Classical physics is generally regarded as deterministic, as opposed to quantum mechanics that is considered the first theory to have introduced genuine indeterminism into physics. We challenge this view by arguing that the alleged determinism of classical physics relies on the tacit, metaphysical assumption that there exists an actual value of every physical quantity, with its infinite predetermined digits (which we name principle of infinite precision). Building on recent information-theoretic arguments showing that the principle of infinite precision (which translates into the attribution of a physical meaning to mathematical real numbers) leads to unphysical consequences, we consider possible alternative indeterministic interpretations of classical physics. We also link those to well-known interpretations of quantum mechanics. In particular, we propose a model of classical indeterminism based on finite information quantities (FIQs). Moreover, we discuss the perspectives that an indeterministic physics could open (such as strong emergence), as well as some potential problematic issues. Finally, we make evident that any indeterministic interpretation of physics would have to deal with the problem of explaining how the indeterminate values become determinate, a problem known in the context of quantum mechanics as (part of) the “quantum measurement problem.” We discuss some similarities between the classical and the quantum measurement problems, and propose ideas for possible solutions (e.g., “collapse models” and “top-down causation”).

Understanding cause-effect relationships is a crucial part of the scientific process. As Bell's theorem shows, within a given causal structure, classical and quantum physics impose different constraints on the correlations that are realizable, a fundamental feature that has technological applications. However, in general it is difficult to distinguish the set of classical and quantum correlations within a causal structure. Here we investigate a method to do this based on using entropy vectors for Tsallis entropies. We derive constraints on the Tsallis entropies that are implied by (conditional) independence between classical random variables and apply these to causal structures. We find that the number of independent constraints needed to characterize the causal structure is prohibitively high such that the computations required for the standard entropy vector method cannot be employed even for small causal structures. Instead, without solving the whole problem, we find new Tsallis entropic constraints for the triangle causal structure by generalizing known Shannon constraints. Our results reveal mathematical properties of classical and quantum Tsallis entropies and highlight difficulties of using Tsallis entropies for analyzing causal structures.

In the space of quantum channels, we establish the geometry that allows us to make statistical predictions about relative volumes of entanglement breaking channels among all the Gaussian quantum channels. The underlying metric is constructed using the Choi-Jamiołkowski isomorphism between the continuous-variable Gaussian states and channels. This construction involves the Hilbert-Schmidt distance in quantum state space. The volume element of the one-mode Gaussian channels can be expressed in terms of local symplectic invariants. We analytically compute the relative volumes of the one-mode Gaussian entanglement breaking and incompatibility breaking channels. Finally, we show that, when given the purities of the Choi-Jamiołkowski state of the channel, one can determine whether or not such channel is incompatibility breaking.

We present a verifiable and blind protocol for assisted universal quantum computing on continuous-variable (CV) platforms. This protocol is experimentally friendly to the client, as it only requires Gaussian-operation capabilities from the latter. Moreover, the server does not require universal quantum-computational power either, its only function being to supply the client with copies of a single-mode non-Gaussian state. Universality is attained based on state injection of the server's non-Gaussian supplies. The protocol is automatically blind because the non-Gaussian resource requested to the server is always the same, regardless of the specific computation. Verification, in turn, is possible thanks to an efficient non-Gaussian state fidelity test where we assume identical state preparation by the server. It is based on Gaussian measurements by the client on the injected states, which is potentially interesting on its own. The division of quantum hardware between client and server assumed here is in agreement with the experimental constraints expected in realistic schemes for CV cloud quantum computing.

We study the effect of crystal lattice vibrations on grazing-incidence fast atom diffraction (GIFAD) from insulator surfaces. To describe the phonon contribution to GIFAD we introduce a semiquantum method named phonon-surface initial value representation (P-SIVR), which represents the surface with a harmonic-crystal model, while the scattering process is described by means of the surface initial value representation approach, including phonon excitations. Expressions for the partial scattering probabilities involving zero- and one-phonon exchange are derived. In particular, the P-SIVR approach for zero-phonon scattering is applied to study the influence of thermal lattice vibrations on GIFAD patterns for Ne/LiF(001) at room temperature. It is found that the thermal lattice fluctuations introduce a polar-angle spread into the projectile distributions, which can affect the relative intensities of the interference maxima, even giving rise to interference subpatterns depending on the incidence conditions. Present results are in agreement with the available experiments.

