We propose that strong photon-exciton coupling performed by a plasmonic nanoantenna and a single emitter can be protected in the well-designed topological photonic structure as an environment. Topological robustness leads to a reduction of metal loss, which makes Rabi splitting much larger. The strong coupling regime gets more stable in the topological systems because the sensitivity characterized by Rabi splitting can always remain small compared to the sensitive nontopological systems. Moreover, we show that the Rabi splitting under topological protection is immune to defects or impurities that can destroy strong coupling in nontopological systems. This topologically protected strong coupling mechanism offers more improvement in the applications of on-chip quantum integration, single quantum sources, and quantum information processing.

We present a generalization of the chain-mapping technique that applies to few-atom multimode systems by making use of coupling-matrix transformations. This is extremely useful for tensor-network simulations of the multimode Dicke model and the multispin-boson model because their coupling structures are altered from the star form to the chain form with near-neighbor interactions. Our approach produces an equivalent Hamiltonian with the latter coupling form, which we call the band Hamiltonian, and we demonstrate its equivalence to the multimode Dicke Hamiltonian. In the single-atom case, our approach reduces to the chain-mapping technique. When considering several tens of field modes, we have found that tensor-network simulation of two atoms in the ultrastrong-coupling regime is possible with our approach. We demonstrate this by considering a pair of entangled atoms confined in a cavity, interacting with 30 electromagnetic modes.

The light-matter interactions for an emitter coupling to the bulk region of a Hofstadter lattice were recently investigated by De Bernardis et al. [Phys. Rev. Lett. 126, 103603 (2021)]. We propose light-matter interactions in an extended Hofstadter lattice with the next-nearest-neighbor (NNN) couplings. Compared with the standard Hofstadter lattice, the NNN couplings break the mirror symmetry and the energy bands are not flat, but are dispersive with nonzero group velocity. In contrast to the study by De Bernardis et al., when a two-level emitter interacts with the bulk region of the extended Hofstadter lattice, the emitter is no longer trapped by the coherent oscillations and can radiate photons unidirectionally. The chiral mechanism stems from the broken mirror symmetry. Both the radiation rate and the chirality periodically change with the emitter's coupling position. All of those particular features can be realized on the photonic lattice platform and may find potential application in chiral quantum information processing.

We theoretically study the photon-assisted tunneling (PAT) in a $\mathcal{PT}$- symmetric triple-well potential (TWP) with balanced gain-loss between the noncentral wells and neutral central well. We show that the application of an ac drive in the central well permits to control the Rabi frequency of the population oscillation between the noncentral wells of the TWP. In particular, when a multiple of the driving frequency matches the chemical potential in the central well, an enhancement of the Rabi frequency is observed. Very importantly, we show that PAT resonantly extends the domain of the parameter space with a real spectrum. This is achieved for a gain-loss parameter well above its critical value in the nondriven case, which allows for stable Rabi oscillations in a strong gain-loss scenario. Moreover, within a Floquet framework, we find an analytical estimation of the critical gain-loss parameter for the different resonance values of the driving frequency. We also discuss possible physical realizations of our model.

Universal quantum computing requires nonstabilizer (magic) quantum states. Quantifying the nonstabilizerness and relating it to other quantum resources is vital for characterizing the complexity of quantum many-body systems. In this work, we prove that a quantum state is a stabilizer if and only if all states belonging to its Clifford orbit have a flat probability distribution on the computational basis. This implies, in particular, that multifractal states are nonstabilizers. We introduce multifractal flatness, a measure based on the participation entropy that quantifies the wave-function distribution flatness. We demonstrate that this quantity is analytically related to the stabilizer entropy of the state and present several examples elucidating the relationship between multifractality and nonstabilizerness. In particular, we show that the multifractal flatness provides an experimentally and computationally viable nonstabilizerness certification. Our work unravels the direct relation between the nonstabilizerness of a quantum state and its wave-function structure.

The nonlocal correlations of noisy quantum systems are important for both understanding nature and developing quantum technology. We consider the correlations of star and chain quantum networks in which noisy entanglement sources are measured by nonsignaling parties. We derive the necessary and sufficient conditions for when a broad family of star and chain $n$-locality inequalities achieve their maximal quantum violation assuming that each party's dichotomic observables are separable across qudit systems. When pairs of local dichotomic observables are considered on qubit systems, we derive maximal $n$-local violations that are larger and more robust to noise than the maximal $n$-locality violations reported previously. To obtain these larger values, we consider observables that we have not found in previous studies. Thus, we gain insights into self-testing entanglement sources and measurements in star and chain networks.

A universal quantum computer is an ultimate pursuit, which should possess the ability to perform entangling gate operations in parallel with high quality in a scalable fashion. However, for a long trapped-ion chain, the simultaneous implementation of two-qubit quantum gates is a challenging task due to the drastic increase of the crosstalk resulting from the collective motional modes. In this paper, by utilizing the structure of the localized motional modes in the long mixed-species ion chain, we propose a highly efficient linear iterative scheme to eliminate the crosstalk within the neighboring pairs. We show that this scheme allows the realization of high-fidelity, low-crosstalk, scalable, parallel two-qubit gates with only a few pulse segments for the long chain. In addition, by considering the practical experimental feasibility, we optimize the laser power and improve the robustness against the random static drifts of the motional frequencies.

