Papers

The accurate description of electron correlations remains a major challenge in atomic calculations. In order to perform accurate calculations, it is necessary to consider the various types of electron correlations what often leads to extensive CSF expansions. This work presents further development of the method based on the second-order perturbation theory to identify the most significant CSFs that have the greatest influence on core-valence, core, core-core and valence-valence correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1) and G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 3, 139-161 (2024) (https://doi.org/10.3952/physics.2024.64.3.1)]. The method is extended to include additionally valence-valence electron correlations. It can be applied for an atom or ion with any number of valence electrons for calculation of energy spectra and other properties. Meanwhile, the correlations which can not be included according to perturbation theory are accounted for in a regular way. The use of the developed method allows a significant reduction of CSFs especially for complex atoms and ions. As an example of its application, the atomic calculations of the energy structure for Se~III ion are presented.

Grasp package is based on the relativistic configuration interaction in which accurate calculations, accounting for valence, valence-valence, core-valence, core, and core-core electron correlations, often rely on massive CSF expansions. This paper presents further development of the method based on the second-order perturbation theory for finding the most important CSFs that have the greatest influence on the core-valence, core, and core-core correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-Valence Correlations, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3) and G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core Correlations, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1)]. In this extension, the perturbation theory accounts for electron core-valence, core, and core-core correlations where an atom or ion has any number of valence electrons for calculation of energy spectra and other properties. Meanwhile the rest of the correlations are accounted for in a traditional way. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for calculations of the energy structure and E1 transition properties of Fe XV ion.

Understanding how optical orbital angular momentum (OAM) is transferred to matter requires treating recoil and translational motion alongside the internal electronic dynamics. We develop a center-of-mass-resolved theory of one-photon ionization of hydrogen by a monochromatic Laguerre–Gaussian beam and show that the Bessel-vortex photoelectron predicted in fixed-target models is a preparation-dependent limit. For a sharply defined atomic center-of-mass momentum, the recoil records the photon-cone azimuth, and tracing over it generally destroys the coherence required for a pure electron vortex. In the small-transverse-retardation regime, the optical OAM is transferred predominantly to the center-of-mass motion and hence, in the laboratory frame, to the proton. Finite-retardation corrections redistribute angular momentum between center-of-mass and relative motion, while an additional correlation contribution to the electron and proton angular momenta can be tuned through the spatial uncertainty of the atomic center of mass. These results reveal atomic recoil as a key element of OAM transfer in photoionization.

The paper presents a further development of the method G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order of Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-Valence Correlations, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), based on a combination of the relativistic configuration interaction method and on the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form. In this extension the perturbation theory accounts for both electron core-valence and core correlations when an atom or ion has any number of valence electrons meanwhile relativistic configuration interaction accounts for the rest of correlations. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for energy structure calculation of Fe XV ion.

We present a feasibility study demonstrating how recent advances in quantum-sensing technologies can facilitate stringent comparisons between theoretical predictions and experimental measurements of contact-free transitions in muonic atoms. Such comparisons can probe previously unexplored regions of the parameter space governing spin-independent muon-proton interactions and disentangle the extraction of fundamental constants from searches for physics beyond the Standard Model.

We formulate Hartree–Fock as a density-matrix renormalization group (DMRG) sweep of a single Slater determinant, assuming a density–density electron–electron interaction. We compress the occupied state and long-range interaction separately, reducing each sweep step to a small local Fock problem. Exchange is retained throughout. Uniform antiferromagnetic hydrogen chains provide an almost ideal setting for this approach, while retaining the Coulomb interaction and its $1/r$ tail. We initialize and converge a chain of 100,000 electrons in 1.8 million spatial basis functions in about two hours on a 64-GB Mac mini, using less than a third of its memory. The work per sweep is nearly proportional to chain length, and the number of sweeps needed for convergence changes little from 1000 to 100,000 atoms. DMRG's compression of states and environments thus makes large HF calculations with long-range Hartree and exchange practical on an ordinary desktop computer.

