Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics Atomic Physics

physics.atom-ph Watch Atomic Physics

Monday 21 September

Atomic Physics

Anomalously enhanced lifetimes of low angular momentum Rydberg states in singly charged alkaline-earth metal ions

Simon Euchner, Weibin Li and Igor Lesanovsky

Trapped ions excited to high-lying electronic states, so-called Rydberg states, open new opportunities for quantum simulation and quantum computing. Generally, the fidelity of quantum coherent operations critically depends on the longevity of Rydberg states. However, scaling laws predict that the lifetimes of Rydberg states in singly charged alkaline-earth metal ions are 16 times shorter, compared to their neutral atom counterparts. Here, we show that this is not generally the case. We report an anomalous lifetime enhancement of certain low angular momentum ionic Rydberg series by factors larger than eight. The anomaly is present at both zero and finite temperature, although it is caused by different mechanisms. At zero temperature, the anomalously enhanced lifetimes are caused by accidental cancellations of the relevant dipole transition matrix elements, while at room temperature the anomaly originates from the enlarged energetic separation of ionic Rydberg levels with respect to neutral-atom levels.
Read the full abstract

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

From harmonic to sound-like oscillations in a quantum gas confined in a gravity compensated shell trap

Matthieu Cassus, Rishabh Sharma, Maxime Pesche et al. (+4 more)

We study the center of mass oscillations of a quantum gas in a shell shaped trap in the presence of a vertical force opposed to gravity. The measured harmonic frequency at the bottom of the shell is compared with an analytical formula for the trap potential including corrections beyond the rotating wave approximation. When gravity is partially compensated, a quartic correction to the harmonic motion has to be included due to the shell curvature. As gravity is nearly canceled, the quantum gas occupies a large fraction of the lower hemisphere. Driving the center of mass induces internal excitations in the quantum gas, whose time evolution is governed by the presence of sound waves. Relaxation processes induce a strong damping of the center of mass oscillation in this limit.
Read the full abstract

All authors Matthieu Cassus, Rishabh Sharma, Maxime Pesche, Laurent Longchambon, Thomas Badr, Romain Dubessy, Hélène Perrin

Atomic Physics

Vector Measurements Using Integrated Radio Frequency Atomic Magnetometers

Ayse Marasli, Thomas W. Kornack, D. Casey Oware et al. (+1 more)

We demonstrate reconstruction of three-dimensional radio-frequency (RF) magnetic-field vectors using a pair of integrated RF atomic magnetometers operated with orthogonal bias-field orientations. A theoretical and experimental analysis identifies a phase-ambiguity dead band that limits reconstruction when the two sensor responses become nearly identical. Measurements performed in an unshielded laboratory environment demonstrate accurate reconstruction of RF magnetic-field orientations and validate the predicted dependence of reconstruction accuracy on signal imbalance. These results establish integrated RF atomic magnetometers as a compact and sensitive platform for directional RF magnetic-field sensing, particularly at low frequencies, and provide a foundation for portable source-localization and field-mapping applications.
Read the full abstract

All authors Ayse Marasli, Thomas W. Kornack, D. Casey Oware, Karen L. Sauer

Atomic Physics · Cross-listed from quant-ph

Collective advantage from a minimal record in a quantum information engine

Kangqiao Liu, Jie Gu and Deyou Chen

For a single particle, a quantum information engine can turn measurement fluctuations into transport by raising a barrier behind the particle each time its position is measured. When many particles are present, the barrier still depends on just one number, the position of the leftmost particle, so we let the demon measure that order statistic and nothing else. A demon that resolves every position instead pays a record entropy that grows with particle number, even though the extra distinctions never change where the barrier is placed. We show that the coarser measurement supplies an energy that is bounded independently of particle number, and that this bound yields a ceiling on the record entropy that falls as the filling increases. At the same tilt, the collective engine then delivers $44\%$ more work per recorded nat than independent single-particle engines, each with its own optimized cycle time and each running at equal or greater power per particle. Pauli blocking ends this advantage once the accessible region just above the wall fills. We also evaluate the coherence that the coarse measurement leaves behind, and the cost of placing the barrier imprecisely.
Read the full abstract

Sunday 20 September

Atomic Physics

Energy and Angular-Momentum Redistribution in Hydrogen Migdal Ionization

Haoyang Li, Zeyu Li, Ning Liu et al. (+2 more)

