Magnetic monopoles are crucial in explaining the quantization of electric charges and quantum Hall effects, while artificially creating a minimal magnetic monopole in experiments remains a challenge. Here we develop a flexible way to simulate a half-integer-type monopole in Bose gases and investigate the induced vortex dynamics on a sphere. We list the possible experiment parameter settings for different isotopes and discuss their experimental feasibility. With the assumption of a rigid monopole-vortex structure, we analytically predict the vortex trajectory in an external magnetic field. We then confirm the result by numerically solving the Gross-Pitaevskii equation, which employs two gauges simultaneously (the Wu-Yang approach) to prevent singularity in the one-gauge method when a monopole is present. The study offers significant insight into the characteristics of monopoles and vortices, facilitating avenues for experimental validation.

X-ray diffraction imaging is a powerful tool for exploring microscopic structures. However, conventional x-ray diffraction imaging using synchrotron radiation relies on high-brilliance sources, which hinders its wide application in laboratory scenarios. Here we propose a multiangle lensless imaging method that allows for the simultaneous measurement of the sample's Fourier information from different angles. The Fourier-transform diffraction pattern of the sample can be obtained through spatial correlation calculation. Benefiting from the multiangle strategy, a significant improvement in the quality of the diffraction pattern can be achieved. In proof-of-concept simulations, we have successfully extracted the sample's Fourier information and retrieved its spatial distribution with a radiation flux as low as 1 photon/${\mathrm{mrad}}^2\text{s}$. Our research may enrich the panel of laboratory-based x-ray diffraction imaging techniques.

Designs, structures connected to averaging with respect to a given measure using finite sets of points, have proven themselves to be invaluable tools across the field of quantum information, finding their uses in state and process tomography, key distribution, and others. In this work, we introduce a concept of pushforward designs that allows us to obtain new structures from already existing ones by mapping them between the spaces, with specific examples including simplex designs and mixed state designs from complex projective designs. Based on the general concept, we put forward a structure called channel $[t,k]$-design, allowing for averaging over space of quantum channels for systems in contact with an environment of dimension $k$. Based on this notion, we introduce the concept of effective environment dimensionality $k^{*}$, which we estimate for the IBM Kyoto quantum computer to be below 2.2 for times up to $350\mu \text{s}$.

Formulas for the combined nuclear-recoil and finite-nuclear-size effects of orders ${\left(Z\alpha \right)}^5$ and ${\left(Z\alpha \right)}^6$ are derived without any expansion in the nuclear-charge radius $r_C$, making them applicable to both electronic and muonic atoms. The obtained results are particularly relevant for high-precision determinations of root-mean-square charge radii from muonic atom spectroscopy. We demonstrate that calculations of the atomic isotope shift based on the widely used Breit approximation give rise to an unphysical nuclear-size contribution that is linear in the nuclear-charge radius $r_C$ at order ${\left(Z\alpha \right)}^5$. This spurious term vanishes in a full QED treatment, leaving the correct contribution quadratic in $r_C$. For electronic atoms, this quadratic term is significantly smaller than the spurious linear contribution.

Multiphoton electromagnetically induced transparency (EIT) of atomic vapors involves several intermediate atomic levels. The substructure of these levels and their collisional interactions can drastically alter experimental EIT signals. Here we report on hyperfine structure and collision effects in three-photon Rydberg EIT on the cascade $5S_{1/2}\to 5P_{1/2}\to 5D_{3/2}\to 25F_{5/2}$ in a room-temperature ${}^{85}\mathrm{Rb}$ vapor cell. In our measurements of EIT spectra, we identify two types of EIT signatures that correspond with distinct excitation pathways and atomic velocity classes in the atomic vapor. The $5D_{3/2}$ hyperfine structure and Autler-Townes splittings lead to complex patterns in the EIT spectra, which we analyze with the aid of 10-level EIT simulations. Adding 50 mTorr of Ar gas alters the EIT spectra and induces an additional, third EIT mode. Based on our simulation results, we attribute these changes to hyperfine collisions in the Rb $5D_{3/2}$ level. Our study may become useful in quantum technologies involving Rydberg EIT and hyperfine collisions in vapor cells, including noninvasive spatiotemporally resolved electric-field sensing of electric fields in low-pressure plasmas.

