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Physics Physics Atomic Physics

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Thursday 13 August

Atomic Physics

Precision calculations of the hyperfine constants and isotope and isomer shifts in low-lying states of 229Th3+

S.G. Porsev and M.S. Safronova

We present high-precision calculations of the hyperfine constants, isotope shift, and isomer shift in low-lying states of Th3+ relevant to spectroscopy of the 229Th nuclear isomer. The removal energy and hyperfine constants are calculated using a relativistic coupled-cluster method including single, double, and triple excitations, demonstrating the importance of higher-order correlation effects. The isotope shift of the 5f_5/2 -7s transition is evaluated using both the CI+MBPT and CI+all-order methods, providing an estimate of the theoretical uncertainty. We find that the isotope shift is dominated by the field shift, with the mass shift contributing negligibly. Combining the calculated field-shift coefficient with the measured difference in the nuclear mean-square charge radii of the ground and isomeric states, we predict the 7s isomer shift to be (Delta E^(m,g))= 0.9(1) GHz. These results provide benchmark atomic data for Th3+ and support ongoing precision spectroscopy of 229Th and the development of a nuclear clock.
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Atomic Physics

Strong-field Herman-Kluk propagator method for high-harmonic generation in molecules

Phi-Hung Tran, Hao Quan Truong, R. Esteban Goetz et al. (+1 more)

We extend our recently developed semiclassical strong-field Herman-Kluk (SFHK) propagator method to calculate high-order harmonic generation (HHG) in diatomic molecules driven by few-cycle intense laser fields. On the example of applications to H2 and N2, we show that our method, based on a combination of the Herman-Kluk propagator and the strong-field approximation, can provide very accurate results for both HHG yield and phase, nearly identical to those from the exact numerical solutions of the time-dependent Schrodinger equation. To compare with experimental measurements, averaging over molecular orientations must be performed. Here we demonstrate a distinct and powerful advantage of the SFHK, as its Monte Carlo sampling for the integration over the alignment distribution can be efficiently combined with the integration over the initial momentum distributions of electron wave-packet right after the tunnel exit. Therefore, the total number of trajectories used for the alignment-averaged HHG spectrum does not increase much compared to that for a single fixed alignment. Similar to atomic targets, the main computational task in the SFHK is to solve the classical Hamiltonian equations for the active electron in the combined electron-target ion potential and electron-laser interaction. The motion of the center of each electron wave packet in the continuum, represented by a coherent state, is governed by an independent classical trajectory so that the computation can be parallelized very efficiently.
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All authors Phi-Hung Tran, Hao Quan Truong, R. Esteban Goetz, Anh-Thu Le

Atomic Physics

Dual-species alkali and alkaline-earth-like optical tweezer arrays via interferometrically aligned high-NA objectives

K. Weber, M. McMaster, M. Anderson et al. (+7 more)

We have developed a dual-species optical tweezer array apparatus combining $^{87}\text{Rb}$ and $^{174}\text{Yb}$ atoms with a permanent hybrid Twyman-Green–Fizeau interferometer, which provides precision co-alignment of two opposing 0.6-numerical aperture (NA) objectives and the high NA beams that pass through the system. This technique is extensible to other tweezer platforms operating at high numerical aperture across widely-separated wavelengths. Here we present simultaneous trapping and single-site resolved imaging of both species in co-aligned tweezer arrays with $^{87}\text{Rb}$ confined at $840\ \rm{nm}$ and $^{174}\text{Yb}$ at $532\ \rm{nm}$. The platform provides a foundation for hybrid quantum register operation, including mid-circuit measurements and asymmetric intra- and inter-species interactions, greatly expanding the capabilities of neutral atom arrays.
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All authors K. Weber, M. McMaster, M. Anderson, J. Tu, S. E. Eustice, N. A. Schine, I. B. Spielman, J. V. Porto, S. L. Rolston, S. Subhankar

Atomic Physics

Critical Microwave Mach-Zehnder-Type Interferometry with Dual-LO Rydberg Atoms

Jun-Rong Chen, Guo-Qing Qin, Peng-Fu Liang et al. (+7 more)

High-precision phase measurement of microwave fields underpins a wide range of applications, including wireless communications, distributed radar, plasma diagnostics, and antenna metrology. Existing Rydberg-atom-based approaches, however, often face trade-offs among phase resolution, measurement range, and system complexity. Here we demonstrate a Rydberg-atom-based microwave Mach-Zehnder-type interferometer using a dual-local-oscillator configuration. The two local oscillators establish two coherent interferometric pathways in the Rydberg medium. Their coherent mixing with the signal field produces an interferometric intermediate-frequency output governed by a phase-to-intensity transfer characteristic that enables critical-point enhancement. This scheme supports direct phase retrieval with a resolution exceeding $0.1^\circ$ and unambiguous full $360^\circ$ phase coverage with the reconfigurable dual-LO architecture. Moreover, near the critical interference point, the system exhibits a sharply enhanced phase-to-amplitude transduction, where weak amplitude variations are converted into pronounced phase responses, yielding a sensitivity enhancement exceeding 25 dB. Besides, the same interferometric transfer mechanism enables microwave propagation-distance and polarization metrology, achieving a propagation-distance precision below 20 $\mu$m at 5.7 GHz together with a polarization-angle resolution exceeding $0.1^\circ$. This approach eliminates the need for complex optical configurations and lock-in detection, providing a simple, scalable, and reconfigurable Mach-Zehnder-type quantum microwave interferometry framework for multifunctional high-precision microwave metrology.
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All authors Jun-Rong Chen, Guo-Qing Qin, Peng-Fu Liang, He Hao, Ming-Min Zhao, Ling-Qiang Meng, Gui-Lan Li, Min-Jian Zhao, Bin-Bin Wei, Hao Tian

