We introduce a taxonomy for partially coherent optical fields spanning multiple degrees of freedom (DOF) based on the rank of the associated coherence matrix (the number of nonzero eigenvalues). When DOF comprise two spatial modes and polarization, a fourfold classification emerges, with rank-1 fields corresponding to fully coherent fields. We demonstrate theoretically and confirm experimentally that these classes have different properties. Specifically, whereas rank-2 fields can always be rendered separable with respect to its DOF via a unitary transformation, rank-3 fields are always nonseparable. Consequently, the entropy for a rank-2 field can always be concentrated into a single DOF (thus ridding the other DOF of statistical fluctuations), whereas some entropy is always “locked” in one DOF of a rank-3 field. These results offer insight into the dynamics of optical coherence upon traversing systems or media that couple DOF.

We perform calculations of the electronic structure of ${\mathrm{Cm}}^{15+}$ and ${\mathrm{Bk}}^{16+}$ ions and demonstrate that they have transitions which combine the features of atomic optical clocks with the enhanced sensitivity to the variations of the fine-structure constant $\alpha$. The high sensitivity is due to large nuclear charge $Z$, high ionization degree $Z_i$, and the effect of level crossing, which enables optical transitions between states of different configurations. These are the $6p_{1/2}-5f_{5/2}$ and $6p_{1/2}-5f_{7/2}$ transitions in the single-valence electron approximation. The variation of $\alpha$ may be due to the interaction with scalar and pseudoscalar (axion) dark-matter fields. Therefore, ${\mathrm{Cm}}^{15+}$ and ${\mathrm{Bk}}^{16+}$ clocks are promising candidates to search for these fields.

Optical parametric oscillation based on a monolithic resonator is an important way to generate a coherent laser with a narrow linewidth and a wide tunable range in a long wavelength, which can be used in spectroscopy and quantum source generation. In this Letter, we demonstrate doubly resonant optical parametric oscillation with natural phase matching based on the box resonator with $Q$ up to $5.68\times {10}^7$. Moreover, we realized a $1\text{−}\mu \mathrm{m}$ laser with a 1-kHz linewidth, a 200-mW output power, and a 153.94-nm wavelength tuning range. Furthermore, the monolithic box resonator has the potential to achieve a fully integrated high-power laser, and it can also be used for highly efficient spontaneous parametric down-conversion and bright narrow-band biphoton generation.

We study universal off-diagonal correlations in transverse quantum fluids (TQF); a new class of quasi-one-dimensional superfluids featuring long-range-ordered ground states. These exhibit unique self-similar space-time relations scaling with $x^2/D\tau$ that serve as fingerprints of the specific states. The results obtained with the effective field theory are found to be in perfect agreement with ab initio simulations of hard-core bosons on a lattice; a simple microscopic realization of TQF. This allows an accurate determination—at nonzero temperature and finite system size—of such key ground-state properties as the condensate and superfluid densities, and characteristic parameter $D$.

Optical fiber Fabry-Perot cavities have been a development facilitating the efficient integration of high-finesse cavities into fiber-optic assemblies. In this work, we demonstrate coupling of two high-finesse fiber cavities by direct photon tunneling between them. We detect the coupled mode spectra and demonstrate the variability of coupling strength and dissipation rates for different transverse modes. Moreover, we observe very narrow spectral features resulting from a dynamical generalization of electromagnetically induced transparency showing that even dissipative systems without metastable states can feature long-lived coherences.

We uncover the exact athermal eigenstates in the Bose-Hubbard (BH) model with a three-body constraint, motivated by the exact construction of quantum many-body scar (QMBS) states in the $S=1$ $XY$ model. These states are generated by applying an $\mathrm{SU}\left(2\right)$ ladder operator consisting of a linear combination of two-particle annihilation operators to the fully occupied state. By using the improved Holstein-Primakoff expansion, we clarify that the QMBS states in the $S=1$ $XY$ model are equivalent to those in the constrained BH model with additional correlated hopping terms. We also find that, in the strong-coupling limit of the constrained BH model, the QMBS state exists as the lowest-energy eigenstate of the effective model in the highest-energy sector. This fact enables us to prepare the QMBS states in a certain adiabatic process and opens up the possibility of observing them in ultracold-atom experiments.

We propose a ponderomotive trapping mechanism for circular Rydberg atoms that consists in threading the Rydberg orbital with a tightly focused Gaussian laser beam. The trap exhibits remarkable properties: it can be made effectively linear, extremely nonlinear, or have the same trapping frequency, depth, or nonlinearity for distant Rydberg states. The mechanism is capable of efficiently trapping highly excited Rydberg states with a single active electron, as well as ground-state atoms using a single beam. Alternatively, the Rydberg atom can be efficiently trapped by the same beam used to excite it, relaxing optical constraints in well-shielded environments.

