We consider a collision model representation of nonequilibrium dynamics for an externally driven open quantum system. Specifically we investigate the nondemolition quasiprobability distributions (QPDFs) of work and heat in both Markovian and non-Markovian regimes. In this model, work and heat correspond to different evolution processes, and their contributions can be distinguished. For the system state with initial coherence, in both Markovian and non-Markovian regimes, negative quasiprobabilities at half of the energy gap of the system for work and the variation of internal energy appear, which is considered to be a witness of the quantumness of the system. We also find that when the external driving speed slows down, the quantumness of the system is weakened, and when the driving speed is slow enough, the negative quasiprobability will disappear and the results of the QPDF coincide with those of the two-measurement protocol. Most importantly, we find that non-Markovianity can enhance the quantumness of the system.

Quantum state engineering, namely, the generation and control of arbitrary quantum states, is drawing more and more attention due to its wide applications in quantum information and computation. However, there is no general method in theory, and the existing schemes also depend heavily on the selected experimental platform. In this article, we give two schemes for the generating task of arbitrary quantum state in $c$-partite $d$-dimensional system, both of which are based on a discrete-time quantum walk with a $2^c$-dimensional time- and position-dependent coin. The first procedure is a $d$-step quantum walk where all the $d$ coins are nonidentity, while the second procedure is an $O\left(d\right)$-step quantum walk where only $O(logd)$ coins are nonidentity. A concrete example of preparing generalized Bell states is given to demonstrate the first scheme we proposed. Furthermore, the first scheme can be applied to give an alternative approach to the quantum state preparation problem which is one of the fundamental tasks of quantum information processing. We design circuits for quantum state preparation with the help of our quantum state engineering scheme that match the best current result in both size and depth of the circuit asymptotically.

Communication scenarios between two parties can be implemented by first encoding messages into some states of a physical system which acts as the physical medium of the communication and then decoding the messages by measuring the state of the system. We show that already in the simplest possible scenarios it is possible to detect a definite, unbounded advantage of quantum systems over classical systems. We do this by constructing a family of operationally meaningful communication tasks, each of which, on the one hand, can be implemented by using just a single qubit but which, on the other hand, require an unboundedly larger classical system for classical implementation. Furthermore, we show that even though, with the additional resource of shared randomness, the proposed communication tasks can be implemented by both quantum and classical systems of the same size, the number of coordinated actions needed for the classical implementation also grows unboundedly. In particular, no finite storage can be used to store all the coordinated actions required to implement all possible quantum communication tasks with classical systems. As a consequence, shared randomness cannot be viewed as a free resource.

Atomic orbital close-coupling calculations involving three active electrons within a full configuration interaction formalism are used to investigate projectile excitation. Cross sections for the production of the autoionizing $\left(2s2p{}^{3}P\right)$ states in 0.5–1.5 MeV/u collisions of ${\mathrm{C}}^{4+}\left(1s2s{}^{3}S\right)$ and ${\mathrm{O}}^{6+}\left(1s2s{}^{3}S\right)$ ions with He are presented. Results are compared to accompanying $0^{\circ }$ Auger projectile spectroscopy measurements. While the projectile energy dependence of the theoretical results is in overall agreement with experiment, theory is found to be somewhat smaller than experiment. Critical comparisons to first-order Born and a minimal basis close-coupling calculation indicate that the use of low-order perturbative treatments and related interpretations may be questionable in this energy range. Such a nonperturbative treatment, which does not rely on any scaling parameters or renormalization, is seen to provide an important advance in the modeling of multielectron multi-open-shell quantum systems under ultrafast perturbations, whose understanding seems to still be incomplete.

Ongoing experimental efforts to measure with unprecedented precision electron-capture probabilities challenge the current theoretical models. The short range of the weak interaction necessitates an accurate description of the atomic structure down to the nucleus region. A recent electron-capture modeling has been modified in order to test the influence of three different atomic descriptions on the decay and shaking probabilities. To this end, a specific atomic modeling was developed in the framework of the relativistic density-functional theory, exploring several exchange-correlation functionals and self-interaction-corrected models. It was found that the probabilities of total shaking, tested on both photoionization and electron-capture processes, depend strongly on the accuracy of the atomic modeling. Predictions of capture probabilities have been compared with experimental values evaluated from available published data for different radionuclides from ${}^7\mathrm{Be}$ to ${}^{138}\mathrm{La}$. New high-precision measurements are strongly encouraged because the accuracy of the current experimental values is insufficient to test the models beyond the inner shells.