MARVEL's first direct observation of Migdal ionization in neutron scattering marks an experimental milestone and opens a new avenue for probing electronic response to nuclear recoil. Hydrogen, both the simplest atom and a constituent of its molecular target, provides a controlled benchmark. Within the nonrelativistic sudden approximation, we compute its energy-differential and integrated ionization probabilities with the full recoil phase. At the recoil parameter $\beta\equiv v_N/(\alpha c)=1.04$, the full-to-dipole spectral ratio rises from $0.43$ when the emitted-electron energy is $1\%$ of the hydrogen binding energy to $5.0$ when it is $2.3$ times that energy. Near $\beta=10$, partial waves with orbital angular momentum $\ell\ge3$ carry more than $90\%$ of the calculated continuum probability. An independent bound-state-closure evaluation verifies the absolute normalization: at eight recoil values, its ionization probabilities agree with the continuum-integrated results to relative discrepancies below $4.4\times10^{-7}$. These results extend the hydrogen dipole response to the fast-neutron regime and establish energy and angular-momentum redistribution as linked consequences of resolving the recoil phase across an atom.
Read the full abstract

All authors Haoyang Li, Zeyu Li, Ning Liu, Chuan-Yang Xing, Bin Zhu

Saturday 19 September

Atomic Physics

The use of coherent states in the excitation and ionization of atoms by a short symmetric pulse

Jorge E. Miraglia

We propose a new model for describing the excitation of atoms by short symmetric pulses. The theory is based on the impulse approximation and incorporates a confining potential approximated by a harmonic oscillator. Results are presented for a wide variety of parameters, including field intensity and laser frequency. Permitted and forbidden transitions are analyzed in detail. The photon energy spectrum presents peaks attributed to multiphoton absorption. Our model demonstrates robustness and reliability, paving the way for addressing more complex scenarios.
Read the full abstract

Atomic Physics

Loss induced dynamics of optical pulses in saturable nonlinear media

Golam Ali Sekh

We consider pulse propagation in a saturable nonlinear coupler whose other arm is dissipative and other is transparent. A flow of energy from transparent to dissipative arm takes place for weak value of dissipation and the coupler losses its energy. The energy loss of the coupler reduces for strong dissipation. This energy loss depends on the saturable nonlinearity. We find that the flow of relative energy at the output of a finite-sized coupler has a peak at a particular value of nonlinear strength. The peak value decreases with the increase of dissipation and it vanishes for stronger dissipation due to Zeno effect.
Read the full abstract

Atomic Physics · Cross-listed from physics.optics

Rubidium referenced Kerr comb with cavity phase matching

Xinwei Yi, Kunpeng Jia, Jingru Ji et al. (+6 more)

Phase matching is a fundamental problem in nonlinear optics that is normally constrained by material dispersion. The limited operation wavelengths within phase matching window limits the application, including the precise metrology using Kerr combs. Demanding applications like compact optical clock and astronomical spectroscopy requires atomic reference around 800 nm, where the natural phase matching is challenging. Here we revisit the concept of cavity phase matching (CPM), and fully reveal its advantage to engineer artificial phase matching beyond material dispersion. With the access of CPM condition in a monolithic high-Q fiber Fabry-Pérot resonator featuring a macroscopic cavity length, we achieve low noise Kerr comb generation around 800 nm, within the power budget of a single-mode laser diode. Inside a pump-integrated package of 19 cm3, low phase noise of -125 dBc/Hz at 100 kHz offset frequency is achieved for a 10.1 GHz repetition rate. Most importantly, the generated Kerr comb has been directly referenced to rubidium atomic transition for long-term stable operation. This result not only opens a new way for Kerr comb generation at arbitrary wavelengths, but also can be generalized to any other nonlinear optical frequency conversion application.
Read the full abstract

All authors Xinwei Yi, Kunpeng Jia, Jingru Ji, Zhong Yan, Biaobing Jin, Zhenlin Wang, Wei Liang, Shi-Ning Zhu, Zhenda Xie

Friday 18 September

Atomic Physics · Cross-listed from quant-ph

Persistent Quantum-Enhanced Frequency Sensing with T^{-3/2} Scaling

Clayton Z.C. Ho, Hao Wu, Grant D. Mitts et al. (+2 more)