We report the absolute frequency measurement of the $4s$ $ ^{2}S_{1/2}\leftrightarrow 3d$ $^{2}D_{5/2}$ $^{40}$Ca$^{+}$ clock transition with respect to the SI second. To perform this measurement, a link between our laboratory in Innsbruck and the clocks realizing the Coordinated Universal Time at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig was installed and characterized using the Global Navigation Satellite System GNSS. The comparison between our clock and the ones at PTB was done using the Precise Point Positioning technique. After the evaluation of the systematic shifts, the measured transition frequency is 411 042 129 776 401.2$\pm$0.6 Hz with a fractional uncertainty of 1.5 $\times$ 10$^{-15}$. The stability of the clock measurements was also corroborated by comparing two different calcium ion clock experiments, which share the clock laser source at our institute. Furthermore, after careful evaluation of the trap-drive induced ac magnetic fields, we estimate ac Zeeman shifts on the $D_{5/2}$ sublevels and reevaluate the Landé g-factor of the $3d$ $^{2}D_{5/2}$ level to be g$_{5/2}= 1.200329(1)$.

We present a theoretical study of interactions between Rydberg macrodimers, molecular bound states of Rydberg atoms, and the largest known neutral homonuclear diatomic molecules. Accounting for the large number of molecular interaction channels from four interacting Rydberg atoms, we show that macrodimer-macrodimer interactions are anisotropic and similar in strength and range to atomic-state Rydberg interactions. Our analysis reveals the presence of two-atom, three-atom, and four-atom contributions in the bimolecular system, and elucidates how these interactions are rooted in the underlying atomic Rydberg-state couplings. Our calculations of the excitation blockade between macrodimers are in reasonable agreement with experimentally observed signals, and pave the way for the exploration of optically controlled collective quantum dynamics in molecular systems.

The General Relativistic Atomic Structure package [Grasp2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2019), DOI: 10.1016/j.cpc.2018.10.032], is based on multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction (RCI) methods for energy structure calculations. Atomic state function used in the program is built from the set of configuration state functions (CSFs). The valence-valence, core-valence and core-core correlations are explicitly included through expansions over CSFs in RCI. We present a combination of RCI and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in irreducible tensorial form to account for electron core-valence correlations when an atom or ion has any number of valence electrons. This newly developed method, which offers two ways of use, allows a significant reduction of the CSF space for complex atoms and ions. We also demonstrate how the method and program works for energy structure calculation of Cl III element.

We propose a state-dependent diffusion model for strongly driven thermal-atom spectra. Starting from the trajectory-dependent internal-state evolution of individual atoms, we derive a closed spatial equation for the local density-matrix field using a velocity-moment expansion. Measurements of an $^{85}$Rb atomic-filter transmission spectrum agree well with the model up to a maximum Gaussian peak intensity of $1.27\times10^{3}$ W/cm$^2$, approaching six orders of magnitude above the $^{85}$Rb D2-line saturation intensity. Counterintuitively, the model reveals an anomalous optical-pumping pathway in which intense light transfers atoms from nominally dark states into bright states. Hyperfine Paschen–Back splitting selectively enhances this anomalous pathway while suppressing conventional optical pumping, allowing the filter to maintain approximately 97$\%$ transmission at the highest intensity studied. This work provides a framework for controlling strongly driven atomic ensembles and designing saturation-resistant atomic optical devices.

The influence of the diagonal Born–Oppenheimer correction (DBOC) on the electronic structure of light diatomic molecules subjected to strong magnetic fields is investigated. H$_2$, HeH$^+$, and LiH are considered, using both the Hartree–Fock (HF) approximation and configuration interaction with single and double excitations (CISD). The analysis covers magnetic field strengths up to $B_\parallel = 0.2$ a.u. ($4.7\times10^{4}$~T), relevant to astrophysical conditions near magnetic white dwarfs. Although the correction noticeably shifts total electronic energies, it varies smoothly with internuclear distance and depends only weakly on the field, so that it enters the vibrational transition frequencies as a nearly field-independent offset, shifting the fundamental interval by about $1$~cm$^{-1}$ and the higher levels by up to $15$ cm$^{-1}$. These shifts exceed the $0.1$–$2.0$ cm$^{-1}$ accuracy currently attainable for molecular lines in the atmospheres of magnetic white dwarfs. Comparison of HF and CISD results shows that electron correlation has a non-negligible effect on the DBOC, most pronounced for the strongly ionic LiH bond.

