Search

We report the observation of the hyperfine spectrum of the weak P(63)4-4 line of the B-X electronic transition of molecular iodine 127I2 near 652.4 nm, using frequency-modulated saturated absorption spectroscopy. Through the precise measurements of the absolute frequencies of hyperfine components, we estimate electric quadrupole and magnetic spin-rotation constants. Additionally, we determine the center of gravity of the P(63) transition of the 4-4 vibrational band, resulting in a 250-fold improvement in the precision of its position. We also note an interesting overlap of the hyperfine transitions of P(63)4-4 line with the UV 1S0-3P1 narrow intercombination transition of cadmium atoms, which occurs near the second harmonic of the master laser radiation, corresponding to 326.2 nm. This study contributes to updating the iodine atlas, improving the precision of the empirical formulae, and providing an important frequency reference for precision spectroscopy of the narrow intercombination transition of atomic cadmium.

The evolution of quantum optical systems is determined by three key factors: the interactions with their surrounding environment, externally controlled lasers and between the different system components. Understanding the interplay between the three dynamical contributions is essential for the study of out-of-equilibrium phenomena as well as technological applications. The present study investigates open system phenomena in driven optical systems coupled simultaneously to a bosonic field. For a linear system of micro-cavities coupled to a photonic crystal, it is analytically shown that environmental interaction and external control cause significant non-Markovian corrections to the applied coherent drive. Additionally, collective cross-driving effects arise when multiple modes are coupled to the same field, where a laser applied to one mode effectively drives other modes. Based on the linear solution, a non-Markovian master equation for two-level emitters is derived. Remarkably, the proposed equation of motion remains accurate even for moderate driving intensities, where emitters cannot be approximated by bosonic modes. The influence of the non-linearity is analyzed and benchmarked against an exact pseudo-mode solution, and compared with established master equations in the Markovian regime. Within this regime, the comparison demonstrates the presence of short-time non-Markovian effects at times well beyond the inverse of the environment's bandwidth, and memory effects induced by short laser pulses. These findings offer valuable insights into the driven open system dynamics of quantum optical systems, impurities embedded in solid-state materials, molecular systems, and more, paving the way for precise control of their quantum states.

Sub-micrometer scale light patterns play a pivotal role in various fields, including biology, biophysics, and AMO physics. High-resolution, in situ observation of light profiles is essential for their design and application. However, current methods are constrained by limited spatial resolution and sensitivity. Additionally, no existing techniques allow for super-resolution imaging of the polarization profile, which is critical for precise control of atomic and molecular quantum states. Here, we present an atom camera technique for in situ imaging of light patterns with a single ultracold atom held by an optical tweezers as a probe. By scanning the atom's position in steps of sub-micrometers and detecting the energy shift on the spin states, we reconstruct high-resolution 2D images of the light field. Leveraging the extraordinarily long coherence time and polarization-sensitive transitions in the spin structure of the atom, we achieve highly sensitive imaging both for intensity and polarization. We demonstrate this technique by characterizing the polarization in a tightly-focused beam, observing its unique non-trivial profile for the first time. The spatial resolution is limited only by the uncertainty of the atom's position, which we suppress down to the level of quantum fluctuations (~25 nm) in the tweezers' ground state. We thus obtain far better resolution than the optical diffraction limit, as well as than the previous ones obtained with a thermal atom fluctuating in the trap. This method enables the analysis and design of submicron-scale light patterns, providing a powerful tool for applications requiring precise light manipulation.

We investigated the influence of sub-cycle driving fields on high-order harmonic generation (HHG), with a focus on intrinsic chirp, carrier-envelope phase (CEP), and number of laser cycles. Our findings reveals that the center frequency of a laser pulse scales as $\tau^{-5/4}$ with pulse duration $\tau$, and that attochirp exhibits a similar dependence on pulse duration. Additionally, we identified CEP-specific trends in harmonic yield: it increases as $\tau^{5/4}$ for $\phi_0=0^\circ$ and decreases as $\tau^{-4.1}$ for $\phi_0= -90^\circ$. Although sub-cycle pulses can generate intense isolated attosecond pulses (IAPs), they also tend to produce higher attochirp and reduced cutoff energies. However, effective compensation for attochirp can mitigate these drawbacks, thereby increasing the capability of sub-cycle pulses to generate short-duration, high-intensity IAPs. These results offer valuable insights into HHG using sub-cycle pulses and have important implications for the advancement of ultrafast light sources and the understanding of ultrafast phenomena at the attosecond timescale., Comment: 9 pages, 9 figures

We produce atomic beams of neutral titanium (Ti) atoms in their metastable $3d^{3}(^4F){4}s$ $a^5F_5$ state by laser ablation into He, N$_2$, and Ar buffer gases. The high temperatures realized in the ablation process populate the $a^5F_5$ level without the need for optical pumping. Remarkably, we observe that Ti atoms in the $a^5F_5$ state survive $1000$'s of collisions with He and Ar buffer gas atoms without being quenched to lower-energy states. We study the yield of Ti atoms when ablated into buffer gases of varying species and pressure, quantify diffusion cross sections and quenching rates based on a simple model, and provide insight into optimal design parameters for an ablation cell. Using a 3.3$\,$cm ablation cell with interchangeable exit apertures, we produce metastable atom beams and quantify their brilliance and velocity distributions as functions of buffer gas pressure.