Quantum sensing uses nonclassical states to improve measurement sensitivity, but the same states that provide metrological gain also decohere more rapidly. This limits the usable interrogation time and, in practice, often precludes improvement in ultimate sensitivity - realized useful quantum advantage has consequently remained rare. Here, we restore persistent quantum advantage by embedding Fock-state enhancement within a quantum heterodyne (Qdyne) protocol, decoupling sensitivity from the decoherence-limited interrogation time {\tau}. Measurements are acquired at short {\tau} where the quantum-enhanced gain is optimal, while precision accumulates with the total measurement time. Demonstrated on the motional mode of a trapped 40Ca+ ion, we observe quantum-enhanced precision that persists to measurement times seven orders of magnitude beyond the dephasing limit, scaling as T^{-3/2} with no indication of saturation. Using the n=3 Fock state, we reach a frequency precision of 0.5uHz relative to an 86MHz carrier, achieving a fractional precision ~6x10^{-15}. This represents a quantum-enhanced gain of 7.1(10) dB over the n=0 state, in agreement with Fisher information predictions. This is the first demonstration of Qdyne beyond solid-state spin-defects. Further, by using the quantum harmonic oscillator to perform frequency mixing, we extend operation beyond 1GHz, two orders of magnitude above the ceiling of pulsed dynamical-decoupling implementations. These results recover quantum advantage at the long timescales required to improve ultimate sensitivity, with direct implications for nanoscale NMR and quantum logic spectroscopy.
Read the full abstract

All authors Clayton Z.C. Ho, Hao Wu, Grant D. Mitts, Joshua A. Rabinowitz, Eric R. Hudson

Atomic Physics · Cross-listed from quant-ph

Single-atom-based asynchronous photonic interconnect for scalable modular quantum computing

Jérémy Raskop, Nadav Kandel, Geva Arwas et al. (+6 more)

Scaling quantum computation beyond the capacity of a single quantum processing unit requires quantum interconnects between modular processors. Optical photons are natural carriers for distributing entanglement between these processors. Most loss-resilient protocols use photonic Bell-state measurements based on the linear-optics type-II fusion gate. The resulting entanglement rate scales quadratically with each processor's typically low photon-delivery probability. Here we analyze a memory-assisted quantum interconnect using a near-deterministic, robust photon–atom controlled-$Z$ gate via a single atom trapped in a high-finesse cavity. Detecting and measuring a photon from one processor heralds entanglement between that processor and the atom. This entanglement is preserved while the process repeats with the second processor until the second photon is detected and measured. Reading out the atomic qubit finalizes the entanglement between the processors. As the entanglement is mediated by the atom, the photons from both processors do not need to be indistinguishable, removing a major source of infidelity. Furthermore, by removing the simultaneous photon-arrival requirement, the protocol allows the entanglement rate to scale linearly rather than quadratically with photon-arrival probability over a wide parameter range. We derive entanglement rates under realistic parameters, accounting for decay of the atom's entanglement with the first processor and for decoherence caused by unheralded photon interactions. The nanosecond-scale of the gate and read-out operations leads to orders-of-magnitude entanglement-rate gain over linear optics, removing a key bottleneck in modular quantum computing.
Read the full abstract

All authors Jérémy Raskop, Nadav Kandel, Geva Arwas, Yaniv Amichy, Yaron Jarach, Tal Kanonich, Andrei Militaru, Johannes Fink, Barak Dayan

Atomic Physics

A CSFG-based neural network basis-selection method for large-scale RCI calculations within GRASPG

Chaofan Shi, Shaowei Tian, Ran Si et al. (+3 more)

We present a neural network (NN) basis-selection method for large-scale relativistic configuration interaction (RCI) calculations in GRASPG. The method employs configuration state function generators (CSFGs), each of which generates a set of configuration state functions (CSFs) with the same spin-angular couplings, as the basic selection units for the NN. A constant-orbital feature-elimination strategy removes feature channels whose values remain unchanged across the CSFG pool. The CSFG representation reduces the number of learning units processed by the NN by more than one order of magnitude, while constant-orbital feature elimination further reduces the dimensionality of the NN input. Combined with the high-performance GRASPG framework, the method improves the efficiency of both NN selection and subsequent RCI calculations, maintaining a balance between accuracy and computational cost. In a moderate Ni(12+) benchmark, where the corresponding full-space RCI calculation is still feasible, the CSFs generated by the retained CSFG sets reproduce the full-space RCI results at the few inverse-centimeter level for the target states. For the representative J = 0, even-parity block, the complete workflow reduces the wall time by 75.6 percent, and the peak memory required by a single RCI calculation is reduced by a factor of 10.1. In a larger-scale calculation with a full CSF expansion containing 1.27 x 10^9 CSFs, the method retains only 1.1-1.9 percent of the full-space CSFs and yields energy levels in good agreement with experimental data and other resource-intensive theoretical calculations.
Read the full abstract

All authors Chaofan Shi, Shaowei Tian, Ran Si, Gediminas Gaigalas, Per Jönsson, Chongyang Chen

Thursday 17 September

Atomic Physics

Integration of the NIST Spectroscopic Plate Archive into the Harvard Plate Stacks

