In this paper, an alternative kind of electron circle butterfly vortex beam (ECBVB) based on the butterfly catastrophe is introduced, and its propagation characteristics in free space and constant magnetic field are numerically discussed. In free space, the ECBVB exhibits autofocusing and self-healing properties, and the probability flow density vector and cross-section intensity distribution are also analyzed. Compared to that in the free space, the focusing intensity of the ECBVB in the magnetic field increases by two orders of magnitude. By changing the distribution factor, the magnetic flux density, and the second-order chirp factor, the autofocusing properties of the ECBVB can be adjusted flexibly. In addition, adjusting the topological charges and the initial transverse velocity of the ECBVB is conducive to obtaining the desired propagation behavior of the ECBVB.

Noise in quantum devices is generally considered detrimental to computational accuracy. However, the recent proposal of noise-assisted simulation has demonstrated that noise can be an asset in digital quantum simulations of open systems on noisy intermediate-scale quantum (NISQ) devices. In this context, we introduce an optimized decoherence rate control scheme that can significantly reduce computational requirements by multiple orders of magnitude, in comparison to the original noise-assisted simulation. We further extend this approach to encompass Lindblad equations with time-dependent coefficients, using only quantum error characterization and mitigation techniques. This extension allows for the perturbative simulation of non-Markovian dynamics on NISQ devices, eliminating the need for ancilla qubits or midcircuit measurements. Our contributions are validated through numerical experiments on an emulated IBM Quantum device. Overall, our paper offers valuable optimizations that bring current quantum processors closer to effectively simulating realistic open systems.

We consider an exact analytical formulation of the wave function for quantum tunneling decay, given as an expansion in terms of the bound, antibound, and resonant states, for the time-honored problem of a particle initially confined by a potential. We find that the interference term between a bound state and its corresponding antibound state may favor a decay process in which the probability density spreads throughout space in a nonexponential fashion.

Continuous-time quantum walks provide an alternative method for quantum search problems. Most earlier studies confirmed that quadratic speedup exists in some synthetic Hamiltonians, but whether there is quadratic speedup in real physical systems remains elusive. Here, we investigate three physical systems with long-range atom-atom interaction which are possibly good candidates for realizing the quantum search, including one-dimensional atom arrays either trapped in an optical lattice or coupled to a waveguide near the band edge or dispersively coupled to a good cavity. We find that all three systems can provide a near-optimal quantum search if there is no dissipation. However, if the dissipation is considered, only the latter two systems (i.e., waveguide-QED and cavity-QED systems) can still have high success probabilities because they can significantly enhance the atom-atom interaction even if they are far apart and the spectra gap can be much larger, which can reduce the search time and the effects of dissipation significantly. Our studies here can provide helpful instructions for realizing quantum search in real physical systems in the noisy intermediate-scale quantum era.

We study entanglement activation in a generalized entanglement swapping process involving two Bell pairs and generalized measurements. The conventional understanding posits entangled measurements as both necessary and sufficient for establishing entanglement between distant parties. In this study, we reassess the role of measurement operators in entanglement generation within a generalized entanglement swapping process. We focus on maximally entangled two-qubit initial states and generalized measurements, investigating the necessity and sufficiency conditions for entangled measurement operators. By utilizing two Bell pairs, (1, 2) shared between Alice and Bob, and (3, 4) shared between Bob and Charlie, we demonstrate that while entangled measurements are sufficient, they are not indispensable for establishing entanglement between spatially separated observers. Through a sequential approach, if Bob performs an initial measurement which is not able to establish entanglement then followed by another measurement after postprocessing the first measurement it is possible to establish entanglement. We identify specific criteria for different measurement operators that enable the potential for performing a second measurement to establish entanglement. Our findings highlight the feasibility of generating entanglement between distant parties through a combination of measurements, shedding light on entanglement distribution in quantum networks. Additionally, we showcase through illustrative examples how successive measurements enhance entanglement compared to single measurements, underscoring the practical benefits of our approach in enhancing entanglement. Moreover, our protocol extends beyond bipartite qubit states to higher-dimensional maximally entangled states, emphasizing its versatility and applicability.

Quantum-electrodynamical density-functional theory (QEDFT) provides a promising avenue for exploring complex light-matter interactions in optical cavities for real materials. Similar to conventional density-functional theory, the Kohn-Sham formulation of QEDFT needs approximations for the generally unknown exchange-correlation functional. In addition to the usual electron-electron exchange-correlation potential, an approximation for the electron-photon exchange-correlation potential is needed. A recent electron-photon exchange functional [C. Schäfer et al., Proc. Natl. Acad. Sci. USA 118, e2110464118 (2021)], derived from the equation of motion of the nonrelativistic Pauli-Fierz Hamiltonian, shows robust performance in one-dimensional systems across weak- and strong-coupling regimes. Yet, its performance in reproducing electron densities in higher dimensions remains unexplored. Here we consider this QEDFT functional approximation from one- to three-dimensional finite systems and across weak to strong light-matter couplings. The electron-photon exchange approximation provides excellent results in the ultrastrong-coupling regime. However, to ensure accuracy also in the weak-coupling regime across higher dimensions, we introduce a computationally efficient renormalization factor for the electron-photon exchange functional, which accounts for part of the electron-photon correlation contribution. These findings extend the applicability of photon-exchange-based functionals to realistic cavity-matter systems, fostering the field of cavity QED (quantum-electrodynamics) materials engineering.