Atomic Physics · Cross-listed from quant-ph

Shots-to-Approximate-Solution Scaling in Neutral-Atom Quantum Optimization

Junwoo Jung and Jaewook Ahn

Whether neutral-atom quantum optimization protocols exhibit genuine concentration toward low-energy solution structure remains an open question. Here, we introduce a shots-to-approximate-solution metric, STS(r), where r denotes the approximation ratio, and evaluate it using postprocessed outputs modeled by a degeneracy-weighted shell distribution governed by a single effective parameter, $\beta$, that quantifies concentration toward near-optimal independent sets. To extract the genuine concentration effect in the quantum data, we apply identical postprocessing to both experimental bitstrings and randomly generated bitstrings with matched excitation density, thereby constructing an excitation-matched random baseline. Experiments on programmable Rydberg-atom arrays with system sizes up to 125 sites show that quantum annealing consistently exceeds the random baseline, demonstrating enhanced concentration toward low-energy solution structure beyond what can be attributed solely to excitation density. The results further reveal two distinct target-dependent regimes. For near-exact targets with $r \approx 1$, the required shot count grows exponentially with system size and is reduced at the same exponential level by quantum annealing within the shell-model description. By contrast, for relaxed targets, the shot cost becomes effectively constant, and the corresponding quantum enhancement diminishes, with the classical postprocessing heuristic alone reaching the target in order-unity attempts. Together, these results establish an operational method for quantifying quantum optimization performance and clarify the regimes under which quantum approaches can yield practical benefits.
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Atomic Physics

Precision Positronium Spectroscopy as a Test of the Helium Ionization Energy Anomaly

J. Pérez-Ríos and D. B. Cassidy

Precise measurements of the metastable helium (1s)(2s)$\,^3S_1$ ionization energy have revealed a 9$\sigma$ discrepancy with QED theory that persists in isotopic measurements, suggesting a leptophilic bosonic interaction as a possible explanation. A subsequent investigation of such interactions has concluded that only a scalar boson interaction is consistent with the He observations. Taking this as a starting point, we derive the response of positronium energy levels to the corresponding finite-range Yukawa potential, using exact hydrogenic matrix elements and a numerical helium calculation. Across the viable mediator-mass range of 0-800 eV, the He anomaly interpreted in this way implies a positronium 1$^3$S$_1 \rightarrow 2^3$S$_1$ shift ranging from 0.250-0.850 MHz, and a 2S-ionization shift of 0.14-0.21 MHz. We discuss the feasibility of observing these shifts experimentally.
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Atomic Physics

Predissociation dynamics of charged long-range Rydberg molecules

Neethu Abraham, P. Giannakeas and Matthew T. Eiles

We investigate predissociation in homonuclear ($^{87}$Rb$^*$$^{87}$Rb$^+$) and heteronuclear ($^{87}$Rb$^*$$^{7}$Li$^+$) long-range Rydberg atom-ion molecules. Owing to their micron-scale bond lengths, these dissociate on time scales far removed from those of more tightly bound diatomic molecules. We employ the eigenchannel $R$-matrix method to compute predissociation rates for a broad range of principal quantum numbers $n$. The rates depend strongly on the mass, but more remarkably display a rapid and periodic variation as a function of $n$ as well as within a single vibrational ladder. A semiclassical Landau-Zener-Stückelberg analysis reveals that Stückelberg interference governs the decay process and produces the observed variation in the molecular lifetime. Although the heavy mass of the homonuclear Rb molecule constrains its predissociation rates to a sub-kHz level, the lighter molecule $^{87}$Rb$^*$$^{7}$Li$^+$ dissociates on time scales competitive with radiative and collisional decay. This can enable in situ study of non-adiabatic decay via ion microscopy.
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Wednesday 12 August

Atomic Physics · Cross-listed from cond-mat.mtrl-sci

Mechanisms of Nanoscroll Formation and Particle Encapsulation in Janus MXenes

Sasan Rezaee, Fatemeh Mohammad Dezashibi, Ould el Moctar et al. (+1 more)

Morphology transfer of 2D Janus MXenes into nanoscrolls unlocks unusual properties. Although a scalable synthesis route has been experimentally verified, the atomistic mechanism underlying nanoscroll formation remains poorly understood. We use large-scale reactive molecular dynamics simulations, validated against density functional theory (DFT) and experimental structural and elastic properties, to investigate stability and quantify the driving forces and geometry governing nanoscroll formation in three Janus MXenes, (Tx)Ti2C(Ty), where (Tx) and (Ty) denote the bottom and top surface terminations among bare (-b), -O, and -OH. Both square and infinitely wide flakes with lengths ranging from 10 to over 120 nm are simulated. We find that 1-7% lattice-induced strain generates a bending moment in these structures. The sheet scrolls, curves, or forms a nanotube depending on the resulting curvature and initial sheet size. For MXenes with an initial length of 120 nm, multiwalled nanoscrolls form with interlayer distances of around 0.7 nm and inner diameters of about 7 nm for (O)Ti2C(OH) and (b)Ti2C(OH), whereas (b)Ti2C(O) instead produces a much larger interlayer distance of around 1.7 nm and an inner diameter exceeding 20 nm. We show that spontaneous scrolling of a Janus MXene in the presence of an anchored nanoparticle produces a core@shell composite, in which the particle locally deforms the nanoscroll and widens the interlayer channels. This locally tunable, enlarged interlayer spacing offers a promising design route for MXene-based energy-storage electrodes. However, our simulations reveal H2 gas release during encapsulation, which promotes nanobubble formation that can reduce battery life.
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All authors Sasan Rezaee, Fatemeh Mohammad Dezashibi, Ould el Moctar, Hossein Darban