The chemical bond of carbon monoxide (CO) is the strongest bond. It plays a crucial role in thermochemistry and serves as a benchmark for electronic structure calculations. The most accurate value to date has been obtained by analyzing its predissociation spectra related to the lowest energy dissociation channel, achieving an uncertainty of $6\mathrm{c}{\mathrm{m}}^{-1}$. In this work, we measured the bond-dissociation energy of CO by recording the CO rotationally resolved, sharp-rising the $\mathrm{C}\left({}^{1}D_2\right)$ fragment yield spectrum related to the $\mathrm{C}\left({}^{1}D_2\right)+\mathrm{O}\left({}^{1}D_2\right)$ threshold. The sharp rising steps at the thresholds in the fragment yield spectrum are caused by the predissociation of broad vibronic bands of superexcited states. The thresholds were validated by the velocity map images of the $\mathrm{C}\left({}^{1}D_2\right)$. The determined bond-dissociation energy is 89 602.80 (±0.10) $\mathrm{c}{\mathrm{m}}^{-1}$, representing an improvement in accuracy of over one order of magnitude compared to the previous values.

We present a method to precisely measure the frequencies of transitions to high-$n$ Rydberg states of the hydrogen atom which are not subject to uncontrolled systematic shifts caused by stray electric fields. The method consists in recording Stark spectra of the field-insensitive $k=0$ Stark states and the field-sensitive $k=\pm 2$ Stark states, which are used to calibrate the electric field strength. We illustrate this method with measurements of transitions from the $2s(f=0\text{and}1)$ hyperfine levels in the presence of intentionally applied electric fields with strengths in the range between 0.4 and $1.6\mathrm{V}\mathrm{c}{\mathrm{m}}^{-1}$. The slightly field-dependent $k=0$ level energies are corrected with a precisely calculated shift to obtain the corresponding Bohr energies $(-c{R}_{\mathrm{H}}/n^2)$. The energy difference between $n=20$ and $n=24$ obtained with our method agrees with Bohr's formula within the 10-kHz experimental uncertainty. We also determined the hyperfine splitting of the $2s$ state by taking the difference between transition frequencies from the $2s(f=0\text{and}1)$ levels to the $n=20,k=0$ Stark states. Our results demonstrate the possibility of carrying out precision measurements in high-$n$ hydrogenic quantum states.

We experimentally investigated the photoionization and fragmentation of a van der Waals cluster of argon dimer (${\mathrm{Ar}}_2$) exposed to intense laser fields. By performing femtosecond pump-probe experiments in a reaction microscope, we tracked the spatiotemporal evolution of the nuclear wave packet (NWP) launching onto the excited bound states of ${{\mathrm{Ar}}_2}^{+}$. By interrogating the measured time-resolved vibrational structures in the kinetic energy spectra obtained from Coulomb explosion imaging of the ${{\mathrm{Ar}}_2}^{+}$ NWP, the vibrational revival and rotational excitation of the long-living rovibrational NWP were observed in real time. The vibrational populations of the NWP on the potential curves of three excited bound states of ${{\mathrm{Ar}}_2}^{+}$, i.e., $I{\left(3/2\right)}_g, II{\left(1/2\right)}_u$, and $I{\left(3/2\right)}_u$, were identified by the Fourier analysis of the time-dependent kinetic energy spectra of nuclear fragments.

Quantum squeezed states offer metrological enhancement as compared to their classical counterparts. Here, we devise and numerically explore a method for performing SU(1,1) interferometry beyond the standard quantum limit, using quasi-cyclic nonlinear wave mixing dynamics of ultracold atoms in a ring cavity. The method is based on generating quantum correlations between many atoms via photon-mediated optomechanical interaction. Timescales of the interferometer operation are here given by the inverse of photonic recoil frequency, and are orders of magnitude shorter than the timescales of collisional spin mixing–based interferometers. Such shorter timescales should enable not only faster measurement cycles but also lower atomic losses from the trap during measurement, which may lead to significant quantum metrological gain in matter-wave interferometry with state-of-the-art cavity setups.

We theoretically investigate three-body correlations on the top of a Fermi sea in one-dimensional spinless fermions with antisymmetrized two- and three-body attractive interactions. By investigating the variational problem of three-body states above the Fermi sea, we illuminate the fate of the in-medium three-body cluster states (namely, Cooper triples in the presence of Fermi sea) in the special case with pure attractive three-body interaction as well as in the case with the coexistence of two- and three-body interactions. Our results testify that the fermion-dimer repulsion is canceled by including the three-body interactions, and stable three-body clusters can be formed. We further feature a phase diagram consisting of the $p$-wave Cooper pairing and Cooper tripling phases in a plane of $p$-wave two- and three-body coupling strengths.