We consider the problem of determining the state of an unknown quantum sequence without error. The elements of the given sequence are drawn with equal probability from a known set of linearly independent pure quantum states with the property that their mutual inner products are all real and equal. This problem can be posed as an instance of unambiguous state discrimination where the states correspond to that of all possible sequences having the same length as the given one. We calculate the optimum probability by solving the optimality conditions of a semidefinite program. The optimum value is achievable by measuring individual members of the sequence, and no collective measurement is necessary.

With the increased power consumption of modern computer components, heat-based circuitry has become ever more relevant due to a lower power expense to process logic bits of information. In heat-based circuits, computations are performed by driving heat currents through a circuit using a temperature difference. Utilizing harmonic oscillators and three-level quantum rectifiers as base components, we study three different heat-based circuits: a series configuration of diodes, a parallel configuration of diodes, and a diode bridge rectifier. We demonstrate the required functionality of each circuit for use as heat-based analogues of standard electronic components. Furthermore, the diode bridge rectifier is found to give a consistent sign of the output bias independent of the input bias, thus rectifying the input. Our results prove the theoretical feasibility of combining heat current components into heat-based circuits. The three circuits should be realizable using several of the current quantum technology platforms.

The twin-field quantum key distribution (TF-QKD) protocol and its variants provide promising solutions to long-distance information-theoretic-secure communication, which can surpass the fundamental rate-loss bound without quantum repeaters. Different from other variants, the discrete-phase-randomized TF-QKD variant only needs to modulate weak coherent sources with random discrete phases, which avoids the necessity of modulating continuously randomized phases and can be implemented with current technology. However, the discrete-phase-randomized variant compromises the performance of TF-QKD under high channel losses and error rates. To overcome this dilemma, we propose to adopt the advantage distillation method to improve the performance of discrete-phase-randomized TF-QKD, and analyze its security in the asymptotic case. Without changing the optical hardware of TF-QKD systems, the proposed scheme can improve the secret key rate under high channel losses and error rates, and extend the tolerable channel loss as well.

We investigate signatures of non-Markovianity in the dynamics of a periodically driven qubit coupled to a dissipative bosonic environment. We propagate the dynamics of the reduced density matrix of the qubit by integrating the numerically exact hierarchical equations of motion. Non-Markovian features are quantified by comparing on an equal footing the predictions from diverse and complementary approaches to quantum dissipation. In particular, we analyze the distinguishability of quantum states, the decay of the volume accessible to the qubit on the Hilbert space, the negativity of the canonical rates in the generalized Lindblad equation, and the relaxation of the memory kernels in the Nakajima-Zwanzig generalized quantum master equation. We study the effects of controlled driving on the coherent dynamics of the system. We show that a suitable external field can offset the ergodic relaxation of time-correlation functions, increase distinguishability over time, and strengthen non-Markovian effects witnessed by the canonical dissipation channels. We furthermore observe the phenomenon of eternal non-Markovianity for sufficiently small system-bath coupling and we discuss how this can be enhanced by modulating the frequency of the external drive. This work provides a broad theoretical analysis of quantum dissipation in the framework of open quantum dynamics and quantum information.

We consider stellar interferometry in the continuous-variable (CV) quantum information formalism and use the quantum Fisher information (QFI) to characterize the performance of three key strategies: direct interferometry (DI), local heterodyne measurement, and a CV teleportation-based strategy. In the lossless regime, we show that a squeezing parameter of $r\approx 2$ (18 dB) is required to reach $\sim 95\%$ of the QFI achievable with DI; such a squeezing level is beyond what has been achieved experimentally. In the low-loss regime, the CV teleportation strategy becomes inferior to DI, and the performance gap widens as loss increases. Curiously, in the high-loss regime, a small region of loss exists where the CV teleportation strategy slightly outperforms both DI and local heterodyne, representing a transition in the optimal strategy. We describe this advantage as limited because it occurs for a small region of loss, and the magnitude of the advantage is also small. We argue that practical difficulties further impede achieving any quantum advantage, limiting the merits of a CV teleportation-based strategy for stellar interferometry.

We measured the product-state distribution and its dependence on the hydrogen isotope for the mutual neutralization between ${}^{16}\mathrm{O}^{+}$ and ${}^{1,2}\mathrm{H}^{-}$ at the double electrostatic ion-beam storage ring DESIREE for center-of-mass collision energies below 100 meV. We find at least six product channels into ground-state hydrogen and oxygen in different excited states. The majority of oxygen products populate terms corresponding to $2s^2{2p}^3{(}^4{S}^{\circ })4s$ with ${}^5\mathrm{S}^{\circ }$ as the main reaction product. We also observe product channels into terms corresponding to $2s^2{2p}^3{(}^{4}S)3p$. Collisions with the heavier hydrogen isotope yield a branching into these lower excited states smaller than collisions with ${}^1\mathrm{H}^{-}$. The observed reaction products agree with the theoretical predictions. The detailed branching fractions, however, differ between the theoretical results, and none of them fully agree with the experiment.