We investigate the generation and characterization of higher-order harmonics in the probe-laser absorption arising from nonlinear interactions in an electromagnetically induced transparency (EIT) ladder system involving Rydberg states and driven by two microwave fields in the heterodyne configuration. We characterize the amplitude and phase of the generated harmonics as a function of the relative frequency and phase of the applied microwave fields. The phase of the $n^{\mathrm{th}}$ harmonic follows the relation $\phi_n=n\phi$, demonstrating phase multiplication and suggesting that higher-order harmonics may offer an enhanced phase response for phase-sensitive measurements. We further characterize the harmonic amplitudes and bandwidths and find that the measured bandwidths are significantly larger than the intrinsic Rydberg-state linewidth, consistent with power broadening under the experimental conditions. The experimental observations are supported by density-matrix calculations, which reproduce the key features of the measured harmonic response.

The hyperfine structure that the nitrogen-vacancy (NV) center in diamond has with its nitrogen nucleus is of immense importance for quantum sensing and quantum computing. Current methods of calculating the NV hyperfine energy eigenvalues and eigenstates with respect to an axial magnetic field - i.e., calculating the NV Breit-Rabi formula - resort to numerical methods and analytic approximations. Here we provide an exact, closed-form expression to the NV hyperfine energy eigenvalues and eigenstates for both the nitrogen-14 and -15 cases.

Accurate relativistic multiconfiguration calculations of correlation-sensitive atomic properties are often limited by the rapid growth of configuration state function expansions when a single common orthonormal orbital basis is used. In this work, a partitioned correlation function interaction (PCFI) method is developed for relativistic atomic structure calculations. The correlation space is separated into physically motivated components, which are optimized independently with correlation-specific orbital sets. The interactions between configuration spaces constructed from mutually non-orthogonal orbital sets are evaluated using biorthonormal transformations, allowing different correlation effects to be combined in a compact final interaction calculation. Full details of the method are provided, emphasizing its connection to configuration state function generators (CSFGs), which significantly reduce the time required to construct the Hamiltonian matrix in conventional RCI calculations. Applications to the neutral Li, Be, and Al atoms are presented for energy levels, mass shifts and hyperfine structure constants. Compared with conventional relativistic configuration interaction (RCI) calculations that rely on a single orbital basis, PCFI produces more compact and predictable convergence patterns for both total and transition energies. It also offers greater stability for correlation-sensitive properties such as specific mass shifts and hyperfine constants. By using property-oriented partitions, PCFI captures core-polarization effects more effectively, thereby reducing the oscillatory behavior often observed in standard RCI approaches. Overall, the results demonstrate that PCFI provides a promising and computationally efficient framework for accurate relativistic multiconfiguration calculations of correlation-dependent atomic properties.

We derive a unified set of scaling equations for Bose-Einstein condensates in time-dependent harmonic traps, connecting the weakly interacting Gaussian regime to the strongly interacting Thomas-Fermi regime. The exact Gross-Pitaevskii ground-state density is taken as a fixed profile in rescaled coordinates, with its dynamics described by three scaling factors corresponding to compression or expansion along the three spatial directions. The resulting equations contain no adjustable parameter, since their coefficients are determined once from the initial state. They recover analytically the Gaussian variational and Thomas-Fermi scaling equations in their respective limits and satisfy an axis-resolved virial theorem. The approach also yields the global phase and the low-lying collective-mode frequencies of the condensate. We benchmark the model against three-dimensional Gross-Pitaevskii simulations and against measured expansion energies. The model remains accurate across all interaction regimes, in strongly anisotropic traps, and along time-dependent sequences including a relatively fast quench, up to the point where the underlying frozen-profile hypothesis, shared by all three scaling approaches, breaks down.

In epsilon-near-zero (ENZ) materials, the vanishing real linear permittivity results in the leading-order contribution to the displacement field being nonlinear in the electric field, making conventional canonical quantization approaches highly non-trivial. Existing treatments generally quantize the linear modes first and introduce nonlinear interactions subsequently, an ordering that becomes inadequate in the ENZ regime. Here, we provide, to our knowledge, the first effective single-excitation quantization in which the near-zero linear response, leading nonlinearity, and loss jointly determine the elementary excitation. Using a solvable microscopic atomic system as a theoretical scaffold, we find that this excitation is a polariton: a dressed quasiparticle with partly field and partly material excitations whose coefficients can be parameterized by macroscopic susceptibilities. While this work considers a leading-order $\chi^{(3)}$ nonlinearity, the framework could be generalized to include other nonlinear corrections, including a controllable second-order susceptibility $\chi^{(2)}$ and systematic higher-order contributions $\chi^{(n)}$, $n>2$. Our findings pave the way toward practical applications in quantum photonics, such as single-photon non-demolition detection, by leveraging the strong nonlinearities intrinsic to zero-index materials.

