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Thursday 1 October

Atomic Physics

A Compact, High-Data-Rate, High-Sensitivity GMOT-Based Light-Pulse Atom Interferometer toward Time-Multiplexed, Multi-Axis Inertial Sensing

Benjamin Smith, Adrian Orozco and Jongmin Lee

Light-pulse atom interferometry has emerged as a promising approach for developing quantum inertial and gravity sensors for real-world applications, but achieving robust operation in dynamic environments without sacrificing sensitivity remains challenging. To mitigate performance degradations resulting from vibration-induced noise and mismatches in the spatial overlap between free-falling atoms and light pulses, we demonstrate a first-of-a-kind high-data-rate, high-sensitivity grating magneto-optical trap (GMOT)-based light-pulse atom interferometer (LPAI). This system uses a compact, rugged GMOT architecture, based on an in-vacuum microfabricated grating chip and a single laser-cooling beam, to enable high-data-rate GMOT-based cold-atom generation with sub-Doppler cooling. Our GMOT-based LPAI operates at high data rates (up to 100 Hz), while simultaneously achieving both high acceleration sensitivity (550 ng/rt-Hz at 20 Hz, 1.49 ug/rt-Hz at 45 Hz, and 6.31 ug/rt-Hz at 70 Hz) and good bias stability (71 ng). This compact, rugged architecture paves the way for field-deployable quantum inertial and gravity sensors in high dynamics and for time-multiplexed, multi-axis inertial sensing.
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Atomic Physics · Cross-listed from physics.chem-ph

State-selective molecular orientation by vibrational Autler-Townes adiabatic passage

Meng-Yi Yu, Ya-Nan Lv, Cun-Feng Cheng et al. (+1 more)

Control of molecular angular momentum orientation enables state-resolved studies of molecular interactions and provides a basis for quantum information processing. Here we propose all-optical Autler-Townes state-selective adiabatic passage (ASAP) to prepare molecules in a single $|J,M\rangle$ sublevel. An Autler-Townes branch created by a strong coupling field is selectively populated and adiabatically mapped onto the target vibrational state. We resolve detuning-dependent rovibrational Autler-Townes splitting in $^{13}$CO$_2$, establishing the spectroscopic basis for the selective excitation of the target dressed branch. The density-matrix model calibrated by these spectra predicts transfer approaching 90%. The scheme can exploit millisecond vibrational radiative lifetimes within the electronic ground state and extend to polar and nonpolar molecules with infrared-active vibrational modes.
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All authors Meng-Yi Yu, Ya-Nan Lv, Cun-Feng Cheng, Shui-Ming Hu

Atomic Physics · Cross-listed from quant-ph

Telecom-Band Optical Transitions of Erbium Atoms in Rare-Gas Solids

Evgenii Zaitsev, Alec Dinerstein, Shan Zou et al. (+6 more)

Rare-earth (RE) atoms, such as erbium (Er), have inner-shell optical transitions in the near-infrared, some of which are in the telecom bands. These transitions are largely insensitive to the host environment due to effective shielding by the filled outer shells. Cryogenic rare-gas (RG) solids, such as solid neon (Ne) and argon (Ar), combine high chemical purity with a nearly nuclear-spin-free environment, making them attractive solid hosts for preserving optical and spin coherence. In this work, we isolate neutral Er atoms in solid Ne and Ar at 6 K and characterize their emission by steady-state and time-resolved photoluminescence (PL) spectroscopy. In both hosts, we observe several near-infrared transitions between 1000–1500 nm, including inner-shell emission in the telecom O and E bands. The $4f \rightarrow 5d$ transition near 1299 nm forms a multiplet of narrow components, consistent with crystal-field splitting, and decays on a microsecond timescale. The $4f \rightarrow 4f$ transition near 1437 nm shows a matrix shift below 1 cm$^{-1}$ in both hosts. In solid Ne, its inhomogeneous linewidth is bounded by the spectrometer resolution to < 22 GHz, and its PL lifetime reaches up to 78.9 ms, close to the estimated radiative limit. Thermal annealing extends the 1437 nm lifetime in Ne and suppresses the phonon sidebands relative to the zero-phonon lines in Ar. These results identify RG solids as promising hosts for long-lived telecom-band Er emission and provide a foundation for future spin-photon interfaces and hybrid quantum architectures.
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All authors Evgenii Zaitsev, Alec Dinerstein, Shan Zou, Charles Peretti, Yutian Wen, Wei Guo, Gregory V. Hartland, Yizhong Huang, Dafei Jin

Wednesday 30 September

Atomic Physics

Nonrelativistic expansions of Dirac-Coulomb energy and first order relativistic Breit potential corrections for light Atomic and molecular systems

