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Physics Physics Atomic Physics

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Thursday 27 August

Atomic Physics · Cross-listed from physics.optics

Dual-Symmetrized Construction of Electromagnetic Beams Beyond the Paraxial Approximation with an Explicit Separation of Scalar and Vectorial Corrections

Abdullah F. Alharbi and Kayn A. Forbes

We develop a perturbative framework for constructing the fields of electromagnetic beams beyond the paraxial approximation, in which the vectorial correction is shared symmetrically between the electric and magnetic fields and separated from the isotropic scalar correction. The method is based on a direct iterative derivation from Maxwell equations and combines complementary electric-first and magnetic-first constructions, thereby removing the construction-dependent assignment of the vectorial correction to either the electric or magnetic field. In addition, the scalar envelope correction is obtained independently from the isotropic co-polar contribution to the solutions of the higher-order Helmholtz equation. The resulting corrected fields apply to an arbitrary paraxial envelope and input Jones polarization.
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Atomic Physics · Cross-listed from quant-ph

Adiabatic Otto-like quantum thermodynamical cycle in the non-quasi-static regime

Salvador J. Robles-Pérez and Salvador Castillo-Rivera

We show a finite-time Otto-like quantum thermodynamic cycle that preserves the adiabatic population structure of a time-dependent harmonic oscillator in the non-quasi-static regime. In the conventional energy representation, finite-rate driving induces non-adiabatic population redistribution and leaves residual excitations after the Hamiltonian has returned to its initial value. We show that this difficulty can be avoided by formulating the dynamics in the Lewis-Riesenfeld invariant representation, without modifying the physical Hamiltonian through auxiliary counterdiabatic driving. For a parametric Mathieu protocol, quantum inertia produces a mismatch between the spatial width of the working mode and its transient dressed energy scale. We propose an experimental implementation of this scheme in a trapped-ion Paul trap using stimulated Raman interactions, with independent control of the laser detuning and beam intersection angle. This provides a finite-time implementation in which the invariant population structure is preserved while the physical trap frequency evolves non-quasi-statically. Our results establish a clear distinction between adiabatic operation and quasi-static driving, providing a route toward finite-time quantum thermal cycles that retain the adiabatic energy structure without requiring the quasi-static limit.
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Atomic Physics · Cross-listed from hep-ph

Atomic structure calculations for constraining new electron-electron forces

Cameron J. West and Benjamin M. Roberts

We present a general approach for calculating new electron-electron interactions with atomic structure theory, include dominant many-body effects, and extract bounds for parity-odd cases. The procedure is valid for any mediator mass and improves previous calculations by including many-body corrections to the new interaction through the time-dependent Hartree-Fock method. Bounds on coupling strengths are then extracted for scalar-pseudoscalar and vector-axial vector interactions by comparison with experimental atomic electric dipole moments and parity non-conserving (PNC) transitions respectively. In the latter case, our calculations rule out any coupling-mass ratio |g^e_V g^e_A|/m_X^2 greater than 10^-11 MeV^-2 above m_X ~ 10 MeV, covering a previously unconstrained mass region. We also report an updated calculation of the regular (Standard Model) electron-electron Z^0 exchange contribution to the 6s-7s PNC transition amplitude E_PNC in cesium.
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Wednesday 26 August

Atomic Physics · Cross-listed from quant-ph

Detuning-robust Rydberg entangling gates from echoed pulses

Zhubing Jia, Yichao Yu, Xiye Hu et al. (+4 more)

Rydberg-based two-qubit gate fidelities in neutral atom arrays are limited chiefly by laser intensity inhomogeneity and by detuning errors from frequency miscalibration, background-field drift, intermediate state light shift and Doppler shifts. Quantum optimal control can suppress the former, but no pulse can render a controlled-Z gate first-order insensitive to detuning. Here we show that this obstruction can be circumvented by designing Rydberg gate pulses with every leading-order detuning error relegated to single-qubit Z-rotations, which an echoed sequence removes. The resulting maximally-entangling ZZ gate has no leading-order response to arbitrary detunings on either atom, maintaining an infidelity below $10^{-3}$ within a much wider range of single-atom detunings than the time-optimal gates. We further show that a large fraction of residual error is dominated by population outside the computational subspace, which can be converted into heralded erasures. Our results significantly reduce the requirements on laser frequency stability and intensity homogeneity, field calibration and atomic temperature toward practical fault-tolerant quantum computing with neutral atoms.
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All authors Zhubing Jia, Yichao Yu, Xiye Hu, Lintao Li, Jacob Zheng, Christopher Monroe, Jacob P. Covey

Atomic Physics · Cross-listed from quant-ph

Structured Non-Locality and Emergent Locality in Cavity-QED Many-Body Dynamics

Mark A. Oehlgrien, Błażej Jaworowski, Darrick E. Chang et al. (+1 more)