Earlier, a significant enhancement of the nondipole parameters $\gamma_{2p}$, $\delta_{2p}$, and $\zeta_{2p} = \gamma_{2p} + 3\delta_{2p}$ in the photoelectron angular distribution for Ne $2p$ photoionization, owing to resonance interference between dipole ($E1$) and quadrupole ($E2$) transitions, was predicted. This enhancement manifests as narrow resonance spikes in the parameters due to the low-energy $2s \rightarrow 3p$ and $2s \rightarrow 4p$ dipole, as well as the $2s \rightarrow 3d$ quadrupole autoionizing resonances. Given the unique nature of this predicted enhancement, it requires further validation. Specifically, whether these narrow spikes in $\gamma_{2p}$, $\delta_{2p}$, and $\zeta_{2p}$ will or will not retain their values for experimental observation if one accounts for a typical finite frequency spread in the ionizing radiation. To address this, we revisit the previous study, now incorporating the effect of frequency spread in the ionizing radiation, assuming a spread as large as $5$ meV at the half-maximum of the radiation's intensity. We demonstrate in the present paper that while the frequency spread does affect the resonance enhancement of $\gamma_{2p}$, $\delta_{2p}$, and $\zeta_{2p}$, these parameters still retain quantitatively significant values to be observed experimentally. The corresponding calculations were performed using the random phase approximation with exchange, which accounts for interchannel coupling in both dipole and quadrupole photoionization amplitudes., Comment: 5 pages, 3 fighures, 24 references

We calculated QED corrections to the $E1$ transition amplitudes in Ne-like iron and nickel. For the $2p \to 3d$ transitions the dominant effect came from the many-electron mixing, or electronic correlations. For the $2p \to 3s$ transitions the correlation and one-electron effects were comparable and tended to compensate each other. Our ab initio calculations showed that vertex corrections were negligible for both types of transitions. Other QED corrections were accurately reproduced by including effective QEDMOD operator in the many-electron relativistic configuration interaction calculation., Comment: 7 pages, no figures

In trapped-atom quantum computers, high-fidelity control of optical qubits is challenging due to the motion of atoms in the trap. If not corrected, the atom motion gets entangled with the qubit degrees of freedom through two fundamental mechanisms, (i) photon recoil and (ii) thermal motion, both leading to a reduction of the gate fidelity. We develop motion-insensitive pulses that suppress both sources of infidelity by modulating the phase of the driving laser field in time. To eliminate photon recoil, we use bang-bang pulses$-$derived using time-optimal control$-$which shorten the gate duration by about 20 times compared to conventional pulses. However, even when photon recoil is eliminated, we find that the gate error does not vanish, but is rather limited by a bound arising from thermal motion-induced entanglement. Remarkably, this bound is independent of the Rabi frequency, meaning that, unlike for photon recoil, operating in the resolved sideband regime does not mitigate this source of infidelity. To overcome this bound, we derive smooth-phase pulses, which allow for a further reduction of the gate error by more than an order of magnitude for typical thermal atoms. Motion-insensitive pulses can be refined to compensate for laser inhomogeneities, enhancing the gate performance in practical situations. Our results are validated through simulations of one-qubit gates operating on the optical clock transition of ${}^{88}$Sr atoms trapped in an optical tweezers array., Comment: 22 pages, 10 figures

The behavior of an atomic system is influenced by introducing a metallic surface. This work explores how the decay landscape can be altered by the presence of sharp corners. We examine two scenarios: the modified spontaneous decay of a single atom, which leads us to speculate about potential applications in microscopy, and the case of a more fundamental, theoretical interest - the behavior of an entangled pair of atoms near a corner. The latter, when two atoms are positioned ``out of the line of sight'' opens up a possible line of investigation into devices which are able to ``see around corners''.

Most of the matter in the universe is in the form of dark matter. However, dark matter has never been observed to interact with normal matter in laboratory experiments. ALPs -- ultralight axionlike particles -- are a class of dark matter models that are consistent with astrophysical constraints, and produce measurable signatures in the form of oscillating violations of discrete symmetries in nuclei. We report the first results from a search for oscillating parity-odd time-reversal-odd nuclear moments of $^{153}$Eu ions in a crystal, which leads to an experimental constraint on the ALP-gluon coupling strength across a wide band of ALP masses.

After nearly fifty years of searching, the vacuum ultraviolet $^{229}$Th nuclear isomeric transition has recently been directly laser excited [1,2] and measured with high spectroscopic precision [3]. Nuclear clocks based on this transition are expected to be more robust [4,5] than and may outperform [6,7] current optical atomic clocks. They also promise sensitive tests for new physics beyond the standard model [5,8,9]. In light of these important advances and applications, a dramatic increase in the need for $^{229}$Th spectroscopy targets in a variety of platforms is anticipated. However, the growth and handling of high-concentration $^{229}$Th-doped crystals [5] used in previous measurements [1-3,10] are challenging due to the scarcity and radioactivity of the $^{229}$Th material. Here, we demonstrate a potentially scalable solution to these problems by demonstrating laser excitation of the nuclear transition in $^{229}$ThF$_4$ thin films grown with a physical vapor deposition process, consuming only micrograms of $^{229}$Th material. The $^{229}$ThF$_4$ thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical \thor-doped crystals [1-3,10]. The high nuclear emitter density in $^{229}$ThF$_4$ also potentially enables quantum optics studies in a new regime. Finally, we describe the operation and present the estimation of the performance of a nuclear clock based on a defect-free ThF$_4$ crystal., Comment: 15 pages, 3 figures

In an experiment on three-photon laser excitation $5S_{1/2} \to 5P_{3/2} \to 6S_{1/2} \to 37P_{3/2}$ of a single $^{87}$Rb Rydberg atom in an optical dipole trap, we have observed for the first time three-photon Rabi oscillations between the ground and the Rydberg states. The single atom was detected optically by measuring the signal of resonant fluorescence with a low-noise sCMOS video camera. Relative probability of the atom to remain in the trap after the action of three synchronized laser excitation pulses was measured for their durations varied in the range from 100 ns to 2 $\mu$s. A specific feature of the experiment was the usage of intense laser radiation at the wavelength of 1367 nm on the second excitation step, which provided the single-photon Rabi frequency up to 2 GHz to control the effective detunings of the intermediate levels of the three-photon transition due to ac Stark effect. We have detected Rabi oscillations with frequency from 1 to 5 MHz depending on the intensities of the laser pulses on the first and the second excitation steps with the coherence time of 0.7-0.8 $\mu$s. The ways to increase the coherence time and contrast of the three-photon Rabi oscillations for applications in quantum information processing with Rydberg atoms are discussed., Comment: 14 pages, 6 figures