Wanping Zhou, Sanjiang Yang and Chen Tong

The nonrelativistic expansion method is applied to the Dirac-Coulomb energy and first order relativistic Breit potential corrections for light atomic and molecular systems to derive high-order effective energy correction operators for few-body systems. It is found that effective operators at the $m\alpha^8$ order contain incompletely separable divergences. These divergences must be canceled jointly with divergences arising from second- and third-order perturbations of lower-order energy correction operators, and such cancellation can be accomplished automatically by the nonrelativistic numerical expansion approach. Using Gaussian basis sets, we numerically compute contributions to the Dirac-Coulomb energy and relativistic Breit potential corrections up to order $m\alpha^8$ for the ground states of the hydrogen atom, hydrogen molecular ion, helium atom, and hydrogen molecule. These results confirm the reliability of the present method and enable its extension to more complex systems.
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Atomic Physics

Nuclear moments, charge radii, and magnetization distribution parameters of Ag isotopes from laser spectroscopy and ab initio electronic-structure calculations

Leonid V. Skripnikov, Bram van den Borne, Michail Athanasakis-Kaklamanakis et al. (+2 more)

The nuclear electromagnetic moments and mean-square charge radii of several silver (Ag) isotopes deduced from recent laser spectroscopy studies in the mass region $A=$ 96-121 are determined using high-accuracy electronic structure calculations performed in this work. We report hyperfine structure and isotope-shift atomic factors calculated with the relativistic coupled cluster approach, including single, double, triple, and perturbative quadruple excitations, CCSDT(Q). Following a systematic theoretical uncertainty analysis, we show that at the precision now achieved (sub-percent uncertainties in some cases), quantum electrodynamic effects become significant. We also show that the isotope-dependent effect in the hyperfine structure due to the non-point-like nuclear magnetization distribution can be extracted with negligible dependence on the assumed nuclear magnetization model at the present level of precision. This also yields a nuclear magnetic dipole moment that is corrected for the hyperfine anomaly induced by the Bohr-Weisskopf effect. In terms of the nuclear electric quadrupole moments, the uncertainty in the electric-field gradient used to extract the quadrupole moments from laser spectroscopy has also been reduced by one to two orders of magnitude relative to values used in previous studies. Finally, the nuclear charge radii of Ag isotopes are extracted using field- and mass-shift factors from our coupled cluster calculations, and the difference in mean-square charge radii between $^{107,109}$Ag agrees with the value deduced from muonic X-ray spectroscopy.
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All authors Leonid V. Skripnikov, Bram van den Borne, Michail Athanasakis-Kaklamanakis, Gleb Penyazkov, Ruben P. de Groote

Atomic Physics · Cross-listed from quant-ph

Parallel algebraic surgery for qLDPC codes with constant shuttling depth

Tian-Gang Zhou, Boren Gu, Jens Eisert et al. (+1 more)

Reconfigurable atom arrays provide a promising platform for high-rate quantum low-density parity-check codes, but their computational advantage depends on whether logical operations can be implemented without incurring prohibitive shuttling and space overheads. We introduce algebraic surgery for lifted product codes, co-designing the logical measurements, auxiliary codes, and atom shuttling to enable hardware-efficient Pauli-product measurements. These protocols provide flexible logical addressability subject to the cyclic-symmetry constraint, enabling a broad class of parallel logical measurements, including canonical logical operators with heavily overlapping physical supports and joint measurements within or between code blocks even with different lift sizes, while achieving constant shuttling depth on neutral-atom processors under explicit layout assumptions. In a representative hardware-model benchmark, a cycle supporting 33 parallel canonical logical measurements is about $2\times$ faster than the compared single-observable graph-based surgery schedules, with competitive qubit overhead. These shuttling and circuit-level simulations confirm that the algebraic structure of quantum low-density parity-check codes can be used not only to reduce space overhead, but also to simplify physical implementation and expand the set of efficiently accessible logical operations on neutral-atom processors.
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All authors Tian-Gang Zhou, Boren Gu, Jens Eisert, Chen Zhao

Atomic Physics

Radiative Data for As III, Se III, Hf IV, and Tl IV: HFR and MCDHF Calculations for Hot Subdwarf Spectroscopy

Jérôme Deprince, Lucas Maison, Solène Beauraind et al. (+3 more)

Accurate oscillator strengths for doubly and triply ionised heavy elements are required for quantitative spectroscopy of hot subdwarfs, but available data remain sparse. We present new radiative data for As III, Se III, Hf IV and Tl IV, calculated with the pseudo-relativistic Hartree-Fock (HFR) method including core-polarization effects and semi-empirical adjustment of radial parameters to experimental energy levels. Independent multiconfiguration Dirac-Hartree-Fock (MCDHF) computations were also performed for As III, Hf IV and Tl IV, while published MCDHF data were adopted for Se III to assess the reliability of the HFR oscillator strengths. The largest discrepancies between the two approaches are mainly associated with weak transitions, strong cancellation effects, or significant gauge disagreement. For strong transitions satisfying the adopted reliability criteria, we found a good agreement between the oscillator strengths obtained by both methods. The new data have already been applied to the spectra of the heavy-metal hot subdwarfs LS IV-14$^\circ$116 and EC 22536-5304, enabling abundance determinations for As, Se, Hf, and Tl and providing additional lines for future spectroscopic studies.
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All authors Jérôme Deprince, Lucas Maison, Solène Beauraind, Hélène Dupuis, Matti Dorsch, Pascal Quinet