Atomic Physics · Cross-listed from cond-mat.mtrl-sci

Energy-Dependent Dechanneling in Cu: Insights from Monte Carlo Channeling Simulations

Przemyslaw Jozwik, Cyprian Mieszczynski, Renata Ratajczak et al. (+1 more)

Ion channeling and backscattering techniques are powerful tools for studying crystal lattice disorders and defect structures in crystalline materials. However, the accurate interpretation of channeling phenomena necessitates the utilization of simulation models that account for the intricate interactions between point defects, dislocations, and extended defect clusters. The present paper introduces a Monte Carlo method that reproduces experimental spectra over a wide range of analyzing beam energies and enables quantitative identification of defect types and distributions. The simulations reveal characteristic energy dependencies that distinguish point defects from extended defects, offering a novel perspective on disturbances caused, for example, by ion implantation in metals and semiconductors. To this end, the McChasy code has been developed as a flexible and accessible tool for scientists, enabling the modeling of various crystal systems, including complex semiconductors, multilayer epitaxial films, and oxide crystals. The program's integration of experimental data on ion channeling with defect modeling establishes a robust framework for defect analysis in materials science. The present article expounds upon the simulation capabilities of the program by reproducing the characteristic "elbows" in channeling spectra that were previously observed in experiments conducted on Cu crystals.
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All authors Przemyslaw Jozwik, Cyprian Mieszczynski, Renata Ratajczak, Andrzej Turos

Tuesday 11 August

Atomic Physics

Compact Actively-Shielded Magnetic Field Coil within Mu-Metal Shields for ACME Electric Dipole Moment Measurements

S. Liu, M. Watts, C. Diver et al. (+13 more)

A system of actively-shielded coils and mu-metal shields is devised, constructed and shown to provide the stable and spatially uniform magnetic field needed for the ACME III electron electric dipole moment (eEDM) measurement. Two layers of current-carrying coils, enclosed within three layers of ferromagnetic shields, produce a field that varies by less than 1 nT (10 $\uG$) within the 1 m $\times$ 4.2 cm $\times$ 4.2 cm interior volume in which a beam of ThO molecules are probed as they precess. The demountable shields are constructed from rectangular mu-metal plates. The largest, with a mass of 19 kg and an area of 2.18 m $\times$ 0.75 m, is easily carried by two people and just fits within a large available annealing oven. The assembly design facilitates low-stress mounting and handling to suppress changes in the magnetic properties of the mu metal, and also provides modular access to apparatus within the coils for maintenance and upgrades. The nearly static external ambient field is reduced within the shielded precession volume by up to a factor of $10^5$. During the magnetic field reversals that ACME uses to suppress systematic uncertainties, the “actively-shielded” coil largely cancels out its external fringing field to minimize the magnetization of the mu metal. Even though the shields are only 10 cm outside the coils, shield degaussing after every magnetic field reversal is not required. The non-reversing residual field stays below 1 nT for up to 17 hours when the field is reversed every 30 seconds, for example. The measured performance, compared to the previous generation ACME II apparatus, suggests that the magnetic-field-related systematic uncertainties for ACME III will be smaller by an estimated factor of 40 despite a five times longer precession volume and the use of three magnetic shielding layers rather than five.
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All authors S. Liu, M. Watts, C. Diver, D. G. Ang, C. Meisenhelder, X. Fan, B. Hao, D. Lascar, A. Hiramoto, T. Masuda, P. Hu, Z. Han, X. Wu, D. DeMille, J. M. Doyle, G. Gabrielse

Atomic Physics · Cross-listed from nucl-th

Laser spectroscopy illuminates the $N=32$ shell closure

Tim E. Lellinger, Liss V. Rodriguez, Patrick Muller et al. (+29 more)

Atomic nuclei are strongly correlated quantum many-body systems, and how their shell structure evolves with increasing neutron excess remains a central open question in nuclear physics. Calcium isotopes are an ideal testing ground: alongside the traditional magic numbers $N=20,28$, new shell closures have been proposed at $N=32,34$ ($^{52,54}\mathrm{Ca}$). While the charge radius rises rapidly towards $N=32$, further moments and radii in the isotopic chain have remained inaccessible due to the low production yield of a few ions per second. Here we apply a highly sensitive collinear laser spectroscopy technique, which reveals a strikingly simple behaviour: adding one neutron to $^{52}\mathrm{Ca}$ yields a pure single-particle magnetic dipole moment in $^{53}\mathrm{Ca}$, while the charge-radius slope towards $^{54}\mathrm{Ca}$ exceeds that towards $^{52}\mathrm{Ca}$. This provides strong evidence for a robust $N=32$ shell closure and stringently constrains nuclear structure models.
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All authors Tim E. Lellinger, Liss V. Rodriguez, Patrick Muller, Osama Ahmad, Mark L. Bissell, Klaus Blaum, Emily Burbach, Bradley Cheal, Till Fabritz, Ronald F. Garcia Ruiz, Matthias Heinz, Jack Hughes, Phillip Imgram, Kristian Konig, Yinshen Liu, Bernhard Maass, Edward N. Matthews, Takayuki Miyagi, Witold Nazarewicz, Rainer Neugart, Gerda Neyens, Lukas Nies, Wilfried Nortershauser, Julian Palmes, Peter Plattner, Paul-Gerhard Reinhard, Laura Renth, Rodolfo Sanchez, Achim Schwenk, Julien Spahn, Xiaofei Yang, Deyan T. Yordanov