Quantum Darwinism (QD) proposes that classical objectivity emerges from the broadcast of information about a microscopic degree of freedom into multiple fractions of a many-body environment. Such a broadcast of information is in sharp contrast with its scrambling under strong interaction. It was recently shown that quantum dynamics interpolating between broadcasting and scrambling may display sharp phase transitions of information propagation, named QD-encoding transitions. Here we initiate their systematic study in generic, non-Clifford settings. First, in a general theoretical setup where the information propagation is modeled as an isometry, whose input qudit is entangled with a reference, we propose a probe of the transitions—the distribution of the density matrix of the reference after measuring an environment fraction. This probe measures the classical correlation between the fraction and the injected information. We then apply the framework to two similar models defined by a tensor network on an expanding tree, modeling a noisy apparatus that attempts to broadcast the $z$ component of a spin-half. We derive an exact recursion relation of the density matrix distribution, which we analyze analytically and numerically. As a result we find three phases: QD, intermediate, and encoding, and two continuous transitions. The encoding-intermediate transition describes the establishment of nonzero correlation between the reference and a small environment fraction, and can be probed by a “coarse-grained” measure of the total spin-$z$ of the fraction, which becomes non-Gaussian and symmetry breaking in the intermediate space. The QD-intermediate transition is about whether the correlation is perfect. It must be probed by fined-grained measures and corresponds to a subtler symmetry breaking in the replica space.

Algorithms with unitary oracles can be nested, which makes them extremely versatile. An example is the phase estimation algorithm used in many candidate algorithms for quantum speedup. The search for new quantum algorithms benefits from understanding their limitations: Some tasks are impossible in quantum circuits, although their classical versions are easy, for example, cloning. An example with a unitary oracle $U$ is the if clause, the task to implement controlled $U$ (up to the phase on $U$). In classical computation the conditional statement is easy and essential. In quantum circuits the if clause was shown impossible from one query to $U$. Is it possible from polynomially many queries? Here we unify algorithms with a unitary oracle and develop a topological method to prove their limitations: No number of queries to $U$ and $U^{†}$ lets quantum circuits implement the if clause, even if admitting approximations, postselection, and relaxed causality. We also show limitations of process tomography, oracle neutralization, and $\sqrt[dimU]{U}, U^T$, and $U^{†}$ algorithms. Our results strengthen an advantage of linear optics, challenge the experiments on relaxed causality, and motivate new algorithms with many-outcome measurements.

Reaching a given target quantum state with high fidelity and fast operation speed close to the quantum limit represents an important goal in quantum information science. Here we experimentally demonstrate superadiabatic quantum driving to achieve population transfer in a three-level solid-state spin system at ambient conditions. Starting from traditional stimulated Raman adiabatic passage (STIRAP), our approach implements superadiabatic corrections to the STIRAP Hamiltonian with several pulse shapes, including the paradigmatic Gaussian shapes and trigonometric pulse shapes that guarantee an operation speed equal to the quantum limit. It requires no intense microwave pulses or long transfer times and shows an enhanced robustness against pulse imperfections. Thereby, these results might provide a useful tool for quantum information processing and the coherent manipulation of quantum systems.

In the quasistatic regimes of nonlinear Breit-Wheeler and trident pair creation, the rates can exhibit a nonanalytic dependency on the fundamental coupling of quantum electrodynamics, in a form similar to Schwinger vacuum pair creation. To reach this tunneling regime requires satisfying competing requirements: a high-intensity but low quantum strong-field parameter with sufficient pair creation to be observed. Using a locally monochromatic approach, we identify the parameter regime where tunneling pair creation could be measured in experiment. Studying several scenarios of collisions with focused Gaussian pulses, including a bremsstrahlung and an inverse Compton source for nonlinear Breit-Wheeler and a Gaussian electron beam for nonlinear trident, we find the position of the tunneling parameter regime to be well defined and robust.