Jacob Ward, Thom Burns, Lisa Bravata et al. (+2 more)

For many decades, the National Institute of Standards and Technology (NIST) Atomic Spectroscopy Group housed a growing collection of thousands of photographic glass plate negatives. With the closure of the NIST Atomic Spectroscopy Group in March 2025, the irreplaceable collection needed a new home. Staff from NIST were contacted by staff from the Harvard Plate Stacks at the Center for Astrophysics | Harvard & Smithsonian (CfA). The Harvard Plate Stacks is the largest collection of astronomical glass plates in the world, with over 500,000 glass plate negatives from the 1880s to the 1990s. Given the long-standing history of the Harvard Plate Stacks and the expertise of the staff, it was decided that the NIST archive would move to the CfA. We summarize the contents of this collection regarding the instruments used and the spectra measured, and we present the tools and procedures we use for digitizing the collection. This includes the use of calibrated flatbed scanners for digitizing the plates themselves, as well as the digitization of correlated lab notebooks with important metadata associated with the plates.
Read the full abstract

All authors Jacob Ward, Thom Burns, Lisa Bravata, Gillian Nave, Adam Foster

Atomic Physics

Effective Conservation and Bistability of Atomic Alignment under Strong Spin~Exchange

Anton K. Vershovskii

We present a phenomenological model of anomalous alignment signals in dense cesium vapor under linearly polarized pumping and fast spin exchange near zero magnetic field. Despite the absence of a conservation law for rank-2 angular momentum, our recent experiments reveal anisotropic narrow resonances, hysteresis, and bistability. We attribute these effects to a stretched state forming a collective mode in which orientation and alignment are bidirectionally coupled. This mode acts as a reservoir, preserving the essential properties of alignment despite rapid spin exchange.
Read the full abstract

Atomic Physics · Cross-listed from quant-ph

Neutral atom quantum computing for materials science and quantum chemistry

J. D. Pritchard

Neutral atom arrays have emerged as versatile platforms for performing both digital and analogue quantum computing and simulation, with demonstrations ranging from large-scale programmable Hamiltonians realising topological phases or weighted graph optimisation to error-corrected logical qubits with transverse gate operations. This paper provides a broad overview to the neutral atom platform, and the potential applications relevant to materials science and quantum chemistry.
Read the full abstract

Atomic Physics

Small-Angle Differential Cross Sections for Symmetrical Resonant Charge Exchange in Molecular Hydrogen

Jibak Mukherjee, Kamal Kumar, Harpreet Singh et al. (+2 more)

We measured state selective scattering angle distributions in non-dissociative-state single electron capture in $\lbrace 5, 7.5, 10\rbrace$ keV/u, $\left[\mathrm{H^+ + H_2}\right]$ and $\left[\mathrm{H_2^+ + H_2}\right]$ collisions, using Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS). In our measurements, range of the scattering angle was small where diffraction effect is expected to take place, and, the ground state electron capture - symmetrical resonant channel for the $\mathrm{H_2^+}$ projectile and near resonant channel for the $\mathrm{H^+}$ projectile - was fully resolved from other channels. We analyzed the data considering $\mathrm{H_2^+}$ and $\mathrm{H_2}$ possess two independent-identical scattering centers and exhibit multi center interference effect. By comparing these equal-velocity collisions, we investigated the atomic nature of the individual scattering centers. We observed Fraunhofer diffraction from a circular aperture like patterns with equal fringe widths, for both the projectiles, in ground state channel. We applied a simple toy model to reconstruct the circular apertures.
Read the full abstract

All authors Jibak Mukherjee, Kamal Kumar, Harpreet Singh, Manojit Das, Deepankar Misra

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

Odd/Even or Half ? Entanglement Anomaly in the Bose-Hubbard model

Humberto E. López-Hernández and Santiago F. Caballero-Benitez

The area law relates the bipartite entanglement entropy of a quantum many-body ground state to the size of the boundary between the subsystems, but the geometry of this boundary is rarely discussed. We inspect this in the 1D Bose-Hubbard model at fixed density by comparing four spatial bipartitions of the periodic lattice: first half, second half, even sites, and odd sites; sharing the same number of sites but differing in how the boundary is arranged. We find analytical limits with perturbation theory: in the Mott insulator the contiguous cut obeys the area lay while the alternating cut obeys a volume law $S\propto N_s$, in this sense an anomaly, and for the superfluid both cuts colapse to the binomial saturation due to delocalization of the state. We formulate these limits as a statement about the many-body problem using a generalized slave-boson approach based on mean-field with quantum fluctuations while verifying with Exact Diagonalization (ED) for small lattice sizes and Densitiy Matrix Renormalization Group (DMRG) simulations for $N_s\gg 1$. The slave-boson Gaussian ground state allows to compute the entanglement entropy from a reduced correlation matrix for any desired bipartition consistent with ED and DMRG results. Using slave bosons the computational cost is set by the local cutoff $n_{\max}$ rather than the Hilbert space dimension, so we can reach lattice sizes far beyond ED. Our method is capable of establishing the partition-dependent scaling laws as a many-body feature, not only a finite-size effect, in great agreement with the ED for $N_s\in[4,10]$ and DMRG for larger lattice sizes.
Read the full abstract