We investigate computationally the quantum dynamics of a metastable ${}^{40}\mathrm{K}{}^{87}\mathrm{Rb}$ complex in the ground electronic state ($X{}^1{\mathrm{\Sigma }}^{+}$) under an intense continuous-wave low-frequency field. We focus on an initial condition where the atoms are quasibound in an orbiting resonance with an energy that corresponds to a kinetic temperature of 62 mK and with a lifetime of 3 ns. A microwave field is tuned either to another lower-lying orbiting resonance or to a high-lying bound vibrational level. In both cases, we observe a transient photoacceleration of the half-collision. However, the photodissociation of the complex is suppressed by strong quasibound-free Rabi oscillations, although it still dissociates nonradiatively with the lifetime of the initial orbiting resonance. During the transient period, a sizable multiphoton association in high-lying vibrational levels is achieved, accompanied by a development of a wide rotational distribution. Therefore, this mechanism seems promising as the basis of a general strategy for the controlled formation of diatomic molecules from gases at millikelvin temperatures.

We study the effects of spin degrees of freedom and wave-function symmetries on double ionization in three-electron systems. Each electron is assigned one spatial degree of freedom. The resulting three-dimensional Schrödinger equation is integrated numerically using grid-based Fourier transforms. We reveal three-electron effects on the double ionization yield by comparing signals for different ionization channels. We explain our findings by the existence of fundamental differences between three-electronic and truly two-electronic spin-resolved ionization schemes. We find, for instance, that double ionization from a three-electron system is dominated by electrons that have the opposite spin.

We demonstrate and characterize that a carrier-envelope-offset-phase (CEP)–controlled ultrashort chirped field is an efficient and robust mechanism to modify the dissociation dynamics of molecular hydrogen. Different dissociation pathways are collectively induced and their interference contributes to the kinetic-energy release spectra. Chirping is able to efficiently manipulate the interferences of different dissociation pathways. We demonstrate a linear relationship between chirp and CEP dependent dissociation as well as directional electron localization.

We theoretically investigate strong-coupling properties of a Bose-Fermi mixture. In the mass- and population-balanced case, two of the authors have shown that a strong heteropairing interaction in this mixture brings about coupling phenomena between Fermi atomic excitations and Bose atomic and composite molecular excitations, that appear as an anomalous multiple peak structure in the single-particle spectral weight (SW) [Kharga, Inotani, Hanai, and Ohashi, J. Phys. Soc. Jpn. 86, 084301 (2017)]. In this paper, we show that, although these many-body phenomena are sensitive to mass and population imbalances between the Bose and Fermi components, SW still exhibits the multiple peak structure in moderately mass-imbalanced ${}^{87}\mathrm{Rb}\text{−}{}^{40}\mathrm{K}$ and ${}^{23}\mathrm{Na}\text{−}{}^{40}\mathrm{K}$ mixtures. We also point out that the photoemission spectrum is a useful quantity to observe this spectral anomaly. Since a real trapped Bose-Fermi mixture is usually accompanied by mass and (local) population imbalances, our results would contribute to the study of a strongly interacting Bose-Fermi mixture, under realistic imbalanced conditions.

The interaction between atoms in a two-component Bose-Einstein condensate (BEC) is effectively modulated by the Rabi oscillation. This periodic modulation of the effective interaction is shown to generate Faraday patterns through parametric resonance. We show that there are multiple resonances arising from the density and spin waves in a two-component BEC and investigate the interplay between the Faraday-pattern formation and the phase separation.

We report on the experimental investigation of the phase coherence of a Bose-Einstein condensate in an optical antidot lattice (ADL). In the ADL, a series of potential hills are arranged on a two-dimensional (2D) square lattice and crisscrossing channels with zero ac Stark shift form a 2D mesh with multiple junctions. Due to these structural features, matter wave interference released from the ADL is clearly visible even at antidot heights of the 300 times the photon recoil energy. However, phase coherence is significantly reduced at extremely tall antidot heights and atom hopping is suppressed. We explain this loss of coherence by introducing a periodic effective potential felt by the atoms on the mesh lines, which is the result of the quantization of the faster atomic motion in the orthogonal direction. This effective potential localizes atoms at the junctions, forming a bundle of tubelike gases. Using the Bose-Hubbard model, we interpret the coherence properties in terms of a 2D Josephson junction array. We have also observed the emergence of vortexlike holes after merging the tubelike gases. We discuss the effect of transverse thermal phase fluctuations and interpret the appearance of the vortexlike holes as a possible signature of the Berezinskii-Kosterlitz-Thouless crossover in the 2D lattice plane.

We study tunneling properties of Higgs modes in superfluid Bose gases in optical lattices in the presence of a potential barrier introduced by local modulation of hopping amplitude. Solving the time-dependent Ginzburg-Landau equation, Higgs modes are found to exhibit perfect transmission through a potential barrier if the barrier strength is weak. There exists, on the other hand, localized Higgs bound states in the presence of a strong potential barrier. We find that the perfect transmission disappears at the critical barrier strength above which one of the odd antibound states turns into a true bound state. We demonstrate that the perfect transmission of Higgs modes is mediated by resonance with the antibound states of Higgs modes.