We study time-delays in atomic multiphoton ionization (MPI) using the phase-sensitive detection of photoelectron vortices. Photoelectron vortices are created by MPI with counter-rotating circularly polarized (CRCP) ultrashort double pulse sequences. The vortices are characterized by a spiral-shaped photoelectron momentum distribution (PMD) resulting from the Ramsey-type interference of the partial photoelectron wave packets created by each pulse. The slope of the spiral arms encodes the time-delay between the partial wave packets with interferometric precision. We study the ionization time-delay in the (1+2) resonance-enhanced multiphoton ionization (REMPI) of potassium atoms using femtosecond CRCP white-light supercontinuum pulses. Pairwise interference of the partial wave packets with a reference wave packet gives rise to vortices of different rotational symmetry, which are superimposed to form the total PMD. The PMD is reconstructed tomographically and decomposed into the vortices using 3D Fourier analysis. From the energy-dependent spectral phases of the vortices, we retrieve a resonant ionization delay in the order of 1 fs, much shorter than the pulse duration. Our results demonstrate the power of photoelectron vortices for the accurate determination of photoionization time-delays and open up new perspectives for photoelectron chronoscopy including the measurement of ionization delays on the attosecond timescale., Comment: 11 pages, 5 figures

The static dipole polarizabilities of group 11 elements (Cu, Ag, and Au) are computed using the relativistic coupled-cluster method with single, double, and perturbative triple excitations. Three types of relativistic effects on dipole polarizabilities are investigated: scalar-relativistic, spin-orbit coupling (SOC), and fully relativistic Dirac-Coulomb contributions. The final recommended values, including uncertainties, are $46.91 \pm 1.30$ for Cu, $50.97 \pm 1.88$ for Ag, and $36.68 \pm 0.62$ for Au. Our results show close agreement with the values recommended in the 2018 table of static dipole polarizabilities for neutral elements [Mol. Phys. \textbf{117}, 1200 (2019)], with reduced uncertainties for Ag and Au. The analysis indicates that scalar-relativistic effects are the dominant relativistic contribution for these elements, while SOC effects are negligible. The influence of electron correlation across all relativistic regimes is also evaluated, demonstrating its significant role in the accurate calculation of dipole polarizabilities.

The distributions $P(M_L,M_S)$ of the total magnetic quantum numbers $M_L$ and $M_S$ for $N$ electrons of angular momentum $\ell$, as well as the enumeration of $LS$ spectroscopic terms and spectral lines, are crucial for the calculation of atomic structure and spectra, in particular for the modeling of emission or absorption properties of hot plasmas. However, no explicit formula for $P(M_L,M_S)$ is known yet. In the present work, we show that the generating function for the cumulants, which characterize the distribution, obeys a recurrence relation, similar to the Newton-Girard identities relating elementary symmetric polynomials to power sums. This enables us to provide an explicit formula for the generating function. We also analyze the possibility of representing the $P(M_L,M_S)$ distribution by a bi-variate Gram-Charlier series, which coefficients are obtained from the knowledge of the exact moments of $P(M_L,M_S)$. It is shown that a simple approximation is obtained by truncating this series to the first few terms, though it is not convergent., Comment: submitted to J. Phys. B: At. Mol. Opt. Phys

A cylindrical microwave cavity resonator operating in the TM$_{0,1,0}$ mode was excited using an interferometric configuration that allowed manipulation of the electric field and potential within the resonator by adjusting the phase and amplitude in the two interferometer arms driving the resonator. With precise tuning of the phase and amplitude, 25 dB suppression of the electric field at the resonance frequency was achieved while simultaneously resonantly enhancing the amplitude of the time-varying electric-scalar potential. Under these balanced conditions, the system demonstrated extreme dispersion in the cavity response due to the introduction of an anti-resonance at the resonance frequency. This creates a phenomenon similar to electromagnetically induced transparency, leading to an increase in the cavity phase response by an order of magnitude. This work presents an experimental setup with the features that will allow the electric-scalar Aharonov-Bohm effect to be tested under conditions involving a time-varying electric-scalar potential, without the presence of an electric field or magnetic vector potential, an experiment that has not yet been realised.

This paper develops a general data-driven approach to stochastic elastoplastic modelling that leverages atomistic simulation data directly rather than by fitting parameters. The approach is developed in the context of metallic glasses, which present inherent complexities due to their disordered structure. By harvesting statistics from simulated metallic glass shear response histories, the material state is mapped onto a two-dimensional state space consisting of the shear stress and the inelastic contribution to the potential energy. The resulting elastoplastic model is intrinsically stochastic and represented as a non-deterministic dynamical map. The state space statistics provide insights into the deformation physics of metallic glasses, revealing that two state variables are sufficient to describe the main features of the elastoplastic response. In this two-dimensional state space, the gradually quenched metallic glass rejuvenates during the initial quasi-elastic shearing, ultimately reaching a steady state that fluctuates about a fixed point in the state space as rejuvenation and aging balance., Comment: 22 pages, 5 figures

Orbit-based methods are widespread in strong-field laser-matter interaction. They provide a framework in which photoelectron momentum distributions can be interpreted as the quantum interference between different semi-classical pathways the electron can take on its way to the detector, which brings with it great predictive power. The transition amplitude of an electron going from a bound state to a final continuum state is often written as multiple integrals, which can be computed either numerically, or by employing the saddle-point method. If one computes the momentum distribution via a saddle-point method, the obtained distribution is highly dependent on the time window from which the saddle points are selected for inclusion in the "sum over paths". In many cases, this leads to the distributions not even satisfying the basic symmetry requirements and often containing many more oscillations and interference fringes than their numerically integrated counterparts. Using the strong-field approximation, we find that the manual enforcement of the energy-conservation condition on the momentum distribution calculated via the saddle-point method provides a unique momentum distribution which satisfies the symmetry requirements of the system and which is in a good agreement with the numerical results. We illustrate our findings using the example of the Ar atom ionized by a selection of monochromatic and bichromatic linearly polarized fields., Comment: 11 pages, 10 figures

