With high-order harmonic generation (HHG) from Su-Schrieffer-Heeger (SSH) chains considered as a paradigm example, the mechanism of HHG in the presence of edge states (ESs) is clarified from the perspective of the underlying three-step processes and their interference. This is done by analyzing the HHG contributions from the states of different types, with the energy of the ESs possibly being modified within the band gap. The ES energy shift introduces asymmetry in the transitions between the ESs and the two bands; in such a generic setting, it is found that the ES-induced HHG plateau can be either attributed to the contribution from the initially occupied ES alone, or alternatively understood as a consequence of interfering contributions from the ES and the valence band. On the basis of the three-step processes, it is shown that the ES-induced plateau can be described with semiclassical trajectories for the electron-hole dynamics in real space. This work also demonstrates the possibility of the ES-induced HHG being outweighed by the interband HHG for long chains, underlining the importance of the length scale of the system for observing the ES-induced HHG enhancement in practice.

Motivated by the recent realization of space-borne Bose-Einstein Condensates (BECs) under microgravity conditions, we extend the understanding of ultracold dipolar bosonic gases by exploring their behavior in a novel trapping configuration known as the “bubble trap” topology. Utilizing the three-dimensional numerical simulations within the extended Gross-Pitaevskii framework, we unveil diverse ground-state phases in this static curved topology. Subsequently, we investigate the influence of rotation on a dipolar BEC confined to the surface of a spherical bubble. Our findings reveal that the rotation of a bubble trap at certain rotation frequencies can modify the effective local dipole-dipole interaction strength, leading to the induction of supersolidity and the formation of quantum droplets. In addition, we demonstrate that a bubble trap can sustain high circulation, with the flow persisting for a longer time. Significantly, adjusting the rf detuning parameter allows the condensate to achieve hypersonic velocity. Finally, we also explore the impact of drastic change in the topological nature of the trap on the rotating dipolar BEC, transitioning from a filled shell trap to a bubble trap and vice versa. Based on the results of the topological transition, we propose a dynamic protocol to drive the interacting atomic gas into the quantum Hall regime.

We present a theoretical study of a polarization beam splitter (PBS), different from the conventional time-reversal symmetry one, where a specific linearly polarized light on two opposite sides can be totally reflected into the incident one and can be transparent to incident to its orthogonal linearly polarized light on only one side. We employ the mechanism via an exceptional point and finite periodicity of non-Hermitian $\mathcal{PT}$ symmetry. We design such a PBS made of a finite periodic structure in which each unit cell has a delicate balance of gain and loss in spatial distribution. In order to obtain total reflection for one of two orthogonal polarizations of the incident wave, the unit cell has to be operated at some $\mathcal{PT}$-symmetry phase of the reflection band. To have a single-sided transparency for its orthogonal polarized light, the unit cell should be designed at an exceptional point as well as have asymmetric reflectance. Interestingly, such a single-sided transparent phenomenon is independent of the total number of unit cells. We believe this unidirectional PBS may stimulate a new route to polarization control.

The resource theory of contextuality considers resourceful objects to be probabilistic data tables, known as correlations or behaviors, that fail to have an explanation in terms of Kochen-Specker noncontextual models. In this work, we advance this resource theory, considering free operations to be noncontextual wirings (NCWs). We show that all such wirings form a convex set. When restricted to Bell scenarios, we show that such wirings are not equivalent to local operations assisted by a common source of classical shared randomness (LOSR). The set of all NCW operations contains LOSR, but is strictly larger. We also prove several elementary facts about how different resources can be converted via NCW. As a concrete example, we show that there are pairs of behaviors that cannot be converted one into the other using NCW. Since resource conversion mathematically induces a pre-order over the set of all behaviors, our results reveal the intricate ordering induced by NCW in scenarios beyond Bell scenarios.

