Microwave Transitions Research Articles

Dual-frequency optical-microwave atomic clocks based on cesium atoms

133Cs, the only stable cesium (Cs) isotope, is one of the most investigated elements in atomic spectroscopy and was used to realize the atomic clock in 1955. Among all atomic clocks, the cesium atomic clock has a special place, since the current unit of time is based on a microwave transition in the Cs atom. In addition, the long lifetime of the 6P3/2 state and simple preparation technique of Cs vapor cells have great relevance to quantum and atom optics experiments, which suggests the use of the 6S−6P D2 transition as an optical frequency standard. In this work, using one laser as the local oscillator and Cs atoms as the quantum reference, we realize two atomic clocks at the optical and microwave frequencies. Both clocks can be freely switched or simultaneously output. The optical clock, based on the vapor cell, continuously operated with a frequency stability of 3.9×10−13 at 1 s, decreasing to 2.2×10−13 at 32 s, which was frequency-stabilized by modulation transfer spectroscopy and estimated by an optical comb. Then, applying this stabilized laser to an optically pumped Cs beam atomic clock to reduce the laser frequency noise, we obtained a microwave clock with a frequency stability of 1.8×10−12/τ, reaching 6×10−15 at 105 s. This study demonstrates an attractive feature for the commercialization and deployment of optical and microwave clocks, and will guide the further development of integrated atomic clocks with better stability. Therefore, this study holds significant practical implications for future applications in satellite navigation, communication, and timing.

Ground-state phase diagram and parity-flipping microwave transitions in a gate-tunable Josephson junction

Ground-state phase diagram and parity-flipping microwave transitions in a gate-tunable Josephson junction

Coherent interface between optical and microwave photons on an integrated superconducting atom chip

Sub-wavelength arrays of atoms exhibit remarkable optical properties, analogous to those of phased array antennas, such as collimated directional emission or nearly perfect reflection of light near the collective resonance frequency. We propose to use a single-sheet sub-wavelength array of atoms as a switchable mirror to achieve a coherent interface between propagating optical photons and microwave photons in a superconducting coplanar waveguide resonator. In the proposed setup, the atomic array is located near the surface of the integrated superconducting chip containing the microwave cavity and optical waveguide. A driving laser couples the excited atomic state to Rydberg states with strong microwave transition. Then the presence or absence of a microwave photon in the superconducting cavity makes the atomic array transparent or reflective to the incoming optical pulses of proper frequency and finite bandwidth.

On the performance of composite schemes in determining equilibrium molecular structures.

Determination of equilibrium molecular structures is an essential ingredient in predicting spectroscopic parameters that help in identifying molecular carriers of microwave transitions. Here, the performance of two different ab initio composite approaches for obtaining equilibrium structures, "energy scheme" and "geometry scheme," is explored and compared to semi-experimental equilibrium structures. This study is performed for a set of 11 molecules which includes diatomics, linear triatomics, and a few non-linear molecules. The ab initio calculations were performed using three tiers of composite chemical recipes. The current results show that as the overall rigor of calculation is increased, the semi-experimental and the ab initio numbers agree to within 0.0003 Å for all molecules in the test set. The composite approach based on correcting the potential energy surface (energy scheme) and the one based on correcting the geometry directly (geometry scheme) show excellent agreement with each other. This work represents a step toward development of efficient and highly accurate procedures for computing ab initio equilibrium structures.

Enhanced microwave-atom coupling via quadrupole transition-dressed Rydberg atoms

The power broadening of a coupling laser can be converted into two-photon detuning by electromagnetically induced transparency (EIT), resulting in a residual Doppler effect. The residual Doppler effect in a ladder-type EIT in a room-temperature atom ensemble is further amplified through a wavelength mismatch effect between the probe and coupling laser beams, which reduces the atomic coupling of light or microwaves. We measured the Rydberg spectra of the electric dipole (E1) and electric quadrupole (E2) microwave transitions, demonstrating that the reduction in the Rydberg EIT signal can be recovered through far-off-resonance E2 microwave transition dressing and achieving an 8-dB enhancement in the Rydberg EIT signal. The frequency-dependent dressing of the E2 transition enables the shift of the dressed Rydberg states to be tuned, thereby providing a scalable approach to optimize the interaction between the Rydberg state and microwave field.

