We experimentally investigate the nonlinear optical pulse dynamics of ultrashort laser pulses propagating in gas-filled hollow capillary fibers in different dispersion regimes, which are achieved by tuning the gas pressure. When the pulse propagates in the anomalous dispersion regime we observe soliton dynamics accompanied with soliton-plasma effects, such as self-compression, resonant dispersive-wave emission in the fundamental as well as in higher-order modes, soliton blueshifting, and ionization-induced pulse splitting. Propagation of the pulse in the vicinity of the zero-dispersion wavelength results in pulse splitting and subsequent cross-phase modulation leading to the generation of an additional frequency-shifted band and a three-octave broad supercontinuum. In the case of pulses propagating in normal dispersion we observe the generation of a broad and flat supercontinuum. In this regime, the experimental results are less well described by simulations that consider only the propagation dynamics inside the fiber. Free-space simulations of the beam propagation in the bulk gas, before the capillary entrance, suggest that this discrepancy is caused by self-focusing and ionization altering the pulse spatial and temporal shape, affecting both the coupling efficiency and the subsequent propagation inside the capillary.

Rydberg atoms are remarkable tools for the quantum simulation of spin arrays. Circular Rydberg atoms open the way to simulations over very long time scales, using a combination of laser trapping of the atoms and spontaneous-emission inhibition, as shown in the proposal of an XXZ spin-array simulator based on chains of trapped circular atoms [Nguyen et al., Phys. Rev. X 8, 011032 (2018)]. Such simulators could reach regimes (thermalization, glassy dynamics) that are out of the reach of those based on ordinary, low-angular-momentum short-lived Rydberg atoms. Over the promised long time scales, the unavoidable coupling of the spin dynamics with the atomic motion in the traps may play an important role. We study here the interplay between the spin exchange and motional dynamics in the simple case of two interacting circular Rydberg atoms confined in harmonic traps. The time evolution is solved exactly when the position dependence of the dipole-dipole interaction terms can be linearized over the extension of the atomic motion. We present numerical simulations in more complex cases, using the realistic parameters of the simulator proposal. We discuss three applications. First, we show that realistic experimental parameters lead to a regime in which atomic and spin dynamics become fully entangled, generating interesting nonclassical motional states. We also show that, in other parameter regions, the spin dynamics notably depends on the initial temperature of the atoms in the trap, providing a sensitive motional thermometry method. Last, and most importantly, we discuss the range of parameters in which the motion has negligible influence over the spin dynamics.

We explore the effect of tunable integrability-breaking dipole-dipole interactions in the equilibrium states of highly magnetic one-dimensional (1D) Bose gases of dysprosium at low temperatures. We experimentally observe that in the strongly correlated Tonks-Girardeau regime, rapidity and momentum distributions are nearly unaffected by the dipolar interactions. By contrast, we also observe that significant changes of these distributions occur when decreasing the strength of the contact interactions. We show that the main experimental observations are captured by modeling the system as an array of 1D gases with only contact interactions, dressed by the contribution of the short-range part of the dipolar interactions. Improvements to theory-experiment correspondence will require different tools tailored to near-integrable models possessing both short- and long-range interactions.

We apply the adiabatic-nuclei molecular convergent close-coupling (MCCC) method to the study of elastic scattering and rotational excitation of ${\mathrm{H}}_2$ by 0.01–20-eV electrons. Integral cross sections are presented for all rotational transitions with $\left|\mathrm{\Delta }N\right|\le 2$ and $N_i=0\text{–}31$ within the $v=0$ vibrational level and differential cross sections for a selection of transitions. Agreement with the available measurements and previous calculations is mostly excellent, depending on the transition and incident energy. We suggest possible reasons, and argue for the accuracy of the MCCC data.

