-degenerate Rydberg levels, tuned via a local oscillator to the incident signal of interest. The advantage of the star setup is subtle because it only restores the overall sensitivity to the expected Doppler-limited value, compensating for additional significant off-resonance reductions where differently moving atom sub-populations destructively interfere with each other in the net signal. An additional unique advantage of local oscillator tuning is that it leads to vastly narrower line widths, as low as ∼10 kHz set by the intrinsic Rydberg state lifetimes, rather than the typical ∼10 MHz scale set by the core state lifetimes. Intuitively, with this setup the two Rydberg states may be tuned to act as an independent high-q cavity, a point of view supported by a study of the frequency-dependence of the antenna resonant response. There are a number of practical experimental advances, especially larger ∼1 cm laser beam widths, required to suppress various extrinsic line broadening effects and to fully exploit this ‘Rydberg superheterodyne’ response.

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Frequency characteristics of collimated blue light generated by four-wave mixing in cesium vapor.

The frequency evaluation of collimated blue light (CBL) generated by parametric four-wave mixing (FWM) in hot atomic vapor is presented. The cesium (133Cs) atoms are excited from the 6S1/2 ground state to 8S1/2 excited state with the 852 and 795 nm pump lasers, producing an optical field at 4.2 µm through an amplified spontaneous emission via population inversion on the 8S1/2 → 7P3/2 transition and the 456 nm CBL via FWM on the 7P3/2 → 6S1/2 transition. The frequency shift of 456 nm CBL has been measured by velocity-selective optical pumping spectral technique when the frequency of any one of two pumping lasers is tuned. The ratio of the frequency shift of 456 nm CBL to the two-photon frequency detuning of two pumping lasers is 0.8912, implying that the generated 4.2 µm light frequency is also correspondingly shifted.

Utilizing quantum coherence in Cs Rydberg atoms for high-sensitivity room-temperature terahertz detection: a theoretical exploration

In recent years, terahertz (THz) technology has made significant progress in numerous applications; however, the highly sensitive, room-temperature THz detectors are still rare, which is one of the bottlenecks in THz research. In this paper, we proposed a room-temperature electrometry method for THz detection by laser spectroscopy of cesium (Cs133) Rydberg atoms, and conducted a comprehensive investigation of the five-level system involving electromagnetically induced transparency (EIT), electromagnetically induced absorption (EIA), and Autler–Townes (AT) splitting in Cs133 cascades. By solving the Lindblad master equation, we found that the influence of the THz electric field, probe laser, dressing laser, and Rydberg laser on the ground state atomic population as well as the coherence between the ground state and the Rydberg state, plays a crucial role in the transformation and amplitude of the EIT and EIA signals. Temperature and the atomic vapor cell’s dimensions affect the number of Cs133 atoms involved in the detection, and ultimately determine the sensitivity. We predicted the proposed quantum coherence THz detection method has a remarkable sensitivity of as low as 10−9 V m−1 Hz−1/2. This research offers a valuable theoretical basis for implementing and optimizing quantum coherence effects based on Rydberg atoms for THz wave detection with high sensitivity and room-temperature operation.

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.

Coherent control on the generation and annihilation of a pseudospin-induced optical vortex in a honeycomb photonic lattice.

We experimentally investigate the coherently controllable generation and annihilation of a pseudospin-induced optical vortex in an optically induced honeycomb photonic lattice in a Λ-type 85Rb atomic vapor cell. Three Gaussian coupling beams are coupled into the atomic gases to form a hexagonal interference pattern, which can induce a honeycomb photonic lattice under electromagnetically induced transparency. Then, two probe beams interfere with each other to form periodical fringes and cover one set of sublattice in the honeycomb lattice, corresponding to excite the K or K' valleys in momentum space. By properly adjusting the experimental parameters, the generation and annihilation of the induced optical vortex can be effectively controlled. The theoretical simulations based on the Dirac and Schrödinger equations are performed to explore the underlying mechanisms, which will support the observations. The demonstrated properties of such controllable optical vortex may lay the foundation for the design of vortex-based optical devices with multidimensional tunability.

Non‐Hermitian Control of Multimode Duan‐PPT Criteria and Steering in Energy‐Level Cascaded Four‐Wave Mixing Processes

AbstractThe non‐Hermitian singularity control of multimode entanglement in the energy‐level cascaded four‐wave mixing system within a single atomic vapor is of great significance and importance. In this study, a non‐Hermiticity system by means of quasi‐quantization of energy‐band based on non‐Hermiticity systems is constructed. By employing atomic coherence in the non‐Hermiticity system, high‐dimensional quantized photon correlations underdressed field‐induced parity‐time (PT) symmetry and symmetry breaking through the quantization of energy levels are studied. Such a phenomenon happens at microscopic (nanoscale) when the eigenvalues of dressed energy‐level and multimode entanglement are considered for both real and imaginary parts symmetry breaking. Double dressing effect is observed with more coherent channels and larger information capacity than single dressing in the energy‐level cascaded four‐wave mixing system. The study found that the splitting of the real part is larger than an imaginary part in a second‐order system, and the imaginary part splitting is also greater than the real part splitting in a third‐order system. The real part (in phase) is constructive dressing quantization, and the imaginary (out of phase) is destructive dressing quantization. Exceptional points (EP points) can be used to enhance sensitivity detection of entanglement quantum state.