The potential of circulating antideuterons ($\mathrm{\overline{d}}$) in the AD/ELENA facility at CERN is currently under investigation. Approximately 100 $\mathrm{\overline{d}}$ per bunch could be delivered as a $100\,\mathrm{keV}$ beam based on measured cross-sections. These $\mathrm{\overline{d}}$ could be further decelerated to $12\,\mathrm{keV}$ using the GBAR scheme, enabling the synthesis of antideuterium ($\mathrm{\overline{D}}$) via charge exchange with positronium, a technique demonstrated with $6\,\mathrm{keV}$ antiprotons for antihydrogen production. While this would demonstrate the production of low-energy $\mathrm{\overline{D}}$, higher fluxes are required to facilitate spectroscopic studies. We propose enhancing the anti-atom production by using laser-excited positronium in the $2P$ state within a cavity, which is expected to increase the $\mathrm{\overline{D}}(2S)$ production cross-section by almost an order of magnitude for $\mathrm{\overline{d}}$ with $2\,\mathrm{keV}$ energy. The ELENA team is currently studying the possibility of increasing the $\mathrm{\overline{d}}$ rate using an optimized new target geometry. We present the projected precision for measuring the antideuterium Lamb shift and extracting the antideuteron charge radius, as a function of the beam flux.

Gravitational wave science transforms research beyond general relativity and gravity. The signals detected not only reveal the nature of cataclysmic events and exotic objects in galaxies, but also test the models for the equation of state and color superconducting vortex alignment in neutron stars, as well as for the distribution of cosmological dark matter and their characteristic coupling with ordinary matter as new physics beyond the standard model of elementary particles. Measurement sensitivity is crucial to advance along those lines. One of the rapidly developing frontiers is quantum enhanced interferometry applied into the gravitational wave detectors. Progress achieved by LIGO, Virgo and KAGRA detectors brings exciting prospects. Here, we introduce an orbital atomic sensor using a squeezed $p$-orbital Bose-Einstein condensate in an ultracold atomic optical lattice to project the gravitational wave signal received by a usual LIGO setup into a phase-sensitive entangled state. Simulation data show the detection sensitivity improves over the quantum noise of LIGO by approximately one order of magnitude in key frequency ranges. This advance enables about three-order-of-magnitude increase in detection volume, significantly advancing the potential of using gravitational waves to detect dark matter and black holes., Comment: 6+53 pages, 4+14 figures, 1 table

Since their first theoretical proposal [Ngoko Djiokap et al., Phys. Rev. Lett. 115, 113004 (2015)] and experimental demonstration [Pengel et al., Phys. Rev. Lett. 118, 053003 (2017)], free electron vortices (FEVs) have attracted considerable attention. Recently, a new class of unusually shaped FEVs, termed `reversible electron spirals', has been proposed theoretically [Strandquist et al., Phys. Rev. A 106, 043110 (2022)] for atomic single-photon ionization by two oppositely chirped and counterrotating circularly polarized (CRCP) attosecond pulses. Building on this concept, we present the first experimental demonstration of shaped FEVs created by atomic multiphoton ionization (MPI) using oppositely chirped CRCP femtosecond pulse pairs. In MPI by polarization-shaped pulses, several shaped FEVs of different rotational symmetry are superimposed resulting in the total photoelectron wave packet observed in the experiment. We employ velocity map imaging techniques to measure the photoelectron momentum distribution (PMD) and reconstruct the three-dimensional PMD by photoelectron tomography. Fourier analysis is used to decompose the measured PMD into the contributing FEVs with different rotational symmetries. The experimental results are supported by an analytical model and reproduced by numerical simulations, which provide insight into the role of resonant intermediate states. Our approach allows us to retrieve spectral information from the shaped laser field and the signatures of the MPI dynamics inscribed within the shaped FEVs., Comment: 12 pages, 6 figures

We discuss the single-quantum positron annihilation with a bound electron in the near threshold region. The angular distribution and the total cross section are considered. We obtain a simple analytical expression for the Coulomb potential and for the screened potential. It is worth noting that the obtained results for the screened potential are universal and independent of the explicit form of the atomic potential. It is shown that screening significantly increases the cross section. We also obtain the analogous results for bound-free $e^+e^-$ photoproduction., Comment: 9 pages, 3 figures

While quantum master equations (QMEs) are the primary workhorse in quantum information science, quantum optics, spectroscopy, and quantum thermodynamics, verifying complete positivity of the associated $N$-level quantum dynamical maps remains an outstanding challenge for $N\ge 3$. We address this challenge by establishing a direct mapping between the Liouvillian and Kossakowski matrices of an arbitrary Markovian QME. The mapping relies on the Moore-Penrose pseudo-inverse of a rectangular matrix composed of the structure constants of SU$(N)$. As an application, we establish complete positivity of the quantum optical Bloch-Redfield QME for a three-level V-system driven by incoherent light. Our approach makes it possible to test QMEs for complete positivity without solving them, and to restore complete positivity by keeping only non-negative eigenvalues of the Kossakowski matrix.

We study the phase between the oscillating (rf) excitation field and the detected (light) power modulation in scalar rf-driven optically pumped magnetometers (OPMs), in particular in the $M_x$ configuration. While the static dependence of the demodulation phase on the direction of the external static magnetic field vector can be largely overcome by aligning the oscillating rf field along the light propagation direction, we show that a dynamic (transient) phase response can appear under tilts of the magnetic field. We analytically solve the corresponding modified Bloch equation and obtain agreement with experimental observations in an $M_x$ magnetometer setup using a paraffin-coated Cs vapor cell. The results reveal fundamental limitations of $M_x$ magnetometers in terms of response time and accuracy, in particular when operated with active electronic feedback, e.g., using a phase-locked loop. Thus, the work is highly relevant in important magnetometry applications, where the direction of the quasi-static magnetic field of interest is not known \textit{a priori} and/or not constant over time, or in measurements, in which a large detection bandwidth is paramount. Such conditions are encountered, e.g., in geomagnetic surveying, in particular with mobile platforms., Comment: 11 pages, 9 figures