Molecular laser cooling and trapping requires addressing all spontaneous decays to excited vibrational states that occur at the $\gtrsim {10}^{-4}\text{–}{10}^{-5}$ level, which is accomplished by driving repumping transitions out of these states. However, the transitions must first be identified spectroscopically at high resolution. A typical approach is to prepare molecules in excited vibrational states via optical cycling and pumping, which requires multiple high-power lasers. Here, we demonstrate a general method to perform this spectroscopy without the need for optical cycling. We produce molecules in excited vibrational states by using optically driven chemical reactions in a cryogenic buffer gas cell, and implement frequency-modulated absorption to perform direct, sensitive, high-resolution spectroscopy. We demonstrate this technique by measuring the spectrum of the $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(1,0,0)\text{–}\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(3,0,0)$ band in ${}^{174}\mathrm{YbOH}$. We identify the specific vibrational repump transitions needed for photon cycling, and combine our data with previous measurements of the $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(1,0,0)\text{–}\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(0,0,0)$ band to determine all of the relevant spectral constants of the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(3,0,0)$ state. This technique achieves high signal to noise, can be further improved to measure increasingly high-lying vibrational states, and is applicable to other molecular species favorable for laser cooling.

We study the fundamental limits of the precision of estimating parameters of a quantum matter system when it is probed by a traveling pulse of quantum light. In particular, we focus on the estimation of the interaction strength between the pulse and a two-level atom, equivalent to the estimation of the dipole moment. Our analysis of single-photon pulses highlights the interplay between the information gained from the absorption of the photon by the atom as measured in absorption spectroscopy and the perturbation to the temporal mode of the photon due to spontaneous emission. Beyond the single-photon regime, we introduce an approximate model to study more general states of light in the limit of short pulses, where spontaneous emission can be neglected. We also show that for a vast class of entangled biphoton states, quantum entanglement between the signal mode interacting with the atom and the idler mode provides no fundamental advantage and the same precision can be obtained with a separable state. We conclude by studying the estimation of the electric dipole moment of a sodium atom using quantum light. Our work initiates a quantum information-theoretic methodology for developing the theory and practice of quantum light spectroscopy.

Here we present a four-channel model that incorporates a magnetically tunable Feshbach resonance in a system of three atoms that interact via pairwise van der Waals interactions. Our method is designed to model recent experiments where the tunability of the scattering length has been used to study three-body Efimov states, which appear in the limit of a diverging two-body scattering length. Using this model, we calculate three-body adiabatic and effective potential curves and study how the strength (or width) of the Feshbach resonance affects the three-body effective hyperradial potential that is connected to the Efimov effect. We find that the position of the repulsive barrier, which has been used to explain the so-called van der Waals universality in broad resonances, is slightly shifted as the narrow-resonance limit is approached and that this shift is correlated to the appearance of two avoided crossings in the adiabatic energy landscape. More importantly, the attractive well is markedly shifted upward in energy and is extremely shallow for the narrowest resonance. We argue that this behavior is connected to the breakdown of van der Waals universality for weak (narrow) resonances.

We investigate a scalable trapped-ion array architecture for quantum control of many particles, extending techniques to access multiple dimensions. Our experimental study focuses on automated loading and shuttling of single ${\mathrm{Mg}}^{+}$ ions within our platform that contains up to 13 trapping sites in a three-dimensional arrangement. When shuttling ions from a loading hub to multiple sites, we achieve a success rate of over 0.99 999 and demonstrate coherence preservation and coherent manipulation of superposition states of a hyperfine qubit during the process. Our findings suggest promising applications of these techniques in future large-scale quantum architectures.

The high-fidelity storage of quantum information is crucial for quantum computation and communication. Many experimental platforms for these applications exhibit highly biased noise, with good resilience to spin depolarization undermined by high dephasing rates. In this work, we demonstrate that the memory performance of a noise-biased trapped-ion-qubit memory can be greatly improved by incorporating error correction of dephasing errors through teleportation of the information between two repetition codes written on a pair of qubit registers in the same trap. While the technical requirements of error correction are often considerable, we show that our protocol can be achieved with a single global entangling phase gate of remarkably low fidelity, leveraging the fact that the gate errors are also dominated by dephasing-type processes. By rebalancing the logical spin-flip and dephasing error rates, we show that for realistic parameters our memory can exhibit error rates up to two orders of magnitude lower than the unprotected physical qubits, thus providing a useful means of improving memory performance in trapped-ion systems where field-insensitive qubits are not available.

Oscillations of extended source distributions that produce no radiation outside the domain of the source have been long known to be possible in all wave problems, including electromagnetism, acoustics, and even gravitational waves. In almost all demonstrations of these sources, called nonradiating sources in optics and nonpropagating excitations in acoustics, the oscillations are monochromatic or small displacement vibrations of a rigid distribution. Here, we demonstrate how it is possible to theoretically construct nonradiating sources of any size that possess orbital motion of any radius. Examples are given for two-dimensional scalar wave problems.