Atomic Physics · Cross-listed from nucl-ex

First measurement of kaonic deuterium X-ray transitions

Massimiliano Bazzi, Francesco Clozza, Carlo Guaraldo et al. (+38 more)

The study of the strong interaction among hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the experimentally inaccessible $K^-n$ interaction at threshold energy. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DA$\Phi$NE collider. We determine the strong-interaction shift and width of the $1s$ level to be $\varepsilon_{1s}=-810.9\pm24.5\,(\mathrm{stat})\pm2.1\,(\mathrm{syst})\,\mathrm{eV}$ and $\Gamma_{1s}=812\pm97\,(\mathrm{stat})\pm33\,(\mathrm{syst})\,\mathrm{eV}$, respectively. This measurement constitutes the most precise experimental determination of the $K^-d$ strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent $K^-N$ scattering lengths, with implications for the description of the nature of the first predicted hadronic molecular state, the $\Lambda(1405)$, and neutron-rich matter.
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All authors Massimiliano Bazzi, Francesco Clozza, Carlo Guaraldo, Mihail Antoniu Iliescu, Alessandro Scordo, Francesco Sgaramella, Diana Sirghi, Florin Sirghi, Johann Zmeskal, Leonardo Abbene, Claude Amsler, Francesco Artibani, Giacomo Borghi, Damir Bosnar, Mario Bragadireanu, Antonino Buttacavoli, Marco Carminati, Alberto Clozza, Luca De Paolis, Raffaele Del Grande, Kamil Dulski, Carlo Fiorini, Ivica Friščić, Masa Iwasaki, Aleksander Khreptak, Simone Manti, Johann Marton, Catia Milardi, Pawel Moskal, Fabrizio Napolitano, Hiroaki Ohnishi, Kristian Piscicchia, Fabio Principato, Michał Silarski, Magdalena Skurzok, Antonio Spallone, Kairo Toho, Marlene Tüchler, Oton Vazquez Doce, Eberhard Widmann, Catalina Curceanu

Atomic Physics · Cross-listed from quant-ph

Helium-like ions $(Z,e,e)$ in Lagrange Mesh method, interpolating the highly-accurate energy spectra vs. Z

H Olivares-Pilon, JC Lopez-Vieyra and AV Turbiner

Two alternative approaches for studying Helium-like atomic ions in non-relativistic quantum mechanics are proposed: (I) a numerical approach, based on the Lagrange-mesh method which can easily reach up to 14-15 significant digits in the energy spectrum for any nuclear charge $Z$ with modest CPU time in single processor mode and (II) a highly-accurate, few-parametric interpolation formula for the energies vs. $Z$. The interpolation formula of general nature is proposed, it can be applied to the energies of any excited state of the helium-like sequence. It is based on matching the $1/Z$-expansion at large $Z$ and the Puiseux expansion with integer and half-integer powers around the so-called second critical charge $Z_B$, introduced by F and D Stillinger (1969, 1974), confirmed by the present authors in 2019 for the ground state $1^1 S$, then revisited here, and extended to the excited states in the present work. For example for the first two spin-singlet $1^1 S$, $2^1 S$ and the first two spin-triplet $2^3 S$, $3^3 S$ states this interpolation formula with nine free parameters can reach an accuracy of 10-14 significant digits (s.d.) in the energies for any physically-relevant nuclear charge $Z$, giving absolute accuracy at large $Z$. Many results are obtained for the first time.
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Monday 10 August

Atomic Physics · Cross-listed from quant-ph

A Quantum Coherence Microscope in the Hubbard Regime

Lin Su, Michal Szurek, Alec Douglas et al. (+2 more)

Quantum coherence underlies collective quantum phenomena and emerging quantum technologies. Quantum gas microscopes have transformed quantum simulation by providing projective snapshots of many-body states with single-atom resolution, but spatially resolved measurements of off-diagonal correlations have remained elusive. Here, using the Talbot effect, we introduce a quantum coherence microscope that maps off-diagonal correlations onto site-resolved density signals with near-single-site resolution. We use this technique to locally probe the superfluid-Mott transition in a layer of a three-dimensional optical lattice and to measure coherence beyond nearest neighbors in an engineered potential landscape. By mapping off-diagonal correlations onto density signals through controlled Talbot evolution, this work opens new possibilities for accessing observables beyond the density basis through tailored matter-wave evolution and recapture.
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All authors Lin Su, Michal Szurek, Alec Douglas, Ceren B. Dag, Markus Greiner

Atomic Physics

Resonant photoionization dynamics during optical trapping of lithium atoms

K. Foster, S. Majumdar and D. Fischer

Photoionization induced by trapping and auxiliary laser fields is an inherent feature of many laser-cooling and optical trapping experiments, yet its microscopic dynamics are rarely investigated directly. In this work, we employ a reaction microscope implementing an event-by-event photoionization time retrieval technique to extend momentum-resolved photoelectron spectroscopy to continuous-wave laser–atom interactions. We investigate low-intensity multicolor photoionization of laser-cooled lithium atoms confined in an all-optical trap. Complete three-dimensional electron momentum distributions and kinetic-energy spectra recorded for different laser wavelengths and polarization configurations identify resonant excitation of the $5p$ and $5f$ states and reveal an additional ionization channel following spontaneous decay from the $5f$ to the $4d$ state. A pronounced polarization dependence of the photoionization yield is explained by magnetic-sublevel selection rules and the coherent interference of different virtual excitation pathways. These results demonstrate that reaction microscopy combined with event-by-event time reconstruction provides a powerful approach for investigating microscopic electronic dynamics in laser-cooled atomic systems and offers new insight into photoionization processes occurring during optical trapping.
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Atomic Physics