Quantum stabilizer codes face the problem of low coding rate. In this article, following the idea of a recursively expanding Tanner graph proposed in our previous work, we try to construct new stabilizer codes with high coding rate, and propose an XZ-type Tanner-graph-recursive-expansion (XZ-TGRE) code and Tanner-graph-recursive-expansion hypergraph product (TGRE-HP) code. The XZ-TGRE code has a zero asymptotic coding rate, but its coding rate tends to zero extremely slowly with the growth of the code length. Under the same code length, its coding rate is much higher than that of the surface code. The coding rate of TGRE-HP is the constant 0.2, which is the highest constant coding rate of stabilizer codes to our best knowledge. We prove that the code distance of the XZ-TGRE code scales as $O(logN)$ and that of the TGRE-HP code scales as $O(log\sqrt{N})$, where $N$ is the code length. Moreover, the code capacity noise threshold of the XZ-TGRE code is around 0.078, and that of the TGRE-HP code is around 0.096. This articles shows that the idea of a recursively expanding Tanner graph might have potential to construct quantum codes with good performance.

In this paper, we present two quantum entanglement swapping schemes, a single-channel scheme and a dual-channel scheme, based on fiber channel transmission. We theoretically calculated the Einstein-Podolsky-Rosen- (EPR-) type variance and symmetry parameter factors of deterministic quantum entanglement swapping in these two schemes. By comparing the quantum entanglement swapping of the single- and dual-channel schemes, we show that the transmission distance of the dual-channel scheme is much longer than that of the single-channel scheme. Interestingly, the quantum correlation strength and symmetry of the two remote modes after deterministic quantum entanglement swapping are significantly improved when the optimal classical gain and loss efficiency of the loss channel are chosen. Moreover, the entanglement swapping will be robust and not suffer from sudden death when the entangled optical modes are transmitted in the lossy fiber channel. We also show that nonzero entanglement enables deterministic quantum entanglement swapping under both schemes when the EPR entanglement is a pure state. The two optimized schemes provide feasible technical references for long-distance metropolitan quantum communication.

High-fidelity and robust quantum gates are essential for quantum information processing, with neutral Rydberg atoms trapped in optical tweezer arrays serving as a versatile platform for the implementation. We propose a rapid adiabatic passage (RAP) scheme for achieving a high-fidelity controlled-$Z$ (CZ) gate on a neutral-atom Rydberg platform. Utilizing only global laser dressing, our scheme involves echoing two identical RAP pulses within the Rydberg blockade regime to realize a CZ gate and can be readily extended to a ${\mathrm{C}}^k\mathrm{Z}$ gate with additional qubits. We predict a CZ gate with fidelity over 0.9995 using alkali-metal atom parameters, and a CCZ gate with fidelity exceeding 0.999. Moreover, the direct utilization of echoing RAP pulses enables the implementation of a four-bit CCCZ gate at fidelity over 0.996 without further optimization. The proposed scheme, remarkably robust to variations in driving fields and realistic decoherence effects, holds promise for future quantum information processing applications.

For an accurate theoretical description of muonic bound systems, it is crucial to consistently treat relativistic and recoil corrections to vacuum polarization. The one-loop vacuum-polarization effect is by far the dominant quantum electrodynamic (QED) energy correction for bound muons, being of order $\alpha {\left(Z\alpha \right)}^2{m}_r$, where $\alpha$ is the fine-structure constant, $Z$ is the nuclear charge number, and $m_r$ is the reduced mass. Gauge invariance of the relativistic and recoil corrections to vacuum polarization of order $\alpha {\left(Z\alpha \right)}^4{m}_r$ is investigated with respect to nonretarded and standard, renormalized variants of Coulomb gauge. The invariance is shown after including three-photon exchange diagrams. Our derivation is based on an adapted form of nonrelativistic quantum electrodynamics for bound muon systems (${\mathrm{NRQED}}_{\mu }$), which is a version of NRQED where the hard scale is set at the muon mass instead of the electron mass. Updated values for the gauge-independent corrections for one-muon ions with nuclear charge numbers $Z=1,2,6$ are presented.