We propose a scheme for probing vibronic coherence in charge migration in molecules utilizing strong-field sequential double ionization. To demonstrate the feasibility of this approach, we perform full simulations of a pump-probe scheme employing few-cycle intense infrared pulses for ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$. We predict that the vibronic coherence between the pumped states will be directly imprinted in experimental observables such as kinetic energy release spectra and branching ratios of the dissociative dications. Our simulations are based on the recently developed density matrix approach for sequential double ionization model [C. H. Yuen and C. D. Lin, Phys. Rev. A 106, 023120 (2022)], which is capable of efficiently accounting for molecular orientations and enabling direct comparison with experimental results. Our findings strongly encourage the use of this probing scheme in future charge migration experiments.

The authors propose a tool for assessing the accuracy of approximate electronic wave functions produced by diverse electronic structure calculations. The plots of $f_n=(\frac{{\pi }^2}{{\nu }_n}{)}^{1/4}\frac{\langle {\psi }_n\left(\vec{r}\right)\left|{\left[\mathrm{\Phi }\left(\vec{r}\right)\right]}^{1/4}\right|{\psi }_n\left(\vec{r}\right)\rangle }{\langle {\psi }_n\left(\vec{r}\right)\left|\widehat{T}\right|{\psi }_n\left(\vec{r}\right)\rangle }$ vs ${\nu }_n$, where ${\psi }_n\left(\vec{r}\right)$ is the $n\mathrm{th}$ natural (spin) orbital, ${\nu }_n$ is its occupation number, $\mathrm{\Phi }\left(\vec{r}\right)$ is the on-top two-electron density, and $\widehat{T}$ is the kinetic energy operator, are found to vividly reveal inaccuracies of the underlying wave functions. As such, they provide synthetic yet detailed visual information well suited for accuracy assessments especially in the cases of approaches employing unstandardized basis sets and/or energy minimizations with unascertainable global convergence characteristics.

Motivated by the recent experimental realization of a two-particle fractional quantum Hall state of ultracold atoms in a small optical lattice [J. Léonard, S. Kim, J. Kwan, P. Segura, F. Grusdt, C. Repellin, N. Goldman, and M. Greiner, Nature (London) 619, 495 (2023)], we propose a minimal setup to create and observe a quasihole in such a system. We find that clear signatures of a quasihole state with two or three atoms can be obtained through a standard site-resolved density measurement provided that the system is appropriately modified with simple additional potential profiles. By adding a single-site repulsive potential to pin the quasihole and superimposing a harmonic trap on top of the optical lattice to keep the particles away from the system edge, we determine via exact diagonalization an optimal range for system parameters such as the magnetic flux and the strengths of the additional potentials that would favor the creation of the quasihole state. We hope that our results will be a useful guide for a possible proof-of-principle experiment that will demonstrate controllable creation of a simple quasihole state in a condensed-matter system, which will pave the way for the observation of the anyonic statistics of quasiholes in a more complex system.

We introduce an efficient and accurate readout measurement scheme for single and multiqubit states. Our method uses Bayesian inference to build an assignment probability distribution for each qubit state based on a reference characterization of the detector response functions. This allows us to account for system imperfections and thermal noise within the assignment of the computational basis. We benchmark our protocol on a quantum device with five superconducting qubits, testing initial state preparation for single- and two-qubit states and an application of the Bernstein-Vazirani algorithm executed on five qubits. Our method shows a substantial reduction of the readout error and promises advantages for near-term and future quantum devices.

We study localized nonlinear modes guided by the valley-Hall domain walls in staggered photonic graphene. We describe their propagation dynamics in the long-wavelength limit by a nonlinear Dirac-like model including spatial dispersion terms. It leads to a modified nonlinear Schrödinger equation for the wave-field amplitude that remarkably incorporates a nonlinear velocity term. We find that this nonlinear velocity correction results in a counterintuitive stabilization effect for relatively high-amplitude plane-wave-like edge states, which we confirm by calculation of complex-valued small-amplitude perturbation spectra and direct numerical simulation of propagation dynamics in staggered honeycomb waveguide lattices with on-site Kerr nonlinearity. Our results highlight the importance of taking into account higher-order nonlinearities in topological wave media and are relevant to a variety of nonlinear photonic systems described by Dirac-like Hamiltonians.

We study general lattice bosons with long-range hopping and long-range interactions decaying as ${|x-y|}^{-\alpha }$ with $\alpha \in (d+2,2d+1)$. We find a linear light cone for the information propagation starting from suitable initial states. We apply these bounds to estimate the minimal time needed for quantum messaging, for the propagation of quantum correlations, and for quantum state control. The proofs are based on the ASTLO method (adiabatic spacetime localization observables). Our results pose previously unforeseen limitations on the applicability of fast-transfer and entanglement-generation protocols developed for breaking linear light cones in long-range and/or bosonic systems.

