We study the creation and breakdown of a quantized vortex shear layer forming between a stationary Bose-Einstein condensate and a stirred-in persistent current. Once turbulence is established, we characterize the progressive clustering of the vortices, showing that the cluster number follows a power-law decay with time, similar to decaying turbulence in other two-dimensional systems. Numerical study of the system demonstrates good agreement of the experimental data with a point vortex model that includes damping and noise. With increasing vortex number in the computational model, we observe a convergence of the power-law exponent to a fixed value.

Motivated by ongoing pump-probe spectroscopy experiments, this work develops a theoretical framework for describing the rovibrational wave-packet dynamics that ensues when a single weakly bound van der Waals trimer is exposed to a short, subpicosecond linearly polarized pump laser pulse. The intensity $I$ of the pump laser is chosen such that excitation and ionization of the electronic degrees of freedom are negligible, while excitation of the wave packet in the nuclear degrees of freedom is non-negligible. The numerical treatment, which takes advantage of the fact that the laser pulse is very short compared to typical molecular time scales, is based on a wave-packet decomposition that utilizes hyperspherical coordinates. The framework is applied to the extremely floppy bosonic helium trimer. A convergence analysis of the partial-wave decomposition is conducted. The kinetic-energy release and orientation dynamics are presented. While the dynamics of more strongly bound van der Waals trimers such as, e.g., the argon trimer, display negligible coupling between vibrational and rotational degrees of freedom, rendering a description within a rigid-body picture appropriate, those of weakly bound trimers display non-negligible coupling between vibrational and rotational degrees of freedom, rendering a description within a rigid-body picture inappropriate. It is shown that a model that constructs the helium trimer dynamics from the dynamics of the helium dimer captures a number of key characteristics of the alignment signal, including the interference between different angular momentum wave-packet components.

Controlling wave transmission is crucial for various applications. In this work we apply the concept of unitary control to manipulate multiport wave transmission. Unitary control aims to control the behaviors of a set of orthogonal waves simultaneously. The approach fully harnesses the capability of wavefront shaping techniques, with promising applications in communication, imaging, and photonic integrated circuits. Here we present a detailed theory of unitary control of wave transmission, focusing on two key characteristics: total (power) transmittance and direct (field) transmission. The total transmittance for an input port represents the fraction of total transmitted power with respect to the input power for a wave incident from an input port. The direct transmission for an input port denotes the complex transmission amplitude from that input port to its corresponding output port. We address two main questions: (i) the achievable total transmittance and direct transmission for each port and (ii) the configuration of unitary control to attain desired transmission values for each port. Our theory illustrates that unitary control enables uniform total transmittance and direct transmission across any medium. Furthermore, we show that reciprocity and energy conservation enforce direct symmetry constraints on wave transmission in both the forward and backward directions under unitary control.

While perturbation theories constitute a significant foundation of modern quantum system analysis, extending them from the Hermitian to the non-Hermitian regime remains a nontrivial task. In this work, we generalize the Rayleigh-Schrödinger perturbation theory to the non-Hermitian regime by employing a geometric formalism. This framework allows us to compute perturbative corrections to eigenstates and eigenvalues of Hamiltonians iteratively to any order. Furthermore, we observe that the recursion equation for the eigenstates resembles the form of the Girard-Newton formulas, which helps us uncover the general solution to the recursion equation. Moreover, we demonstrate that the perturbation method proposed in this paper reduces to the standard Rayleigh-Schrödinger perturbation theory in the Hermitian regime.