We investigate the behavior of geometric phase (GP) and geometric entanglement (GE), a multipartite entanglement measure, across quantum phase transitions in Rydberg atom chains. Using density-matrix renormalization-group calculations and finite-size scaling analysis, we characterize the critical properties of transitions between disordered and ordered phases. Both quantities exhibit characteristic scaling near transition points, with the disorder to the $Z_2$ ordered phase transition showing behavior consistent with the Ising universality class, while the disorder to the $Z_3$ phase transition displays distinct critical properties. We demonstrate that GP and GE serve as sensitive probes of quantum criticality, providing consistent critical parameters and scaling behavior. A unifying description of these geometric quantities from a quantum geometry perspective is explored, and an interferometric setup for their potential measurement is discussed. Our results provide insights into the interplay between geometric phase and multipartite entanglement near quantum phase transitions in Rydberg-atom systems, revealing how these quantities reflect the underlying critical behavior in these complex quantum many-body systems.

The optical geometric phase (OGP) is directly associated with the polarization of light. We investigate the physical principles underlying the occurrence of the OGP for a single-mode light beam propagating in a single-mode optical fiber wound into a circular helix configuration, with and without stress-induced birefringence. The effects of the curvature and torsion of the helical fiber on the rotation of the polarization vector and the associated OGP are discussed. Analytic expressions are derived for the polarization vector and Stokes parameters for any initial polarization state of the light entering the helical fiber, as well as for the OGP of the light as a function of helix arclength. Additionally, the intensity of a superposition of the initial and final beams, which depends on the final OGP, is derived. Furthermore, the relationship between the OGP and the solid angle subtended by the tangent vector of the helix plotted on the Poincaré sphere is analyzed and the effects of fluctuations of the parameters specifying the geometry and the material characteristics of the helical fiber on the OGP are considered. We also point out that the OGP is a geometric phase and not a topological phase and therefore is not topologically protected against local perturbations which can adversely affect fault tolerance.

Magnons can serve as a bridge between spin, phonon, and photon systems, which renders them suitable for constructing hybrid systems. An important application of such hybrid systems is generating entanglement between different platforms. As magnons can support a broad variety of states, e.g., Fock states, squeezed states, or coherent states, and hybrid states can be produced with cavities or spins, there are many different kinds of entangled states in magnon systems. In this paper, we consider the entanglement of cat-state-like throughout states, which can be generated in magnon systems with parametric pumps beyond the parametric stable intensities. However, estimating the entanglement in such states is challenging due to their multiphoton and non-Gaussian properties. Here, we apply a modular variable-based projection, which maps the catlike states to spin states, preserving the encoded information. After the projection, Bell's inequality is employed to detect the entanglement in the effective spin states. Our numerical analysis provides the conditions for generating catlike entanglement in magnon systems and can be conveniently extended to other entangled states that may be formed by magnon and spin systems.

Collision models describe the sequential interactions of a system with independent ancillas. Motivated by recent advances in neutral atom arrays, here we investigate a model where the ancillas are governed by a classical controller that allows them to queue up while they wait for their turn to interact with the system. The ancillas can undergo individual open dynamics while they wait, which could cause them to, e.g., decohere. The system, which plays the role of the server in the queue, can also undergo its own open dynamics whenever it is idle. We show that this framework greatly generalizes existing approaches for quantum collision models, recovering the deterministic and stochastic formulations in the appropriate limits. Next, we show how the combination of queueing dynamics with quantum collisions introduces rich dynamical phenomena, including phase transitions and a sharp dependence on the queue statistics.

We provide a class of lower bounds for concurrence based on symmetric measurements. We show that our lower bounds estimate the quantum entanglement better than some existing lower bounds by detailed examples. Moreover, our lower bounds can be experimentally identified without state tomography.