Cavity quantum electrodynamics (QED) modifies many-body systems by combining cavity-mediated collective interactions with microscopic short-range interactions. The resulting dynamics lies between the local and fully collective limits, such that neither locality nor collectivity alone provides a complete organizing principle. In the clean conceptual limit of dominant collective coupling, we show that the effective dynamics within each energetically isolated subspace is generically controlled by whether that subspace admits a local product-state basis, and identify exceptions imposed by angular-momentum selection rules. Product-state subspaces generically retain the spatial structure of the microscopic interaction. Entangled subspaces instead generically dress local processes with global operators, generating non-local but highly structured dynamics. We illustrate this by deriving the corresponding effective Hamiltonians in two representative cavity-QED spin models. The cavity-isolated subspace thus becomes a resource for generating competing short-range interactions or globally conditioned local processes, opening a class of many-body dynamics without local or fully collective counterparts.
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All authors Mark A. Oehlgrien, Błażej Jaworowski, Darrick E. Chang, Charlie-Ray Mann

Atomic Physics

Robust watt-level continuous-wave deep-ultraviolet lasers near 230 nm

J. Cai, M. Stoepper, P. Agarwal et al. (+20 more)

Continuous-wave (CW) deep-ultraviolet (DUV) lasers near 230~nm enable laser cooling of AlF, Cd, and Zn, but second-harmonic generation below 237~nm relies in practice on beta-barium borate (BBO), whose walk-off and UV-induced degradation hinder sustained operation. We demonstrate compact, affordable VECSEL-based systems informed by four years of operating 14 DUV cavities in 12 laser systems across six European laboratories. External LBO cavities produce nearly 4~W at 463~nm with 94% cavity efficiency. We compare spherically and elliptically focused Brewster-cut BBO cavities with a normal-incidence AR-coated design. The AR-coated cavity delivers the highest power and efficiency, reaching 1.0~W at 51% cavity and 44% external efficiency; the spherical Brewster cavity reaches 700~mW and maintains constant circulating power over 70~h, while elliptical focusing reduces peak intensity sixfold and improves beam quality, albeit with greater alignment sensitivity. Collaboration-designed DUV optics, AlF spectroscopy, and Cd trapping validate the system.
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All authors J. Cai, M. Stoepper, P. Agarwal, L. Palánki, C. Alarcón-Robledo, W. W. W. Liu, P. Kukreja, R. Ferstl, H. Foltas, L. Möller, D. J. Brown, C. J. H. Rich, M. Chiarotti, T. Uusitalo, R. Thomas, J. Domarkas, M. Guina, J.-P. Penttinen, S. Stellmer, N. Poli, S. C. Wright, S. Hannig, S. Truppe

Tuesday 25 August

Atomic Physics

High-density Optical Quantum Sensors with Pulsed Probe Read-out for Correlated Spin-Noise Reduction

Igor Savukov and Young Jin Kim

Optical quantum sensors based on alkali-metal atoms enable highly sensitive magnetic-field measurements at room temperature. Their ultimate performance is limited by intrinsic spin noise once technical noise sources are sufficiently suppressed. Reducing and characterizing this noise is therefore essential for improving sensor sensitivity and for investigating quantum-enhanced sensing protocols. Here we investigate correlated spin fluctuations in a radio-frequency optical quantum sensor based on a high-density potassium vapor cell using a pulsed probe readout scheme. The system employs orthogonal pump and probe laser beams, while a static magnetic field defines the sensing frequency and synchronizes the probe pulses with the spin precession. To detect weak spin correlations, we implement a measurement protocol that combines periodic probing, phase cycling, and window-shifted acquisition. Phase cycling suppresses reproducible probe-induced coherent transients, while subtraction of temporally correlated signals acquired within the spin-relaxation time reduces the measured spin-noise level. The observed noise reduction is consistent with temporal spin correlations, including those expected in spin-squeezing protocols, although the present measurements do not uniquely distinguish this interpretation from other correlated-noise mechanisms. The demonstrated measurement protocol provides a practical route toward operating warm-vapor optical quantum sensors closer to their fundamental spin-noise limit and may benefit radio-frequency magnetometry and sensing of weak coherent signals, including emerging dark-matter detection schemes.
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Atomic Physics · Cross-listed from cond-mat.quant-gas

Roton Instability in Quantum Droplets with Finite-Range Soft-Core Interaction

Avra Banerjee

We investigate the emergence of roton instability in self-bound quantum droplets interacting via a finite-range soft-core potential modeled by a Heaviside step interaction. The ground-state properties are obtained by solving the extended Gross-Pitaevskii equation including Lee-Huang-Yang corrections with a nonlocal interaction term. The collective excitation spectrum reveals the formation and progressive softening of a roton minimum as the interaction strength and range increase. When the roton energy approaches zero, the system becomes unstable, signaling the onset of density modulation. The rotonic behavior is further characterized through the static structure factor, which exhibits pronounced peaks at the roton momentum.
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Atomic Physics · Cross-listed from quant-ph

Geometry-controlled correlated electric-field noise in enclosed ion traps from billiard return spectra