Atomic Physics · Cross-listed from quant-ph

Rayleigh-Wood Threshold Controls Nonlinear Photon Correlations in Atomic Arrays

Zai-Cheng Xiao and Li-Ping Yang

Two-dimensional atomic arrays provide versatile free-space quantum optical interfaces by coupling photons to collective lattice modes. Here we show that the Rayleigh–Wood anomaly provides a sharp control mechanism for both linear and nonlinear photon scattering from a single atomic layer. As the lattice spacing crosses the diffraction threshold, newly opened radiative channels rapidly broaden the dominant collective modes, converting specular reflection into diffuse off-axis scattering. In transmission, momentum-space Fano interference between the incident and collectively scattered fields produces single-photon intensity zeros that strongly reshape the momentum-space correlation pattern. An integrated nonlinear contrast reveals a pronounced channel asymmetry: upon opening the Rayleigh channels, the connected two-photon contribution drops by several orders of magnitude relative to the factorized background in transmission, while remaining close to unity in reflection. These results establish radiative diffraction thresholds as a control principle for quantum nonlinear optics in single-layer atomic arrays.
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Tuesday 29 September

Atomic Physics · Cross-listed from quant-ph

Towards noble gas quantum optical magnetometry using direct ultraviolet detection

James Maldaner and Gil Porat

We analyze a novel approach for quantum magnetic sensing via optical detection of nuclear spin precession in a noble gas. The detection is carried out with an ultraviolet frequency comb laser, so no alkali vapor is required to be mixed with the noble gas during the sensing stage, allowing for hours-long spin relaxation time at room temperature. Our analysis reveals that combining high laser power and low laser intensity noise is crucial to achieving and exceeding state-of-the-art magnetometric performance, including that of cryogenic magnetometers. We find operational regimes where either fundamental or technical noise dominate, which directs experimental effort towards increasing laser power or lowering laser intensity noise, respectively. We also show that optimizing beam size is key to achieving optimal sensitivity. Our calculations predict that a record-breaking sensitivity of $24~\mathrm{aT}/\sqrt{\mathrm{Hz}}$ is achievable in 10 minutes with a 10 W ultraviolet laser with a relative intensity noise of -100 dBc/Hz.
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Atomic Physics · Cross-listed from quant-ph

Proposal for matter-wave interferometry with a rare-earth-doped microparticle

Chris Overstreet

Matter-wave interferometers are sensitive probes of low energy physics and have been used for precise tests of gravity and quantum mechanics. These applications would benefit from interfering particles of higher mass, but observing the interference of a large particle is challenging due to the need to control its initial state and to avoid decoherence. Here we propose to demonstrate matter-wave interference of a microparticle with an embedded rare-earth ion. Optical transitions of the rare-earth ion will impart momentum to the microparticle's center of mass. The use of a time-symmetric interferometer geometry and a rare-earth ion state with angular momentum $J = 1/2$ will eliminate sensitivity to the initial conditions of the microparticle. We show that the rates of all relevant external decoherence mechanisms either decrease or remain constant as the microparticle mass is increased, allowing decoherence to be avoided by using sufficiently large particles. An apparatus at moderate vacuum levels will support microparticle interferometry with up to $10^3$ photons per beam splitter and millisecond coherence time. This demonstration will establish microparticle interferometry as a new platform for quantum sensing, improving searches for minimal modifications of quantum mechanics by up to three orders of magnitude in the near term and laying the foundation for future gravitational tests.
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Atomic Physics · Cross-listed from physics.chem-ph

A Machine-Learned Interatomic Potential Free-Energy Surface for the First Step of MIL-101(Cr) Secondary Building Unit Formation

Orlando A. Mendible-Barreto and Yamil J. Colón

Metal-organic framework (MOF) self-assembly mechanisms remain poorly characterized because ab initio molecular dynamics (AIMD) are accurate but too computationally expensive to converge the free-energy surfaces (FES) that govern secondary building unit (SBU) nucleation and growth. This work addresses that limitation for the first step of MIL-101(Cr) SBU formation. Using MACE-POLAR-M, a long-range-aware equivariant machine-learned interatomic potential fine-tuned on a compact DFT reference dataset built from exploratory metadynamics, this work obtains a converged 2D FES for this step at a level of theory ({\omega}B97M-V/def2-TZVPP) at which AIMD would be prohibitively expensive. The pre-trained model samples relevant configurations but gets the thermodynamics wrong, predicting an endothermic reaction and a false global minimum. Fine-tuning corrects both, recovering the expected exothermic process and the correct product basin in agreement with proposed literature mechanisms. The resulting FES also refines the mechanism. It shows that water release from the chromium center proceeds stepwise, through two sequential energy barriers, rather than the single concerted step originally proposed. We find that model accuracy is specific to the reaction coordinate and does not extend to the dissociated fragment configurations excluded from fine-tuning, a direct consequence of the training-data choice that protects accuracy along the reaction path for the FES prediction task. Together, these results establish a validated, computationally tractable route to obtain free-energy surfaces for MOF formation chemistry, transferable to other reactions where AIMD remains prohibitive, and identify training-data composition as the key determinant of which reaction properties a fine-tuned checkpoint can reliably describe.
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Atomic Physics · Cross-listed from nucl-th