We investigate, by means of the scattering approach, the Casimir-Polder interaction between a neutral anisotropic polarizable particle and a corrugated surface made of a realistic material. By focusing on the lateral force (arising from the presence of corrugation on the surface), we investigate the conditions for the particle to be attracted to the nearest corrugation peak or valley, or to an intermediate point between a peak and a valley, with such behaviors called peak, valley, and intermediate regimes, respectively. Such regimes of the lateral force were recently predicted in the literature, but in the context of the van der Waals interaction and considering the surface made of some ideal material (a perfectly conducting or a nondispersive dielectric). Here, we investigate how the occurrence of the mentioned regimes is affected by the consideration of realistic dielectric properties for the surface and also of the retardation in the interaction. In this context, we show that the consideration of a dispersive surface, when compared to the mentioned idealized materials, can amplify the occurrence of the valley and intermediate regimes. Moreover, regarding the consideration of retardation, we show that it has a small influence on the occurrence of the valley regime, but, for the intermediate ones, can either amplify or inhibit them. Such investigation provides a more precise description of the interaction between an anisotropic particle and a corrugated surface, giving a better understanding of the nontrivial aspects of the lateral Casimir-Polder force.

Improving the resolution of fluorescence microscopy beyond the diffraction limit can be achieved by acquiring and processing multiple images of the sample under different illumination patterns (periodic grids, focused beams, or more generally speckles). When the illuminations are known, the superresolved reconstruction is generally formed from a linear combination of the multiple diffraction-limited images, and the resolution gain is easily determined. On the other hand, when the illuminations are unknown, the resolution gain is seldom well defined. In this work, we consider the recent random illumination microscopy (RIM) technique where the illuminations are unknown speckles and the reconstructions are formed from the variance of the images. We show that an unambiguous twofold resolution gain can be obtained only when the speckle correlation length coincides with the width of the observation point spread function. Last, we analyze the difference between the variance-based techniques using random speckled illuminations (as in RIM) and those obtained using random fluorophore activation (as in superresolution optical fluctuation imaging).

Quantum electrodynamics (QED) is the most accurate of all experimentally verified physical theories. How QED and other theories of fundamental interactions couple to gravity through special unitary symmetries, on which the standard model of particle physics is based, is, however, still unknown. Here we develop a coupling between the electromagnetic field, Dirac electron-positron field, and the gravitational field based on an eight-component spinorial representation of the electromagnetic field. Our spinorial representation is analogous to the well-known representation of particles in the Dirac theory but it is given in terms of $8\times 8$ bosonic gamma matrices. In distinction from earlier works on the spinorial representations of the electromagnetic field, we reformulate QED using eight-component spinors. This enables us to introduce the generating Lagrangian density of gravity based on the special unitary symmetry of the eight-dimensional spinor space. The generating Lagrangian density of gravity plays, in the definition of the gauge theory of gravity and its symmetric stress-energy-momentum tensor source term, a similar role as the conventional Lagrangian density of the free Dirac field plays in the definition of the gauge theory of QED and its electric four-current density source term. The fundamental consequence, the Yang-Mills gauge theory of unified gravity, is studied in a separate work [arXiv:2310.01460], where the theory is also extended to cover the other fundamental interactions of the standard model. We devote ample space for details of the eight-spinor QED to provide solid mathematical basis for the present work and the related work on the Yang-Mills gauge theory of unified gravity.

In this work, we investigate the semiclassical limit of a simple bosonic quantum many-body system exhibiting both integrable and chaotic behavior. A classical Hamiltonian is derived using coherent states. The transition from regularity to chaos in classical dynamics is visualized through Poincaré sections. Classical trajectories in phase space closely resemble the projections of the Husimi functions of eigenstates with similar energy, even in chaotic cases. It is demonstrated that this correlation is more evident when projecting the eigenstates onto the Fock states. The analysis is carried out at a critical energy where the eigenstates are maximally delocalized in the Fock basis. Despite the imperfect delocalization, its influence is present in the classical and quantum properties under investigation. The study systematically establishes quantum-classical correspondence for a bosonic many-body system with more than two wells, even within the chaotic region.

Quantum digital signature (QDS) is the quantum version of its classical counterpart and can offer security against attacks of repudiation, signature forging, and external eavesdropping on the basis of quantum-mechanical no-go principles. Here we propose a QDS scheme based on quantum counterfactuality, which leverages the concept of interaction-free measurement. Employing the idea behind twin-field cryptography, we show how this two-way protocol can be turned into an equivalent noncounterfactual, one-way protocol that is both more practical and also theoretically helpful in assessing the experimental feasibility of the first protocol. The proposed QDS protocol can be experimentally implemented with current quantum technology.

