In a seminal paper [P. Hayden and J. Preskill, J. High Energy Phys. 09 (2007) 120], Hayden and Preskill showed that information can be retrieved from a black hole that is sufficiently scrambling, assuming that the retriever has perfect control of the emitted Hawking radiation and perfect knowledge of the internal dynamics of the black hole. In this paper, we show that for $t$-doped Clifford black holes—that is, black holes modeled by random Clifford circuits doped with an amount $t$ of non-Clifford resources—an information retrieval decoder can be learned with fidelity scaling as $exp(-\alpha t)$ using quantum machine learning while having access only to out-of-time-order correlation functions. We show that the crossover between learnability and nonlearnability is driven by the amount of nonstabilizerness present in the black hole and sketch a different approach to quantum complexity.

We consider the orientation of linear and symmetric-top molecules induced by laser and delayed terahertz (THz) pulses at high rotational temperatures (up to room temperature). We introduce an echo-assisted approach in which the achieved transient molecular orientation is an order of magnitude higher than the orientation produced by a single THz pulse. The laser pulse first dissects the wide molecular phase-space distribution into multiple narrow strips (filaments), each being cold and evolving separately. A subsequent THz pulse causes a substantial transient orientation of the individual filaments, which leads to an enhanced orientation of the whole molecular ensemble at later times via the echo mechanism. This enhanced degree of orientation is important in attosecond science, chemical reaction control, ultrafast molecular imaging, and other domains of physics.

Genuine multipartite nonlocality (GMN), the strongest form of multipartite nonlocality that describes fully collective nonlocal correlations among all experimental parties, can be observed when different distant parties each locally measure a particle from a shared entangled many-particle state. For the demonstration of GMN, the experimentally observed statistics are typically postselected: Events for which some parties do not detect a particle must be discarded. This coincidence postselection generally leads to the detection loophole that invalidates a proper nonlocality demonstration. In this work, we address how to close the detection loophole for a coincidence detection in demonstrations of nonlocality and GMN. We first show that if the number of detected particles is conserved, i.e., using ideal and noiseless experimental devices, one can employ causal diagrams and the no-signaling principle to prove that a coincidence postselection cannot create any detection loophole. Furthermore, for realistic experimental devices with finite detection efficiencies, we show how a general Bell inequality can be sharpened such that its new version is still valid after a postselection of the measurement data. In this case, there are threshold detection efficiencies that, if surpassed in the experiment, lead to the possibility of demonstrating nonlocality and GMN without opening the detection loophole. Our results imply that genuine $N$-partite nonlocality can be generated from $N$ independent particle sources even when allowing for nonideal detectors.

Collisions between trapped atoms or trapped molecules with room-temperature particles in the surrounding vacuum induce loss of the trapped population at a rate proportional to the density of the background gas particles. The total velocity-averaged loss-rate coefficient $\langle {\sigma }_{\mathrm{tot}}v\rangle$ for such collisions and the variation of the loss rate with trap depth has been shown to depend only on the long-range interaction potential between the collision partners. This collision universality was previously used to realize a self-calibrating, atom-based, primary pressure standard and was validated by indirect comparison with an orifice flow standard. Here, we use collision universality to measure $\langle {\sigma }_{\mathrm{tot}}v\rangle =6.44\left(11\right)\left(5\right)\times {10}^{-15}{\mathrm{m}}^3/\mathrm{s}$ for Rb-Rb collisions and deduce the corresponding $C_6=4688\left(198\right)\left(95\right)E_h{a}_0^6$, in agreement with predictions based upon ab initio calculated and previously measured $C_6$ values.

Two optically pumped atomic magnetometer geometries, with sub-$\mathrm{fT}/\sqrt{\mathrm{Hz}}$ sensitivity for radio frequencies, are contrasted: one with a probe beam of high power and few passes through the atoms, the other with low power and many passes. Theoretical noise sensitivity for these conditions is modeled and compared to experimental values, with the latter geometry achieving a sensitivity of 0.19 $\pm$ 0.02 $\mathrm{fT}/\sqrt{\mathrm{Hz}}$. Further, a general approach for choosing probe parameters to optimize sensitivity is given. With the use of a $\lambda$/2 wave plate, both systems are also configured to act as an intrinsic gradiometer, enabling the rejection of common-mode interference. Common-mode interference is reduced by over 50 dB in both geometries.