Neutron-nucleus scattering in an $L^2$-integrable basis

Bui Minh Loc and Calvin W. Johnson

First-principles calculations of scattering off quantum many-body systems such as atoms and nuclei is important but nontrivial, requiring large-dimension ($10^3$ to $10^8$ or more) bases. For the first time we apply to many-body targets a recently developed approach to find phase shifts in $L^2$-integrable bases, computing neutron-nucleus scattering using the same interactions as ab initio models of nuclei, in very small (dimension 3-6) bases. Our work shows the mean field dominates low-energy nuclear scattering; it also provides a foundation for more efficient future methodologies.
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Atomic Physics

Surface-Induced Spectral Broadening during Efficient Two-Photon Excitation of Cold $^{133}\text{Cs}$ Atoms near an Optical Nanofiber

Yuan Jiang, Xiaodong Qi, Nicolás Vera Paz et al. (+5 more)

We report the experimental observation of the $^{\text{133}}$Cs 6S$_{\text{1/2}}$ to 6D$_{\text{5/2}}$ single-frequency two-photon transition at low excitation power using an optical nanofiber embedded in a cold atom cloud. We investigate the 917 nm fluorescence spectra modified by the surface-induced interaction of the nanofiber, which exhibits a pronounced asymmetric broadening with a distinct red-shifted tail. We present a systematic theoretical description of the two-photon transition process of atoms near a nanofiber surface, considering atomic angular momentum coupling, guided-mode decay rate, and surface-induced van der Waals interactions. Owing to the tight spatial confinement provided by the guided evanescent field, efficient nonlinear excitation is realized at excitation powers down to tens of microwatts, corresponding to a reduction of approximately four orders of magnitude relative to typical free-space implementations. Our work reveals the interplay among waveguide-modified radiative dynamics, surface-induced interactions, and the spatial distribution of atoms around the nanofiber, and provides insights into further studies on nonlinear optical transitions and surface-mediated atomic dynamics in waveguide quantum electrodynamics systems.
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All authors Yuan Jiang, Xiaodong Qi, Nicolás Vera Paz, Yilin Chen, Tanbin Wu, Dianqiang Su, Pablo Solano, Yanting Zhao

Atomic Physics · Cross-listed from quant-ph

Measuring the spin of a spin-1/2 and getting a result of 7

Joseph McGowan IV, Nicholas Mantella, Noah Baker et al. (+1 more)

The weak value of an operator is the average result of measuring that operator on a quantum system given specified initial and final states. The overlap between these states appears in the denominator of the weak value, and thus if that overlap is small, the weak value can be arbitrarily large. In 1988, Albert, Aharonov, and Vaidman proposed a weak Stern-Gerlach experiment which would be able to measure a so-called anomalous weak value, a measurement result which lies out- side of the eigenvalue spectrum of the operator being measured. Though anomalous weak values have been measured in numerous optical systems, here we present the first such realization of this experiment as originally proposed. By placing a Bose-Einstein condensate of 87Rb in a magnetic gradient and performing an unlikely postselection, we measure an effective magnification of a weak magnetic momentum kick (~ 8 $\mu$m/s) by a factor of 14. We also demonstrate that increasing the momentum kick decreases the "weakness" of the measurement and reduces the amplification.
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All authors Joseph McGowan IV, Nicholas Mantella, Noah Baker, Aephraim M. Steinberg

Atomic Physics

Spin-exchange interactions between circular Rydberg atoms over long times

Andrés Durán-Hernández, Gautier Creutzer, Aurore Alice Young et al. (+5 more)

Arrays of neutral atoms excited to Rydberg levels have emerged as one of the most promising platforms for quantum computation and simulation. With the hope to outperform classical devices, the number of atoms has been increased by orders of magnitude. However, the interaction time, i.e., the maximum accumulated time during which an atom interacts with its neighbours, has been limited to a few microseconds only. This restrains the number of gates per atom or prevents the simulation of long-time dynamics of quantum many-body systems. Here, we observe the spin-exchange interaction between two spin 1/2s encoded in laser-trapped circular Rydberg atoms over more than $60\mu s$ and 40 spin-oscillation periods, improving the state of the art by an order of magnitude. These unprecedented timescales allow us to record for weak atomic trapping a collapse and revival of the spin-exchange oscillation contrast induced by spin-motion coupling. Our results constitute the first observation of this coupling with laser-trapped Rydberg atoms. To counteract its detrimental effect for quantum simulation, we demonstrate a novel dynamical decoupling method that prevents the collapse of the spin oscillations. This method exploits the advantages of our recently developed hybrid platform that enables the measurement and the optical manipulation of long-lived circular Rydberg atoms with auxiliary Rydberg atoms. This work opens a direct route to long-duration quantum simulation of strongly-interacting many-body systems.
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All authors Andrés Durán-Hernández, Gautier Creutzer, Aurore Alice Young, Abderrahmane Kassid, Yohann Machu, Jean-Michel Raimond, Michel Brune, Clément Sayrin

