arXiv subjects

Georg Raithel

Publications and source records attributed to Georg Raithel.

At least 37 records · Page 2Linked to original sources

arXiv2022

Dynamic polarizability of the $^{85}$Rb $5D_{3/2}$-state in 1064 nm light

We report a measurement of the dynamic (ac) scalar polarizability of the $5D_{3/2}$ state in $^{85}$Rb atoms at a laser wavelength of 1064~nm. Contrary to a recent measurement in Phys. Rev. \textbf{A} 104, 063304 (2021), the experiments are performed in a low-intensity regime in which the ac shift is less than the $5D_{3/2}$ state's hyperfine structure, as utilized in numerous experiments with cold, trapped atoms. The extracted ac polarizability is $α_{5D_{3/2}} = -499\pm59$~a.u., within the uncertainty of the aforementioned previous result. The calibration of the 1064~nm light intensity, performed by analyzing light shifts of the D1 line, is the main source of uncertainty. Our results are useful for applications of the Rb $5D_{3/2}$ state in metrology, quantum sensing, and fundamental-physics research on Rydberg atoms and molecules.

physics.atom-ph↗

arXiv2022

Principles of tractor atom interferometry

We present possible design concepts for a tractor atom interferometer (TAI) based on three-dimensional confinement and transport of ultracold atoms. The confinement reduces device size and wave-packet dispersion, enables arbitrary holding times, and facilitates control to create complex trajectories that allow for optimization to cancel unwanted sensitivity, fast splitting and recombination, and suppression of detrimental nonadiabatic excitation. Thus, the design allows for further advancement of compact, high-sensitivity, quantum sensing technology. In particular, we focus on the implementation of quantum-enhanced accelerometers and gyroscopes. We discuss TAI protocols for both spin-dependent and scalar trapping potentials. Using optimal control theory, we demonstrate the splitting of the wave function on a time scale two orders of magnitude shorter than the previous proposal using adiabatic dynamics, thus maximizing the time spent at full separation, where the interferometric phase is accumulated. Lastly, we explore the possibility of including non-classical correlations between the atoms to improve sensitivity. The performance estimates for TAI give a promising perspective for atom-interferometry-based sensing, significantly exceeding the sensitivities of current state-of-the-art devices.

physics.atom-ph↗

arXiv2022

Hyperfine Structure of $nP_{1/2}$ Rydberg States in $^{85}$Rb

We measure the hyperfine structure of $nP_{1/2}$ Rydberg states using mm-wave spectroscopy on an ensemble of laser-cooled $^{85}$Rb atoms. Systematic uncertainties in our measurement from the Zeeman splittings induced by stray magnetic fields and dipole-dipole interactions between two Rydberg atoms are factored in with the obtained statistical uncertainty. Our final measurement of the $nP_{1/2}$ hyperfine coupling constant is $A_{\text{hfs}}=1.443(31)$~GHz. This measurement is useful for studies of long-range Rydberg molecules, Rydberg electrometry, and quantum simulation with dipole-dipole interactions involving $nP_{1/2}$ atoms.

physics.atom-ph↗

arXiv2022

Nonadiabatic decay of metastable states on coupled linear potentials

Avoided crossings of level pairs with opposite slopes can form potential energy curves for the external degree of freedom of quantum particles. We investigate nonadiabatic decay of metastable states on such avoided crossings (MSACs) using diabatic and adiabatic representations. The system is described by a single scaled adiabaticity parameter, $V$. The time-independent two-component Schrödinger equation is solved in both representations, and the nonadiabatic lifetimes of MSACs are determined from a wave-function flux calculation and from the Breit-Wigner formula, leading to four lifetime values for each MSAC. We also solve the time-dependent Schrödinger equation in both pictures and derive the MSAC lifetimes from wave-function decay. The sets of six non-perturbative values for the MSAC lifetimes agree well, validating the approaches. As the adiabaticity parameter $V$ is increased by about a factor of ten, the MSAC character transitions from marginally to highly stable, with the lifetimes increasing by about ten orders of magnitude. The $ν$-dependence of the lifetimes in several regimes is discussed. Time-dependent perturbation theory is found to yield approximate lifetimes that deviate by $\lesssim 30\%$ from the non-perturbative results, while predictions based on the semi-classical Landau-Zener tunneling equation are found to be up to a factor of twenty off, over the ranges of $V$ and $ν$ studied. The results are relevant to numerous atomic and molecular systems with quantum states on intersecting, coupled potential energy curves.