We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

A correlated multichannel computation of the generalized oscillator-strength density for electrons scattering off randomly oriented molecular hydrogen at the internuclear separation of 1.4 $a_0$ is being presented. The numerical procedure features a novel free-boundary method based on configuration interaction of ionic orbitals expanded in B splines using prolate-spheroidal coordinates. Satisfactory agreement between the present and both experimental as well as other theoretical results has been found, thus providing a view on the Bethe surface for energy transfers up to of 558 eV. The systematic and robust convergence behavior of the method further allowed for assessing the validity of the binary-encounter approximation, providing a confirmation of experimentally determined Compton defects for H$_2$ using a single consistent theoretical description. Overall, the present findings are expected to be helpful for calculating highly accurate energy-loss spectra for fast electrons passing through and ionizing molecular hydrogen gas or its isotopologues.

Accurate calibration of electromagnetic field strength in the terahertz (THz) frequency regime remains challenging due to the limited availability of SI-traceable field sensors. Here we demonstrate SI-traceable calibration and performance benchmarking of a commercial photomixer-based THz transmitter-receiver system operating near 204 GHz using Rydberg electric-field sensing in a thermal atomic vapor. The THz electric field is extracted from the Autler-Townes (AT) effect of the cesium $17D_{5/2}\rightarrow18P_{3/2}$ Rydberg transition. We measure the strength of AT-split lines as a function of THz detuning from resonance to find the on-resonant Rabi frequency, which, together with atomic transition dipole moments and fundamental constants, yields the THz electric field. The atomically measured field calibrates the photomixer transmitter field and power, while simultaneous measurements with a commercial InGaAs photomixer receiver calibrate the receiver's current-to-field responsivity and convert its current-noise floor into an absolute noise-equivalent THz electric-field sensitivity. Our study demonstrates that Rydberg atomic sensors provide a practical method for SI-traceable calibration and benchmarking of THz transmitter and receiver systems, and for the establishment of a quantitative link between state-of-the-art and absolute atom-based THz sensors.

Atomic ionization in superintense x-ray fields is studied through numerical solutions of the time-dependent Schrödinger equation including nondipole corrections. The role of the Coulomb potential of the atomic core in the nondipole regime is analyzed for a linearly polarized laser field. In the considered high-frequency and high-intensity stabilization regime, the photoelectron spectra are dominated by a near-zero-energy structure, while above-threshold ionization peaks are suppressed. Two sub-regimes in the nondipole case are identified based on the scaling of the Coulomb momentum transfer, when the Coulomb effect during the interaction with the laser field is either significant or minor. The Coulomb influenced regime sets in within the realm of relatively low field strengths, high laser frequencies, and long pulse durations. An intuitive model explaining the distinct features in the photoelectron momentum distributions and the Coulomb effect scaling is provided.

We report on the study of the impact of laser beam profile inhomogeneities on the acceleration measurements of a quantum accelerometer in space. This sensor uses a low ballistic expansion source based on delta-kick collimated Bose-Einstein condensates, and an interferometer configuration based on a sequence of Raman double diffraction beamsplitters, best suited to the microgravity environment. We characterize both phase and intensity fluctuations in terms of power spectral densities and calculate their impact on the interferometer phase, averaging over all trajectories of the atoms, via numerical simulations based on randomly drawn laser profiles as well as via analytical treatments. We show that high quality optics, such as those realized for gravitational wave detectors, combined with large initial size atomic sources, will allow to reduce interferometer phase bias and fluctuations to the order of 1 mrad corresponding to accelerations in the low 10 -12 m.s -2 range.

Cryogenic buffer-gas cells are widely used to produce cold molecular beams, but the microscopic dynamics governing beam formation remain challenging to model. Here we present fully kinetic simulations of a cryogenic buffer-gas cell using the Direct Simulation Monte Carlo method implemented in the PICLas framework, treating the buffer gas and ablated molecules within a single unified model. We capture characteristic features of cryogenic buffer-gas sources, including plume cooling, directed transport toward the aperture, and the formation of a slow molecular beam, while also resolving energy transfer from the hot ablation plume to the helium buffer gas that is inaccessible to existing approaches relying on the background-gas approximation. Our results demonstrate that fully kinetic simulations can provide detailed insights into buffer-gas cell dynamics and open a route toward a systematic optimization of such sources.