We present refined values of the hyperfine splitting frequencies of the ground $|g\rangle =|4f^{13}{(}^2{F}^o)6s^2,J=7/2\rangle$ and clock $|c\rangle =|4f^{13}{(}^2{F}^o)6s^2,J=5/2\rangle$ states of thulium atoms, $f_g^{\text{HFS}}=1496550658.23\left(3\right)$ Hz and $f_c^{\text{HFS}}=2113946873.08\left(9\right)$ Hz, respectively. The measurements are performed on an ultracold atomic ensemble in an optical lattice using combined microwave and optical transition spectroscopy. The achieved measurement accuracy of less than 0.1 ppb represents an improvement of 2 and 7 orders of magnitude for $f_g^{\text{HFS}}$ and $f_c^{\text{HFS}}$, respectively, compared to the previously published values. We also refine the value of the Landé $g$-factor of the clock level to $g_c=0.854786\left(12\right)$. The results of this work can be used in the frequency standards and quantum simulators based on thulium atoms being developed today, as well as in a number of fundamental studies that require precise knowledge of the hyperfine structure characteristics of various elements.

We study by real-time wave-packet simulations the sequential two-photon dissociation of the ${\mathrm{MgH}}^{+}$ molecule, under intense ultraviolet laser pulses of narrow spectral width. By a resonant coupling, one-photon Rabi oscillations are generated between two vibrational levels of the molecule, belonging to two different bound electronic states. These vibronic Rabi oscillations are probed upon absorption of further photons from the same laser pulse, that gradually promote the molecule to a dissociative electronic state. Calculating the energy spectrum of the photofragments explicitly analytically, we elucidate the physical origin of the main spectral features—such as the splitting, shifting, asymmetry, and multipeak pattern—identified by accurate numerical simulations. We find that the pronounced spectral intensity modulations result from the interference of fragment amplitudes that are generated during the distinct Rabi cycles in the upper and lower dynamically dressed states, formed upon the resonant coupling with the laser pulse. These intensity modulations are sensitively influenced by the resonant and nonresonant Stark effects, and can be manipulated by the parameters of the applied laser pulse. Our results contribute to the understanding and control of ultrafast coherent phenomena via the energy spectrum of particles emitted during the dynamical process under investigation.

We study the late-time dynamics of two particles confined in one spatial dimension and subject to two-body losses. The dynamics is exactly described by a non-Hermitian Hamiltonian that can be analytically studied both in the continuum and on a lattice. The asymptotic decay rate and the universal power-law form of the decay of the number of particles are exactly computed in the whole parameter space of the problem. When in the initial state the two particles are far apart, the average number of particles in the setup decays with time $t$ as $t^{-1/2}$; a different power law, $t^{-3/2}$, is found when the two particles overlap in the initial state. These results are valid both in the continuum and on a lattice, but in the latter case a logarithmic correction appears.

The quantum Rabi model (QRM) is a fundamental model for light-matter interactions. A fascinating feature of the QRM is that it manifests a quantum phase transition which is applicable for critical quantum metrology (CQM). Effective application for CQM needs the exact location of the transition point, however the conventional expression for transition coupling is only valid in the extreme limit of low frequency, while apart from zero frequency an accurate location is still lacking. In the present work we conversely use the quantum Fisher information (QFI) in the CQM to identify the transition coupling, which reveals that transition coupling indeed deviates greatly from the conventional one once a finite frequency is turned on. Polaron picture is applied to analytically reproduce the numeric QFI. An accurate expression for the transition coupling is obtained by inspiration from the revealed fractional-power-law effect of polaron frequency renormalization. From the QFI in the polaron picture we find that the transition occurs around a point where the effective velocity and the susceptibility of the expected value of mode quadrature reach maximum. Our result provides an accurate reference of transition couplings for quantum metrology at nonzero frequencies. The formulation of the QFI in the polaron picture also prepares an analytic method with an accurate compensation for the parameter regime difficult to access for the numerics. Besides the integer/fractional-power-law analysis to extract the underlying physics of transition, the QFI/velocity relation may also add some insight in bridging the QFI and transition observables.

The release of the causal structure of physical events from a well-defined order to an indefinite order stimulates remarkable enhancements in various quantum information tasks. Some of these advantages, however, are questioned for the ambiguous role of the control system in the quantum switch, which is an experimentally realized process with an indefinite causal structure. In communications, for example, not only the superposition of alternative causal orders, but also the superposition of alternative trajectories can accelerate information transmissions. Here, we follow the proposal of Liu et al. [Phys. Rev. Lett. 129, 230604 (2022)], and examine the information enhancement effect of indefinite causal orders with the toolkit of thermodynamics in a photonic platform. Specifically, we simulate the thermal interaction between a system qubit and two heat baths embedded in a quantum switch by implementing the corresponding switched thermal channels. Although its action on the system qubit only is thermally free, our results suggest that the quantum switch should be seen as a resource when the control qubit is also considered. Moreover, we characterize the non-Markovian property in this scenario by measuring the information backflows from the heat baths to the system qubit.