Ayush Nadiger

We ask how passive conducting geometry determines the spatial structure of electric-field noise seen by trapped ions. From a boundary-potential covariance and the Dirichlet Green function we construct the $N$-ion electric-field cross-spectral matrix and its blockwise motional Kossakowski generator. In a parallel slab, billiard unfolding turns the electrostatic response into a return-depth measure and yields an exact return-pair functional for arbitrary stationary surface spectra. For every finite equal-height ion array, the passive cover increases the normal-field covariance matrix in the positive-semidefinite ordering and decreases the tangential-field covariance matrix in the same ordering: all collective normal-field coordinates acquire more absolute noise, while all collective tangential coordinates acquire less. At $h=2d$ the local-noise single-ion ratios are exactly $\zeta(3)$ and $\eta(3)$. Diagonalizing the equal-frequency covariance identifies collective environmental noise eigenchannels and a geometry-dependent noise rank; within a degenerate frequency block these become the Lindblad jump channels. In a ten-ion example, closing the cover to $h=2d$ lowers the participation rank from 5.61 to 5.11 while increasing the leading channel's share from 23.7% to 28.6%; a primitive Mølmer-Sørensen calculation shows how the projected covariance sets the weak-heating gate exposure. Beyond parallel walls, specular paths emerge as large-$q_z$ saddles of the screened boundary operator. Across 16 curved covers, the fitted electrostatic decay exponent correlates at 0.9991 with the independently computed shortest specular excess length, while separate tests resolve focusing and competing saddles.
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Atomic Physics

Measurement of the O$^{-}$ Photodetachment cross-section in the electrostatic storage ring FLSR

Oliver Forstner, Thorben Niemeyer, Andrey I. Bondarev et al. (+10 more)

The achievable precision of photodetachment studies via tunable laser light has been investigated on circulating oxygen anions at the room-temperature electrostatic low-energy storage ring of Frankfurt University (FLSR) in preparation of investigations on molecular species. For this purpose, the FLSR, originally designed for reaction dynamics studies on positive ions, was upgraded by a source for anions, by the installation of a tunable high repetition rate laser system and by implementation of a transversal interaction region between laser and ion beam. Results on the electron affinity and the ground state fine structure of O$^{-}$, which both serve as a calibration standard, are discussed, exhibiting the performance and accuracy of this new spectroscopic application of the FLSR.
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All authors Oliver Forstner, Thorben Niemeyer, Andrey I. Bondarev, Markus Dworak, Vadim Gadelshin, Raphael Hasse, Lothar Schmidt, Markus Schöffler, Matou Stemmler, Kurt E. Stiebing, Dominik Studer, Klaus Wendt, Patric Ziel

Monday 24 August

Atomic Physics

Multi-hour stable trapping and threshold steady state of non-laser-coolable ions with ultracold atoms in a hybrid trap

Satyabrata Baidya and Sourav Dutta

We report multi-hour stable trapping and steady state of non-laser-coolable Cs$^{+}$ ions in a linear Paul trap, achieved via resonant charge-exchange (RCE) cooling with a precisely centered ultracold Cs cloud. Without cold atoms, all ions are lost within 3 minutes. With centered cold atoms, RCE cooling establishes a stable population of ions for 6 hours with no measurable decay – more than two orders of magnitude longer hold times compared to prior hybrid atom-ion systems. We observe a threshold behavior in the steady-state number of ions ($N_{s}$): initial ion loadings above $N_{s}$ ions converge downward to $N_{s}$ ions and remain constant thereafter; initial loadings below $N_{s}$ ions show no measurable decay. The dynamics is governed by a competition between ion-ion rf heating and ion-atom collisional cooling. The prolonged, simultaneous ion-atom trapping suggests an upper bound on the three-body recombination-induced Cs$_{2}^{+}$ formation rate constant: $k_{3} << 1.4 \times 10^{-25} cm^{6} s^{-1}$. This remarkable realization of long-lived steady state overcomes a critical limitation of prior hybrid atom-ion systems and enables extended studies of ultracold ion-neutral chemistry, rare inelastic collisions, and sympathetic cooling routes for complex molecular ions.
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Atomic Physics · Cross-listed from cond-mat.quant-gas

Observation of electron spin interactions between Rydberg atoms

Le Ruan, Ziqi Zhou, Yuchen Guo et al. (+2 more)

We report the observation of electron spin interactions between Rydberg atoms, which are driven by spin-orbit coupling through second-order dipole perturbation and exhibit a spatial anisotropy governed by the atomic configuration. Specifically, we observe coherent electron spin exchange dynamics, with the measured coupling strength agreeing well with both numerical calculations and theoretical models. Furthermore, we show that global microwave dressing enables active engineering and dynamical freezing of the spin exchange by introducing a differential AC Stark shift between the participating states. Additionally, we achieve tunability of the interaction by applying a stronger magnetic field, which effectively modifies the energy contributions of the underlying spin-orbit coupling channels. Finally, measuring spin dynamics in one-dimensional multi-atom chains aligned parallel or perpendicular to the magnetic field provides a self-consistent validation of the anisotropic XXZ framework. This electron spin interaction natively features spin-position coupling and enables a natural mapping onto the Heisenberg-Kitaev model. Our findings reveal a new class of electron spin-spin interactions among Rydberg atoms, expanding the scope of quantum simulation with Rydberg atom arrays.
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All authors Le Ruan, Ziqi Zhou, Yuchen Guo, Chengshu Li, Cheng Chen