Cold Atom Gravimeter Based on an Atomic Fountain and a Microwave Transition

A method based on measuring the shift of Ramsey spectral line in an atomic fountain in the gravitational field has been proposed to develop an atomic gravimeter involving the atomic fountain on ultracold atoms. The accuracy of the measurement of the gravitational acceleration with a fountain microwave frequency standard on Cs atoms is \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta g = 2 \ imes {{10}^{{ - 6}}}g{\ ext{/}}\\sqrt {{{\ au }_{{\ ext{a}}}}} $$\\end{document}. The achievable accuracy at the integration time τa = 10 000 s is \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta g \\approx 2 \ imes {{10}^{{ - 8}}}g \\approx 20{\\kern 1pt} $$\\end{document} μGal.

Tune-out wavelengths of Rydberg atoms

The atomic polarizability represents the response characteristics of atoms to externally applied electro-magnetic fields. The wavelength (or frequency) at which the dynamic polarizability of an atom is equal to zero is referred to as the tune-out wavelength (or frequency). Spectroscopy technology based on the tune-out effect has potential applications in quantum precision measurement, quantum computation and quantum communication. Related research topics include the measurement of fundamental physical constants and strong interactions. The tune-out wavelengths of atoms in low-lying states primarily fall within the optical band, where the theoretical calculations and experimental measurements have significant progress. However, for Rydberg atoms in highly excited states, theoretical calculations are challenging due to their high density of atomic states. The difficulty of experimental measurement arises from small splitting of adjacent atomic energy levels. In this paper, we demonstrate the tune-out wavelengths measurement for Rydberg atoms in a cesium vapor cell at room temperature. We utilize a two-photon cascade excitation to prepare Rydberg states and employ amplitude-modulation electromagnetically-induced transparency (AM-EIT) spectroscopy to measure the tune-out wavelength. By continuously scanning the microwave frequencies, we obtain AM-EIT signals of Rydberg atoms. At near-resonant microwave transition wavelengths, strong AM-EIT signals are observed due to microwave-atom coupling. Conversely, at tune-out wavelengths, the dynamically polarization-induced destructive interference in neighboring energy states occurs which leads to the weak AM-EIT signals. The AM-EIT provides a spectral resolution of about 10 MHz. We have developed a simplified three-level model to calculate the tune-out wavelength. The results of our theoretical calculations are consistent with the experimental findings within a range of ±90 MHz.

Reinvestigation of the ν3-ν6 Coriolis interaction in trifluoroiodomethane.

The lowest-frequency fundamental ν6 of trifluoroiodomethane (CF3I) has never been directly observed and analyzed at high resolution in the gas phase. The ν6(e) level interacts with ν3(a1) at 286.297 cm-1via a b-axis Coriolis interaction, which perturbs the rotational structure of both levels. In this work, we report low-J microwave transitions (for J ranging from 0-2) within the ν6 vibrational level. The l-type doubling observed in our spectrum agreed poorly with the predictions of previously published models of the interacting ν3-ν6 levels, prompting us to refine the model. We performed ab initio anharmonic force-field calculations, which were used to constrain some of the parameters, and which served as a check on some of the floated parameters. We fit a dataset consisting of 3593 transitions, which combined our measurements with previous microwave, millimeter wave, and high-resolution infrared observations. A reasonable set of fit parameters is obtained with ν6 = 267.28 cm-1, but we cannot rule out a lower value of ν6 = 261.5 cm-1 consistent with analyses of the vibrational level structure.

A new six-dimensional abinitio potential energy surface and rovibrational spectra for the N2-CO2 complex.