Atomic Physics

All-optical switching in a trapped ion cavity QED system: a comparative study

Abhijit Kundu, Vijay Bhatt and Arijit Sharma

We investigate the transient dynamics of cavity-EIT-based all-optical switching in a system of trapped ions coupled to an optical cavity through numerical simulations. In contrast to steady-state analysis, the time-dependent response provides direct insight into the switching speed, transient dynamics, and achievable switching contrast. We consider three distinct switching schemes and systematically compare their performance as a function of the relevant system parameters. The switching contrast is evaluated from the time-dependent cavity output and used to characterize the performance of each scheme. For the four-level N-type system, we find distinct trade-offs between switching through suppression of the cavity-EIT signal and switching through resonance shifting, with the former exhibiting a faster temporal response. The corresponding three-level scheme can achieve near-unity switching contrast with substantially shorter switching pulses, although it does not provide an independent switching control field. These results establish the performance limits and trade-offs of different cavity-EIT-based switching schemes and provide guidelines for optimizing their operation for applications such as high-speed optical gating, frequency-selective photon routing, frequency-multiplexed quantum communication, etc.
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Atomic Physics

Shortcut to Adiabatic Transfer in a Four-Level N-type System using Counterdiabatic Driving

Marius Romuald Kamsap, Simon Evehe Ndong, Maïk Delon Mboumba et al. (+5 more)

The stimulated Raman shortcut-to-adiabatic passage (STIRSAP) technique has been demonstrated to accelerate adiabatic population transfer processes. Traditionally applied to three-level atomic systems, this method enables rapid and efficient population transfer in a short interaction time. In this work, we extend this approach to a four-level N -type system driven by three laser fields. Under the three-photon phase matching condition, the first-order Doppler effect can be completely eliminated, making this configuration more suitable for applications in frequency metrology and quantum information processing. By adiabatically eliminating the intermediate state, the four-level system is effectively reduced to a two-level model, enabling the application of counterdiabatic driving without requiring additional couplings. This approach allows for fast and efficient population transfer between metastable states. We analyze the influence of laser intensity peaks and detuning, and we show that the transfer time is significantly shorter than that achieved with the STIRAP technique. Moreover, we also show 1 that an optimal coupling strength between the ground and metastable states further minimizes the operation time.
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All authors Marius Romuald Kamsap, Simon Evehe Ndong, Maïk Delon Mboumba, Mathurin Esouague Ateuafack, Christian Kenfack-Sadem, Thierry Blanchard Ekogo, Alain-Brice Moubissi, Caroline Champenois

Atomic Physics · Cross-listed from quant-ph

A magnetic-field insensitive gate set for trapped-ion nuclear spin qubits

Jonathan Paul Home, Jeremy Flannery, Matteo Mazzanti et al. (+2 more)

We outline a complete set of operations for manipulating nuclear spin qubits of trapped-ions stored in high magnetic fields such as required for Penning trapping, where the nuclear and electron spins are largely decoupled due to the dominance of the external field Hamiltonian. The reduced nuclear magnetic moment results in insensitivity to external magnetic fields compared to the use of an electron spin, but also makes the nuclear spin hard to manipulate on fast timescales. To maintain speed, we propose a two-qubit phase gate technique which utilizes the electron spin, but for which the qubit remains protected from magnetic fields through retaining the nuclear encoding. This method works for magnetic-field insensitive qubits at lower fields as well as for both microwave and laser field gradients.
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All authors Jonathan Paul Home, Jeremy Flannery, Matteo Mazzanti, Jan Apolin, Shreyans Jain

Atomic Physics

Attosecond circular-dichroism spectroscopy of hole ring currents

Guangru Bai, Zhihui Lyu, Jinlei Liu et al. (+2 more)

Ultrafast ionization of atoms by circularly polarized few-cycle laser pulses generates a hole ring currents, offering a route for ultrafast manipulation of magnetism. Here we explore the subcycle formation of these currents whose circulation direction is determined by the driving-field helicity, whereas their magnitude is governed by the quantum coherence of the residual ion. We show that the correlated ion-photoelectron dynamics can be probed with attosecond transient-absorption circular dichroism. Using the Wigner-Eckart theorem, we derive a linear relation between state-resolved dichroic absorption and the orbital and spin angular-momentum projections of the hole, thereby extending the Thole-Carra magnetic CD sum rules from static X-ray spectroscopy to attosecond electron dynamics. The modulation depth of the dichroic signal provides a direct optical measure of the coherence injected by ionization, and its dependence on the pump-pulse duration reveals a competition between coherence build-up and ionization-induced dephasing. These findings demonstrate the potential of attosecond circular dichroism for probing ionic coherence and highlight the role of quantum coherence in ultrafast angular momentum exchange between light and matter.
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All authors Guangru Bai, Zhihui Lyu, Jinlei Liu, Jing Zhao, Zengxiu Zhao