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

Universal Spin-Position Coupled Rydberg Interactions

Chengshu Li and Hui Zhai

Strong interactions between $s$-orbital Rydberg atoms underpin atom-array-based quantum computation and quantum simulation. Typically, the spin dependence of these interactions is negligible and plays no practical role. In this Letter, we uncover that a strong electron-spin-dependent Rydberg interaction can emerge when the principal quantum numbers of the two $s$-orbital atoms differ by a sweet-spot value. This interaction originates from the fine-structure splitting of nearby $p$ orbitals, which endows it with distinct symmetry properties such that the electron spins are coupled to the relative position of the two atoms, featuring a spatially defined anisotropy. We further demonstrate that this interaction admits a universal form, independent of the principal quantum numbers, and highlight its fundamental distinction from conventional magnetic dipolar interactions, establishing it as a new type of native magnetic interaction in nature. Our findings introduce a new element to the Rydberg quantum simulation toolbox. As a concrete application, we propose a native realization of the Kitaev-Heisenberg model, which hosts an unusual stripe phase as a quantum many-body manifestation of spin-space locking.
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Atomic Physics

Extreme-ultraviolet spectroscopy using quantum logic: a feasibility study for the 1S-2S transition in singly-ionized helium

A. Martínez de Velasco, V.P.J. Barbé, E.L. Gründeman et al. (+10 more)

Extreme-ultraviolet (XUV) spectroscopy represents an important new direction in precision physics, with potential applications ranging from the metrology of fundamental constants to tests of physics beyond the Standard Model. However, the application of quantum control methods for precision spectroscopy remains an open challenge in the XUV range. Here we present a novel quantum logic (QL) spectroscopy method for precision spectroscopy of weak XUV transitions, and numerically validate its feasibility for the $1S-2S$ transition at 40.81\,eV in singly-ionized helium (He$^{+}$). We propose a scheme based on a single He$^{+}$ ion co-trapped with a Be$^{+}$ ion in a Paul trap, and He$^{+}$ excitation with pairs of frequency-comb (FC) laser pulses upconverted to the XUV via High-Harmonic Generation (HHG). We investigate a nondestructive QL scheme to detect $1S-2S$ excitation, and compare its performance with a destructive readout based on state-selective ionization. Phase coherence of the XUV light is modelled and an optical cavity is used to filter the FC pulses prior to HHG. We model the motional excitation dynamics of trapped ions outside the Lamb-Dicke regime, and numerically validate a scheme we proposed in \cite{Grundeman} to cancel the first-order Doppler broadening and the recoil shift by synchronizing the ion's secular period with the time delay between the two excitation pulses. We show that precision spectroscopy of the $1S-2S$ transition in He$^{+}$ at the 10 kHz level is feasible, for improved tests of quantum electrodynamics (QED), a measurement of the Rydberg constant $R_{\infty}$ independent of hydrogen measurements, or an improved determination of the alpha particle and helion charge radii. The proposed method may also be applied to XUV spectroscopy of other ions outside the Lamb-Dicke regime.
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All authors A. Martínez de Velasco, V.P.J. Barbé, E.L. Gründeman, A. Díaz Calderón, M. Collombon, J.J. Krauth, C.F. Roth, M. Favier, R. Taieb, T.E. Mehlstäubler, P.O. Schmidt, L.S. Dreissen, K.S.E. Eikema

Atomic Physics · Cross-listed from quant-ph

Dual-Isotope Sympathetic Cooling in a Long Ion Chain

Tianyi Wang and Marko Cetina

Owing to their high controllability and connectivity, one-dimensional ion chains are attractive building blocks for near-term quantum computers. However, long ion chains are susceptible to motional heating caused by fluctuating external electric fields. To enable deep computations, this source of noise must be suppressed without inducing qubit decoherence or degrading qubit connectivity. We demonstrate steady-state mid-circuit sympathetic cooling of all computationally-relevant motional modes of a 23-ion chain consisting of \qubit qubit and \coolant coolant ions without using any qubit operations. In a room-temperature system, our cooling scheme preserves the mean phonon occupations of the long-wavelength axial and radial modes near their values following state preparation, while keeping the modes used to implement entangling gates near their ground states throughout a 56-ms circuit. Crucially, we show that our cooling sequence preserves qubit coherence, and evaluate its impact on single- and two-qubit gate operations. Additionally, we demonstrate a parallel qubit reset protocol leveraging the shared radial mode coupling between species. Our sympathetic cooling scheme represents a critical step toward reducing gate errors in individually-addressed long ion chains and establishes a versatile platform for simulating open quantum systems.
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Atomic Physics · Cross-listed from physics.optics

Revealing Hidden Orbital Pathways in NonThermal Hot Carrier Relaxation of MXenes via NonSecular Redfield Quantum Kinetics