Stroboscopic Raman Spectroscopy of Atom Optics in Quasi-Bragg Regime

Joel Gomes Baptista, Louis Pagot, Sébastien Merlet et al. (+2 more)

Quasi-Bragg regime is a good compromise for large-momentum-transfer atom interferometry, allowing for scaling up the interferometric area, while constraining the population of unwanted states. Separation of momentum states via standard time of flight methods, however, can be challenging when using laser-cooled atoms, rather than ultracold atoms with sub-recoil velocity distribution. To overcome this limit, we use Raman spectroscopy for stroboscopic sampling of the atomic state evolution in momentum space during the interrogating laser pulses. We quantitatively characterize atom optics employing two-photon (2___k) and multi-photon (6___k) Bragg transitions, the latter being optionally enhanced with optimal control protocol. We closely match the observed dynamics of the atomic state with simulations. Finally, we perform momentum spectroscopy of the output states in a 6___k Bragg gravimeter.
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All authors Joel Gomes Baptista, Louis Pagot, Sébastien Merlet, Leonid Sidorenkov, Franck Pereira Dos Santos

Sunday 9 August

Atomic Physics

Rotational laser spectroscopy of the $X^1\Sigma_g^+\rightarrow B^1\Pi_u$ transition of $\text{Rb}_2$ molecule in a supersonic beam: As good as it gets

David Rodríguez Fernández, Manuel Alejandro Lefrán Torres, Jaime Javier Borges Márquez et al. (+6 more)

High-resolution laser spectroscopy of the $^{85}\mathrm{Rb}_2$, $^{85}\mathrm{Rb}^{87}\mathrm{Rb}$, and $^{87}\mathrm{Rb}_2$ isotopologues has been performed in a supersonic molecular beam using a continuous-wave (cw) tunable diode laser. A total of 958 rovibronic transitions were recorded up to $7~\mathrm{cm}^{-1}$ below the vibrational band heads of the $X^1\Sigma_g^+(v''=0)\rightarrow B^1\Pi_u(v'=1,2)$ and $X^1\Sigma_g^+(v''=1)\rightarrow B^1\Pi_u(v'=1)$ bands, with a spectral resolution of $3.3\times10^{-4}$~cm$^{-1}$. Although restricted to the $v'=1$ and $v'=2$ vibrational levels of the excited $B^1\Pi_u$ state, the measurements extend previous work by Amiot and Vergès [Chemical Physics Letters 274, 91 (1997)] through substantially higher resolution and dense low-$J'$ rotational data for all three isotopologues. A global least-squares analysis combining the new and published data, yields improved Dunham coefficients for the excited $B^1\Pi_u$ state, significantly refines rotational and rovibrational coupling constants. In addition, the $\Lambda$-doubling constants of $B^1\Pi_u$ state were determined for the three isotopologues.
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All authors David Rodríguez Fernández, Manuel Alejandro Lefrán Torres, Jaime Javier Borges Márquez, Marcos Roberto Cardoso, Amrendra Pandey, Romain Vexiau, Olivier Dulieu, Nadia Bouloufa-Maafa, Luis Gustavo Marcassa

Atomic Physics

Multiple ionization and charge equilibration in slow, multiply charged $\mathrm{Ar^{q+} + Ar}$ collision studied via L-MM Auger-Meitner electron spectroscopy

Rohit Tyagi, L. C. Tribedi, M. K. Harbola et al. (+1 more)

We report energy and angle resolved absolute cross section measurements for LMM Auger-Meitner electron emission following collisions of hundred keV protons and $\mathrm{Ar^{3+/6+}}$ ion with an atomic Ar target. The double differential cross section spectra show distinct contributions from target and projectile Auger-Meitner decay. The projectile emission exhibits the expected Doppler shift for various angles of electron emission, and the measured peak energies are in excellent agreement with kinematic calculations. The energy integrated cross sections show isotropic angular distribution for target and projectile species in their respective rest frames. The Auger-Meitner peak energy for target as well as projectile emission show significant difference in comparison to the characteristic L-MM Auger-Meitner energy peak from atomic Ar. The experimental measurements have been complimented with development of a theoretical model to calculate the transition probabilities corresponding to prominent L-MM Auger-Meitner transitions in neutral and multiply charged Ar atom. Comparison between measured and calculated spectra shows that the measured emission peak at approximately 150 eV originates from Auger-Meitner decay of $\mathrm{Ar^{4+}}$ ions. The peak energies for target and projectile emission are found to be equal, independent of the initial projectile charge state. This indicates that the decay occurs following extensive multiple ionization, charge exchange processes resulting in charge-state equilibration of the collision partners. The results demonstrate that collision-induced electronic rearrangement strongly modifies the Auger-Meitner spectra and provide evidence for an equilibrium target-projectile charge state in low-energy $\mathrm{Ar^{q+} - Ar}$ collisions.
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All authors Rohit Tyagi, L. C. Tribedi, M. K. Harbola, A. H. Kelkar

Saturday 8 August

Atomic Physics

Thorium-229 in its Highest Charge States: Single-Ion Nuclear Clocks for Tests of Fundamental Interactions