Atomic Physics

Observation of multiphoton entanglement in resonance fluoresce

Xiao-Long Zhou, Jian Wang, Ze-Min Shen et al. (+8 more)

Resonance fluorescence, the process in which a single two-level quantum emitter interacts with a near-resonant coherent light, is a cornerstone of quantum optics as a paradigmatic light-matter interaction. Quantum phenomena in resonance fluorescence have been accounted for in terms of one- and two-photon processes; however, the physical processes arising from the interaction of a single two-level atom with higher photon numbers remain unexplored experimentally. Here we experimentally reveal the multiphoton scattering nature of resonance fluorescence, which intrinsically gives rise to multiphoton entanglement. By accessing quantum fluctuations in the field emitted from a cavity-quantum electrodynamics system, we resolve third- and fourth-order photon scattering events from a single two-level atom. In the three-photon component, the scattered photons are shown to be genuinely energy-time entangled, as verified by a violation of Svetlichny's inequality. As a demonstration of an application, a quantum secret sharing protocol (QSS) is implemented using this entangled photon source. Our study refines the descriptive framework of resonance fluorescence and broadens the scope of its investigation. It also establishes a fundamentally simple route for generating multiphoton entangled states for quantum information processing and quantum metrology.
Read the full abstract

All authors Xiao-Long Zhou, Jian Wang, Ze-Min Shen, Dong-Yu Huang, Si-Jian He, Qi-Yang Huang, Yi-Jia Liu, Yu-Shu Chen, Quan Jiang, Chuan-Feng Li, Guang-Can Guo

Wednesday 16 September

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

Radial dam breaks in a two-dimensional droplet bearing environment

F. Bristy, S. Chandramouli, G. A. Bougas et al. (+3 more)

The controlled dynamical generation of radial dam break flows (DBFs) is demonstrated in two-dimensional droplet environments. These ultracold mixtures feature competing mean-field and quantum fluctuation effects and are initialized on a disk-shaped uniform density. Depending on the value of the latter, reflecting also the dominance of attractive or repulsive interactions, three dynamical response regimes are identified. At small densities a moving wavetrain of bright ring solitons is observed (dubbed ring DBF), at intermediate densities a ring kink-dispersive shock wave, while at large densities the flows encompass composite ring kink-rarefaction waves moving towards the center. The emergence of these patterns, whose formation would be prohibited in two-dimensional Kerr media due to wave-collapse, is rooted in the competition between attraction and repulsion inherent to droplet environments, modeled by the extended Gross-Pitaevskii equation. The characterization of the ensuing nonlinear waveforms is further corroborated by reduced models based on the cubic-quintic nonlinear Schrödinger equation. The different wave patterns emanating from dam break flows can be experimentally realized using current state-of-the-art ultracold atom experiments.
Read the full abstract

All authors F. Bristy, S. Chandramouli, G. A. Bougas, G. C. Katsimiga, P. G. Kevrekidis, S. I. Mistakidis

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

Cavity-induced intertwining of density and pairing order in a degenerate Fermi gas

Sankalp Sharma, Farokh Mivehvar, Helmut Ritsch et al. (+1 more)

Recent quantum gas cavity-QED experiments demonstrated simultaneous coupling of photons to single atom transitions as well as correlated pairs of ultracold fermions trapped inside optical cavities. This enables simultaneous control over density ordering and pairing. Using extensive numerical simulations, we show that in a transversely driven, two-component degenerate Fermi gas, the interplay of cavity-induced and bare atom–atom interactions controls not only the power threshold for self-organization, but also the type of spatial ordering in the $\mathbb Z_2$-symmetry-broken superradiant state. In the repulsive interaction regime, unpaired or weakly paired fermions first self-organize through a charge-density-wave instability, and finite-momentum pairing only occurs at much stronger pump strengths. In contrast, an attractive superfluid undergoes a joint density–pairing instability, directly entering into intertwined phase with charge-density-wave and pair-density-wave orders. At strong pumping the photon-enhanced pair interaction generates localized density and pairing order even when the bare contact interaction is repulsive. In this cavity-dominated regime strong spatial localization suppresses the long range superfluid coherence. Our results identify the role of cavity-induced atomic interactions in supporting intertwined fermionic orders and pave the way for exploring exotic states with multiple orders in highly controlled hybrid light-matter systems.
Read the full abstract