Ali Asghar Molavi Choobini, Abbas Chimeh and Jinhui Zhong

Non-thermal carrier relaxation is routinely inferred from population dynamics or spectroscopic observables, yet neither class of quantity uniquely identifies the microscopic channels through which energy and coherence are redistributed. We introduce a pathway-resolved quantum-kinetic framework that simultaneously projects ultrafast relaxation onto orbital populations, directional inter-orbital transferes, coherence, spectroscopic visibility, and a hidden-pathway sector of the dynamical transfer network. Application to MXenes exposes strongly non-uniform orbital redistribution together with material-specific hierarchies of microscopic transfer channels. Temperature, excitation amplitude, and dissipative parameters modulate pathway competition and spectral amplitudes while leaving the identity of the dominant channels largely intact. Instantaneous transfer contributions, cumulative directional transfer, coherence, and spectroscopic visibility are shown to follow inequivalent hierarchical orderings. This non-equivalence isolates a set of hidden pathways that remain dynamically consequential despite weak conventional spectroscopic signatures. The resulting time energy coherence representation recasts nonthermal relaxation as a structured dynamical network comprising observable and hidden sectors, thereby providing a general methodology for resolving microscopic orbital transfer pathways in driven quantum materials.
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Atomic Physics · Cross-listed from physics.optics

Quantum Hydrodynamic Framework of Coherent Terahertz Emission in MXenes Driven via Engineered Femtosecond Waveforms

Ali Asghar Molavi Choobini, Abbas Chimeh and Jinhui Zhong

Coherent terahertz (THz) emitters based on low dimensional quantum materials have attracted significant interest for compact broadband photonic technologies. However, theoretical descriptions that consistently connect microscopic quantum dynamics to emitted THz radiation remain limited for MXenes, whose electronic properties are governed by transition metal d orbitals and chemically tunable surface terminations. A multiscale density-matrix formalism for coherent THz generation in metallic MXenes driven by engineered three color femtosecond waveforms is developed. Material-specific electronic structures are described by parameterized multiband tight binding Hamiltonians, while ultrafast carrier dynamics are treated using a non-secular Redfield master equation that explicitly retains interband coherence, carrier populations, electron phonon interactions, impurity scattering, and environment-induced relaxation. The transient photocurrent is explicitly decomposed into population and coherence driven contributions and linked to the emitted THz field through its time derivative, establishing a direct connection between microscopic quantum dynamics and macroscopic radiation. The results show that environmental coupling does not merely attenuate THz emission, but redistributes coherent and population currents and reshapes the emitted waveform in both the time and frequency domains. Systematic investigations of optical waveform parameters, effective electronic structure, and open system relaxation identify physically grounded strategies for enhancing broadband THz generation. The proposed methodology establishes a transferable microscopic design platform for connecting material specific electronic structure, quantum coherence, open system relaxation, nonlinear carrier transport, and coherent THz emission across MXenes and related low dimensional quantum materials.
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Atomic Physics

Efficient Separation of the Isomeric State $^{26\text{m}}\text{Al}$ from the Intense Ground State Background via Sequential Optical Pumping in Collinear Laser Spectroscopy

Hoon Yu, Jung Bog Kim, Cheolmin Ham et al. (+1 more)

We propose a novel, highly efficient method for isolating the isomeric state $^{26\text{m}}\text{Al}$ from an overwhelming ground-state $^{26\text{g}}\text{Al}$ background (isomeric ratio $\sim 20:1$) using optical pumping through a 2.0 m flight zone in collinear laser spectroscopy (CLS). To investigate the underlying optical pumping (OP) dynamics, we developed a comprehensive rate equation framework. While the transition pathways can be intuitively conceptualized via a primary 7-manifold scheme, our numerical simulation solves the full 47-level rate equations by explicitly accounting for all degenerate Zeeman sublevels ($m_F$) to rigorously incorporate polarization selection rules and Clebsch-Gordan coefficients. When the continuous acceleration voltage matches the resonance conditions of the $^{26\text{g}}\text{Al}$ hyperfine transitions, the ground-state atoms undergo a 100% efficient transition into uncoupled dark states within the 2.0 m flight zone. Consequently, background fluorescence from the ground state is completely suppressed in the detection chamber, whereas $^{26\text{m}}\text{Al}$ atoms utilize a closed cycling structure to survive the flight zone, yielding a high-intensity, background-free resonance peak.
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All authors Hoon Yu, Jung Bog Kim, Cheolmin Ham, Sung Jong Park

Atomic Physics

Exchange and core-polarization effects on Rydberg-transition electric-dipole matrix elements in Rb and Cs

Yu Shi-Cheng, Zhen-Xiang Zhong and Cheng-Bin Li

Microwave electric-field measurements with Rydberg atoms require accurate Rydberg-transition electric-dipole matrix elements. We calculate these matrix elements for Rb and Cs using a Dirac-Fock plus core-polarization method, which core-valence exchange is treated explicitly and core-valence correlation is represented by a cutoff core-polarization potential. A smooth cutoff-radius model fitted to quantum-defect energies reproduces the target energies with MHz-level residuals for states up to $n=90$. Comparisons with model-potential matrix elements and internal length-velocity consistency show that the $s$-$p$ transitions are generally the most robust, whereas the $p$-$d$ and $d$-$f$ transitions show stronger atom- and branch-dependent sensitivity to short-range modeling. The largest relative differences arise from radial-integral cancellation, where short-range phase changes are amplified by the small final matrix element. These results provide a practical reliability assessment for Rydberg-transition electric-dipole matrix elements used in field-sensing applications.
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Atomic Physics · Cross-listed from physics.app-ph