Quantum memory systems are vital in quantum information processing for dependable storage and retrieval of quantum states. Inspired by classical reliability theories that synthesize reliable computing systems from unreliable components, we formalize the problem of reliable storage of quantum information using noisy components. We introduce the notion of stable quantum memories and define the storage rate as the ratio of the number of logical qubits to the total number of physical qubits as well as the circuit complexity of the decoder, which includes both quantum gates and measurements. We demonstrate that a strictly positive storage rate can be achieved by constructing a quantum memory system with quantum expander codes. Moreover, by reducing the reliable storage problem to reliable quantum communication, we provide upper bounds on the achievable storage capacity. In the case of physical qubits corrupted by noise satisfying hypercontractivity conditions, we provide a tighter upper bound on storage capacity using an entropy dissipation argument. Furthermore, observing that the time complexity of the decoder scales nontrivially with the number of physical qubits, achieving asymptotic rates may not be possible due to the induced dependence of the noise on the number of physical qubits. In this constrained nonasymptotic setting, we derive upper bounds on storage capacity using finite blocklength communication bounds. Finally, we numerically analyze the gap between upper and lower bounds in both asymptotic and nonasymptotic cases, and provide suggestions to tighten the gap.

The task of discriminating between two known quantum channels is a well-known binary-hypothesis-testing task. We present a variational quantum algorithm with a parameterized state preparation and two-outcome positive operator-valued measure which defines the acceptance criteria for the hypothesis test. Both the state preparation and measurement are simultaneously optimized using the success probability of single-shot discrimination as an objective function which can be calculated using localized measurements. Under constrained signal-mode photon-number quantum illumination we match the performance of known optimal two-mode probes by simulating a bosonic circuit. Our results show that variational algorithms can prepare optimal states for binary hypothesis testing with resource constraints.

The paper presents an analysis of entangling and nonlocal operations in a quantum nondemolition (QND) interaction between multimode light with orbital angular momentum and an atomic ensemble. A protocol consists of two QND operations with rotations of quadratures of atomic spin coherence and light between them. This protocol provides a wide range of two-qubit operations, while the multimode nature of the chosen degrees of freedom allows the implementation of parallel operations over multiple two-qubit systems. We have used the formalism of equivalence classes and local invariants to evaluate the properties of two-qubit transformations. It is shown that, when selecting suitable values of the governing parameters, such as the duration of each of the two QND interactions and the rotation angles of the qubits, the protocol allows to realize a deterministic nonlocal SWAP operation and entangling $\sqrt{\text{SWAP}}$ operation with probability $\frac{1}{3}$.

This work explores the important role of quantum routers in communication networks and investigates the increase in efficiency using memories and multiplexing strategies. Motivated by the bipartite setup introduced by Abruzzo et al. [Phys. Rev. A 89, 012303 (2014)] for finite-range multiplexing in quantum repeaters, we extend the study to an $N$-partite network with a router as a central station. We present a general protocol for $N$ parties after defining the underlying matching problem and we calculate the router rate for different $N$. We analyze the improvement due to multiplexing and analyze the secret key rate with explicit results for the tripartite network. Investigating strategic qubit selection for the Greenberger-Horne-Zeilinger measurements, we show that using cutoffs to remove qubits after a certain number of rounds and consistently combining qubits with the lowest number of storage rounds leads to an optimal secret key rate.

We have measured fully differential cross sections (FDCSs) for ionization of helium by 75 keV proton impact. Data were analyzed for electrons ejected into the scattering plane at projectile energy losses well below and above the matching velocity and for scattering angles ranging between 0.1 and 0.5 mrad. Earlier, we observed clear signatures of the postcollision interaction (PCI) at the matching velocity; however, in the current data these signatures are completely absent at small energy losses and residues remain at large energy losses. At small energy losses the FDCSs are dominated by non-PCI higher-order effects.