All authors Sankalp Sharma, Farokh Mivehvar, Helmut Ritsch, Tomasz Wasak

Atomic Physics

Improved systematic uncertainty evaluation of the $^{171}$Yb optical lattice clock NMIJ-Yb1 with uncertainty of $2.6\times10^{-17}$

Takumi Kobayashi, Akiko Nishiyama, Ikuhiko Saito et al. (+4 more)

We report a systematic uncertainty evaluation of the $^{171}$Yb optical lattice clock NMIJ-Yb1 (NMIJ: National Metrology Institute of Japan) with a fractional frequency uncertainty of $2.6\times10^{-17}$, improved by a factor of 3.8 compared with our previous uncertainty. The uncertainty of the lattice light shift is reduced to $1.6\times10^{-17}$ by preparing axially sideband-cooled atoms in a shallow optical lattice. Different models to calculate the lattice light shift are compared, taking account of possible model-dependent biases due to the treatment of the radial motion of atoms trapped in the optical lattice. The uncertainty of the blackbody radiation shift reaches $7.0\times10^{-18}$ by measuring the radiative temperature at the position of atoms with an in-vacuum temperature sensor. We also demonstrate the nearly continuous operation of NMIJ-Yb1 with an uptime of 91.3 $\%$ for 10 days, showing the potential for future improvement of the calibration uncertainty of International Atomic Time.
Read the full abstract

All authors Takumi Kobayashi, Akiko Nishiyama, Ikuhiko Saito, Daisuke Akamatsu, Akio Kawasaki, Shintaro Nagase, Masami Yasuda

Atomic Physics · Cross-listed from physics.plasm-ph

X-Ray Spectroscopy for Characterizing Stimulated Raman Scattering in Inertial Confinement Fusion

Tianluo Luo, Zeyang Li, Yunping Wang et al. (+4 more)

Accurate characterization of stimulated Raman scattering (SRS) remains a critical challenge in inertial confinement fusion (ICF), as SRS not only scatters laser energy but also generates suprathermal electrons that preheat the fuel and degrade implosion performance. Conventional backscatter diagnostics provide direct measurements of SRS but cannot collect the entire scattered-light signal, limiting the accurate characterization of SRS strength. Using a non-local thermodynamic equilibrium collisional-radiative model with a double-Maxwellian electron distribution, we systematically investigate how suprathermal electrons modify the titanium K-shell x-ray emission spectra. The spectra exhibit high sensitivity to the suprathermal-electron fraction at relatively low bulk electron temperatures, making them particularly suitable for diagnosing suprathermal electrons during the early stage of ICF, when even a small suprathermal-electron population can compromise fuel compression. The calculated spectra reproduce experimental measurements from the Nova Laser Facility with good agreement, and the inferred suprathermal-electron fractions show improved consistency with independently measured SRS losses compared with the original spectral analysis by Glenzer~\href{https://doi.org/10.1103/PhysRevLett.81.365} {\text{[S. H. Glenzer et al., Phys. Rev. Lett. 81, 365(1998)]}}. These results demonstrate that K-shell spectroscopy, combined with accurate NLTE collisional-radiative modeling, provides a reliable probe of SRS strength in laser-produced plasmas. Hence, this approach may be extended to spatially resolved diagnosis of SRS strength, offering a promising complement to conventional backscatter diagnostics.
Read the full abstract

All authors Tianluo Luo, Zeyang Li, Yunping Wang, Zhihao Yang, Zhencen He, Dong Yang, Zhimin Hu

Atomic Physics · Cross-listed from hep-ph

Probing Lorentz-violating scalar forces and dark matter with precision matter and antimatter experiments

Yevgeny V. Stadnik

We explore a class of Lorentz-violating scalar-field models where the effects of the scalar field on antimatter can be strongly enhanced compared to matter. Non-trivial differences in phenomenology arise for spectroscopy measurements depending on whether the scalar field changes slowly or rapidly on the atomic scale. We highlight opportunities for precision tests in the laboratory including dark matter searches, in particular with spectroscopy and interferometry measurements, as well as certain types of antimatter experiments.
Read the full abstract

Atomic Physics

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Three-Particle Feynman Diagram Contribution to Core-Valence Correlations