We simulate the Gross-Pitaevskii equation to model the development of turbulence in a quantum fluid confined by a cuboid box potential and forced by shaking along one axis. We observe the development of isotropic turbulence from anisotropic forcing for a broad range of forcing amplitudes and characterize the states through their Fourier spectra, vortex distributions, and spatial correlations. For weak forcing the steady-state wave-action spectrum exhibits a $k^{-3.5}$ scaling over wave number $k$; further decomposition uncovers the same power law in both compressible kinetic energy and quantum pressure, while the bulk superfluid remains phase coherent and free from extended vortices. As the forcing energy exceeds the chemical potential, extended vortices develop in the bulk, disrupting the $k^{-3.5}$ scaling. The spectrum then transitions to a $k^{-7/3}$ regime for compressible kinetic energy only, associated with dense vortex turbulence, and phase coherence limited to the healing length. The strong forcing regime is consistent with an inverse cascade of compressible energy driven by small-scale vortex annihilation.

Recently we introduced a local photon approach for modeling the quantized electromagnetic field in position space. Using this approach, we define the momentum of light in this paper as in quantum mechanics as the generator for spatial translation. Afterward, we analyze the momentum dynamics of photonic wave packets which transition from air into a denser dielectric medium. Our analysis shines new light onto the Abraham-Minkowski controversy, which highlights the intricacies involved in the characterization of the momentum of the electromagnetic field. Although our results align with Minkowski's theory and with the definition of the canonical momentum of light in quantum electrodynamics, there are also some crucial differences.

Magic trapping of ground and Rydberg states, which equalizes the AC Stark shifts of these two levels, enables increased ground-to-Rydberg state coherence times. We measure via photon storage and retrieval how the ground-to-Rydberg state coherence depends on trap wavelength for two different traps and find different optimal wavelengths for a one-dimensional optical lattice trap and a running wave optical dipole trap. Comparison to theory reveals that this is caused by the Rydberg electron sampling different potential landscapes. The observed difference increases for higher principal quantum numbers, where the extent of the Rydberg electron wave function becomes larger than the optical lattice period. Our analysis shows that optimal magic trapping conditions depend on the trap geometry, in particular for optical lattices and tweezers.

This article solves two major tasks that frequently arise in the theory of electron collisions with a target molecular cation. First, it extends the energy-dependent frame transformation (EDFT) treatment, which is needed to map fixed-nuclei electron-molecule scattering matrices into an energy-dependent laboratory-frame scattering matrix with vibrational channel indices. The EDFT mapping can now be carried out even when the target molecule possesses multiple low-energy potential curves, significantly transcending previous applications. Second, it implements a method to extract the rest of the full laboratory-frame scattering matrix, i.e., the columns and rows describing input and/or output dissociation channels. The treatment is benchmarked in this article against the essentially exact solution of a refined two-dimensional model of the singlet gerade $\mathrm{\Sigma }$ symmetry of ${\mathrm{H}}_2$. Our tests demonstrate that the theory accurately maps fixed-nuclei scattering information, of the type provided by existing electron-molecule computer codes, into a laboratory-frame scattering matrix that includes both ionization and dissociation. This treatment can provide a general framework applicable to a broad class of electron collision processes involving diatomic target ions, suitable for an accurate description of challenging processes such as dissociative recombination.

Even though the one-dimensional contact interaction requires no regularization, renormalization methods have been shown to improve the convergence of numerical calculations considerably. In this work, we compare and contrast these methods: “the running coupling constant” where the two-body ground-state energy is used as a renormalization condition, and two effective interaction approaches that include information about the ground as well as excited states. In particular, we calculate the energies and densities of few-fermion systems in a harmonic oscillator with the configuration-interaction method and compare the results based upon renormalized and bare interactions. We find that the use of the running coupling constant instead of the bare interaction improves convergence significantly. A comparison with an effective interaction, which is designed to reproduce the relative part of the energy spectrum of two particles, showed a similar improvement. The effective interaction provides an additional improvement if the center-of-mass excitations are included in the construction. Finally, we discuss the transformation of observables alongside the renormalization of the potential, and demonstrate that this might be an essential ingredient for accurate numerical calculations.