quant-ph↗

arXiv2021

Gauge effects in bound-bound Rydberg-transition matrix elements

Accurate data on electric-dipole transition matrix elements (EDTMs) for bound-bound Rydberg-atom transitions become increasingly important in science and technology. Here we compute radial EDTMs of rubidium using the length, velocity and acceleration gauges for electric-dipole-allowed transitions between states with principal and angular-momentum quantum numbers ranging from 15 to 100. Wave-functions are computed based upon model potentials from Marinescu et al., Phys. Rev. A {\bf{49}}, 982 (1994). Length-gauge EDTMs, often used for low-$\ell$ transitions, are found to deviate from the fundamentally more accurate velocity-gauge EDTMs by relative amounts of up to $\sim 10^{-3}$. We discuss the physical reasons for the observed gauge differences, explain the conditions for applicability of the velocity and length gauges for different transition series, and present a decision tree of how to choose EDTMs. Implications for contemporary Rydberg-atom applications are discussed.

physics.atom-ph↗

arXiv2021

Non-adiabatic decay of Rydberg-atom-ion molecules

The decay of Rydberg-atom-ion molecules (RAIMs) due to non-adiabatic couplings between electronic potential energy surfaces is investigated. We employ the Born-Huang representation and perform numerical simulations using a Crank-Nicolson algorithm. The non-adiabatic lifetimes of rubidium RAIMs for the lowest ten vibrational states, $ν$, are computed for selected Rydberg principal quantum numbers, $n$. The non-adiabatic lifetimes are found to generally exceed the radiative Rydberg-atom lifetimes. We observe and explain a trend of the lifetimes as a function of $ν$ and $n$, and attribute irregularities to quantum interference arising from a shallow potential well in an inner potential surface. Our results will be useful for future spectroscopic studies of RAIMs.

physics.atom-ph↗

arXiv2021

AC polarizability and photoionization cross-section measurements in an optical lattice

We use double-resonant two-photon laser spectroscopy to measure the dynamic scalar polarizability of the rubidium 5$D_{3/2}$ level, $α^{S}_{5D_{3/2}}$, at a wavelength of $λ=1064$~nm. Since $λ$ is shorter than the photoionization (PI) limit of the Rb 5$D_{3/2}$ level, $α^{S}_{5D_{3/2}}$ depends on both bound-bound and bound-free transition matrix elements. The level also undergoes significant broadening due to PI. The $1064$-nm field is applied in the form of a deep optical lattice ($\sim10^{5}$~photon recoils) generated by an in-vacuum field-enhancement cavity. In our spectroscopic method, we use known dynamic polarizabilities to eliminate the need to measure the light intensity. Our method yields, in atomic units, $α^{S}_{5D_{3/2}}=-524(17)$, in agreement with estimates. Additionally, we extract the $5D_{3/2}$ photoionization cross section $σ$ at $1064$~nm from spectral linewidths; we find $σ=44(1)$~Mb.

physics.atom-ph↗

arXiv2021

Photoionization of Rydberg Atoms in Optical Lattices

We develop a formalism for photoionization (PI) and potential energy curves (PECs) of Rydberg atoms in ponderomotive optical lattices and apply it to examples covering several regimes of the optical-lattice depth. The effect of lattice-induced PI on Rydberg-atom lifetime ranges from noticeable to highly dominant when compared with natural decay. The PI behavior is governed by the generally rapid decrease of the PI cross sections as a function of angular-momentum ($\ell$), and by lattice-induced $\ell$-mixing across the optical-lattice PECs. In GHz-deep lattices, $\ell$-mixing leads to a rich PEC structure, and the significant low-$\ell$ PI cross sections are distributed over many lattice-mixed Rydberg states. In lattices less than several tens-of-MHz deep, atoms on low-$\ell$ PECs are essentially $\ell$-mixing-free and maintain large PI cross sections, while atoms on high-$\ell$ PECs trend towards being PI-free. Characterization of PI in GHz-deep Rydberg-atom lattices may be beneficial for optical control and quantum-state manipulation of Rydberg atoms, while data on PI in shallower lattices are potentially useful in high-precision spectroscopy and quantum-computing applications of lattice-confined Rydberg atoms.

physics.atom-ph↗

arXiv2021

Measurement of DC and AC electric fields inside an atomic vapor cell with wall-integrated electrodes

We present and characterize an atomic vapor cell with silicon ring electrodes directly embedded between borosilicate glass tubes. The cell is assembled with an anodic bonding method and is filled with Rb vapor. The ring electrodes can be externally connectorized for application of electric fields to the inside of the cell. An atom-based, all-optical, laser-spectroscopic field sensing method is employed to measure electric fields in the cell. Here, the Stark effect of electric-field-sensitive rubidium Rydberg atoms is exploited to measure DC electric fields in the cell of $\sim$5 V/cm, with a relative uncertainty of 10%. Measurement results are compared with DC field calculations, allowing us to quantify electric-field attenuation due to free surface charges inside the cell. We further measure the propagation of microwave fields into the cell, using Autler-Townes splitting of Rydberg levels as a field probe. Results are obtained for a range of microwave powers and polarization angles relative to the cell's ring electrodes. We compare the results with microwave-field calculations. Applications are discussed.