C. Brandau, P. Micke, I. Hartl et al. (+6 more)

The prospects and the implementation of single-ion nuclear clocks of $^{229}$Th$^{q+}$ ions in their highest charge states $q=90, \ldots, 87$ are discussed. Highly-ionized-thorium clocks are ideal for tests of fundamental interactions since the ions are elementary quantum systems composed of only a few building blocks. Two cases of $^{229}$Th$^{q+}$ clocks excel: a) one-electron $^{229}$Th$^{89+}$ that combines two nuclear-clock transitions in the VUV with hyperfine IR atomic-clock transitions, and, b) fully ionized $^{229}$Th$^{90+}$ which constitutes the prototype of a nuclear clock, one without any electrons. We evaluate the feasibility of such clocks by means of quantum logic spectroscopy (QLS) in linear Paul traps. Due to its universal nature, the QLS approach allows for systematic clock comparisons using different charge states as well as different spectroscopy transitions on the same experimental platform. A valuable asset towards single-ion $^{229}$Th$^{q+}$ clocks is the process of nuclear hyperfine mixing that enables the tunability of the natural linewidth of the clock transition over more than five orders of magnitude by changing the charge state.
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All authors C. Brandau, P. Micke, I. Hartl, C. M. Heyl, P. Indelicato, Yu. A. Litvinov, R. X. Schüssler, M. Vogel, Th. Stöhlker

Atomic Physics · Cross-listed from quant-ph

Bell nonlocality with directly generated telecom-band spin-photon entanglement

Dong-Yu Huang, Jian Wang, Xiao-Long Zhou et al. (+8 more)

Quantum nonlocality, typically revealed through entanglement distribution across quantum networks, is a cornerstone of quantum information science. Long-distance distribution of entanglement requires the information carrier, i.e. flying photons, to operate in the minimum-loss telecom band of optical fiber. While extensive efforts have been devoted to the direct generation of entanglement between C-band telecom photons and various stationary spins, the verification of quantum nonlocality remains an outstanding challenge. Here, utilizing a dipole transition in rubidium atoms with a wavelength of 1530 nm and a cavity-assisted protocol, we achieve resonant excitation and direct emission of C-band telecom photons from a single atom, generating spin-photon entanglement with a measured Bell state fidelity exceeding 91.4%. We then verify Bell nonlocality by observing a Bell inequality violation of 2.455(77) > 2 using this high-quality entangled pair. These results extend the wavelength of a single-atom quantum emitter to the telecom C-band, achieving sufficiently high-fidelity spin-photon entanglement to finally verify Bell nonlocality. This work thereby provides a promising building block for a large-scale atom-based quantum network capable of distributed quantum metrology and long-distance quantum communication.
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All authors Dong-Yu Huang, Jian Wang, Xiao-Long Zhou, Ze-Min Shen, Si-Jian He, Qi-Yang Huang, Yi-Jia Liu, Yu-Shu Chen, Quan Jiang, Chuan-Feng Li, Guang-Can Guo

Atomic Physics · Cross-listed from cond-mat.quant-gas

Coherent Control of Domain-Wall Transport in an Ultracold Bose Gas

O. Farion, M. Pourzand and J. M. McGuirk

Domain walls are carriers of spin transport whose controlled manipulation underlies a wide range of spintronic and information-processing technologies. Here we demonstrate tunable domain-wall transport in a weakly interacting nondegenerate ultracold Bose gas. We initialize a three-domain pseudo-spin-1/2 texture and observe spontaneous propagation of long-lived domain walls driven by exchange-mediated spin currents. By varying the orientation of the spin domains, we control the balance of spin currents across the walls and thereby tune their trajectories, including reversals of the initial direction of motion. Measurements reveal a crossover from an exchange-stabilized regime, in which coherent spin-exchange collisions suppress wall motion, to a diffusion-dominated regime characterized by rapid transport at thermal velocities. Numerical solutions of a quantum Boltzmann equation reproduce the observed dynamics and identify transverse phase gradients as an important control parameter governing domain-wall propagation. These results establish coherence and phase engineering as tools for programming spin transport in ultracold gases and provide a route toward controllable domain-wall dynamics in atomtronic systems.
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Friday 7 August

Atomic Physics

Probing $P,T$-Symmetry Violation with Optically Trapped Asymmetric Top Molecules

Yuxi Yang, Arian Jadbabaie, Lukáš Félix Pašteka et al. (+3 more)

Searches for $P,T$-violating electromagnetic moments are among the most sensitive probes of physics beyond the Standard Model. Extending beyond current limits will benefit from molecules with fully controllable orientation at low electric fields, long coherence times, and laser coolability—all offered by asymmetric top molecules (ATMs). Exploiting the intrinsic rotational $K$-doubling in ATMs and the associated long-lived ($T_1 \gtrsim 10$ s) parity doublets afforded by $C_{2v}$ symmetry and nuclear-spin statistics, these species combine large electric polarizability with long coherence times in modest laboratory fields. We study alkaline-earth(-like) monoamides, $\mathcal{M}$–NH$_2$ ($\mathcal{M}$ = Ca, Sr, Ba, Yb, Ra), which possess favorable electronic structure for laser cooling. We perform ab initio calculations of fine and hyperfine constants, identifying the importance of relativistic effects in the spin-rotation tensor. An effective Hamiltonian then models the rotational and hyperfine structure of the vibronic ground state, quantifying electron electric dipole moment (EDM) sensitivities and identifying feasible measurement schemes. We compute the effect of external fields and identify engineered clock transitions that suppress sensitivity to external perturbations while retaining strong EDM sensitivity, and characterize the magic trapping conditions that null differential light shifts in an optical trap. Under these conditions we project a statistical electron-EDM sensitivity over an order of magnitude beyond current best experimental limits, with further gains available from increased molecule number and coherence time. Our results establish asymmetric top molecules as a tunable platform for sensitive symmetry-violation measurements with long coherence times.
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All authors Yuxi Yang, Arian Jadbabaie, Lukáš Félix Pašteka, I. Agustín Aucar, Rob G. E. Timmermans, Nicholas R. Hutzler