The high-energy repulsive interaction between nuclei at distances much smaller than the equilibrium bond length is the key quantity determining the nuclear stopping power and atom scattering in keV and MeV radiation events. This interaction is traditionally modeled within orbital-free density functional theory with frozen atomic electron densities, following the Ziegler-Biersack-Littmark (ZBL) model. In this work, we calculate atom pair-specific repulsive interatomic potentials with the ZBL model, and compare them to two kinds of quantum chemical calculations (second-order Møller-Plesset perturbation theory in flexible Gaussian basis sets as well as density functional theory with numerical atomic orbital basis sets) which go well beyond the limitations in the ZBL model, allowing the density to relax in the calculations. We show that the repulsive interatomic potentials predicted by the two quantum chemical models agree within $\sim 1\%$ for potential energies above 30 eV, while the ZBL pair-specific potentials and universal ZBL potentials differ much more from either of these calculations. We provide pair-specific fits of the screening functions in terms of three exponentials to the calculations for all pairs $Z_1\text{−}{Z}_2$ for $1\le Z_i\le 92$, and show that they agree within $\sim 2$% with the raw data. We use these potentials to simulate ion implantation depth profiles in single-crystalline Si and show very good agreement with experiment. However, we also show that under channeling conditions, the attractive part of the potential can affect the depth profiles.

The fragmentation dynamics of diiodoacetylene (${\mathrm{C}}_2{\mathrm{I}}_2$), multiply ionized by low-energy collisions of ${\mathrm{Ar}}^{8+}$, is studied by using a momentum imaging spectrometer. The kinetic energy releases of four-body fragmentation channels of ${\mathrm{C}}_2{\mathrm{I}}_2^{q+}$ are investigated for $q$ up to 10, in which generation of high-$q$ ions requires conversion of the projectile collision energy to the electronic energy. The experimentally observed momentum correlation in the four-body dissociation channels reveals the tendency that the direction of the emitted carbon and iodine ions are mutually perpendicular, in contrast to the intuitive prediction that the fragments of the linear molecule will align. The simulated trajectories of the fragments based on the pure (classical) Coulomb explosion model manifest that the fragmentation scheme can be well described by this model, taking into account the significant Coulombic interactions between dissociating carbon and iodine ions.

Electromagnetic pulse propagation through a plasma layer below the plasma frequency is a genuine classical wave tunneling phenomenon strongly differing from tunneling in dielectric structures due to the specific dispersion of plasma. We consistently examine this phenomenon using direct numerical simulations of a time-dependent wave equation and show that in the low-frequency limit the tunneling time has the frequency-independent asymptotic $2/{\omega }_p$ with ${\omega }_p$ being the plasma frequency, in good correspondence with the analysis in stationary approximation. These results prove that radiation tunneling for plasma principally differs from the other electromagnetic tunneling phenomena which supposedly obey the inverse proportional dependence of the tunneling time on radiation frequency. The Hartman effect (saturation of the tunneling time with layer thickness) is demonstrated for pulse propagation as well with the saturated time getting closer to the asymptotic value as we move deeper into the tunneling regime. We also show that the reflected wave packet build-up gives an efficient tool for the tunneling problem and that reflection develops synchronously with transmission. Our theoretical calculations are supported by experiments with microwave tunneling through the electromagnetic band gap structure (electromagnetic crystal) based on gas discharge plasmas.

Giant atoms introduce promising avenues for enhancing light-matter interaction in waveguides, which plays a crucial role in quantum information processing and quantum state control. In this work, we study the dynamics of a system comprising a single-photon Gaussian pulse initially inside a cavity with giant-atom mirrors coupled to a one-dimensional waveguide. The decay rate of the photon pulse can be significantly minimized by using giant atoms instead of point atoms and by carefully selecting the spacing between the coupling points of the giant atom to the waveguide. The quality factor for the cavity is analyzed by varying the number of atoms, coupling points, and coupling point spacing in each mirror to find the optimal parameters for a high $Q$-factor cavity. Our work contributes to the design of more efficient, high-quality quantum devices such as integrated quantum photonic circuits.