Transient Dynamics and Duty-Cycle Optimization in a Pulse-Wwidth Modulation Bell–Bloom Pumping

Ying-Hao Ye, Ling-Yan Hu, Dui-Gao Yi et al. (+2 more)

We investigate the duty-cycle-dependent atomic response under full-depth intensity pulse-width modulation in Bell–Bloom optical pumping. A time-domain Bloch model explicitly resolves the pump-on/off spin dynamics, yielding piecewise analytical transient solutions and a periodic steady-state description without cycle averaging or harmonic truncation. An extended free-induction-decay method independently determines the effective dark and pump-on transverse-relaxation rates, $W_0$ and $W$. The predicted lock-in responses agree well with experimental results. We find that for each Larmor frequency $\omega_0$, the slope is maximized at a finite pump rate that increases with $\omega_0$. These results provide a practical framework for sensitivity-oriented optimization of the duty cycle and pump rate in PWM-driven atomic magnetometers.
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All authors Ying-Hao Ye, Ling-Yan Hu, Dui-Gao Yi, Zhi-Fei Yu, Bing Chen

Saturday 22 August

Atomic Physics

Bound and Resonant Spectra of Few-Lepton Coulomb Systems

Liang-Zhen Wen, Yao Ma, Zhi-He Shen et al. (+1 more)

We present a unified calculation of bound and resonant states in purely leptonic Coulomb systems: $e^-e^-e^+$ ($\mathrm{Ps}^-$), $\mu^+e^-e^-$ ($\mathrm{Mu}^-$), $\mu^+\mu^+e^-$ ($\mathrm{Mu}_2^+$), $e^+e^+e^-e^-$ ($\mathrm{Ps}_2$), and $\mu^+\mu^+e^-e^-$ ($\mathrm{Mu}_2$). Using an extended stochastic variational method combined with the complex scaling method, we resolve the natural-parity $S$- and $P$-wave spectra. Near their respective $n=2$ thresholds, all three trilepton systems exhibit Gailitis–Damburg sequences generated by $2S$ and $2P$ Stark mixing and the resulting inverse-square attraction. Although microscopically distinct from the Efimov effect, this mechanism produces the same inverse-square asymptotics and geometric scaling. The $\mathrm{Ps}^-$ and $\mathrm{Mu}^-$ systems exhibit resonance sequences of comparable density, whereas the $\mathrm{Mu}_2^+$ produces a much denser spectrum, with 20 resolved members in the $^3P^o$ channel. In $\mathrm{Mu}_2^+$, the deeper states follow molecular Born–Oppenheimer configurations, while the near-threshold spectrum is governed by the atomic $\mathrm{Mu}(2)+\mu^+$ structure. In $\mathrm{Ps}_2$, coupling between threshold-degenerate configurations is essential for a near-threshold bound state. In $\mathrm{Mu}_2$, the Born–Oppenheimer organization of the resonance spectrum is channel dependent.
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All authors Liang-Zhen Wen, Yao Ma, Zhi-He Shen, Shi-Lin Zhu

Friday 21 August

Atomic Physics

Magic Velocity Selection in Atom Interferometry

Yuno Iwasaki, Jack Roth, Madeline Bernstein et al. (+2 more)

Velocity-selective Raman transitions are widely used in atom interferometers to prepare atomic ensembles with narrowly defined momentum distributions. However, differential light shifts between atomic energy levels generate velocity distributions that are correlated with the Raman beam intensity, and therefore with the position of the atoms within the laser beam. We show that these spatially inhomogeneous velocity distributions interact with detuning-dependent systematic effects in a Bragg diffraction-based simultaneous conjugate Ramsey-Bordé interferometer. These interactions can induce systematic phase shifts of order 10 milliradians in the interferometer phase. We further identify a "magic" detuning for velocity selection and show that operating at this detuning suppresses the systematic phase shift. Magic velocity selection eliminates systematic errors arising from correlations between atom velocity and position, facilitating high-resolution atom interferometry experiments targeting sub-part-per-billion accuracy.
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All authors Yuno Iwasaki, Jack Roth, Madeline Bernstein, Andrew Christensen, Holger Mueller