Monday 28 September

Atomic Physics · Cross-listed from cond-mat.str-el

Artificial versus Natural Atoms: The uncanny capability of the many-body Schrödinger equation to produce emergent behavior

Constantine Yannouleas

The paper reviews the theoretical and experimental progress achieved in the last 25 years in understanding the novel physics of artificial atoms and molecules as arising from the formation of Wigner molecules (WMs) of localized (to a stronger or lesser extent) fermionic or bosonic particles, which are finite quantum analogs of the more familiar bulk Wigner crystal. The term artificial atoms, as used here, encompasses a broad range of recently fabricated quantum nanodevices and experimental apparatuses consisting of a finite number of mutually repelling confined particles, including two-dimensional semiconductor and moiré transition metal dichalcogenide quantum dots, as well as trapped ultracold neutral atoms or ions. These nano-sized or micro-sized artificial devices and apparatuses (in single well or multi-well of variable-shape arrangements) hold a great promise for technological applications in the field of quantum information and quantum computers, as well as for advances in fundamental many-body physics. Prominent quantum effects of Wigner molecularization are the strong quenching of the spectral energy gaps, the appearance of rovibational spectra (in analogy with natural molecules), entanglement, and pinning due to an external perturbation. In high magnetic fields or at rapid rotation, WMs provide an alternative theory to the fractional quantum Hall effect. The physics of Wigner molecules is shown to derive from the solutions of the many-body Schrödinger equation (MBSE) in the regime of strong interparticle correlations arising from the dominance of the potential over the kinetic energy, or from a high magnetic field, as well as from a rapid rotation... (continues in the paper).
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Atomic Physics

Qprop-ND: A Nondipole Extension of the Qprop Package for Strong-Field Laser Physics

Haoyuan He, Zhao-Han Zhang, Karen Z. Hatsagortsyan et al. (+1 more)

The Qprop 3.0 package for the solution of the time-dependent Schrödinger equation for an electron in a laser field and atomic potential is extended to incorporate nondipole effects related to the laser wave propagation. The developed code can be used for the simulation of strong field atomic phenomena in the nondipole regime, such as above-threshold ionization, ionization stabilization in high-frequency laser fields, high-order harmonic generation, when the effects connected with the magnetic field are non-negligible or when the laser wavelength is comparable with the atomic size. Similar to the dipole Qprop the wave function is expanded in spherical harmonics, the time-propagation of the wave functions is performed using the Crank- Nicolson approach, and the photoelectron spectra are calculated employing the t-SURFF or i- SURFV methods. The validity and accuracy of the implementation are demonstrated through several illustrative examples.
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All authors Haoyuan He, Zhao-Han Zhang, Karen Z. Hatsagortsyan, Christoph H. KeiteL

Atomic Physics

Raman Transitions in Collinear Laser Spectroscopy for High-Precision Frequency Measurements

Julien Spahn, Hendrik Bodnar, Kristian König et al. (+2 more)

We demonstrate stimulated Raman spectroscopy on dipole-forbidden fine-structure transitions in a fast ion beam. It is applied to the $\mathrm{S}_{1/2}\rightarrow\mathrm{D}_{5/2}$ clock transition in $^{88}\mathrm{Sr}^{+}$ and combined with a subsequent E1 transition to allow for its detection by standard fluorescence detection. Building on this, the $\mathrm{D}_{3/2}\rightarrow\mathrm{D}_{5/2}$ fine-structure splitting is measured directly using a Doppler-free scheme employing two subsequent Raman transitions. These measurements demonstrate a path toward precision collinear laser spectroscopy of narrow transitions on short-lived isotopes beyond the linewidth limit of conventional electric-dipole spectroscopy, which can be used to probe fundamental aspects of atomic and nuclear physics.
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All authors Julien Spahn, Hendrik Bodnar, Kristian König, Wilfried Nörtershäuser, Robbe Van Duyse

Atomic Physics

Reconstructing Molecular-Ion Quantum States with Two-Color Strong-Field Scattering

Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay et al. (+6 more)