Entanglement plays a central role in fundamental tests and practical applications of quantum mechanics. Because entanglement is a feature unique to quantum systems, its observation provides evidence of the quantum nature on the system. Hence, if gravity can generate entanglement between quantum superpositions, this indicates that quantum amplitudes are field sources and gravity is a quantum phenomenon. I study the dual spin-one-half Stern-Gerlach interferometers proposed to test the quantum nature of gravity and show that the Pancharatnam phase displays features that provide a qualitative distinction between semiclassical and quantum signatures of gravity. The semiclassical evolution of the system is equivalent to that of a single interferometer (a two-level system) in an external field. In this case, a phase jump was observed, as expected from the geodesic rule, which dictates the noncyclic evolution of the superposition in the Bloch sphere. In contrast, in the quantum case, the two interferometers are coupled (two two-level systems) and I find that the phase is continuous., Comment: 4 pages, 3 figures

We present and theoretically demonstrate a method for generating helicity-selected near-circularly polarized attosecond pulses in mixed He-Ne gases using bichromatic counter-rotating circularly polarized (BCCP) fields. High-order harmonics driven by BCCP fields exhibit circular polarization for individual orders in the frequency domain, but adjacent orders have opposite helicities. By utilizing the He-Ne mixture, we select only one helical component of the harmonics, resulting in the generation of highly elliptically polarized attosecond pulses in the time domain. Our analyses based on the quantum-orbit theory and the strong field approximation further clarify that the polarization of attosecond pulses is governed by the interference mechanism of high-order harmonics emitted by He and Ne. This combination of BCCP fields and an atomic mixture which requires no alignment in experiments, significantly simplifies the generation of elliptically polarized harmonics dominated by one helical component, thereby paving the way for an efficient and robust method to generate bright attosecond pulses with large ellipticity.

Radiation pressure from Lyman-$\alpha$ (Ly$\alpha$) scattering is a potentially dominant form of early stellar feedback, capable of injecting up to $\sim 100 \, \times$ more momentum into the interstellar medium (ISM) than UV continuum radiation pressure and stellar winds. Ly$\alpha$ feedback is particularly strong in dust-poor environments and is thus especially important during the formation of the first stars and galaxies. As upcoming galaxy formation simulations incorporate Ly$\alpha$ feedback, it is crucial to consider processes that can limit it to avoid placing $\Lambda$CDM in apparent tension with recent \textit{JWST} observations indicating efficient star formation at Cosmic Dawn. We study Ly$\alpha$ feedback using a novel analytical Ly$\alpha$ radiative transfer solution that includes the effects of continuum absorption, gas velocity gradients, Ly$\alpha$ destruction (e.g. by $2p \rightarrow 2s$ transitions), ISM turbulence, and atomic recoil. We verify our solution for uniform clouds using extensive Monte Carlo radiative transfer (MCRT) tests, and resolve a previous discrepancy between analytical and MCRT predictions. We then study the sensitivity of Ly$\alpha$ feedback to the aforementioned effects. While these can dampen Ly$\alpha$ feedback by a factor $\lesssim \textrm{few} \times 10$, we find it remains $\gtrsim 5 - 100 \, \times$ stronger than direct radiation pressure and therefore cannot be neglected. We provide an accurate fit for the Ly$\alpha$ force multiplier $M_{\rm F}$, suitable for implementation in subgrid models for galaxy formation simulations. Our findings highlight the critical role of Ly$\alpha$ feedback in regulating star formation at Cosmic Dawn, and underscore the necessity of incorporating it into simulations to accurately model early galaxy evolution., Comment: Comments welcome! 42 pages (31 pages main text, the rest an extensive Appendix + references), 20 figures

In this paper, we use Clifford algebra $Cl_{2,0}$ to find the 2D orbit of Hydrogen electron under a Coulomb force and a perturbing circularly polarized electric field of light at angular frequency~$\omega$, which is turned on at time $t = 0$ via a unit step switch. Using a coordinate system co-rotating with the electron's unperturbed circular orbit at angular frequency $\omega_0$, we derive the complex nonlinear differential equation for the perturbation which is similar to but different from the Lorentz oscillator equation: (1) the acceleration terms are similar, (2) the damping term coefficient is not real but imaginary due to Coriolis force, (3) the term similar to spring force is not positive but negative, (3) there is a complex conjugate of the perturbation term which has no Lorentz analog but which makes the equation nonlinear, and (4) the angular frequency of the forcing term is not $\omega$ but $\omega - \omega_0$. By imposing that the position and velocity of the electron are continuous at time $t = 0$, we show that the orbit of the electron is a sum of five exponential Fourier terms with frequencies 0, $\omega_0$, $2\omega_0$, $(2\omega_0 - \omega)$, and $\omega$, which correspond to the eccentric, deferent, and three epicycles in Copernican astronomy. We show that at the three resonant light frequencies $0$, $\omega_0$, and $2\omega_0$, the electron's orbit is divergent, but approximates a Keplerian ellipse. At other light frequencies, the orbits are nondivergent with periods that are integer multiples of $\pi/\omega_0$ depending on the frequency ratio $\omega/\omega_0$. And as $\omega/\omega_0\rightarrow \pm\infty$, the orbit approaches the electron's unperturbed circular orbit., Comment: 50 pages, 200+ equations

Optically polarizable nitrogen-vacancy (NV) center in diamond enables the hyperpolarization of $^{13}$C nuclear spins at low magnetic field and room temperature. However, achieving a high level of polarization comparable to conventional dynamic nuclear polarization has remained challenging. Here we demonstrate that, at below 10 mT, a $^{13}$C polarization of 5 % can be obtained, equivalent to an enhancement ratio over $7 \times 10^6$. We used high-purity diamond with a low initial nitrogen concentration ($<$ 1 ppm), which also results in a long storage time exceeding 100 minutes. By aligning the magnetic field along [100], the number of NV spins participating in polarization transfer increases fourfold. We conducted a comprehensive optimization of field intensity and microwave (MW) frequency-sweep parameters for this field orientation. The optimum MW sweep width suggests that polarization transfer occurs primarily to bulk $^{13}$C spins through the integrated solid effect followed by nuclear spin diffusion., Comment: 6 pages, 4 figures

We exploit polarization self-rotation in atomic rubidium vapor to observe spontaneous symmetry breaking and bistability of polarization patterns. We pump the vapor cell with horizontally polarized light while the vertical polarization, which is initially in the vacuum state, is resonated in a ring cavity. Vacuum fluctuations in this mode experience cumulative gain due to the compound action of amplification due to the self-rotation and feedback through the resonator, eventually acquiring a macroscopic magnitude akin to an optical parametric oscillator. The randomness of these fluctuations results in a bistable, random macroscopic polarization pattern at the output. We propose utilizing this mechanism to simulate Ising-like interaction between multiple spatial modes and as a basis for a fully optical coherent Ising machine.