Low-frequency weak electric field measurement based on Rydberg atoms using cavity-enhanced three photon system

Introduction: Rydberg atoms are ideal for measuring electric fields due to their unique physical properties. However, low-frequency electric fields below MHz can be challenging due to the accumulation of ionized free electrons on the atomic vapor cell’s surface, acting as a shield.Method: This paper proposes a Cavity-enhanced three-photon system (CETPS) measurement scheme, which uses a long-wavelength laser to excite the Rydberg state, reducing atomic ionization and enhancing detection spectrum resolution. A theoretical model is proposed to explain the quantum coherence effect of the light field, measured electric field, and the atomic system.Result: The results show that the proposed scheme significantly increases the electromagnetically induced transparency (EIT) spectral peak and narrows the spectral width, resulting in the maximum slope increasing by more than an order of magnitude.Discussion: The paper also discusses the impact of the Rabi frequency of the two laser fields and the coupling coefficient of the optical cavity on the transmission spectrum amplitude and linewidth, along with the optimal configuration of these parameters in the CEPTS scheme.

Mode analysis of spin field of thermal atomic ensembles

The spin dynamics in a thermal atomic vapor cell have been investigated thoroughly over the past decades and have proven to be successful in quantum metrology and memory owing to their long coherent time and manipulation convenience. The existing mean field analysis of spin dynamics among the whole cell is sometimes inaccurate due to the non-uniformity of the ensemble and spatial coupling of multi-physical fields interacting with the ensembles. Here we perform mode analysis onto the quasi-continuous spin field including atomic thermal motion to derive Bloch mode equations and obtain corresponding analytical solutions in diffusion regime. We demonstrate that the widely used mean field dynamics of thermal gas is a particular case in our solution, corresponding to the uniform spatial mode. This mode analysis approach offers a precise method for analyzing the dynamics of the spin ensemble in greater detail from a field perspective, enabling the effective determination of spatially non-uniform multi-physical fields coupling with the spin ensembles, which cannot be accurately analyzed by the mean field method. Furthermore, this work paves the way to address quantum noises and relaxation mechanisms associated with non-uniform fields and inter-atomic interactions, which limit further improvement of ultra-sensitive spin-based sensors.

Effect of Ge inclusion on surface morphologies and the growth mechanism of Cu2(Sn1-xGex)S3 films grown by the sulfurization of Ge/Cu/SnS precursors

The effects of the [Ge]/([Ge]+[Sn]): x ratio on the increase in the surface roughness and growth mechanism of Cu2Sn1-xGexS3 (CTGS) films were examined as a first step toward realizing high-efficiency CTGS solar cells. The surface roughness of the CTGS films did not change significantly up to 450 °C during the sulfurization of the Ge/Cu/SnS precursors, whereas that of the CTGS films increased beyond 500 °C. Further, Cu2GeS3 (CGS) and germanium sulfide (GeS) were observed via X-ray diffraction; these CGS and GeS compounds remained in the upper layer up to 540 °C, and CTGS was formed at 560 °C by the reaction with Cu2SnS3. The increased surface roughness in the CTGS films is attributed to the larger CTGS grain size that increases the x ratios of CTGS and the re-evaporation of vapor atoms (e.g., GeS) that generates a high vapor pressure on the surface of films by forming CGS and GeS compounds. These results confirm that the formation of CGS and GeS compounds, and the formation of dense grains in the CTGS films caused by the deposition of lower x ratios in the CTGS films are effective measures for improving the overall surface roughness.

Generation of subnatural-linewidth orbital angular momentum entangled biphotons using a single driving laser in hot atoms

Orbital angular momentum (OAM) entangled photon pairs with narrow bandwidths play a crucial role in the interaction of light and quantum states of matter. In this article, we demonstrate an approach for generating OAM entangled photon pairs with a narrow bandwidth by using a single driving beam in a 85Rb atomic vapor cell. This single driving beam is able to simultaneously couple two atomic transitions and directly generate OAM entangled biphotons by leveraging the OAM conservation law through the spontaneous four-wave mixing (SFWM) process. The photon pairs exhibit a maximum cross-correlation function value of 27.7 and a linewidth of 4 MHz. The OAM entanglement is confirmed through quantum state tomography, revealing a fidelity of 95.7% and a concurrence of 0.926 when compared to the maximally entangled state. Our scheme is notably simpler than previously proposed schemes and represents the first demonstration of generating subnatural-linewidth entangled photon pairs in hot atomic systems.