Bosonic codes with rotational symmetry are currently one of the best-performing quantum error-correcting codes. Little is known about error propagation and code distance for these rotation codes in contrast with qubit codes and bosonic codes with translation symmetry. We use a general purpose error basis that is naturally suited to codes with rotation symmetry to compute how errors propagate through gates. This error basis allows us to give an explicit error detection, decoding, and correction scheme for any code with rotation symmetry. We also prove that codes with an $N$-fold rotation symmetry have a distance of $(d_n,d_{\theta })=(N,\pi /N)$ with respect to number and rotation errors.

Quantum homogenization is a reservoir-based quantum state approximation protocol, which has been successfully implemented in state transformation on quantum hardware. In this work we move beyond that and propose the homogenization as a novel platform for quantum state stabilization and information protection. Using the Heisenberg exchange interactions formalism, we extend the standard quantum homogenization protocol to the dynamically equivalent ${\left(\mathtt{\text{SWAP}}\right)}^{\alpha }$ formulation. We then demonstrate its applicability on the available noisy intermediate-scale quantum (NISQ) processors by presenting a shallow quantum circuit implementation consisting of a sequence of cnot and single-qubit gates. In light of this, we employ the Beny-Oreshkov generalization of the Knill-Laflamme (KL) conditions for near-optimal recovery channels to show that our proposed ${\left(\mathtt{\text{SWAP}}\right)}^{\alpha }$ quantum homogenization protocol yields a completely positive, trace-preserving (CPTP) map under which the code subspace is correctable. Therefore, the protocol protects quantum information contained in a subsystem of the reservoir Hilbert space under CPTP dynamics.

The dynamic electric dipole polarizabilities of the $5s^2{}^{1}S_0$, $5s5p{}^{3}P_0$, and $5s5p{}^{3}P_2$ states for Cd atoms are calculated using the relativistic configuration interaction plus many-body perturbation theory method. The magic wavelengths for the $5s^2{}^{1}S_0\to 5s5p{}^{3}P_0$ and $5s^2{}^{1}S_0\to 5s5p{}^{3}P_2$ transitions within a range of 300–500 nm are identified. The possibility of achieving triple magic trapping for the transitions $5s^2{}^{1}S_0\to 5s5p{}^{3}P_0$ and $5s^2{}^{1}S_0\to 5s5p{}^{3}P_2$ is investigated. It is found that no common magic wavelength could be identified for achieving triple magic trapping with the linearly polarized light. However, if the degree of ellipticity is between 0.358 and 1, the triple magic trapping can be achieved at 419.88 nm for the $5s^2{}^{1}S_0\to 5s5p{}^{3}P_2$ $(M_i=\pm 2)$ and $5s^2{}^{1}S_0\to 5s5p{}^{3}P_0$ transitions.

Accurate predictions for hydrogen molecular levels require the treatment of electrons and nuclei on equal footing. While nonrelativistic theory has been effectively formulated this way, calculation of relativistic and quantum electrodynamic effects using an exponential basis with explicit correlations that ensure well-controlled numerical precision is much more challenging. In this work, we derive a complete set of integrals for the relativistic correction and demonstrate their application to several of the lowest rovibrational levels. Together with similar advancements for quantum electrodynamic corrections, this will improve the accuracy beyond ${10}^{-9}$ and hopefully explain discrepancies with recent experimental values.

Close to the superfluid plane-wave (PW)–supersolid stripe (ST) phase transition point of a zero-temperature quasi-one-dimensional spin-orbit-coupled Bose gas, we find that an increase in temperature induces a phase transition to the supersolid phase with a broken translational symmetry from the superfluid plane-wave phase. We use the Hartree-Fock-Bogoliubov theory with the Popov approximation to investigate the effect of thermal fluctuations on the collective excitation spectrum and investigate the softening of the spin-dipole mode corresponding to the shift in the quantum critical point. This is in stark contrast to the PW-ST phase transition in a homogeneous system where nonzero temperatures facilitate the melting of the stripe phase.