We study nonclassical correlations in propagating two-mode squeezed microwave states in the presence of noise. We focus on two different types of correlations, namely, quantum entanglement and quantum discord. Quantum discord has various intriguing fundamental properties which require experimental verification, such as the asymptotic robustness to environmental noise. Here, we experimentally investigate quantum discord in propagating two-mode squeezed microwave states generated via superconducting Josephson parametric amplifiers. By exploiting an asymmetric noise injection into these entangled states, we demonstrate the robustness of quantum discord against thermal noise while verifying the sudden death of entanglement. Furthermore, we investigate the difference between quantum discord and entanglement of formation, which can be directly related to the flow of locally inaccessible information between the environment and the bipartite subsystem. We observe a crossover behavior between quantum discord and entanglement for low noise photon numbers, which is a result of the tripartite nature of noise injection. We demonstrate that the difference between entanglement and quantum discord can be related to the security of certain quantum key distribution protocols.

Dissipative soliton Kerr frequency combs in microresonators have recently been demonstrated with the self-injection locking process. In addition to turnkey deterministic comb generation, this mode of operation simplifies dark pulse generation in the normal dispersion regime. Here, the formation process of dark pulses triggered by self-injection locking is studied by regarding them as a pair of switching waves that connect domains having different intracavity powers. The self-injection locking mechanism allows the switching waves to self-regulate their position so that a wide range of comb states can be accessed, and the duty cycle is controlled by the feedback phase. The dark pulse shape is also imaged using the linear optical sampling technique. The results provide physical insights as well as an operational modality for this important class of nonlinear waves.

The collective modes of two-dimensional ordered atomic arrays can modify the radiative environment of embedded atomic impurities. We analyze the role of the lattice geometry on the impurity's emission linewidth by comparing the effective impurity decay rate obtained for all noncentered Bravais lattices and an additional honeycomb lattice. We demonstrate that the lattice geometry plays a crucial role in determining the effective decay rate for the impurity. In particular, we find that the minimal effective decay rate appears in lattices where the number of the impurity's nearest neighbors is maximal and the number of distinct distances among nearest neighbors is minimal. We further show that, in the choice between interstitial and substitutional placement of the impurity, the former always wins by exhibiting a lower decay rate and longer photon storage. For interstitial placements, we determine the optimal impurity position in the lattice plane, which is not necessarily found in the center of the lattice plaquette.

We report on experiments exploring the non-Hermitian dynamics of pairs of two-level atoms tightly confined in an optical lattice and driven by a near-resonant laser. Although spontaneous emission is negligible for the long-lived excited state, two-body dissipation arises from strong inelastic collisions between two atoms in the excited state. We demonstrate quasi-adiabatic control of the internal state of the pairs in the quantum Zeno regime where inelastic losses dominate. Preparing each atom pair in the longest-lived eigenstate of the non-Hermitian Hamiltonian describing the dissipative dynamics, we measure a lifetime enhanced by more than two orders of magnitude in comparison to the bare two-body lifetime. The measured enhancement factor is in quantitative agreement with the expected lifetime of the prepared “non-Hermitian dressed state.”

The interplay between static and dynamic disorder and collective optical response in molecular ensembles is an important characteristic of nanoplasmonic and nanophotonic molecular systems. Here we investigate the cooperative superradiant response of a molecular ensemble of quantum emitters under the influence of environmental disorder, including inhomogeneous broadening (as induced by a static random distribution of the molecular transition frequencies) and motional narrowing (as induced by stochastic modulation of these excitation energies). The effect of inhomogeneous broadening is to destroy the coherence of the collective molecular excitation and suppress superradiant emission. However, fast stochastic modulation of the molecular excitation energy can effectively restore the coherence of the quantum emitters and lead to a recovery of superradiant emission, which is an unexpected manifestation of motional narrowing. For a light-scattering process as induced by an off-resonant incident pulse, stochastic modulation leads to inelastic fluorescence emission at the average excitation energy at long times and suggests that dynamic disorder effects can actually lead to collective excitation of the molecular ensemble.

Gravitationally bound neutrons have become an important tool in the experimental searches for new physics, such as modifications to Newton's force or candidates for dark matter particles. Here we include the relativistic effects of mass-energy equivalence into the model of gravitationally bound neutrons. Specifically, we investigate a correction in a gravitationally bound neutron's Hamiltonian due to the presence of an external magnetic field. We show that the neutron's additional weight due to mass-energy equivalence will cause a small shift in the neutron's eigenenergies and eigenstates, and examine how this relativistic correction would affect experiments with trapped neutrons. We further consider the ultimate precision in estimating the relativistic correction to the precession frequency and find that, at short times, a joint measurement of both the spin and motional degrees of freedom provides a metrological enhancement as compared to a measurement of the spin alone.