Optically trapped Rydberg atoms are a suitable platform to explore quantum many-body physics mediated by long-range atom--atom interactions that can be engineered through externally applied light fields. However, this approach is limited to dipole-allowed transitions and a spatial resolution of the order of the optical wavelength. Here, we theoretically investigate the interaction between free electrons and individual Rydberg atoms as an approach to induce nondipolar transitions with subnanometer spatial precision and a substantial degree of control over the final atomic states. We observe unity-order excitation probabilities produced by a single electron for suitably chosen combinations of electron energies and electron-beam distance to the atom. We further discuss electron--atom entanglement in combination with lateral shaping of the electron followed by postselection. Our results support free electrons as powerful tools to manipulate Rydberg atoms in previously inaccessible ways., Comment: 10 pages, 8 figures, 73 references

We demonstrate the interference of photons scattered from independent ensembles of warm atoms in atomic vapor. It employs finite temporal coherence of light scattered elastically in the forward and backward directions from Doppler-broadened atomic ensembles, such that photons with chaotic photon statistics from two opposite atomic velocity groups contribute to the same detection mode. While the random phase fluctuations of the scattered light caused by a large thermal motion prevent direct observability of the interference in the detected photon rate, the stable frequency difference between photons collected from scattering off counter-propagating laser beams provides strong periodic modulation of the photon coincidence rate with the period given by the detuning of the excitation laser from the atomic resonance. Presented interferometry promises direct applications in Doppler-free atomic and molecular spectroscopy., Comment: 8 pages, 4 figures

The energy levels and transition rates of promising laser-cooling candidate thorium anion Th^- have been experimentally obtained in the current work. Three new excited states between the bound-bound electric dipole (E1) transition of Th^- are observed now, and their energy levels are determined to be 1,847(13), 3,166.8(59) and 3,666(12) cm^{-1}, respectively. Meanwhile, the lifetime of the upper state of that E1 transition is experimentally determined to be 30(2) microseconds, about 3 times shorter than the previous calculated result 86 microseconds, which makes Th^- the most promising candidate for laser cooling of negative ions. Furthermore, the lifetimes of two other short-lived odd-parity excited states of Th^- are also measured to be 59(4) and 53(3)microseconds, respectively., Comment: 13 pages, 4 figures and 1 supplementary information

In muonic bound systems, the dominant radiative correction is due to vacuum polarization. Yet, for the interpretation of precision experiments, self-energy effects are also important. In turn, additional vacuum-polarization loops perturb the self-energy. Here, we show that combined self-energy vacuum-polarization effects can perturb the bound-state self-energy at the percent level in one-muon bound systems with nuclear charges Z = 1-6. We also update previous treatments of the corrections for muonic hydrogen, muonic deuterium, and muonic helium bound systems., Comment: 11 pages; RevTeX

Laser cooling is used to produce ultracold atoms and molecules for quantum science and precision measurement applications. Molecules are more challenging to cool than atoms due to their vibrational and rotational internal degrees of freedom. Molecular rotations lead to the use of type-II transitions ($F \geq F'$) for magneto-optical trapping (MOT). When typical red detuned light frequencies are applied to these transitions, sub-Doppler heating is induced, resulting in higher temperatures and larger molecular cloud sizes than realized with the type-I MOTs most often used with atoms. To improve type-II MOTs, Jarvis et al. PRL 120, 083201 (2018) proposed a blue-detuned MOT to be applied after initial cooling and capture with a red-detuned MOT. This was successfully implemented (Burau et al. PRL 130, 193401 (2023), Jorapur et al. PRL 132, 163403 (2024), Li et al. PRL 132, 233402 (2024)), realizing colder and denser molecular samples. Very recently, Hallas et al. arXiv:2404.03636 (2024) demonstrated a blue-detuned MOT with a "1+2" configuration that resulted in even stronger compression of the molecular cloud. Here, we describe and characterize theoretically the conveyor-belt mechanism that underlies this observed enhanced compression. We perform numerical simulations of the conveyor-belt mechanism using both stochastic Schr\"odinger equation (SSE) and optical Bloch equation (OBE) approaches. We investigate the conveyor-belt MOT characteristics in relation to laser parameters, g-factors, and the structure of the molecular system., Comment: 12 pages, 14 figures

We perform a theoretical study of vacuum polarization corrections to the hyperfine structure in many-electron atoms. Calculations are performed for systems of interest for precision atomic tests of fundamental physics belonging to the alkali-metal atoms and singly-ionized alkaline earths. The vacuum polarization is considered in the Uehling approximation, and we study the many-body effects core relaxation, core polarization, and valence-core correlations in the relativistic framework. We find that for s states, the relative vacuum polarization correction may be well-approximated by that for hydrogen-like ions, though for all other states account of many-body effects -- in particular, the polarization of the core -- is needed to obtain the correct sign and magnitude of the effect.