Atomic Physics · Cross-listed from astro-ph.HE

Excitation and Recombination Data for Nd I-V with Applications to Kilonovae

N. Ferguson, L. P. Mulholland, M. McCann et al. (+2 more)

Neodymium (Nd), a key r-process element, significantly influences the opacity and emergent spectra of kilonovae resulting from neutron star mergers. We present new atomic data for the first five ionization stages of Neodymium, with emphasis on recombination rate coefficients and electron-impact excitation relevant to non-local thermodynamic equilibrium (non-LTE) modelling. Using the relativistic atomic structure code autostructure, we compute energy levels, radiative and dielectronic recombination rates using the isolated-resonance approximation, and excitation data for these ions. Excitation datasets are constructed using both direct (distorted-wave) and resonant excitation approaches, allowing a systematic assessment of the impact of resonance contributions on effective collision strengths. For the case of Nd ii, we compare collisional strengths with those produced by the Dirac Atomic R-matrix Codes (darc). These comparisons demonstrate the importance of resonance-mediated excitation, especially for low-charge ions where near-threshold resonances significantly enhance rates. In terms of recombination for higher ionization stages, dielectronic recombination (DR) is found to dominate over a wide temperature range, while radiative recombination (RR) is comparable with DR at low temperatures for near-neutral species. Our results highlight the pivotal role of non-LTE atomic physics in interpreting kilonovae observations and constraining nucleosynthesis yields. This work strengthens the atomic foundation necessary for linking observed electromagnetic signals to the physics of compact object mergers and heavy element formation.
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All authors N. Ferguson, L. P. Mulholland, M. McCann, C. P. Ballance, M. G. O'Mullane

Atomic Physics

Attosecond Transient Polarimetry

Nicola Mayer, Kylie Gannan, Stephen R Leone et al. (+1 more)

We introduce elliptical-dichroic attosecond transient absorption spectroscopy (eDATAS), an ultrafast attosecond spectroscopy technique in which an atomic gas is probed by elliptically polarized attosecond and near-infrared pulses with an arbitrary angle between the polarization ellipses and a varying time-delay. Using perturbation theory, we show that the transient absorption signal factorizes into form factors whose dependence on pulse ellipticities and polarization-ellipse orientations are governed entirely by dipole selection rules: ellipticity sets the amplitudes of the interfering multiphoton pathways, while the relative orientations of the ellipses control the phase. We reinterpret circular- and linear-dichroic attosecond transient absorption spectroscopy as limiting cases of eDATAS, and validate the theory through an eDATAS measurement in helium, finding excellent agreement. Finally, we demonstrate that eDATAS can also serve as an in situ measurement of the polarization state of the XUV field, avoiding the need for a dedicated XUV polarimeter.
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All authors Nicola Mayer, Kylie Gannan, Stephen R Leone, Lauren B Drescher

Thursday 20 August

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

Self-limiting electrostriction of a single ion in an ultracold polar gas: From mesoscopic ions to crystalline molecular rings

Ruiren Shi, Saajid Chowdhury, Leon Karpa et al. (+1 more)

We investigate the self-assembly of polar molecules around a single ion immersed in an ultracold, dilute two-dimensional molecular gas. The ion aligns and attracts the molecules through charge-dipole interactions, producing a strong electrostrictive accumulation around the impurity, while intermolecular repulsion limits further densification and favors spatially extended configurations. By combining global optimization with diffusion Monte Carlo, we calculate the evaporation energy as a function of the number of molecules bound to the ion. In contrast to conventional charged and van der Waals clusters, the evaporation energy exhibits a plateau-like dependence on cluster size, reflecting the sequential formation of concentric molecular rings. These structures are governed by the topology of the ion's electric field and by the competition between attractive ion-molecule interactions, repulsive intra-ring interactions, and attractive correlations between neighboring rings, rather than by conventional coordination or icosahedral packing. In the weak-interaction regime, the resulting structures form extended mesoscopic molecular ions, whereas stronger interactions produce increasingly rigid, crystal-like molecular rings. We further analyze their stability against thermal perturbations and the time-dependent ion trap and find that a broad range of clusters remain stable under experimentally relevant conditions. The intermolecular repulsion and dipolar geometry also suppress close-range ion-molecule encounters, suggesting an intrinsic shielding mechanism. Our results establish ion-bound polar-molecule clusters as a distinct class of mesoscopic molecular ions and open a route to studying charged impurities in quantum baths with anisotropic interactions.
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All authors Ruiren Shi, Saajid Chowdhury, Leon Karpa, Jesús Pérez-Ríos

Atomic Physics · Cross-listed from quant-ph

Collective Quantum Logic Spectroscopy

Raphael Kaubruegger, Matthew Patkowski, Yicheng Zhang et al. (+3 more)

Scaling trapped-ion quantum sensors from single ions to large ensembles is a key challenge for next-generation precision measurements. At the same time, many ion species of interest for optical clocks and tests of fundamental physics lack closed cycling transitions required for direct laser cooling and state detection. Collective quantum logic spectroscopy addresses both limitations by coupling an ensemble of sensor, or spectroscopy, ions to one or more logic ions that provide sympathetic cooling and state readout. Here, we establish the fundamental performance limits and operating regimes of this protocol, identifying how the interaction strength, interrogation time, and logic-ensemble size govern sensitivity, dynamic range, and robustness to experimental imperfections. We show that quantum-limited sensitivity can be retained even with a single logic ion, while increasing the number of logic ions substantially improves readout efficiency and robustness. Beyond precision metrology, the same collective interface enables many-body measurements relevant to quantum information processing, including parity measurements and stabilizer-like syndrome extraction. Our results establish collective quantum logic spectroscopy as a scalable framework for optical clocks, quantum-enhanced sensing, and trapped-ion quantum information processing.
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All authors Raphael Kaubruegger, Matthew Patkowski, Yicheng Zhang, Robert J. Lewis-Swan, David B. Hume, Ana Maria Rey