Crossed optical dipole traps (ODTs) provide three-dimensional confinement of cold atoms and other optically trappable particles. However, the need to maintain the intersection of the two trapping beams poses strict requirements on alignment stability and limits the ability to move the trap. Here we demonstrate a crossed ODT design that features inherent stability of the beam crossing, allowing the trap to move and remain aligned. The trap consists of a single high-power laser beam, imaged back onto itself at an angle to form a crossed trap. Self-aligning behavior results from employing an imaging system with positive magnification tuned precisely to unity. We employ laser-cooled samples of ${}^6\mathrm{Li}$ atoms to demonstrate that the trap remains well aligned over a 4.3-mm travel range along an axis approximately perpendicular to the plane containing the crossed beams. Our scheme can be applied to bring an atomic cloud held in a crossed ODT close to a surface or field source for various applications in quantum simulation, sensing, and information processing.

Plane electromagnetic waves in a Lorentzian dispersive medium (collection of classical oscillators) with a stepwise periodic modulation of oscillator density are considered. To account for the physical difference between the acts of involving new oscillators into motion and removing oscillators from the motion, different continuity conditions are used at the steps of the increase and decrease of the oscillator density. The continuity conditions are obtained from the general constitutive equations for an arbitrary nonmonotonic time dependence of the oscillator density. It is found that eigenmodes of the periodically modulated medium are decaying even for undamped oscillators. This leads to a decay of an initial wave energy after starting the modulation for any parameters of the modulation. The obtained results disprove many recent predictions that parametric amplification can occur in a Lorentzian medium with modulated oscillator density. Despite energy losses, promising wave transformation regimes, such as frequency multiplication and division with high-amplitude efficiency, are found.

We report the experimental determination of the interspecies $s$-wave scattering length ($a_{34}$) between the $2{}^3{S}_1(F=3/2,m_F=3/2)$ state of ${}^3\mathrm{He}^{*}$ and the $2{}^3{S}_1(m_J=1)$ state of ${}^4\mathrm{He}^{*}$. We determine $a_{34}$ by inducing oscillations in a trapped Bose-Einstein condensate of ${}^4\mathrm{He}^{*}$ and measuring the damping rate of these oscillations due to the presence of ${}^3\mathrm{He}^{*}$ atoms. Our measured value of $a_{34}=30\pm 4$ nm is in good agreement with theoretical predictions. The knowledge of this scattering length is important for many fundamental experiments between these helium isotopes.

A widely used method for mitigating errors in noisy quantum computers is Richardson extrapolation, a technique in which the overall effect of noise on the estimation of quantum expectation values is captured by a single parameter that, after being scaled to larger values, is eventually extrapolated to the zero-noise limit. We generalize this approach by introducing layerwise Richardson extrapolation (LRE), an error mitigation protocol in which the noise of different individual layers (or larger chunks of the circuit) is amplified and the associated expectation values are linearly combined to estimate the zero-noise limit. The coefficients of the linear combination are analytically obtained from the theory of multivariate Lagrange interpolation. LRE leverages the flexible configurational space of layerwise unitary folding, allowing for a more nuanced mitigation of errors by treating the noise level of each layer of the quantum circuit as an independent variable. We provide numerical simulations demonstrating scenarios where LRE achieves superior performance compared to traditional (single-variable) Richardson extrapolation.

We engineer angular momentum eigenstates of a single atom by using an all-optical approach based on the interference of Laguerre-Gaussian beams. We confirm the imprint of angular momentum by measuring the two-dimensional density distribution and by performing Ramsey spectroscopy in a slightly anisotropic trap, which additionally reveals the sense of rotation. This article provides the experimental details on the quantum state control of angular momentum eigenstates reported in P. Lunt et al., Phys. Rev. Lett. 133, 253401 (2024).

Thermal rate coefficients for some atomic collisions have been observed to be remarkably independent of the details of interatomic interactions at short range. This makes these rate coefficients universal functions of the long-range interaction parameters and masses, which was previously exploited to develop a self-defining atomic sensor for ambient pressure. Here we employ rigorous quantum scattering calculations to examine the response of thermally averaged rate coefficients for atom-atom collisions to changes in the interaction potentials. We perform a comprehensive analysis of the universality, and the boundaries thereof, by treating the quantum scattering observables as probabilistic predictions determined by a distribution of interaction potentials. We show that there is a characteristic change of the resulting distributions of rate coefficients, separating light, few-electron atoms, and heavy polarizable atoms. We produce diagrams that illustrate the boundaries of the thermal collision universality at different temperatures and provide guidance for future experiments seeking to exploit the universality.