Molecular species that are suitable for direct laser cooling are typically considered lost or destroyed if they collide with an ambient temperature vacuum wall. Here, we study surface collisions with aluminum monofluoride (AlF), a laser-coolable molecule that survives this process with unusually high probability. We detect the outgoing AlF molecules from a single wall collision via Doppler-sensitive laser-induced fluorescence spectroscopy, using incoming supersonic (pulsed) and thermochemical (continuous) molecular beams. The angular, velocity and rovibrational level distributions of the outgoing molecules show near-complete thermalisation to the wall in a single collision event. We determine an upper limit to the surface residence time of about 5$~\mu$s, and by monitoring the decay in density of pulses of molecules loaded into a small storage volume, we deduce the surface sticking probability for different materials. For a siloxane-coated metallic surface, the sticking probability of AlF is about 0.015, allowing us to accumulate molecules from the thermochemical source into an ambient temperature storage vessel at densities near $10^{8}~$cm$^{-3}$. This provides a route to compact, portable traps for neutral molecules.

Non-Markovian dynamics offer a new route towards engineering non-equilibrium matter, where memory and feedback act as programmable resources for controlling order in time. Here we report the realization of a non-Markovian spin oscillator in a hot vapour $^{129}$Xe-Cs co-magnetometer with programmable feedback delay and gain. By tuning these parameters, we observe a hierarchy of dynamical phases, including time-crystalline response, nonlinear bifurcations, and frequency-comb formation. The measured spectra and phase boundaries are captured by linear stability analysis of delayed Bloch equations, revealing these phenomena as different manifestations of the same memory-induced instability structure. These results establish time-delayed feedback as a powerful strategy for controlling non-equilibrium phases, enabling quantum sensing, frequency referencing, and synchronization within a single spin-based platform.

We realize narrow-linewidth magneto-optical traps of $^{46}$Ti, $^{48}$Ti and $^{50}$Ti atoms based on a 1040 nm-wavelength transition, cooling atoms to a minimum temperature in one dimension of $T_z=990(20)$ nK and a three-dimensional temperature of $T_\mathrm{3D}=1.28(7)$ $\mu$K. Atoms are pre-cooled in a broad-line magneto-optical trap and then transferred with about 25% efficiency to the narrow-line trap. We operate the narrow-line trap in two stages over 85 ms. First, a single cooling beam, blue-detuned from the narrow-linewidth atomic resonance, optically pumps and traps the atoms on a two-dimensional surface where the Zeeman shift from the applied spherical quadrupole magnetic field brings the light nearly to resonance. Second, four additional beams, counter-propagating in the transverse directions, cool and compress the atoms in all dimensions. The high magnetic moment of the laser cooling state makes the dynamics of the narrow-line titanium trap similar to those of other magnetic atoms. We measure the lifetime of the excited state of the transition to be $\tau=8.2(9)$ $\mu$s, indicating a transition linewidth of $\gamma/2\pi =20(2)$ kHz, and also measure isotope shifts on the narrow-line transition. We use Stern-Gerlach separation on the ultracold Ti gas to measure the $m_J$-distribution in the narrow-line magneto-optical trap, finding over 98% of the atoms in the stretched spin state.

We propose and numerically demonstrate a deterministic protocol for preparing and tailoring topological defects in two-dimensional single-species Coulomb crystals confined in radio-frequency traps. In conventional finite-rate quenches through the linear-to-zigzag transition, defects form stochastically from independently chosen broken-symmetry domains, and the quench rate controls the resulting domain structure. We instead use an initial three-dimensional helix structure and planarize it into a deterministic defected state. We demonstrate that the number and approximate axial positions of kinks are encoded by the projected nodes of the initial helix. We find that selected helices can remain on metastable finite-winding branches during planarization and yield reproducible single- or multi-kink states, even in the adiabatic limit. Using the quench rate as an additional control parameter substantially enlarges the set of precursor helices that result in defected states, as a fast planarization can prevent reordering during the quench and freeze in the pre-existing domain pattern. After planarization, the survival and mutual interaction of the defects are governed by their effective Peierls–Nabarro potential landscape. By numerically isolating the interaction energy for the two defect types, we find that the interaction of extended kinks is attractive over the investigated parameter range, while odd kinks exhibit a short-range repulsive barrier tunable by the anisotropy of the trapping potential $\alpha$. Finally, we introduce an experimentally motivated post-selection scheme in which $\alpha$ is used to selectively destabilize, annihilate, or convert targeted defects. Our results provide a route to deterministic single- and multi-kink preparation in single-species Coulomb crystals, enabling controlled studies of defect interactions, transport, and nanofriction.