Strong-field ionization of molecules can prepare coherent superpositions of ionic states whose amplitudes and relative phases govern the ensuing ultrafast dynamics, but accessing this information experimentally remains a challenge. Here we introduce two-color strong-field scattering, in which a strong mid-infrared field ionizes the molecule and launches an electron, while a weak second harmonic field resonantly couples vibronic states of the parent ion during the electron's continuum excursion, thereby introducing structural changes on the sub-laser-cycle timescale. Scanning the relative phase between the two colors controls the ionic evolution and maps it onto phase-dependent sub-angstrom bond-length changes retrieved from the rescattering signal. Using the example of N$_2$, we apply the two-color setup to probe the coherence between different ionization channels and to reconstruct the initial ionic superposition. Our results establish two-color strong-field scattering as a powerful structural approach to characterize the complex amplitudes of ion quantum wavepackets.
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All authors Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay, Vyacheslav Leshchenko, Cosmin I. Blaga, Misha Ivanov, Pierre Agostini, Maria Richter, Louis F. DiMauro

Atomic Physics

Potential-energy surfaces of water and its molecular ions up to H$_2$O$^{3+}$

Giorgio Visentin and Agapi Emmanouilidou

We compute the potential-energy surfaces for molecular ions up to H$_2$O$^{3+}$ with any combinations of outer-valence, inner-valence and core holes. To obtain the potential-energy surfaces, we consider several ab initio techniques based on the CASSCF method and benchmark them with respect to the literature. We thus identify the techniques which produce accurate potential-energy surfaces as a function of the two bond lengths and the angle between the two bond lengths. These potential-energy surfaces will be used in future studies of the interaction of water with free-electron laser pulses. Furthermore, the techniques employed in this work in the context of water can be used to obtain the potential-energy surfaces of other triatomic molecules.
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Atomic Physics · Cross-listed from quant-ph

Cubic Phase Gate with a Trapped Ion Oscillator

Nigel Benjamin Lee Junsheng, Eugene Koh Jun Wei, Mu Young Kim et al. (+1 more)

The motional modes of trapped ions are promising candidates for continuous-variable (CV) quantum computation and simulation. However, to achieve a universal gate set for CV quantum computation, anharmonic nonlinear unitaries are required. Here, we experimentally demonstrate a protocol that allows us to approximate the cubic phase gate. By numerically optimizing the phase angles and amplitudes of a set of state-dependent force pulses, we demonstrate the cubic phase gate for both vacuum and low-$\alpha$ coherent state inputs and verify its performance. Our protocol can also be extended to approximate other nonlinear unitaries.
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All authors Nigel Benjamin Lee Junsheng, Eugene Koh Jun Wei, Mu Young Kim, Dzmitry Matsukevich

Atomic Physics

Interactions and dynamics of metastable triplet-state helium dimer with Ne and Ar

Dibyendu Sardar and François Lique

Helium dimer in its metastable triplet electronic state, He$_2(a~^3\Sigma_u^+)$, is a promising candidate for direct laser cooling and precision measurements. Interactions and collisions involving He$_2(a~^3\Sigma_u^+)$ remain unexplored in ultracold and cold energy domains. Here, we present the first theoretical investigation of intermolecular interactions and collision dynamics of He$_2(a~^3\Sigma_u^+)$+Ne van der Waals complex. For the ground electronic state, $X~^3\mathrm{A}'$, we employ a spin-restricted coupled cluster method with single, double, and noniterative triple excitations. The resulting interaction potential exhibits an extremely shallow well with a depth of 4.612 cm$^{-1}$. We construct a three-dimensional vibrationally averaged potential energy surface. Using this surface, we perform full close-coupling calculations including fine-structure levels of He$_2(a~^3\Sigma_u^+)$ to investigate collisional excitation and quenching induced by Ne. We analyze the low-energy scattering dynamics and model resonant features associated with quasi-bound states supported by interaction potential. Propensity rule for fine-structure conserving transitions is established. We additionally consider He$_2$+Ar collisions and compare their energy dependence and resonance structure with those of He$_2$+Ne. The He$_2$+Ar system exhibits a richer resonance structure, highlighting the sensitivity of low-energy scattering to interaction potential and reduced mass. Calculated PES and scattering properties provide a reliable benchmark for description of He$_2$+Ne van der Waals complex and may be useful for interpretation of future experimental spectra and collision measurements.
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Atomic Physics

Breit interaction in elastic scattering of vortex electron on Hydrogen atomic target

Pengcheng Zhao

The interaction of electron vortex beams with atoms is fundamental to their applications, yet existing studies on elastic scattering have considered only the Coulomb interaction. The role of the Breit interaction, which represents the leading relativistic correction to the Coulomb potential between two electrons, has not been systematically examined. We study the elastic scattering of a \(300\) keV vortex electron by a hydrogen atomic target, with emphasis on the role of the Breit interaction. Comparisons are made between the pure Coulomb contribution and the sum of the Coulomb and Breit contributions. Our results show that the Breit interaction dominates the scattering process in certain kinematic regions when the total angular momentum (TAM) of the vortex electron is sufficiently large, which breaks with the conventional notion that the Breit interaction has little contribution to electron scattering for low-\(Z\) atoms. This phenomenon arises primarily because a vortex electron with large angular momentum possesses a substantial magnetic moment, and the Breit interaction precisely describes the interaction between magnetic moments. We further compare single-atom, mesoscopic, and macroscopic target cases, and show that the target size significantly influences the observability of the Breit-induced effects, with a smaller target size being favorable for observing this phenomenon.
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Atomic Physics · Cross-listed from quant-ph