G. Gaigalas, P. Rynkun and L. Kitovienė

In order to ascertain the precise atomic characteristics, it is important to incorporate a wide range of electron correlations in the computational analysis. However, it is important to note that undertaking such studies will result in substantial increases of the CSF expansions. The present publication, as well as the series of articles that have been published by G. Gaigalas, P. Rynkun, and L. Kitovienė, are dedicated to the analysis and resolution of the problem in question. In this series, a method was developed based on second-order perturbation theory to identify the most important core-valence, core, core-core, and valence-valence correlations. The method under discussion is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form. In this study, the method is further expanded to encompass additional core-valence electron correlations of the third and fourth types. Conversely, the correlations that are not encompassed by perturbation theory are addressed in a conventional manner. This method can be used to calculate the properties of an atom or ion with any number of valence and core electrons. As an example of its application, the atomic calculations of the energy structure and lifetime for Ne II are presented.
Read the full abstract

Atomic Physics

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Three-Particle Feynman Diagram Contribution to Valence-Valence Correlations

G. Gaigalas, P. Rynkun and L. Kitovienė

The method based on the second-order perturbation theory to identify the most important configuration state functions of the various correlations is extended to include valence-valence correlations, which are described by the three-particle Feynman diagram. The extension presented in this work complements the core-valence, core, core-core, and valence-valence correlations which were developed in a series of previous papers by G. Gaigalas, P. Rynkun and L. Kitovienė. Whereas these valence-valence correlations are described by the three-particle Feynman diagram, additional developments to calculate the spin-angular parts of this diagram have been made to the program library librang of the Grasp. As an example of the application of the developed method, the atomic calculations of the energy structure for the Se III are presented. In the present work, this method was also used to select the most significant configuration state functions and to use this basis to solve the self-consistent field equations.
Read the full abstract

Tuesday 15 September

Atomic Physics

Electrostatic quadrupole lens for focusing a cryogenic $^{205}$TlF molecular beam

Pengyu Zhou, Olivier Grasdijk, David DeMille et al. (+7 more)

Precision measurements with molecules require molecular beams with high flux and narrow divergence. Here we present the design, implementation, and characterization of an electrostatic quadrupole lens (EQL) for focusing a cryogenic beam of $^{205}$TlF molecules. The EQL consists of four electrodes operated at spatially alternating potentials up to $\pm 30$ kV. This configuration generates a transverse restoring force that focuses molecules prepared in selected manifold of hyperfine states. At the optimal applied voltage, the EQL increases the detected molecular signal by a factor of $14.4(4)$ at the current detection position. The measured lens gain, transverse Doppler spectra, and transverse spatial profiles are all reproduced by trajectory simulations using independently measured beam parameters as input. Based on this agreement, we project a gain of $16.5(8)$ for the full $7.9~\mathrm{m}$ CeNTREX beamline. These results establish the EQL as a key component for increasing sensitivity in precision experiments using cryogenic beams of polar molecules.
Read the full abstract

All authors Pengyu Zhou, Olivier Grasdijk, David DeMille, Jakob Kastelic, David Kawall, Jianhui Li, Oskari Timgren, Konrad Wenz, Yuanhang Yang, Tanya Zelevinsky

Atomic Physics · Cross-listed from quant-ph

Exact damping-basis continued fractions for few-atom lasers: collective correlations beyond second-order cumulant closure

Stephan Hartmann

We combine the Briegel–Englert damping basis of a lossy cavity mode with the permutation-invariant Liouville basis of \(N\) identical, incoherently pumped two-level emitters. The resulting Liouvillian is exactly block tridiagonal in a single radial field index, with atomic blocks of dimension \(\binom{N+3}{3}\). The stationary state follows from a matrix continued fraction whose asymptotic closure is a linear matrix equation that we prove to be uniquely solvable throughout the dissipative regime \(A>0\), and the same construction in the coherence-one sector yields the emission spectrum. The method is validated against direct diagonalization, weak-pump perturbation theory, and closed-system spectra, reaches \(N=16\) in tens of seconds in the few-quanta regime, and has a quantified precision limit at large photon number. We use it to derive an exact two-atom photon-balance identity that isolates the cavity-induced pair coherence and relates it to a singlet–triplet population difference; to establish an exact pump-order hierarchy of connected correlations for a zero-temperature cavity and a parity property of the minimal collective-spin sector; and to benchmark the second-order cumulant closure used in few-emitter laser theory, which we find to be semi-quantitative for the photon number but to predict the wrong sign of the inter-emitter coherence above inversion. In a good-cavity regime the exact solution shows near-Poissonian statistics and strong line narrowing for two and three emitters.
Read the full abstract