Quantum sensors, like optical lattice clocks, undergo a continuous development from lab-based towards mobile systems. A key aspect in the miniaturization of the experimental setups is the development of compact atom sources. Conventional atom sources for alkaline-earth-like elements consist of a high-power oven and a six-beam magneto-optical trap (MOT) inside of vacuum chamber with extensive flanges, viewports and electrical feedthroughs. Here we present a highly compact vacuum package utilizing key technologies for future quantum sensor systems: A chip-based low-power atomic oven, a planar grating MOT chip, and a miniaturized vacuum pump all held inside an additively manufactured titanium vacuum chamber, featuring custom-sized vacuum flanges. In this miniaturized setup, spanning a volume of only 750 ml, we trap up to $10^5$ Sr atoms in a MOT, requiring an oven heating power below 1 W.

Context. Scattering polarization in the Sr I 4607 Å line is a key diagnostic for small-scale, unresolved magnetic fields in the quiet solar photosphere, inaccessible to Zeeman-based techniques. The complete frequency redistribution (CRD) limit is commonly used to model this line, but its validity and impact on magnetic sensitivity have not been systematically investigated. This is timely given new facilities observing this line with unprecedented accuracy, and future synoptic programs targeting long-term quiet-Sun magnetism. Aims. We assess the CRD limit against the general partial frequency redistribution (PRD) description of scattering for the Sr I 4607 Å polarization, focusing on its magnetic sensitivity via the Hanle effect. Methods. We solved the non-LTE radiative transfer problem for polarized radiation in a semi-empirical 1D plane-parallel static atmosphere, with CRD and PRD scattering, across magnetic field configurations relevant for Hanle diagnostics. Results. For small-scale unresolved fields, where the field acts only via Hanle depolarization of Q/I, CRD and PRD emergent profiles and Hanle sensitivity are essentially identical. For deterministic fields, CRD remains accurate when polarization signals exceed about 0.3%; for weaker signals, PRD effects can appreciably affect the emergent profiles. Conclusions. CRD is adequate for modeling Sr I 4607 Å scattering polarization in the vast majority of observationally relevant cases; PRD effects matter only for weak polarization signals.

Understanding how thermal fluctuations modify or suppress quantum-enhanced sensing is a central problem in quantum metrology. Closely related questions arise in quantum thermodynamics, particularly regarding the relation between the work induced by a signal and the information acquired by a sensor. Here, we establish general relations among the sensitivity of thermal quantum states, as quantified by different quantum Fisher information metrics, their temperature dependence, and the work induced by a unitary signal. We further show that, at high temperature, all monotone QFI metrics coincide to leading order with a universal quantity that can be expressed as the variance of a simple observable and itself defines a lesser-known QFI metric. This emergent uniqueness is reminiscent of the uniqueness of classical Fisher information in information geometry. In continuous-variable systems, the infinite-temperature limit is finite and generically non-zero for quadratic Gaussian signals, while it diverges for higher-degree signals. Remarkably, for any purely quadratic signal generator, the infinite-temperature QFI is at least twice the zero-temperature SLD QFI or, equivalently, at least eight times the ground-state variance of the generator. Consequently, the Cramér–Rao lower bound on the estimator variance is reduced by at least a factor of two. We illustrate these results using harmonic chains of bosonic modes relevant to trapped-ion platforms and quantum field-theoretic models.

We find through direct, time-domain measurement of trapped $\mathrm{Yb}^+$ ions that the excited ${}^3[11/2]_{9/2}^o$ state has a collision-free lifetime of 17.8(6) min, long enough for use in atomic clockwork or quantum information processing. We locate and benchmark a broad “repump” transition at $701\, \mathrm{nm}$ that readily transfers population back into the Doppler cooling cycle with the ground state, which may allow for quantum nondemolition measurement of sub-structure in the metastable manifold. Using a bi-stable Coulomb-crystal manometer, we find that the collisional quenching of this metastable ${}^3[11/2]_{9/2}^o$ manifold by background gas is more efficient than for ${}^2\mathrm{F}_{7/2}^o$, but nonetheless we observe an average lifetime exceeding 10 minutes at the base pressure of our apparatus.