Measurements monitoring the inductive coupling between oscillating radio-frequency magnetic fields and objects of interest create versatile platforms for non-destructive testing. The benefits of ultra low frequency measurements, i.e., below 3 kHz, are sometimes outweighed by the fundamental and technical difficulties related to operating pick-up coils or other field sensors in this frequency range. Inductive measurements with the detection based on a two-photon interaction in rf atomic magnetometers address some of these issues, as the sensor gains an uplift in its operational frequency. The developments reported here integrate the fundamental and applied aspects of the two-photon process in magnetic induction measurements. In this paper, all spectral components of the two-photon process are identified, which result from the non-linear interactions between the rf fields and atoms. A method for the retrieval of the two-photon phase information, which is critical for inductive measurements, is also demonstrated. Furthermore, a self-compensation configuration is introduced, whereby high contrast measurements of defects can be obtained due to the sensor's insensitivity to the primary field, including using simplified instrumentation for this configuration by producing two rf fields with a single rf coil., Comment: 10 pages, 9 figures

Single-ion mass identification is important for atomic and nuclear physics experiments on ions produced with low yields. Cooling the ion to ultra-low temperatures by interacting with a laser-cooled ion will enhance the precision of the measurements. In this paper we present axial-common-mode frequency measurements of balanced and unbalanced Coulomb crystals from the Fourier transform of the fluorescence photons from a Doppler-cooling transition in calcium ions, after probing the ion/crystal with a 5-radiofrequency comb. A single ion non-destructively detected can be used for identification yielding a mass resolving power $m/\Delta m_\mathrm{FWHM}\approx 310$ from the axial common mode. This identification can be performed from a single measurement within times below one second., Comment: 6 pages, 4 figures

The upconversion process for the $Er^{3+}$ ion, when irradiated with IR photons at 980 nm, strongly depends upon the presence of the sensitizer $Yb^{3+}$ ions. There is a good correlation between the relative and absolute concentrations of the activator and sensitizer species and the intensities of the emission lines of the resulted visible spectrum. The ratios between emission intensities in the green band (510-580 nm) and red band (640-700 nm) (i.e., the spectral content) show similarities between different host crystals in which $Er^{3+}$ and $Yb^{3+}$ are embedded, which is an indication that, regardless of the crystalline medium of embedding, the dopant ions interact in some specific and similar ways. In order to reveal the mechanisms for the energy transfer between activator and sensitizer ions, one needs a model for the spatial distribution of these relative to one another, from which some statistical data, like crystal matrix average surrounding radii, could be inferred. Some models of cubic neighboring are presented for the relative concentration ratios of $Er^{3+}:Yb^{3+}$, respectively of 1:2, 1:4, and 1:8.

Entanglement in a many-particle system can enable measurement sensitivities beyond that achievable by only classical correlations. For an ensemble of spins, all-to-all interactions are known to reshape the quantum projection noise, leading to a form of entanglement known as spin squeezing. Here, we demonstrate spin squeezing with strictly short-range contact interactions. In particular, working with ultracold lithium atoms in optical lattices, we utilize superexchange interactions to realize a nearest-neighbor anisotropic Heisenberg model. We investigate the resulting quench dynamics from an initial product state in both one and three dimensions. In 1D, we observe $1.9^{+0.7}_{-0.5}$ dB of spin squeezing in quantitative agreement with theory. However, in 3D, we observe a maximum of $2.0^{+0.7}_{-0.7}$ dB of squeezing, over an order of magnitude smaller than that expected. We demonstrate that this discrepancy arises from the presence of a finite density of holes; both the motion of the holes as well as direct coupling between spin and density qualitatively alter the spin dynamics. Our observations point to the importance of understanding the complex interplay between motional and spin degrees of freedom in quantum simulators.

Neutral and singly ionized states of the Magnesium (Mg) are the origin of several spectral lines that are useful for solar diagnostic purposes. An important element in modeling such solar lines is collisional data of the Mg with different perturbers abundant in the Sun, specially with neutral hydrogen. This work aims at providing complete depolarization and polarization and population transfer data for Mg II due to collisions with hydrogen atoms. For this purpose, a general formalism is employed to calculate the needed rates of MgII due to collisions with hydrogen atoms. The resulting collisional rates are then employed to investigate the impact of collisions on the polarization of 25 Mg II lines relevant to solar applications by solving the governing statistical equilibrium equations within multi-level and multi-term atomic models. We find that the polarization of some Mg II lines starts to be sensitive to collisions for hydrogen density $n_H \!\gtrsim\!$ 10$^{14}$ cm$^{-3}$., Comment: Accepted for publication in Publications of the Astronomical Society of Australia (PASA). 8 pages, 6 tables, 5 figures

We discuss a platform for observing and controlling the interactions between atomic ions and a quantum gas of polar molecules in the ultracold regime. This approach is based on the combination of several recently developed methods in two so-far complementary research domains: ion-atom collisions and studies of ultracold polar molecules. In contrast to collisions between ions and ground-state atoms, which are dominated by losses due to three-body recombination (TBR) already at densities far below those typical for quantum degenerate ensembles, our proposal makes use of polar molecules, their rich level structure, and sensitivity to electric fields to design effective interaction potentials where ion-neutral TBR losses and molecule-molecule losses due to sticky collisions are strongly suppressed. This may enable access to the deep quantum regime of interaction with a broad range of applications including the potential formation of novel many-body self-bound states, quantum simulations, and quantum chemistry between polyatomic molecules., Comment: 17 pages, 9 figures

We measured the transition frequencies of the hyperfine components in the four lines (P(34) 39-0, R(36) 39-0, P(33) 39-0, and R(35) 39-0) of the B-X transitions of molecular iodine at 520.2 nm. The 520.2 nm laser was generated by wavelength-converting the output of a 1560.6 nm external-cavity diode laser using a dual-pitch periodically poled lithium niobate (PPLN) waveguide. The frequencies were measured by counting the heterodyne beats between the laser stabilized at the frequencies of the hyperfine components and a frequency comb synchronized with a hydrogen maser. We determined the transition frequencies of the a1 components with relative uncertainties of 1*10-11; the uncertainty was limited by the impurity of the molecular iodine in the cell. From the measured hyperfine splitting frequencies, we calculated the hyperfine constants of these four transitions to obtain the rotational dependence of the excited-state hyperfine constants.