We study both experimentally and theoretically, considering bosonic atoms in a periodic potential, the influence of interactions in a Talbot interferometer. While interactions decrease the contrast of the revivals, we find that over a wide range of interactions the Talbot signal is still proportional to the phase coherence of the matter wave field. Our results confirm that Talbot interferometry can be a useful tool to study finite-range phase correlations in an optical lattice even in the presence of interactions. The relative robustness of the Talbot signal is supported by the first demonstration of the three-dimensional Talbot effect.

A two-dimensional quantum system of dipoles, with a polarization angle not perpendicular to the plane, shows a transition from a gas to a stripe phase. We have studied the thermal properties of these two phases using the path-integral Monte Carlo (PIMC) method. By simulating the thermal density matrix, PIMC provides exact results for magnitudes of interest such as the superfluid fraction and the one-body density matrix. As it is well known, in two dimensions the superfluid-to-normal phase transition follows the Berezinskii-Kosterlitz-Thouless (BKT) scenario. Our results show that both the anisotropic gas and the stripe phases follow the BKT scaling laws. At fixed density and increasing the tilting angle, the transition temperature decreases in going from the gas to the stripe phase. Superfluidity in the perpendicular direction to the stripes is rather small close to the critical temperature but it becomes larger at lower temperatures, mainly close to the transition to the gas. Our results are in qualitative agreement with the supersolidity observed recently in a quasi-one-dimensional array of dipolar droplets.

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bichromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of an 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin-dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.

We look at what type of arguments can rule out the joint reality (or value definiteness) of two observables of a physical system, such as a qubit, and give several strong yet simple no-go results based on assumptions typically weaker than those considered previously. The first result uses simple geometry combined with a locality assumption to derive device-independent steering inequalities. These may also be regarded as “conditional” Bell inequalities, are simpler in principle to test than standard Bell inequalities, and for two-qubit systems are related to properties of the quantum steering ellipsoid. We also derive a Bell inequality from locality and a one-sided reality assumption and demonstrate a close connection between device-independent steering and Bell nonlocality. Moreover, we obtain a no-go result without the use of locality or noncontextuality assumptions, based on similar geometry and an assumption that we call operational completeness. The latter is related to, but strictly weaker than, preparation noncontextuality. All arguments are given for finite statistics, without requiring any assumption that joint relative frequencies converge to some (unobservable) joint probability distribution. We also generalize a recent strong result of Pusey [M. F. Pusey, Phys. Rev. A 98, 022112 (2018)], for preparation noncontextuality, to the scenarios of device-independent steering and operational completeness.

Recent theoretical and experimental studies have shown the significance of quantum information scrambling (i.e., the spread of quantum information over a system's degrees of freedom) for problems encountered in high-energy physics, quantum information, and condensed matter. Due to the complexity of quantum many-body systems it is plausible that new developments in this field will be achieved by experimental explorations. Since noise effects are inevitably present in experimental implementations, a better theoretical understanding is needed of quantum information scrambling in systems affected by noise. To address this problem we study indicators of quantum scrambling—out-of-time-ordered correlation functions (OTOCs) in open quantum systems. As most experimental protocols for measuring OTOCs are based on backward time evolution, we consider two possible scenarios of joint system-environment dynamics reversal: In the first one the evolution of the environment is reversed, whereas in the second it is not. We derive general formulas for OTOCs in those cases and study in detail the model of a spin chain coupled to the environment of harmonic oscillators. In the latter case we derive expressions for open-system OTOCs in terms of the Feynman-Vernon influence functional. Subsequently, assuming that dephasing dominates over dissipation, we provide bounds on open-system OTOCs and illustrate them for a spectral density known from the spin-boson problem. In addition to being significant for quantum information scrambling, the results also advance the understanding of decoherence in processes involving backward time evolution.

A scheme for determining an arbitrary pure state of a charge qubit by measuring a steady-state current through a single-electron transistor is proposed. In order to increase the sensitivity of the transistor its operating part consists of three quantum dots, the energy levels of which form a symmetrical configuration. Such a choice makes it possible to realize high-precision measurements in a nonresonant steady-state regime when a maximum distance of the qubit from this structure is several hundreds of nanometers. Time-dependent populations of the structure states are obtained; a current and a measurement contrast are calculated as functions of system geometric parameters and the optimal values of these parameters are found.

We present two schemes for quantum teleportation between parties whose local reference frames are misaligned by the action of a compact Lie group $G$. These schemes require no prior alignment of reference frames and are unaffected by arbitrary changes in reference-frame alignment during execution, suiting them to situations of rapid reference-frame drift. Our tight scheme yields improved purity compared to standard teleportation, in some cases substantially—this includes the case of qubit teleportation under arbitrary $\mathrm{SU}\left(2\right)$ reference-frame uncertainty—while communicating no information about either party's reference-frame alignment at any time. Our perfect scheme performs perfect teleportation, but does communicate some reference-frame information. The mathematical foundation of these schemes is a unitary error basis permuted up to a phase by the conjugation action of a finite subgroup of $G$.