Atomic Physics · Cross-listed from hep-ph

Testing Antimatter Couplings with Spectroscopy

Joerg Jaeckel and Lucas Puetter

We investigate how scalar-mediated potentials with Lorentz-violating couplings to Standard Model fermions affect spectroscopic observables in atoms and highly charged ions. Suitable combinations of an ordinary scalar and a time-like component of a Lorentz violating vector coupling allow for a split into "matter" and "antimatter" couplings, at least in the non-relativistic limit. By considering hydrogen and antihydrogen spectra, we access both matter and antimatter couplings. While relativistic effects alone lift degeneracies in ordinary hydrogen, providing indirect access to antimatter couplings, comparisons with antihydrogen measurements lead to significantly improved sensitivity to the antimatter couplings. In highly charged ions, enhanced relativistic effects further amplify the sensitivity, compensating for reduced experimental precision and larger theoretical uncertainties. We obtain the strongest bounds to date for scalar masses $m_\phi \gtrsim 400\:\mathrm{keV}$. For comparison, we estimate astrophysical constraints on the same parameter space, providing strong bounds even on antimatter couplings, despite stars being predominantly composed of matter.
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Atomic Physics · Cross-listed from hep-ph

Optimal Calibration-Free Observable for the Nucleon-Coupling Ratio in a Dual-Alkali Comagnetometer for Dark Matter Searches

Yossi Rosenzweig, Yevgeny Kats, Eli Sarid et al. (+3 more)

A dual-alkali single-cell $^{87}$Rb-$^{39}$K-$^{3}$He comagnetometer can read an axion-like dark matter signal through two optical rotation channels, encoding the ratio $\mathcal{R}=\xi_n/\xi_p$ of the field's neutron and proton spin couplings in their relative response. The inter-species phase difference $\Delta\varphi$ has been proposed as a calibration-free readout that is sensitive to $\mathcal{R}$. Treating the extraction of $\mathcal{R}$ as a statistical estimation problem, we show that the estimate of $\mathcal{R}$ depends on the two channels only through their complex ratio, which splits into $\Delta\varphi$ and an amplitude ratio, of which only $\Delta\varphi$ is insensitive to the relative gain and hence calibration free. For our choice of comagnetometer parameters, above $\sim\!100$ Hz the phase difference alone captures most of the coupling-ratio information. At lower frequencies $\Delta\varphi$ is no longer near-sufficient. Below $\sim\!40$ Hz, the amplitude ratio would improve the precision on $\mathcal{R}$ by a factor of $\gtrsim2$. Recovering that information, however, requires the relative gain to be known sufficiently accurately, so $\Delta\varphi$ remains the robust observable even where it is not the most informative one.
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All authors Yossi Rosenzweig, Yevgeny Kats, Eli Sarid, Menachem Givon, Yonathan Japha, Ron Folman

Atomic Physics

Observation of $\Pi$-symmetry ultralong-range Rydberg molecules

Matthew T. Eiles, Aleksandr Zaitsev, Dominik Dorer et al. (+5 more)

We observe weakly-bound $\Pi$-symmetry electronic states in the spectroscopy of $^{87}$Rb$(nP_{3/2})$+$^{87}$Rb($5S_{1/2}$) ultralong-range Rydberg molecules. We detect these molecules in Rydberg states having principal quantum number $13\le n \le 16$. Their $\Pi$-state character is unambiguously identified via their observed multiplet structure: the $2F+1$ magnetic sublevels of the ground-state rubidium atom separate, as in the Zeeman effect, because of the spin-spin coupling between the Rydberg and valence electrons. We find a rapid decrease in the molecular binding energy $\propto (n-\mu_{P_{3/2}})^{-11}$, where $\mu_{P_{3/2}}$ is the quantum defect, indicating that the low-$n$ regime of Rydberg states is ideally suited for studies of $\Pi$-symmetry molecules. Our observations are in good agreement with Green's function-based calculations for $14\le n\le 16$, with poorer agreement for $n=13$ hinting at the beginning of a breakdown of the Fermi pseudopotential approach at low $n$.
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All authors Matthew T. Eiles, Aleksandr Zaitsev, Dominik Dorer, Shinsuke Haze, Markus Deiß, S. Efe Gürleyen, Chris H. Greene, Johannes Hecker Denschlag

Atomic Physics · Cross-listed from cond-mat.quant-gas

Phase-Noise-Induced Heating in Optical Lattices

Jean Paul Nohra, Cyprien Daix, Joris Verstraten et al. (+5 more)

We experimentally and theoretically study the origin of heating in optical lattices by disentangling the respective roles of intensity and phase noise depending on the lattice parameters. While intensity noise is widely identified as a major limiting factor, we show that phase noise can become the dominant heating source, especially for light atoms and deep optical lattices. We provide a simple theoretical framework to predict the phase-noise-induced heating from the power spectral density of the laser phase noise, which can be measured experimentally. We show that such predictions can accurately reproduce the measured heating rates of lithium-6 atoms in a triangular lattice. Our approach is readily generalized to other lattice geometries and atomic species.
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All authors Jean Paul Nohra, Cyprien Daix, Joris Verstraten, Maxime Dixmerias, Tim de Jongh, Bruno Peaudecerf, Fabrice Gerbier, Tarik Yefsah

Atomic Physics

Quantum sensing of radiofrequency fields using cold Rydberg atoms in a super-molasses trap

Romain Granier, Anthony El Bekai, Miguel Angel Cifuentes Marín et al. (+12 more)