There is a growing interest in high-precision spectroscopy and frequency metrology for fundamental studies using sympathetically cooled highly charged ions (HCIs) embedded in Coulomb crystals of laser-cooled ions. In order to understand how their strong repulsion affects the crystal structure and dynamics, we study the thermal motion and rearrangement of small mixed linear and homogeneous crystals by both measurements and simulations. Cocrystallized HCIs form superlattices and divide the crystal into domains, where different reordering rates, melting points, and localized phase transitions are observed due to decoupling of motional modes across boundaries. These results improve our understanding of homogeneous and inhomogeneous ion strings over a wide range of charge-to-mass ratios. This allows us to test our own simulations of the dynamic behavior of ion strings and gives us confidence in their suitability for applications related to quantum simulation as well as computing and the search for new physics.

Entangled photon pairs form the foundation for many applications in the realm of quantum communication. For fiber-optic transfer of entangled photon pairs, time-bin encoding offers improved stability compared to polarization-encoded qubits. Here, we lay the theoretical foundations to describe the measurement of time-bin-entangled photons. We derive multitime correlation functions of the time-bin-encoded photon pairs, corresponding to quantum state tomographic measurements. Our theory provides a starting point to extend the simulations to include all kinds of loss or decoherence effects that apply in a specific quantum system for realistic simulation for time-bin entanglement from quantum emitters.

A continuous-variable (CV) quantum position verification (QPV) protocol was recently studied and proven to be secure if and only if attackers do not preshare any entanglement. In the discrete-variable (DV) analog of that protocol, it had been shown that modifying how the classical challenge is sent from the verifiers to the prover leads to a lower bound on the amount of entanglement needed by the attackers. In this work we show that similar conclusions can be drawn for CV QPV. We design a CV QPV protocol in which the quantum part of the challenge is a coherent state and the classical part consists of $n$-bit strings coming from both verifiers. We show that the protocol is secure against attackers who have fewer than $cn$ preshared entangled qubits, where $c$ is a constant. The security proof is given for a certain range of attenuation and excess noise and holds even if the quantum information travels arbitrarily slowly.

In this paper we measure all the motional-mode frequencies (common and stretch) of a balanced and an unbalanced two-ion Coulomb crystal in a 7-tesla Penning trap using an electric-dipole transition in ${}^{40}\mathrm{Ca}^{+}$. The three common modes of the balanced crystal were obtained using a laser-pulse measurement technique developed in a previous work for a single ion, whereas the stretch mode frequencies were measured in a stationary state while applying laser cooling. Due to the Coulomb interaction, and the heating of the crystal, nonlinearities appear in the oscillators, which are treated analytically and numerically to obtain the experimental frequency values. The generalized invariance theorem has been tested yielding a relative shift of $-1.0\times {10}^{-6}$ with a relative uncertainty of $4\times {10}^{-6}$. Single-ion frequency measurements are used to assess its validity.

We present a general framework for the computation of structure-agnostic bounds on the performance of passive cloaks over a nonzero bandwidth. We apply this framework in two dimensions to the canonical scenario of cloaking a circular object. We find that perfect cloaking using a finite-sized isotropic cloak is impossible over any bandwidth, with the bounds scaling linearly with the bandwidth before saturating due to the finite size of the cloak and the presence of material loss. The bounds also exhibit linear scaling with material loss in the cloak and linear scaling with the inverse of the radial thickness of the design region before saturation due to finite-size effects or the presence of material loss. The formulation could readily find applications in the development of cloaking devices, setting expectations, and benchmarks for optimal performance.