We report the fragmentation dynamics of double ionization of tetrahydrofuran (THF) induced by electron impact ($E_0=200$ eV). Using a multiparticle coincidence momentum spectrometer, the hydrogen molecule (${\mathrm{H}}_2$) production channel, i.e., double ionization and fragmentation of ${\mathrm{THF}}^{++}\to {\mathrm{H}}_2+{\mathrm{C}}_3{\mathrm{H}}_5{}^{+}+{\mathrm{CHO}}^{+}$, is observed and identified using an ion-ion coincidence map and the correlated projectile energy-loss spectrum. The measured kinetic energy release, combined with ab initio molecular-dynamics simulations and high-level potential energy surface (PES) calculations, reveals the detailed fragmentation dynamics of the ${\mathrm{H}}_2$ production channel. From the measured energy-loss spectrum, we determine the initial ionization mechanism of the fragmentation channel as a double-ionization excited state (3.3 eV above the ground state). The PES calculations reveal several ${\mathrm{H}}_2$ formation pathways, which are all below the energy of the excited state and hence can proceed barrierless. We find that the ${\mathrm{H}}_2$ formation and ejection occur on an ultrafast timescale (approximately $50$ fs), which is followed by ring opening via the C–O bond cleavage and ultimate Coulomb explosion. The present observation of the state-resolved fragmentation mechanism and dynamics is expected to provide valuable insights into the formation process of hydrogen molecules in the interstellar medium, as well as hydrogen storage and production.

A general quantum electrodynamic method for the derivation of nuclear recoil corrections in hydrogenic systems, which are exact in the nuclear charge parameter $Z\alpha$, is introduced. The exemplary derivation is presented for the $O(m/M)$ nuclear pure recoil correction to the hyperfine splitting. The obtained result is verified by comparison to the known ${\left(Z\alpha \right)}^5$ contribution.

Spatial nonuniformity in tight-binding models serves as a source of rich phenomena. In this paper we study a diamond-chain tight-binding model with a spatially increasing magnetic flux at each plaquette. In the numerical studies with various combinations of the minimum and maximum flux values, we find the characteristic dynamics of a particle, namely, a particle slows down when approaching the plaquette with $\pi$ flux. This originates from the fact that the sharply localized eigenstates exist around the $\pi$-flux plaquette. These localized modes can be understood from a squared model of the original one. This characteristic blocked dynamics can be observed in photonic waveguides or cold atoms.

To increase the measured phase of an atom interferometer and improve its sensitivity, researchers attempt to increase the enclosed space-time area using two methods: creating larger separations between the interferometer arms and having longer evolution times. However, increasing the evolution time reduces the bandwidth that can be sampled, whereas decreasing the evolution time worsens the sensitivity. In this paper, we attempt to address this by proposing a setup for high-bandwidth applications, with improved overall sensitivity. This is realized by accelerating and holding the atoms using optical dipole traps. We find that accelerations of up to ${10}^3\text{–}{10}^5$ ${\mathrm{m/s}}^2$ can be achieved using acousto-optic deflectors to move the traps. By comparing the sensitivity of our approach to acceleration as a baseline to traditional atom interferometry, we find a substantial improvement to the state of the art. In the limit of appropriate beam and optics stabilization, sensitivities approaching ${10}^{-14}$ (${\mathrm{m/s}}^2$)/$\sqrt{\mathrm{Hz}}$ may be achievable at 1 Hz, while detection at 1 kHz with a sensitivity an order of magnitude better than traditional free-fall atom interferometers is possible with today's systems.

Optical tweezer arrays of neutral atoms provide a versatile platform for quantum simulation due to the range of interactions and Hamiltonians that can be realized and explored. We propose to simulate a two-component Bose-Hubbard model with power-law hopping using arrays of multilevel Rydberg atoms featuring resonant dipolar interactions. The diversity of states that can be used to encode the local Hilbert space of the Bose-Hubbard model enables control of the relative hopping rate of each component and even the realization of spin-flip hopping. We use numerical simulations to show how multilevel Rydberg atoms provide an opportunity to explore the diverse nonequilibrium quench dynamics of the model. For example, we demonstrate a separation of the relaxation time scales of effective spin and charge degrees of freedom, and observe regimes of slow relaxation when the effective hopping rates of the two components are vastly different due to dynamical constraints arising from hardcore boson interactions. We discuss prospects for studying these effects in state-of-the-art Rydberg tweezer arrays.

Our analysis suggests strongly that stationary pulses exist in nonlinear media with second-, third-, and fourth-order dispersion. A theory, based on the variational approach, is developed for finding approximate parameters of such solitons. It is obtained that the soliton velocity in the retarded reference frame can be different from the inverse of the group velocity of linear waves. It is shown that the interaction of the pulse spectrum with that of linear waves can affect the existence of stationary solitons. These theoretical results are supported by numerical simulations. Transformations between solitons of different systems are derived. A generalization for solitons in media with the highest even-order dispersion is suggested.