New six-dimensional abinitio potential energy surfaces (PESs) for the N2-CO2 complex, which involve the stretching vibration of N2 and the Q3 normal mode for the ν3 asymmetric stretching vibration of CO2, were constructed using the CCSD(T)-F12/AVTZ method with midpoint bond functions. Two vibrational averaged 4D interaction potentials were obtained by integrating over the two intramolecular coordinates. It was found that both PESs possess two equivalent T-shaped global minima as well as two in-plane and one out-of-plane saddle points. Based on these PESs, rovibrational bound states and energy levels were calculated applying the radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm. The splitting of the energy levels between oN2-CO2 and pN2-CO2 for the intermolecular vibrational ground state is determined to be only 0.000 09cm-1 due to the higher barriers. The obtained band origin shift is about +0.471 74cm-1 in the N2-CO2 infrared spectra with CO2 at the ν3 zone, which coincides with the experimental data of +0.483 74cm-1. The frequencies of the in-plane geared-bending for N2-CO2 at the ν3 = 0 and 1 states of CO2 turn out to be 21.6152 and 21.4522cm-1, the latter reproduces the available experimental 21.3793cm-1 value with CO2 at the ν3 zone. The spectral parameters fitted from the rovibrational energy levels show that this dimer is a near prolate asymmetric rotor. The computed microwave transitions as well as the infrared fundamental and combination bands for the complex agree well with the observed data.

Methanol isotopologues as a probe for spatial and temporal variations of the electron-to-proton mass ratio

ABSTRACT We present results on numerical calculations of the sensitivity coefficients, Qμ, of microwave molecular transitions in 13CH3OH and ${\rm CH_3\, ^{18}OH}$ to the hypothetical variation in the fundamental physical constant μ – the electron-to-proton mass ratio. The invariability of μ in time and space is one of the basic assumptions of the Standard Model of particle physics which can be tested at cosmological scales by means of astronomical observations in the Galaxy and external galaxies. Our calculations show that these two methanol isotopologues can be utilized for such tests since their microwave transitions from the frequency interval 1–100 GHz exhibit a large spread in Qμ values which span a range of −109 ≲ Qμ ≲ 78. We show that the thermal emission lines of 13CH3OH observed in the star-forming region NGC 6334I constrain the variability of μ at a level of 3 × 10−8 (1σ), which is in line with the most stringent upper limits obtained previously from observations of methanol (CH3OH) and other molecules in the Galaxy.

Two-Photon Laser Excitation of Rb Rydberg Atoms in the Magneto-Optical Trap and Vapor Cell

We present our experimental results of two-photon laser excitation 5S1/2→5P3/2→nS1/2 of Rb atoms to Rydberg nS1/2 states with a homemade 480 nm laser in the second excitation step. In an experiment with cold Rb atoms, we excited the 42S1/2 state and detected Rydberg atoms with a selective-field-ionization (SFI) detector that provides single-atom resolution. The resonance line shapes well agreed with numerical simulations in a three-level theoretical model. We also studied the multiatom spectra of Rydberg excitation of mesoscopic atom ensembles which are of interest to quantum information processing. In the experiment with hot Rb atoms, we first excited the 30S1/2 state and observed a narrow Rydberg EIT resonance. Its line shape also agreed well with theory. Then, we performed a similar experiment with the higher 41S1/2 state and observed the Autler–Townes splitting of the EIT resonance in the presence of a microwave field, which was in resonance with the microwave transition 41S→41P3/2. This allowed us to measure the average strength of the microwave field and, thus, demonstrate the operation of a Rydberg microwave sensor. We may conclude that the developed homemade laser at 480 nm substantially extends our capabilities for further experiments on quantum information and quantum sensing with Rydberg atoms.

Rydberg excitation through detuned microwave transition in rubidium

We study the excitation of Rydberg states in warm rubidium vapor. Using an inverted wavelength excitation scheme, we observe the effect of microwave coupling between Rydberg states through electromagnetically induced transparency. We observe AC stark shifts of the Rydberg states from the microwave coupling, and demonstrate detuned excitation to a secondary Rydberg state. These results show flexibility in the excitation process and state selection necessary for a variety of wave-mixing processes using Rydberg states.