This paper reports observations of the autodetachment spectrum of ${\mathrm{D}}_2{}^{-}$ and ${\mathrm{HD}}^{-}$, resolved in rovibrational levels presenting lifetimes from 1 to $100\mu \mathrm{s}$. The electronic kinetic-energy release was measured using the velocity-map imaging technique, enhanced by coincidence detection of the neutral species produced. The experimental results are compared with theoretical description of the ab initio–based nonlocal resonance model, confirming the main features predicted by theory while resolving the apparent discrepancy between spontaneous dissociation and detachment experiments by revealing the presence of an additional rovibrational level in ${\mathrm{D}}_2{}^{-}$ not predicted to be sufficiently long-lived by theory.

We demonstrate measurement of quadratic ac Stark shifts between Zeeman sublevels in an ${}^{87}\mathrm{Rb}$ Bose-Einstein condensate using a multistate atomic interferometer. The interferometer can detect a quadratic shift without being affected by relatively large state-independent shifts, thereby improving the measurement precision. We measure quadratic shifts in the total spin $F=2$ state due to the light being near resonant to the $D_1$ line. The agreement between the measured and theoretical detuning dependences of the quadratic shifts confirms the validity of the measurement. We also present results on the suppression of nonlinear spin evolution using near-resonant dual-color light pulses with opposite quadratic shifts.

Many quantitative approaches to the dynamical scrambling of information in quantum systems involve the study of out-of-time-ordered correlators (OTOCs). In this paper we introduce an algebraic OTOC $\left(\mathcal{A}\text{−}\mathrm{OTOC}\right)$ that allows us to study information scrambling of generalized quantum subsystems under quantum channels. For closed quantum systems, this algebraic framework was recently employed to unify quantum information-theoretic notions of operator entanglement, coherence-generating power, and Loschmidt echo. The main focus of this work is to provide a natural generalization of these techniques to open quantum systems. We first show that, for unitary dynamics, the $\mathcal{A}\text{−}\mathrm{OTOC}$ quantifies a generalized notion of information scrambling, namely, between a subalgebra of observables and its commutant. For open quantum systems, on the other hand, we find a competition between the global environmental decoherence and the local scrambling of information. We illustrate this interplay by analytically studying various examples of algebras and quantum channels. To complement our analytical results, we perform numerical simulations of two paradigmatic systems: the $PXP$ model and the Heisenberg $XXX$ model, under dephasing. Our numerical results reveal connections with many-body scars and the stability of decoherence-free subspaces.

The quantum approximate optimization algorithm (QAOA) has the potential of providing a useful quantum advantage on noisy intermediate-scale quantum (NISQ) devices. The effects of uncorrelated noise on variational quantum algorithms such as QAOA have been studied intensively. Recent experimental results, however, show that the errors impacting NISQ devices are significantly correlated. We introduce a model for both spatially and temporally (non-Markovian) correlated errors based on classical environmental fluctuators. The model allows for the independent variation of the marginalized spacetime-local error probability and the correlation strength. Using this model, we study the effects of correlated stochastic noise on QAOA. We find evidence that the performance of QAOA improves as the correlation time or correlation length of the noise is increased at fixed local error probabilities. This shows that noise correlations in themselves need not be detrimental for NISQ algorithms such as QAOA.

Using a quantum processor to embed and process classical data enables the generation of correlations between variables that are inefficient to represent through classical computation. A fundamental question is whether these correlations could be harnessed to enhance learning performances on real data sets. Here we report the use of a neutral atom quantum processor comprising up to 32 qubits to implement machine learning tasks on graph-structured data. To that end, we introduce a quantum feature map to encode the information about graphs in the parameters of a tunable Hamiltonian acting on an array of qubits. Using this tool, we first show that interactions in the quantum system can be used to distinguish nonisomorphic graphs that are locally equivalent. We then realize a toxicity screening experiment, consisting of a binary classification protocol on a biochemistry data set comprising 286 molecules of sizes ranging from 2 to 32 nodes, and obtain results which are comparable to the implementation of the best classical kernels on the same data set. Using techniques to compare the geometry of the feature spaces associated with kernel methods, we then show evidence that the quantum feature map perceives data in an original way, which is hard to replicate using classical kernels.