We investigate fermionic Mott insulators in a geometrically frustrated triangular lattice, a paradigm model system for studying spin liquids and spontaneous time-reversal symmetry breaking. Our study demonstrates the preparation of triangular Mott insulators and reveals antiferromagnetic spin-spin correlations among all nearest neighbors. We employ a real-space triangular-geometry quantum gas microscope to measure density and spin observables. Comparing experimental results with calculations based on numerical linked cluster expansions and quantum Monte Carlo techniques, we demonstrate thermometry in the frustrated system. Our experimental platform introduces an alternative approach to frustrated lattices which paves the way for future investigations of exotic quantum magnetism which may lead to a direct detection of quantum spin liquids in Hubbard systems.

Interaction-free measurement is thought to allow for quantum particles to detect objects along paths they never traveled. As such, it represents one of the most beguiling of quantum phenomena. Here, we present a classical analog of interaction-free measurement using the hydrodynamic pilot-wave system, in which a droplet self-propels across a vibrating fluid surface, guided by a wave of its own making. We argue that existing rationalizations of interaction-free quantum measurement in terms of particles being guided by waveforms allow for a classical description manifest in our hydrodynamic system, wherein the measurement is decidedly not interaction-free.

We study the temporal interference of photoelectrons emitted during the rising and falling edges of intense femtosecond laser pulses, that can ionize atoms via near-resonant transitions. Due to the near-resonant coupling with the laser pulse, the emerging atomic dressed states repel each other, giving rise to the Rabi splitting that is primarily controlled by the laser intensity and detuning. Our numerical and analytical analysis reveals that dynamic interference is observed when the Rabi splitting of the dressed states is maximized while the ionization of the atom remains small. We demonstrate that these two conditions are fulfilled when the atom is driven off resonantly within the one-Rabi-cycle regime at perturbative laser intensities. As a result, the single peak of the photoelectron spectrum found in the weak-field limit is replaced by a pronounced multipeak pattern.

We place a molecular Bose-Einstein condensate in a one-dimensional shaken lattice with a Floquet-engineered dispersion and observe the dynamics in both position and momentum space. At the initial condition of zero momentum, our engineered dispersion is inverted, and therefore unstable. We observe that the condensate is destabilized by the lattice shaking as expected, but rather than decaying incoherently or producing jets, as in other unstable condensates, under our conditions the condensate bifurcates into two portions in momentum space, with each portion subsequently following semi-classical trajectories that suffer minimal spreading in momentum space as they evolve. We can model the evolution with a Gross-Pitaevskii equation, which suggests the initial bifurcation is facilitate by a nearly linear “inverted V”-shaped dispersion at the zone center, while the lack of spreading in momentum space is facilitated by interactions, as in a soliton. We propose that this relatively clean bifurcation in momentum space has applications for counterdiabatic preparation of exotic ground states in many-body quantum simulation schemes.

Atomic emitter ensembles couple collectively to the radiation field. Although an excitation on a single emitter may be short lived, a collection of them can contain a photon several orders of magnitude longer than the single emitter lifetime. We provide the exact conditions for optimal absorption, long-lived and dispersionless storage, and release, of a single photon in a subwavelength one-dimensional lattice of two-level emitters. In particular, we detail two storage schemes. The first is based on the uncovering of approximate flat sections in the single-photon spectrum, such that a single photon can be stored as a wave packet with effective zero group velocity. For the second scheme we exploit the angular dependence of the interactions induced between the emitters and mediated via exchange of virtual photons, which on a ring gives rise to an effective trapping potential for the photon. In both cases, we are able to obtain, within current experimentally accessible parameters, high-fidelity photon storage for times hundreds of times longer than the single emitter lifetime.

The computational power of a quantum computer is limited by the number of qubits available for information processing. Increasing this number within a single device is difficult; it is widely accepted that distributed modular architectures are the solution to large-scale quantum computing. The major challenge in implementing such architectures is the need to exchange quantum information between modules. In this work, we show that a distributed quantum computing architecture with limited capacity to exchange information between modules can accurately solve quantum computational problems. Using the example of a variational quantum eigensolver with an ansatz designed for a two-module (dual-core) architecture, we show that three intermodule operations provide a significant advantage over no intermodule (or serially executed) operations. These results provide a strong indication that near-term modular quantum processors can be an effective alternative to their monolithic counterparts.

The gas-phase technique of noncollinear two-color excitation is adapted to study extreme-ultraviolet high-order harmonic generation (HHG) in magnesium oxide. We observe high-order wave-mixing pathways with brightness comparable to that of the single-color HHG. Simulations reveal that the efficiencies are dominated by the microscopic physics as opposed to macroscopic effects. Building on previous work, we develop a general analytic theory of high-order wave mixing that explains our observations and demonstrates how a perturbative nonlinear optical framework emerges form the interaction between the weak field and the laser-dressed state of the crystal in the strong-field approximation. The theory outlines a photon-mixing picture of high-order wave mixing and connects the strong asymmetry between sum- and difference-frequency pathways to the cutoff in the HHG spectrum. Our work establishes the potential of high-order wave mixing as a probe of the microscopic attosecond physics in solids and points to new opportunities in solid-state strong-field photonics.