Exclusive Effect in Rydberg Atom-Based Multi-Band Microwave Communication

We have demonstrated a Rydberg atom-based two-band communication with the optically excited Rydberg state coupled to another pair of Rydberg states by two microwave fields, respectively. The initial Rydberg state is excited by a three-color electromagnetically-induced absorption in rubidium vapor cell via cascading transitions, with all of them located in infrared bands: a 780 nm laser servers as a probe to monitor the optical transmittancy via transition 5S1/2→5P3/2, 776 nm and 1260 nm lasers are used to couple the states 5P3/2 and 5D5/2 and states 5D5/2 and 44F7/2. Experimentally, we show that two channel communications carried on the two microwave transitions influence each other irreconcilably, so that they cannot work at their most sensitive microwave-optical conversion points simultaneously. For a remarkable communication quality for both channels, the two microwave fields both have to make concessions to reach a common microwave-optical gain. The optimized balance for the two microwave intensities locates at EMW1=6.5 mV/cm and EMW2=5.5 mV/cm in our case. This mutual exclusive influence is theoretically well-explained by an optical Bloch equation considering all optical and microwave field interactions with atoms.

Zeeman-Sisyphus deceleration for heavy molecules with perturbed excited-state structure

We demonstrate and characterize Zeeman-Sisyphus (ZS) deceleration of a beam of ytterbium monohydroxide. Our method uses a combination of large magnetic fields ($\ensuremath{\sim}2.5$ T) and optical spin-flip transitions to decelerate molecules while scattering only $\ensuremath{\sim}10$ photons per molecule. We study the challenges associated with the presence of internal molecular perturbations among the excited electronic states and discuss the methods used to overcome these challenges, including a modified ZS decelerator using microwave and optical transitions.

Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde (CHD2CHO) and first detection towards IRAS 16293-2422

Context. The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined to be orders of magnitude higher than expected from the cosmic abundance of deuterium relative to hydrogen. The increasing number of singly and multi-deuterated species detections helps us to constrain the interplay between gas-phase and solid-state chemistry and to understand better deuterium fractionation in the early stages of star formation. Acetaldehyde is one of the most abundant complex organic molecules (COMs) in star-forming regions and its singly deuterated isotopologues have already been observed towards protostars. Aims. A spectroscopic catalogue for astrophysical purposes is built for doubly deuterated acetaldehyde (CHD2CHO) from measurements in the laboratory. With this accurate catalogue, we aim to search for and detect this species in the interstellar medium and retrieve its column density and abundance. Methods. Sub-millimetre wave transitions were measured for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered internal rotation of its asymmetrical CHD2 methyl group. An analysis of a dataset consisting of previously measured microwave transitions and of the newly measured ones was carried out with an effective Hamiltonian which accounts for the tunnelling of the asymmetrical methyl group. Results. A line position analysis was carried out, allowing us to reproduce 853 transition frequencies with a weighted root mean square standard deviation of 1.7, varying 40 spectroscopic constants. A spectroscopic catalogue for astrophysical purposes was built from the analysis results. Using this catalogue, we were able to detect, for the first time, CHD2CHO towards the low-mass proto-stellar system IRAS 16293-2422 utilising data from the ALMA Proto-stellar Interferometric Line Survey. Conclusions. The first detection of the CHD2CHO species allowed for the derivation of its column density with a value of 1.3×1015 cm−2 and an uncertainty of 10–20%. The resulting D2/D ratio of ~20% is found to be coincident with D2/D ratios derived for other COMs towards IRAS 16293-2422, pointing to a common formation environment with enhanced deuterium fractionation.

Исследование когерентного пленения населенности и динамического эффекта Штарка в ансамблях NV-центров в алмазе при комнатной температуре в микроволновом диапазоне

We study coherent population trapping and AC Stark effect using microwave transitions between the sublevels of the ground state of the NV-center. Sublevels with different projections of the nuclear spin of the nitrogen atom are used to implement the Lambda-scheme. Dependence of the characteristics of the coherent population trapping dip on the control field frequency and intensity is studied. Various schemes for observing the AC Stark effect are considered.