Atomic Physics

Angle-of-Arrival Determination of Radio-Frequency Fields Using Stark-Shifted Rydberg-EIT Spectra

Rajavardhan Talashila, Zoya Popovic, Nikunjkumar Prajapati et al. (+2 more)

We demonstrate a method for determining the magnitude of the angle of arrival (AoA) of a linearly polarized radio-frequency (RF) field using the angle-dependent spectral amplitudes of AC Stark-shifted electromagnetically induced transparency (EIT) resonances. An off-resonant RF field produces distinct Stark shifts of the $|m_J|$ sublevels, while their relative excitation strengths depend strongly on the relative orientation of the RF and optical polarizations. Under the controlled polarization geometry considered here, this dependence enables determination of the AoA magnitude without requiring RF phase measurements or spatially separated sensing locations. We experimentally demonstrate the method at RF frequencies of 1.27 GHz, 2 GHz, 3 GHz, and 4 GHz using a subwavelength cesium vapor cell. Within the $20^\circ-40^\circ$ region of highest angular sensitivity, the estimated repeatability-based $1\sigma$ AoA uncertainty ranges from approximately $0.6^\circ$ to $2^\circ$ across the investigated RF frequencies. A model combining Floquet-Shirley calculations of the RF-dressed Rydberg states with a coherent hyperfine-to-fine-structure optical excitation model qualitatively reproduces the experimental observations. These results establish a path toward compact, phase-independent AoA sensing using spatially localized Rydberg-atom spectroscopy.
Read the full abstract

All authors Rajavardhan Talashila, Zoya Popovic, Nikunjkumar Prajapati, Noah Schlossberger, Christopher L. Holloway

Atomic Physics

Improved calculation of the hyperfine structure of muonic helium

F. A. Martynenko, K. A. Seredina and A. P. Martynenko

Using perturbation theory for the fine-structure constant $\alpha$ and the electron-to-muon mass ratio, we calculated new contributions to the hyperfine structure of the ground state of the muon-electron helium atom. Compared to our previous results, we calculated new corrections in second-order perturbation theory. This calculation reduces the discrepancy between the theoretical value and the new experimental hyperfine structure measurement.
Read the full abstract

Atomic Physics · Cross-listed from quant-ph

Optimal Linear-Rate Conversion of Unknown Mixed Qubit States via SWAP Tests

Sujay Kazi and Iman Marvian

By consuming multiple copies of an unknown qubit state, one can modify its purity while preserving the direction of its Bloch vector. We determine the maximum linear rate at which qubit states of different purities can be interconverted, allowing a nonzero error, quantified, for instance, by the trace distance, provided that it vanishes in the limit of infinitely many copies. Interestingly, the optimal conversion rate is determined by the two eigenvalues of the complex right-logarithmic-derivative (RLD) Fisher information matrix associated with $\mathrm{SU}(2)$ rotations of the qubit state. When the output qubits have higher purity, corresponding to concentration, the optimal rate is given by the ratio of the maximum eigenvalues of the input and output RLD matrices. In contrast, when the output qubits have lower purity, corresponding to dilution, the optimal rate is given by the ratio of their minimum eigenvalues. Remarkably, both concentration and dilution can be implemented using SWAP tests as the only nontrivial two-qubit measurement primitive, together with ancillary qubits initially prepared in maximally mixed states, without requiring any additional two-qubit gates. Our work thus provides a novel operational interpretation of the full complex RLD Fisher information matrix. Crucially, its antisymmetric, purely imaginary part encodes geometric information beyond the statistical distance between density operators and plays an essential role in determining the optimal state-conversion rates.
Read the full abstract

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

Course on two-dimensional quantum gases

Hélène Perrin

This course on two-dimensional quantum gases, prepared for the São Paulo ICTP-SAIFR IVth School on Light and Cold Atoms, is organized into three lectures. The first introductory lecture addresses Bose-Einstein condensation in an ideal gas, the effect of interactions in the weakly interacting limit, Gross-Pitaevskii equation and its hydrodynamic formulation, as well as superfluidity. The second lecture is devoted to the main features of two-dimensional quantum gases: importance of the interactions, enhanced phase fluctuations and the emergence of a quasi long-range order, superfluidity through the Berezinskii-Kosterlitz-Thouless mechanism, scaling symmetry. The third lecture has taken the form of a seminar on fast rotating quasi two-dimensional Bose gases and thermal melting of the vortex lattice. The slides accompanying these notes can be found on the school website: https://www.ictp-saifr.org/slca2025/.
Read the full abstract