We discuss the thermodynamic aspects of a single qubit based device, powered by weak quantum measurements, and feedback controlled by a quantum Maxwell's demon. We discuss both discrete and time-continuous operation of the measurement based device at finite temperature of the reservoir. In the discrete example where a demon acquires information via discrete weak measurements, we find that the thermodynamic variables including the heat exchanged, extractable work, and the entropy produced are completely determined by an information theoretic measure of the demon's perceived arrow of time. We also discuss a realistic time-continuous operation of the device where the feedback is applied after a sequence of weak measurements. In the time-continuous limit, we derive the exact finite-time statistics of work, heat, and entropy changes along individual quantum trajectories of the quantum measurement process, and relate them to the demon's arrow of time.

We report on the observation of Feshbach resonances at low magnetic-field strength (below 10 G) in the Fermi-Fermi mixture of ${}^{161}\mathrm{Dy}$ and ${}^{40}\mathrm{K}$. We characterize five resonances by measurements of interspecies thermalization rates and molecular binding energies. As a case of particular interest for future experiments, we consider a resonance at 7.29 G, which combines accurate magnetic tunability and access to the universal regime of interactions with experimental simplicity. We show that lifetimes of a few hundred milliseconds can be achieved for the optically trapped, resonantly interacting mixture. We also demonstrate the hydrodynamic expansion of the mixture in the strongly interacting regime and the formation of DyK Feshbach molecules. Our work opens up experimental possibilities in view of mass-imbalanced superfluids and related phenomena.

We study the phase shift induced by atomic interactions at the output of an atom interferometer. Due to the mutual interaction between the two overlapping Bose-Einstein condensates, the phase exhibits a spatial profile. We evaluate the phase gradient using a perturbative method based on the Feynman path-integral approach. Our model accounts for the effects of the population imbalance between the two arms of the interferometer and the difference between the scattering lengths of the hyperfine levels. We also investigate these effects experimentally by measuring the interaction phase shift for a set parameters. Our experimental results are well reproduced by our theoretical model.

We present a grid-based implementation of the time-dependent configuration-interaction singles method suitable for computing the strong-field ionization of small gas-phase molecules. After outlining the general equations of motion used in our treatment of this method, we present example calculations of strong-field ionization of $\mathrm{He}, \mathrm{LiH}, {\mathrm{H}}_2\mathrm{O}$, and ${\mathrm{C}}_2{\mathrm{H}}_4$ that demonstrate the utility of our implementation. The following paper [S. Carlström et al., following paper, Phys. Rev. A 106, 042806 (2022)] specializes to the case of spherical symmetry, which is applied to various atoms.

We study theoretically driven quantum dynamics in periodic arrays of two-level qubits coupled to the waveguide. We demonstrate that strongly subradiant eigenstates of the master equation for the density matrix emerge under strong coherent driving for arrays with the anti-Bragg periods $d=\lambda /4,3\lambda /4...$. This happens even though are no such eigenstates at low driving powers and is directly manifested by long-living quantum correlations between the qubits.

We propose a general theoretical approach to the modeling of complex dispersion characteristics of leaky optical modes operating in photonic crystal slabs composed of two coupled high-index contrast gratings. Our analytical model, based on a non-Hermitian Hamiltonian, allows for a unified description of the wide family of optical modes which may be generated within unidimensional photonic crystals. Our theory stands for a variety of illustrative examples relating to the manipulation of bound states in the continuum and exceptional points and can be used as a powerful enabler for the discovery of novel photonic species. Finally, as a proof of concept, we demonstrate experimentally the formation of a Dirac point at the merging of three bound states in the continuum that is the most achieved photonic species discussed in this work.

We show that the Hardy nonlocality condition is equivalent to the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality with additional constraints. We adapt the geometrical optimization of the violation of the CHSH inequality to these additional constraints and show that the Hardy condition is equivalent to optimizing the length difference of two sides in a triangle. Furthermore, we discuss the effects of the different constraints.

Spin-momentum locking is intriguing and observable optically in the surface-plasmon polariton (SPP) waves. Here, we report on its direct electrical detection. In a periodically patterned metallic surface, a circularly polarized light incident in the $Y$ direction generates a unidirectional SPP by spin-momentum locking in the $X$ direction and was detected via optical rectification at the sample edge in the form of a DC voltage or current.

We present a theoretical analysis of two-photon absorption of classical and squeezed light valid when one-photon absorption to an intermediate state is either resonant or far-detuned from resonance, and in both the low- and high-intensity regimes. In this paper we concentrate on continuous-wave excitation, although the approach we develop is more general. We calculate the energy removed from an incident field for typical experimental parameters and consider the limiting cases when the photon pairs are narrowband or broadband compared to the molecular linewidths. We find an enhancement of the two-photon absorption due to resonant contributions from the large squeezed light bandwidth and due to photon bunching in the low-intensity regime. However, in both cases, for the parameters we choose, the one-photon absorption is the dominant process in the region of parameter space where a large enhancement of the two-photon absorption is possible.