We propose a method to probe the precision spectroscopy of an atomic beam using traveling-wave laser beams. The method is demonstrated by measuring the $2{}^{3}S-2{}^{3}P$ transition in a slow helium atomic beam. The first-order Doppler shift could be effectively suppressed by up to three orders of magnitude compared to that induced by the probing light beam. This method avoids using a standing-wave field when probing the spectra, and consequently, it reduces the laser power dependence and eliminates the modulation due to the standing-wave field. Preliminary measurements of the $2{}^{3}S-2{}^{3}P$ transition of ${}^4\mathrm{He}$ indicate that the uncertainty could be reduced to the sub-kHz level.

We visualize the hyperfine depolarization dynamics of electronically excited nitric oxide (NO) molecules. Pump-probe ion-imaging measurements have been performed to track the spatiotemporal propagation of the angular distribution of NO ($A{}^2\mathrm{\Sigma }^{+}, v=0, J=3/2, N=2$), excited by ultraviolet nanosecond laser pump pulses resonant with the $R_{21}(1/2)$ transition. Femtosecond intense probe pulses induced Coulomb explosion of the excited NO molecules, where fragment ${\mathrm{N}}^{+}$ and ${\mathrm{O}}^{+}$ ions were ejected along the direction of the molecular axis just before the explosion. The space-slice imaging coupled with the circularly polarized probe pulse, recently developed in this research group [K. Mizuse et al., Rev. Sci. Instrum. 90, 103107 (2019)] has directly (i.e., without any mathematical reconstruction procedure) provided the two-dimensional section of the molecular-axis distribution, which clearly shows evolution in the nanosecond regime. We have developed a model to reproduce the experimentally captured images by considering a time-dependent density matrix for the excitation of multiple hyperfine states. The model has been proven to be fully compatible with the spherical-tensor-operator formalism [A. J. Orr-Ewing and R. N. Zare, Annu. Rev. Phys. Chem. 45, 315 (1994)], and the initially prepared density matrices have been retrieved successfully from the analysis of time-dependent molecular-axis distribution.

Depending on the way one measures, quantum nonlocality might manifest more visibly. Using basis transformations and interactions on a particle pair, Hardy logically argued that any local hidden variable theory leads to a paradox. Extended from the original work, we introduce a quantum nonlocal scheme for $n$-particle systems using two distinct approaches. First, a theoretical model is derived with analytical results for Hardy's nonlocality conditions and probability. Second, a quantum simulation using quantum circuits is constructed that matches very well to the analytical theory. When demonstrated on real quantum computers for $n=3$, we obtain reasonable results compared to theory. Even at macroscopic scales as $n$ grows, the success probability asymptotes 15.6%, which is stronger than previous results.

The fidelity of gate operations on neutral atom qubits is often limited by fluctuations of the laser drive. Here, we quantify the sensitivity of quantum gate fidelities to laser phase and intensity noise. We first develop models to identify features observed in laser self-heterodyne noise spectra, focusing on the effects of white noise and servo bumps. In the weak-noise regime, characteristic of well-stabilized lasers, we show that an analytical theory based on a perturbative solution of a master equation agrees very well with numerical simulations that incorporate phase noise. We compute quantum gate fidelities for one- and two-photon Rabi oscillations and show that they can be enhanced by an appropriate choice of Rabi frequency relative to spectral noise peaks. We also analyze the influence of intensity noise with spectral support smaller than the Rabi frequency. Our results establish requirements on laser noise levels needed to achieve desired gate fidelities.

Density modeling is the task of learning an unknown probability density function from samples, and is one of the central problems of unsupervised machine learning. In this work, we show that there exists a density modeling problem for which fault-tolerant quantum computers can offer a superpolynomial advantage over classical learning algorithms, given standard cryptographic assumptions. Along the way, we provide a variety of additional results and insights of potential interest for proving future distribution learning separations between quantum and classical learning algorithms. Specifically, we (a) provide an overview of the relationships between hardness results in supervised learning and distribution learning, and (b) show that any weak pseudorandom function can be used to construct a classically hard density modeling problem. The latter result opens up the possibility of proving quantum-classical separations for density modeling based on weaker assumptions than those necessary for pseudorandom functions.