Observation of a topological edge state among localized bulk states in the anisotropic quantum Rabi model

Sungjoo Lim, Chanyang Im, Christopher G. Yale et al. (+7 more)

Topological phases are governed by discrete symmetries that protect boundary modes against local perturbations. When translational periodicity is absent, the bulk states also become localized, so that a topological edge state can no longer be distinguished from them by spatial localization alone. Here, we investigate the topological edge state (TES) and bulk eigenstates of the anisotropic quantum Rabi model (AQRM) in a trapped-ion quantum simulator. The AQRM hosts a topological phase in a one-dimensional synthetic lattice, whose translational symmetry is broken by the non-uniform couplings scaling with the site index. While both the TES and bulk states show localized distributions, we find that the TES exhibits well-defined chirality and near-complete spin–boson separability as signatures of the topological phase, in contrast to the bulk states. Phase-space tomography further reveals that the bosonic component of the TES is a squeezed vacuum state, with squeezing up to 6.45 dB. These results identify the TES through its intrinsic topological signatures and establish eigenstate-level characterization as a route to probing topological phenomena.
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All authors Sungjoo Lim, Chanyang Im, Christopher G. Yale, Brian K. McFarland, Edward C. Tortorici, Daniel S. Lobser, Melissa C. Revelle, Susan M. Clark, Mahn-Soo Choi, Junki Kim

Sunday 27 September

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

Spectral Crossings Diagnose Multiply Quantized Vortex Splitting

Jongheon Baek, Hiroyuki Tajima and Gihwan Nam

A charge-$r$ coupling vortex can remain as one fused order-$r$ zero or split into $r$ nearby unit-charge zeros after weak symmetry breaking. The two configurations have the same total winding and the same number of dark states in the lowest-Landau-level projection, so neither the imposed orbital angular momentum nor the total winding number distinguishes their local geometry. We study this distinction in a two-component Haldane-sphere model coupled by a Raman field. For monopole flux $N$, the detuning $\tau_{\rm c}$ at which a defect branch crosses zero energy scales as $|\tau_{\rm c}|\sim N^{-(r+1)}$ for a fused zero and $N^{-2}$ for resolved unit zeros. A Feshbach reduction establishes these asymptotic laws for the full multiband Hamiltonian, and numerical calculations in a monopole-harmonic basis confirm the fused-vortex scaling for $r=1,2,3$. For a partially split cluster of diameter $d$, the scaling crosses over when $d$ is comparable to the magnetic length $\ell_B$, allowing $d$ to be inferred spectroscopically even below the spatial resolution of direct imaging.
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Atomic Physics · Cross-listed from hep-ex

First measurement of the antihydrogen production cross section through the charge-exchange reaction of low-energy antiprotons with orthopositronium

GBAR Collaboration: P. Adrich, I. Belosevic, M. Chung et al. (+41 more)

The GBAR experiment has measured the formation rate of antihydrogen from antiproton impact on a positronium cloud for antiproton kinetic energies of 4 and 6 keV. This is the first charge-exchange cross section measurement performed using antiproton beams, which are provided by the AD-ELENA facility at CERN. The measured cross section values are $(14.1 \pm 1.3 \mathrm{(stat)} ^{+2.2}_{-1.4} \mathrm{(sys)}) \times 10^{-16}$~cm$^2$ at 6.2 keV energy and $(8.7 \pm 2.4 \mathrm{(stat)} ^{+1.5}_{-0.09} \mathrm{(sys)}) \times 10^{-16}$~cm$^2$ at 4.15 keV energy, and agree with recent theoretical three-body calculations for antihydrogen formation. These measurements are an important input for experiments with antimatter, e.g the planned measurements of antihydrogen gravitational acceleration in the GBAR collaboration.
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All authors GBAR Collaboration: P. Adrich, I. Belosevic, M. Chung, P. Cladé, P. Comini, P. Crivelli, P. Debu, A. Douillet, S. Geffroy, S. Guellati-Khelifa, P. Guichard, P.-A. Hervieux, L. Hilico, P. Indelicato, S. Jonsell, J.-P. Karr, B. Kim, S. Kim, E.-S. Kim, N. Kuroda, B. Lee, L. Liszkay, D. Lunney, G. Manfredi, B. Mansoulié, V. Martimort, M. Matusiak, V. Nesvizhevsky, F. Nez, K. Park, N. Paul, E. Perez, P. Pérez, C. Regenfus, C. Roumegou, J.-Y. Roussé, F. Schmidt-Kaler, K. Szymczyk, T. A. Tanaka, B. Tuchming, D. P. van der Werf, D. Won, S. Wronka, P. Yzombard