We demonstrate the quantum sensing of radiofrequency fields based on cold Rydberg atoms in a super-molasses trap, without the need for magnetic coils. Our approach combines the metrological advantages of cold atoms with a metal-free dielectric sensor head minimizing perturbations to the electromagnetic environment, a feature that was previously restricted to vapor-cell-based devices. Moreover, the absence of inductive loads allows to rapidly alternate between the cooling phase and the Rydberg excitation, leading to trap-loss spectroscopy signals one order of magnitude narrower than for conventional magneto-optical traps. This enables self-calibrated microwave power measurements with an unprecedented dynamic range of 43dB, opening the door to new perspectives of applications in calibration measurements. We also report a scale factor linearity better than 1%, the absence of drifts over several tens of minutes leading to a 3$\mu$V/cm resolution, and the possibility to retrieve the ellipticity of the applied microwave field. By demonstrating a cold-atom metrological platform in a compact dielectric sensor head, this work paves the way for new applications in the field of radiofrequency measurements with Rydberg atoms, and in other fields of quantum sensing based on cold atoms such as magnetometry, gravimetry or inertial navigation.
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All authors Romain Granier, Anthony El Bekai, Miguel Angel Cifuentes Marín, Cédric Blanchard, Nassim Zahzam, Yannick Bidel, Alexandre Bresson, Vilius Atkočius, Chester Camm, Florence Concepcion, Konstantinos Karakostas, Matt Himsworth, Alexander Jantzen, Alexis Bonnin, Sylvain Schwartz

Atomic Physics

Charge-state dynamics of barium ions in high-pressure xenon and its implications for Barium-Tagging in $0\nu\beta\beta$ searches

A. Peralta Conde

Barium tagging (BaTa) is one of the most promising techniques for achieving a nearly background-free search for neutrinoless double-beta decay ($0\nu\beta\beta$) in high-pressure xenon time detection chambers. However, the experimental implementation of BaTa depends critically on the chage-state dynamics of the daughter Ba$^{2+}$ ion produced in the nuclear decay event. In this work, I review the possible recombination channels and evaluate their physical viability. The obtained results indicate that although binary recombination channels are strongly suppressed, three-body recombination assisted by neutral xenon atoms constitutes a physically plausible mechanism for the conversion of Ba$^{2+}$ into Ba$^+$ on timescales -milliseconds- comparable to the characteristic detection times in the NEXT experiment. These results suggest that the barium charge state should be regarded as a dynamical quantity with direct implications for the design and experimental implementation of BaTa techniques.
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Atomic Physics

An ionic clock qubit inside a circular Rydberg atom

Fabian Thielemann, Aaron Götzelmann, Marius Thomas et al. (+4 more)

Neutral atoms trapped in optical tweezers and excited to Rydberg states, together with trapped ions, are among the most advanced platforms for quantum simulation and quantum computing. Current experiments often rely on additional atoms in neighboring traps to encode ancilla qubits for local manipulation and readout. Here, we demonstrate a dual ion-Rydberg system comprising two qubits encoded in two individually controlled electrons of the same alkaline-earth atom. The first, a microwave qubit, is encoded in a pair of circular Rydberg states, while the second, an optical qubit, is encoded on a narrow quadrupole transition of the Rydberg atom's ionic core. We demonstrate coherent control of the optical qubit and achieve coherence times of several hundred microseconds under dynamical decoupling. Furthermore, we realize coherent coupling between the two electrons via electrostatic quadrupole interactions over the large separation between the Rydberg electron and the ionic core, and map out its angular tunability. Finally, we demonstrate a two-qubit operation, reminiscent of a Mølmer-Sørensen gate, that evolves through an entangled state of the two qubits driven by the quadrupole coupling. Our work opens a pathway to exploit a pair of individually controlled electronic qubits with tunable coupling for quantum simulation and quantum metrology.
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All authors Fabian Thielemann, Aaron Götzelmann, Marius Thomas, Einius Pultinevicius, Armin Humić, Christian Hölzl, Florian Meinert

Atomic Physics · Cross-listed from quant-ph

Single-qubit detection by collective phase imprinting

Kritsana Srakaew, Pascal Weckesser, Daniel Adler et al. (+4 more)

The amplification of quantum information carried by a single quantum excitation is a recurring challenge across diverse quantum platforms. The coupling between a single qubit and a mesoscopic ensemble of spins, for example, can be leveraged to realize non-destructive detection of the qubit state. However, realizing robust couplings between such systems is experimentally challenging and typically requires programmable quantum gates or native long-range interactions. Here, we introduce a platform that couples a single qubit, encoded in the ground-to-Rydberg transition of a control atom, to a Rydberg-dressed target ensemble of ground-state atoms trapped in an optical lattice. We show that the state of the control qubit can be coherently mapped onto the ensemble via a qubit-controlled collective phase shift. By Rydberg-dressing the ensemble, the controlled phase shift per target atom becomes independent of the number of target atoms, making the protocol intrinsically insensitive to atom-number fluctuations and atom loss, which are the dominant experimental imperfections in our system. Exploiting the collective response of up to eight target spins, we demonstrate the efficacy of the scheme by realizing non-destructive detection of a single Rydberg excitation with a state-assignment fidelity of $\mathcal{F} = 99.81^{+0.17}_{-1.47}\,\%$. Our approach demonstrates the key ingredients for high-fidelity transfer of quantum information from a single qubit to a mesoscopic ensemble, opening a route to non-destructive mid-circuit readout of Rydberg states and to efficient interfaces between single qubits and photonic modes.
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All authors Kritsana Srakaew, Pascal Weckesser, Daniel Adler, Suchita Agrawal, David Gröters, Immanuel Bloch, Johannes Zeiher