physics.atom-ph↗

arXiv2021

Photoionization of $nS$ and $nD$ Rydberg atoms of Rb and Cs from the near-infrared to the ultraviolet spectral region

We present calculations of the photoionization (PI) cross sections of rubidium and cesium Rydberg atoms for light with wavelengths ranging from the infrared to the ultraviolet, using model potentials from [M. Marinescu, H. R. Sadeghpour, and A. Dalgarno, Phys. Rev. A 49, 982 (1994)]. The origins of pronounced PI minima are identified by investigating the free-electron wavefunctions. These include broad PI minima in the $nS$ to $εP$ PI channels of both Rb and Cs, with free-electron energy $ε$, which are identified as Cooper minima. Much narrower PI minima in the $nD$ to $εF$ channels are due to shape resonances of the free-electron states. We describe possible experimental procedures for measuring the PI minima, and we discuss their implications in fundamental atomic physics as well as in practical applications.

physics.atom-ph↗

arXiv2020

Atom radio-frequency interferometry

We realize and model a Rydberg-state atom interferometer for measurement of phase and intensity of radio-frequency (RF) electromagnetic waves. A phase reference is supplied to the atoms via a modulated laser beam, enabling atomic measurement of the RF wave's phase without an external RF reference wave. The RF and optical fields give rise to closed interferometric loops within the atoms' internal Hilbert space. In our experiment, we construct interferometric loops in the state space $\{ 6P_{3/2}, 90S_{1/2}, 91S_{1/2}, 90P_{3/2} \}$ of cesium and employ them to measure phase and intensity of a 5 GHz RF wave in a room-temperature vapor cell. Electromagnetically induced transparency on the $6S_{1/2}$ to $6P_{3/2}$ transition serves as an all-optical interferometer probe. The RF phase is measured over a range of $π$, and a sensitivity of 2 mrad is achieved. RF phase and amplitude measurements at sub-millimeter optical spatial resolution are demonstrated.

physics.atom-ph↗

arXiv2020

Cesium $nD_{J}$+$6S_{1/2}$ Rydberg molecules and their permanent electric dipole moments

Cs$_2$ Rydberg-ground molecules consisting of a Rydberg, $nD_{J}$ (33 $\leq$ $n$ $\leq$ 39), and a ground state atom, 6$S_{1/2} (F=$3 or 4$)$, are investigated by photo-association spectroscopy in a cold atomic gas. We observe vibrational spectra that correspond to triplet $^TΣ$ and mixed $^{S,T}Σ$ molecular states. We establish scaling laws for the energies of the lowest vibrational states vs principal quantum number and obtain zero-energy singlet and triplet $s$-wave scattering lengths from experimental data and a Fermi model. Line broadening in electric fields reveals the permanent molecular electric-dipole moments; measured values agree well with calculations. We discuss the negative polarity of the dipole moments, which differs from previously reported cases.

physics.atm-clus↗

arXiv2020

A magneto-optical trap with millimeter ball lenses

We present a magneto-optical trap (MOT) design based on millimeter ball lenses, contained within a metal cube of 0.75$^{\prime \prime}$ side length. We present evidence of trapping approximately $4.2\times 10^5$ of $^{85}$Rb atoms with a number density of $3.2\times 10^9$ atoms/cm$^{3}$ and a loading time of 1.3 s. Measurement and a kinetic laser-cooling model are used to characterize the atom trap design. The design provides several advantages over other types of MOTs: the laser power requirement is low, the small lens and cube sizes allow for miniaturization of MOT applications, and the lack of large-diameter optical beam pathways prevents external blackbody radiation from entering the trapping region.

physics.atom-ph↗

arXiv2020

Coulomb Expansion of Cold Non-Neutral Rubidium Plasma

We study the expansion of a cold, non-neutral ion plasma into the vacuum. The plasma is made from cold rubidium atoms in a magneto-optical trap (MOT) and is formed via ultraviolet photoionization. We employ time-delayed plasma extraction and imaging onto a position- and time-sensitive micro-channel plate detector to analyze the plasma. We report on the formation and persistence of plasma shock shells, pair correlations in the plasma, and external-field-induced plasma focusing effects. We also develop trajectory and fluid descriptions to model the data and to gain further insight. The simulations verify the formation of shock shells and correlations, and allow us to model time- and position-dependent density, temperature, and Coulomb coupling parameter, $Γ({\bf{r}},t)$. This analysis both reaffirms the presence of shock shells and verifies that the experimental plasma is strongly coupled.