Study of coherent population trapping and AC Stark effect in ensembles of NV-centers in diamond at room temperature in microwave range

We study coherent population trapping and AC Stark effect using microwave transitions between the sublevels of the ground state of the NV-center. Sublevels with different projections of the nuclear spin of the nitrogen atom are used to implement the -scheme. Dependence of the characteristics of the coherent population trapping dip on the control field frequency and intensity is studied. Various schemes for observing the AC Stark effect are considered. Keywords: NV-center, coherent population trapping, AC Stark.

Detecting chiral asymmetry in the interstellar medium using propylene oxide

Context.Life is distinctly homochiral. The origins of this homochirality are under active debate. Recently, propylene oxide has been detected in the gas-phase interstellar medium (ISM). The enantiomeric composition of ISM propylene oxide may be probed through circular polarization measurements, but accurate estimates of the circular dichroism properties of the microwave transitions of propylene oxide are not available.Aims.Our aim is to develop a model of the circular dichroic activity in torsion–rotation transitions of closed-shell chiral molecules such as propylene oxide. With this model we can estimate the viability, and optimize the observation strategies, of enantiomeric excess detection in ISM propylene oxide.Methods.Circular dichroism in spectral lines manifests through the simultaneous interaction of an electromagnetic radiation field with the molecular electric dipole moment and magnetic dipole moment. We developed techniques to quantify electric dipole and magnetic dipole moments of torsion–rotation transitions by expanding on earlier modeling of the electric and magnetic dipole properties of single torsion–rotation levels. To model the circular dichroism properties of propylene oxide, we used these techniques in combination with ab initio quantum chemical calculations.Results.The expressions for the dichroic activity of the microwave transitions of torsionally active molecules are derived. We find that the torsional motion of molecules exhibiting internal rotation contributes significantly to the total magnetic moment. We present estimates for the dichroic activity of the torsion–rotation transitions of propylene oxide. We predict that the circular polarization fractions of emission lines of enantiopure propylene oxide relevant to astronomical detections are on the order of 10−6.Conclusions.Due to the low predicted circular polarization fractions, we conclude that enantiomeric characterization of propylene oxide in the gas phase of the ISM is impossible with the current astronomical observation techniques. We suggest that only chiral radical species may be viably employed for purposes of enantiomeric excess detection. We estimate that laboratory experiments may be successful in detecting the enantiomeric composition of a mixture of propylene oxide through microwave dichroism spectroscopy.

High Fidelity State Preparation and Measurement of Ion Hyperfine Qubits with I>1/2.

We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than I=1/2. The ground states of these higher nuclear spin isotopes do not afford a simple frequency-selective state preparation scheme. We circumvent this limitation by stroboscopically driving strong and weak transitions, blending fast optical pumping using dipole transitions, and narrow microwave or optical quadrupole transitions. We demonstrate this method with the I=3/2 isotope ^{137}Ba^{+} to achieve a SPAM infidelity of (9.0±1.3)×10^{-5} (-40.5±0.6 dB), facilitating the use of a wider range of ion isotopes with favorable wavelengths and masses for quantum computation.

Topological superfluid defects with discrete point group symmetries

Discrete symmetries are spatially ubiquitous but are often hidden in internal states of systems where they can have especially profound consequences. In this work we create and verify exotic magnetic phases of atomic spinor Bose–Einstein condensates that, despite their continuous character and intrinsic spatial isotropy, exhibit complex discrete polytope symmetries in their topological defects. Using carefully tailored spinor rotations and microwave transitions, we engineer singular line defects whose quantization conditions, exchange statistics, and dynamics are fundamentally determined by these underlying symmetries. We show how filling the vortex line singularities with atoms in a variety of different phases leads to core structures that possess magnetic interfaces with rich combinations of discrete and continuous symmetries. Such defects, with their non-commutative properties, could provide unconventional realizations of quantum information and interferometry.