We theoretically and computationally investigate the cooling of antihydrogen, $\bar{H}$, using optical molasses cooling. This updates the results in Ref. [1] to the current capabilities of the ALPHA experiment. Through Monte Carlo simulation, we show that $\bar{H}$s do not give the standard cooling even in an ideal optical molasses because of their small mass and large transition frequency. For optical molasses cooling in the ALPHA trap, the photons are constrained to travel in one direction only. It is only through the phase space mixing in the trap that cooling in all directions can be achieved. We explore the nontrivial role that laser intensity plays in the cooling. We also investigate the possibility for simultaneously cooling atoms in either of the trapped ground states.

Quantum simulation and metrology with atoms, ions, and molecules often rely on using light fields to manipulate their internal states. The absorbed momentum from the light fields can induce spin-orbit coupling and associated motional-induced (Doppler) dephasing, which may limit the coherence time available for metrology and simulation. We experimentally demonstrate the suppression of Doppler dephasing on a strontium optical clock transition by enabling atomic interactions through a shared mode in a high-finesse optical ring cavity. The interactions create a many-body energy gap that increases with atom number, suppressing motional dephasing when it surpasses the dephasing energy scale. This collective approach offers an alternative to traditional methods, like Lamb-Dicke confinement or M\"ossbauer spectroscopy, for advancing optical quantum sensors and simulations., Comment: Main Text with Supplementary Material, 8 pages, 4 figures

We report on the first deployment of a ytterbium (Yb) transportable optical lattice clock (TOLC), commercially shipping the clock 3,000 km from Boulder, Colorado to Washington DC. The system, composed of a rigidly mounted optical reference cavity, atomic physics package, and an optical frequency comb, fully realizes an independent frequency standard for comparisons in the optical and microwave domains. The shipped Yb TOLC was fully operational within 2 days of arrival, enabling frequency comparisons with rubidium (Rb) fountains at the United States Naval Observatory (USNO). To the best of our knowledge, this represents the first deployment of a fully independent TOLC, including the frequency comb, coherently uniting the optical stability of the Yb TOLC to the microwave output of the Rb fountain., Comment: 5 pages, 4 figures

We describe the design and operation of a high-stability Fabry-Perot cavity, for laser stabilization in cavity quantum-electrodynamics experiments. Our design is based on an inexpensive and readily available uniaxial carbon-fiber reinforced polymer tube spacer, featuring an ultra-low thermal expansion coefficient. As a result, our $136\mathrm{mm}$-long cavity, which has a finesse of ${5160}$, shows a coefficient of thermal expansion of $1.6 \times 10^{-6}~\mathrm{K}^{-1}$. Enclosing it in a hermetic chamber at room-pressure and using a simple temperature stabilization, we observe absolute frequency excursions over a full day below $50~\mathrm{MHz}$ for a laser operating at $446.785\mathrm{THz}$. The frequency stability is limited by the imperfect thermal isolation from the environment and can be corrected using a built-in piezo-electric actuator. In addition, we discuss a different variant of this design and identify future improvements. Our system provides a cost-effective and robust solution for transferring laser stability over different wavelengths, as well as for linewidth reduction or spectral filtering of CW laser sources for applications in quantum science., Comment: 5 pages, 4 figures

The studies of the upconversion response of RE ions in various hosts usually depict a static picture, whereas, at constant illumination, the upconverted emission is also constant. We discovered here that, at least in the case of $Y_2O_3$ doped with $Er^{3+}:Yb^{3+}$, this is not the case. At constant illuminated power, the upconversion emission is not only fluctuating, but it varies in a manner which seems to be a superposition of intensity waves with different frequencies. We present here the results of the measurements we've performed on $Y_2O_3$ with $1\%Er^{3+}-2\%Yb^{3+}$. The origin of this effect remain to be established but it shows that the energy transfers during the upconversion are an interplay of absorption-saturation-emission-relaxation processes., Comment: 6 pages, 8 figures, data presented at Nanobiomat june-2023 conference

The efficiencies and form of the upconversion spectra of rare earth ions embedded in crystalline matrices strongly depend upon the phonon dispersion of these, since the inter-level energy transition probabilities are influenced by the phonon energies. The aim of this study is to show a novel method of influencing the phonon energy values of crystalline $BaY_2O_4$ and, by this, to finely tune the spectra of any rare earth ion as a dopant of it. We used $Er^{3+}$ sensitized by $Yb^{3+}$ as dopants, but the same method can be generalized for other kind of rare earth ions. As such, we synthesized $BaY_2O_4$ and $BaY_2O_4:MgO (BaY_2MgO_5)$ ceramics having as activator-sensitizer pairs the $Er^{3+}$ 1% and $Yb^{3+}$ 2% relative to the substituted $Y^{3+}$. Firstly, we synthesized the mix of precursor metallic oxides by the citrate-gel method, pressed these into pellets, and sintered them to obtain doped crystalline ceramic samples. The ceramic samples were illuminated with 976 nm from a laser diode, and the resulting upconversion spectra of $Er^{3+}$ were measured. $BaY_2O_4$ and $BaY_2O_4:MgO (BaY_2MgO_5)$ have almost the same XRD signature, showing that the crystal unit cells have the same parameters but they differ in the phononic energies due to the presence of the additional MgO. Comparing the results of these two extreme cases $BaY_2O_4$ vs. $BaY_2O_4:MgO (BaY_2MgO_5)$ reveals that the presence of the MgO modifies the upconversion response. So, this study fulfills two goals: First, it reveals the structure of the undocumented $BaY_2O_4:MgO (BaY_2MgO_5)$ and shows how it is based on the crystal structure of $BaY_2O_4$ with $Mg^{2+}$ ions occupying the unit cell interstitions. Secondly, it suggests a method of tuning the phononic energies of $BaY_2O_4$ and, as a consequence, the upconversion response of $Er^{3+}$., Comment: 9 pages, 6 figures

We report the experimental realization of a conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) $\mu$m and a peak number density of $3.6(5) \times 10^{10}$ cm$^{-3}$, a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to $2.6 \times 10^4$ trapped molecules at a temperature of 14(2) $\mu$K with a peak phase-space density of $\sim 2.4 \times 10^{-6}$. This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules., Comment: 7 pages; 4 figures; typos corrected