physics.atom-ph↗

arXiv2020

Deeply bound (24$D_J$ + 5$S_{1/2}$) $^{87}$Rb and $^{85}$Rb molecules for eight spin couplings

We observe long-range $^{85}$Rb and $^{87}$Rb (24$D$+5$S_{1/2}$) Rydberg molecules for eight different spin couplings, with binding energies up to 440~MHz and sub-percent relative uncertainty. Isotopic effects of the molecular binding energies arise from the different masses and nuclear spins. Because the vibrational states involve different spin configurations and cover a wide range of internuclear separations, the states have different dependencies on the $s$-wave and $p$-wave scattering phase shifts for singlet and triplet scattering. Fitting the spectroscopic data, we comprehensively determine all four scattering length functions over the relevant energy range as well as the zero-energy scattering lengths of the two $s$-wave channels. Our unusually high temperature and low density (180 $μ$K, 1 $\times$ 10$^{11}$ cm$^{-3}$) suggest that the molecule excitation occurs through photoassisted collisions.

physics.atom-ph↗

arXiv2019

Expansion Dynamics of Cold Non-Neutral Plasma

We study the expansion of a strongly coupled, non-neutral, and cylindrically arranged ion plasma into the vacuum. The plasma is made from cold rubidium atoms in a magneto-optical trap (MOT) and is formed via ultraviolet photoionization. Higher-density and lower-density plasmas are studied to exhibit different aspects indicative of strong coupling. In a higher-density regime, we report on the formation and persistence of plasma shock fronts, as well as external-field-induced plasma focusing effects. In the lower-density regime, conditions are ideal to observe the development and evolution of nearest-neighbor ion correlations, as well as geometry-induced asymmetries in the pair correlation function. Simulated results from a trajectory model and a fluid model are in good agreement with the measurements.

physics.atom-ph↗

arXiv2019

Optical control of atom-ion collisions using a Rydberg state

We present a method to control collisions between ultracold neutral atoms in the electronic ground state and trapped ions. During the collision, the neutral atom is resonantly excited by a laser to a low-field-seeking Rydberg state, which is repelled by the ion. As the atom is reflected from the ion, it is de-excited back into its electronic ground level. The efficiency of shielding is analyzed as a function of laser frequency and power, initial atom-ion collision energy, and collision angle. The suitability of several Rydberg levels of Na and Rb for shielding is discussed. Useful applications of shielding include the suppression of unwanted chemical reactions between atoms and ions, a prerequisite for controlled atom-ion interactions.

cond-mat.quant-gas↗

arXiv2019

A self-calibrating SI-traceable broadband Rydberg atom-based radio-frequency electric field probe and measurement instrument

We present a self-calibrating, SI-traceable broadband Rydberg-atom-based radio-frequency (RF) electric field probe (the Rydberg Field Probe or RFP) and measurement instrument (Rydberg Field Measurement System or RFMS). The RFMS comprises an atomic RF field probe (RFP), connected by a ruggedized fiber-optic patch cord to a portable mainframe control unit with a software interface for RF measurement and analysis including real-time field readout and RF waveform visualization. The instrument employs electromagnetically induced transparency (EIT) readout of spectral signatures from RF-sensitive Rydberg states of an atomic vapor for continuous, pulsed, and modulated RF field measurement. The RFP exploits resonant and off-resonant Rydberg-field interactions to realize broadband RF measurements at frequencies ranging from ~10 MHz to sub-THz over a wide dynamic range. The RFMS incorporates an RF-field-free atomic reference and a laser-frequency tracker to ensure reliability and accuracy of the RF measurement. We characterize the RFP and measure polar field and polarization patterns of the RFP at 12.6 GHz RF in the far-field of a standard gain horn antenna. Measurements at 2.5 GHz are also performed. Measured patterns are in good agreement with simulations. A detailed calibration procedure and uncertainty analysis are presented that account for deviations from an isotropic response over a $4π$ solid angle, arising from dielectric structures external to the atomic measurement volume. Contributions to the measurement uncertainty from the fundamental atomic measurement method and associated analysis as well as material, geometry, and hardware design choices are accounted for. A calibration (C) factor is used to establish absolute-standard SI-traceable calibration of the RFP. Pulsed and modulated RF field measurement, and time-domain RF-pulse waveform imaging are also demonstrated.

physics.atom-ph↗