System response analysis is a powerful method for analyzing linear time-invariant (LTI) systems. In this work, we have demonstrated that a system response approach can also be applied to analyze the so-called linear space-invariant (LSI) but time-varying problems, which represent a dual of the conventional LTI problems. In this proposed approach, we perform a Fourier transform of the electric field distribution on the space coordinate, rather than in time, and express it in the wave-number domain. Specifically, we express any input signal and its corresponding output in the wave-number domain. Then, the transfer function for the LSI time-varying system can be extracted as a one-time computation by evaluating the ratio of the output signal to the input signal in the wave-number domain. Once the transfer function is extracted, the output response to any input with an arbitrary temporal profile can be computed instantaneously. Furthermore, for a system with a complicated temporal profile, the proposed method allows us to decompose it into several simpler subsystems that appear sequentially in time. The transfer function of that complicated system can be expressed as the product of those of the individual subsystems, such that it can be evaluated more efficiently.

In this paper, we present a scheme to construct a quantum network based on optomagnonic systems where the photon-magnon coupling systems are connected by a waveguide. We derive the effective master equation of magnon modes by eliminating the waveguide modes and optical modes. By diagonalizing the dissipative part of the master equation, we identify dark modes so as to eliminate the effect of the dissipation induced by the waveguide. Employing dark modes, we investigate the quantum state transfer and entangled state generation in the two-node cascaded or chiral quantum network. We extend the method to an $N$-node quantum network and show the generation of a W state. We also consider the influence of experimental imperfections. Our scheme is meaningful for building a quantum network based on a magnonic system.

We propose a gain-assisted enantioselective scheme in dye-doped chiral particles, demonstrating optical pulling and pushing forces that can be tuned using externally controllable parameters. By controlling the concentration of dye molecules and the pumping rate, we achieve all-optical chiral resolution of racemic mixtures and enantioselection of small dipolar chiral particles without relying on interference. This scheme is applicable to both lossless and lossy plasmonic chiral particles, making it a promising approach for chiral sensing, drug discovery, and molecular separation.

We present exotic quantum phases in a quantum Rabi hexagonal ring. A remarkable finding is that the application of an artificial magnetic field to the ring induces long-range interactions, yielding effective next-nearest-neighbor photon hopping in the subrings. This phenomenon gives rise to two chiral superradiant phases in addition to a ferro-superradiant and an antiferro-superradiant phase. As evidence, there appear chiral ground-state currents of photons in the subrings with opposite signs in different chiral phases. The degenerate configurations of the complex order parameters in chiral phases are similar to the in-plane magnetizations of a chiral magnetic. The critical exponents governing the excitation energy in the two chiral phases are identical to those of the Rabi triangle, which depend on the size of the subrings rather than the size of the ring. It is important to classify the universality class of the multiple chiral phase transitions as the size of Rabi ring increases. Furthermore, the implementation of the proposed system is an exciting prospect in quantum simulations for exploring intriguing quantum phases.

Open quantum systems are inherently coupled to their environments, which in turn also obey quantum dynamical rules. Restricting ourselves to dissipative dynamics, here we propose a measure that quantifies how far the action of an environment on a system departs from the influence of classical noise fluctuations. It is based on the lack of commutativity between the initial reservoir state and the total system-environment Hamiltonian. Independently of the nature of the dissipative system evolution, Markovian or non-Markovian, the measure can be written in terms of the dual propagator that defines the evolution of system operators. The physical meaning and properties of the proposed definition are discussed in detail and also characterized through different paradigmatic dissipative Markovian and non-Markovian open quantum dynamics.

With analytical treatment, the classical dynamics of an ultrarelativistic electron in two counterpropagating circularly polarized strong laser beams with either a corotating or counterrotating direction are considered. Assuming that the particle energy is the dominant scale in the setup, an approximate solution is derived, and the influence of the rotational sense on the dynamics is analyzed. Qualitative differences in both electron energy and momentum are found between the corotating and counterrotating laser beams and are confirmed by the exact numerical solution of the classical equation of motion. Despite these differences in the electron trajectory, the radiation spectra of the electron do not deviate qualitatively from each other for configurations with a varying rotational sense of the laser beams. Here, the radiation of an ultrarelativistic electron interacting with counterpropagating laser beams is given in the framework of the Baier-Katkov semiclassical approximation. Several parameter regimes are considered, and the spectra resulting from the two scenarios all have the same shape and only differ quantitatively by a few percent.

Stabilizer entropies (SE) measure deviations from stabilizer resources and as such are a fundamental ingredient for quantum advantage. In particular, the interplay of SE and entanglement is at the root of the complexity of classically simulating quantum many-body systems. In this paper, we study the dynamics of SE in a quantum many-body system away from the equilibrium after a quantum quench in an integrable system. We obtain two main results: (i) we show that SE, despite being an $L$-extensive quantity, equilibrates in a time that scales at most linearly with the subsystem size and (ii) we show that there is a SE length increasing linearly in time, akin to correlations and entanglement spreading.