Atomic Physics

A Protocol for Shielding-Enhanced Loading of Single Polar Molecules into Optical Tweezers

Reuben R. W. Wang, Christian H. Nunez, Conner Williams et al. (+4 more)

We propose the high-fidelity preparation of single bosonic molecules in optical tweezers starting from small tweezer-trapped molecular ensembles. Our scheme combines a static electric field and a microwave field to generate strong, tunable, anisotropic interactions that shield the molecules against two-body collisional loss. We show that this shielding eliminates all long-range bound states, preventing three-body recombination. This elimination persists for all microwave ellipticities, including the experimentally practical limit of linear polarization. Application of an additional electric field gradient can be used to induce controlled spilling of strongly interacting molecules out of the trap until one remains. With realistic experimental parameters, we estimate that single tweezer-trapped NaCs molecules can be isolated from a pair with fidelities exceeding 99%, and $> 95\%$ per site across an array. These results establish collisional shielding with electric fields as an effective tool for preparing highly-filled tweezer arrays of polar molecules.
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All authors Reuben R. W. Wang, Christian H. Nunez, Conner Williams, Amanda Younes, Li Du, H. R. Sadeghpour, Kang-Kuen Ni

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

Competing triangular and stripe supersolid orders in a dipolar quantum gas

Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt et al. (+6 more)

Supersolids are exotic quantum states in which long-range phase coherence coexists, and may interplay, with emergent spatial orders. A particularly rich phase diagram featuring several competing spatial orders is predicted for dipolar supersolids with two-dimensional crystals, yet the experimental observation of this structural variety has remained limited. Here we experimentally form competing triangular and stripe density-modulated states in a quantum gas of highly magnetic atoms confined in a surfboard-shaped trap by tuning contact interaction strength and dipole orientation. We define a structural order parameter and study its statistical behavior. Thereby, we identify both the triangular and stripe phases and the transition between them, the associated critical behavior being marked by enhanced non-Gaussian fluctuations. Furthermore, we observe each spatial structure in both the phase-coherent supersolid regime and the phase-incoherent insulating one, near and far from the unmodulated-to-modulated transition, respectively. Our results establish a versatile platform in which multiple phases of the two-dimensional-supersolid phase diagram, and more generally, intertwined symmetry-breaking phenomena, can be investigated.
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All authors Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt, Jianshun Gao, Julian Kusch, Lennart Hoenen, Manon Ballu, Wyatt Kirkby, Lauriane Chomaz

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

Imaging the vacuum fluctuations of a quantum field

Yansheng Zhang, Feiyang Wang, Yi Jiang et al. (+5 more)

Heisenberg uncertainties lead to inevitable fluctuations in the measurement outcomes for quantum-mechanical observables. For quantum fields, these uncertainties result in random spatial structures in snapshots of a field, even when the field is in its ground (vacuum) state. Such `vacuum fluctuations' are at the heart of a wide range of phenomena, from spontaneous decay processes to the Casimir force and Hawking radiation. Their existence is a key manifestation of the quantumness of the physical world, but usually it is only their consequences that are directly observed. Here, we directly observe spatial vacuum fluctuations of a bosonic quantum field. Our experiments are based on a homogeneous planar atomic Bose–Einstein condensate. The condensate comprises two coherently coupled interacting components (spin states), and the quantum field describes its spin degrees of freedom. In the regime where the interactions dominate over the coherent coupling, our system emulates a (massive relativistic) sine-Gordon field. Images of the field reveal simultaneous fluctuations on different length scales, with scale-dependent amplitudes consistent with theoretical predictions for a vacuum state. Observing such fluctuations in the sine-Gordon limit opens many possibilities for laboratory simulations of relativistic fields in regimes that are presently not theoretically tractable.
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All authors Yansheng Zhang, Feiyang Wang, Yi Jiang, Alexander C. Jenkins, Paul H. C. Wong, Christoph Eigen, Gehrig Carlse, Zoran Hadzibabic

Atomic Physics · Cross-listed from quant-ph

Programmable cavity QED with a fiber-integrated atomic array

Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca et al. (+3 more)

Strong atom-photon interactions in optical cavities are a key resource for quantum information processing, quantum networking, and the exploration of quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer array with a high-cooperativity fiber Fabry-Pérot microcavity. The array is positioned within the cavity mode and individual sites are controlled with subwavelength precision, enabling continuous tuning of the single-atom coupling strength via deterministic displacement through the standing-wave field. For up to five atoms coupled to the cavity, we measure collectively enhanced vacuum Rabi splitting and implement cavity-based non-destructive readout of the number of coupled atoms. These results establish a scalable architecture for cavity-mediated entanglement generation and many-body cavity QED with single-atom control, and they lay the foundation for fiber-integrated quantum network nodes.
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All authors Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca, Marvin Holten, Damien Bloch, Julian Léonard