We introduce a method to achieve nonreciprocal photon blockade in an optical resonator that is chirally coupled to a two-level atom. This approach enables single-excitation and two-excitation resonant conditions to be simultaneously satisfied. The atom-uncoupled optical mode can be blocked with eliminating its two-photon excitation by judiciously selecting parameters, e.g., the optical coupling strength. The chiral interaction between the resonator mode and the atom leads to different optimal parameter conditions for generating photon blockade in the two opposite drivings. This offers a natural way to realize nonreciprocal photon blockade. The nonreciprocity achieved by the chiral cavity-atom interaction diminishes the experimental difficulty by eliminating the need to rotate the resonator. The blockade mode achieves very high purity of single-photon excitation, as characterized by a second-order correlation function of $g^{\left(2\right)}\left(0\right)\sim {10}^{-4}$. In particular, in the nonreciprocal regime, the mean number of photons is significantly higher where photon blockade occurs compared to the general Jaynes-Cummings case. Our findings are particularly relevant for the development of quantum nonreciprocal devices and their applications in quantum information processing, including chiral networks.

We unveil the inherent topological nature from a two-dimensional synthetic parameter space in a single-photon transport problem, with the simple configuration of one waveguide coupled with two four-level atoms driven by external fields. We find that, by tuning the system in the dark-state condition, the system holds two independent phase degrees of freedom from both the photon propagation and the atomic transition. As the direct output, the photon scattering characteristics show the total reflection with the frequency preservation or the complete frequency conversion at the specific choices of two phases. We uncover the underlying topological effect by analyzing the photon scattering amplitudes in the parameter space of two phases, which links to the singularity with nonzero winding numbers. Our results are verified by numerical simulations, and hence point to an alternative perspective for the research at the intersection of single-photon transport and topology, without using the topological geometric arrangement of atoms.

Quantum evolution was recently shown to be equivalent to the mathematical expectation of the stochastic motion described by the Schrödinger equation with momentum-coupled white noise [J. Shao, J. Chem. Phys. 159, 024128 (2023)]. The stochastic formulation provides a convenient means of evaluating quantum propagators because the involved kinetic and potential contributions are disentangled. With the help of the auxiliary functional averaging technique, we apply this scheme to the derivation of the quantum propagators for systems of exponential, linear, harmonic, and $\delta$-function potentials. Notably, our work presents a truly workable expression of the quantum propagator for the exponential potential problem. To demonstrate the features and advantages of this propagator, we use it to calculate the wave-packet dynamics and compare it to the split-operator method.

We compare Steane's and Shor's syndrome extraction methods on the Bacon-Shor code. We propose a straightforward strategy based on postselection to prepare the logical ${|0\rangle }_L$ and ${|+\rangle }_L$ states of the Bacon-Shor code by using flaglike qubits to verify their constituent Greenberger-Horne-Zeilinger states. We perform stabilizer simulations with a circuit-level, depolarizing Pauli error model and find that Steane's method significantly outperforms Shor's. Not only does Steane's method result in pseudothresholds that are about one order of magnitude higher than Shor's, but also its advantage increases monotonically as we go from a distance-3 to a distance-9 Bacon-Shor code. The advantage of Steane's method is the greatest in the regime where gate errors dominate over measurement errors. Some of the circuit constructions we propose for Steane's method are not formally fault tolerant yet outperform the formally fault-tolerant Shor's protocols for experimentally relevant physical error rates. This suggests that constructing formally fault-tolerant circuits that maintain the full code distance is not strictly necessary to guarantee the usefulness of a quantum error-correcting protocol. Despite relying on postselection, we find that our methods can be efficient. These protocols would be naturally implementable on a platform with long-range qubit interactions like trapped ions or neutral atoms.

We investigate the dynamical aspects of the quantum switch and find a particular form of quantum memory emerging out of the switch action. We first analyze the loss of information in a general quantum evolution subjected to a quantum switch and propose a measure to quantify the switch-induced memory. We then derive an uncertainty relation between information loss and switch-induced memory. We explicitly consider the example of depolarizing dynamics and show how it is affected by the action of a quantum switch. For a more detailed analysis, we consider both the control qubit and the final measurement on the control qubit as noisy and investigate the said uncertainty relation. Further, while deriving the Lindblad-type dynamics for the reduced operation of the switch action, we identify that the switch-induced memory actually leads to the emergence of non-Markovianity. Interestingly, we demonstrate that the emergent non-Markovianity can be explicitly attributed to the switch operation by comparing it with other standard measures of non-Markovianity. Our investigation thus paves the way forward to understanding the quantum switch as an emerging non-Markovian quantum memory.