We examine quantum phase transitions in a two-cavity system, where each cavity is described by a three-level quantum Rabi model, and the two cavities are coupled via photon hopping. Combining analytical and numerical methods, we reveal that a reversed superradiant phase transition emerges even under the strong ${\mathit{A}}^2$ term. The photon-hopping interaction circumvents the no-go theorem imposed by the ${\mathit{A}}^2$ term and allows for significant modulation of the phase transitions and critical phenomena. We determine the phase diagrams and scaling functions, and obtain the critical exponents that characterize the universality class. This work elucidates the competition between the intercavity photon hopping and the ${\mathit{A}}^2$ term, providing a pathway to achieve the superradiant phase transition of the three-level quantum Rabi model in cavity quantum electrodynamics and other relevant platforms.

Efficient enhancement of quantum effects is inherently constrained by the core trade-off between coherence improvement and noise suppression, a dilemma particularly acute in entanglement manipulation. Herein, we construct a structurally symmetric cavity magnonic system, which enables the synergistic enhancement of entanglement and directional control of quantum steering, presenting a potential pathway for addressing this challenge. By applying parametric pumping, the nonlinear intermode interactions in the single-squeezed representation are significantly strengthened, triggering a substantial surge in entanglement. Nevertheless, this enhanced squeezing inevitably induces noise amplification. To counteract this, an additional broadband squeezed-vacuum field is introduced to induce destructive interference between the two noise fields. Our theoretical analysis indicates that when the phases of the two noise fields satisfy an optimal matching condition, the amplified noise is effectively suppressed while stronger entanglement is maintained over a broader parameter range. This “coupling-enhancement and noise-cancellation” synergy may help improve the stability of quantum manipulation. Under this noise-canceling mechanism, we further realize precise control over the directionality of quantum steering, supported by mode population analysis. The proposed “squeezing enhancement integrated with noise cancellation” strategy exhibits broad adaptability and could be extended to diverse quantum systems. This work may offer a viable pathway for advancing one-way quantum computing and entanglement-based quantum communications.

The study of information scrambling has profoundly deepened our understanding of many-body quantum systems. Much recent research has been devoted to understanding the interplay between scrambling and decoherence in open systems. Continuing in this vein, we investigate scrambling in a noisy encoding-decoding circuit model. Specifically, we consider an $L$-qubit circuit consisting of a Haar-random unitary, followed by noise acting on a subset of qubits and then by the inverse unitary. Scrambling is measured using the bipartite algebraic out-of-time-order correlator ($\mathcal{A}$-OTOC), which allows us to track information spread between extensively sized subsystems. We derive an analytic expression for the $\mathcal{A}$-OTOC that depends on system size and noise strength. In the thermodynamic limit, this system displays a butterfly effect in which infinitesimal noise induces macroscopic information scrambling. We also perform numerical simulations while relaxing the condition of Haar-randomness, which preliminarily suggest that this effect may manifest in a wider class of random circuit ensembles.

In this work we investigate the average information scrambling and nonlocal nonstabilizerness (magic) generation properties of random Clifford encoding-decoding circuits perturbed by local noise. We quantify these with the bipartite algebraic out-of-time order correlator and average Pauli-entangling power (APEP), respectively. Using recent advances in the representation theory of the Clifford group, we compute both quantities' averages in the limit that the circuits become infinitely large. We observe that both display a so-called butterfly effect whereby noise occurring on finitely many qubits leads to macroscopic information scrambling and nonlocal nonstabilizerness generating power. Finally, we numerically study the relationship between the magic capacity [Proc. R. Soc. A 475, 20190251 (2019)], an operator-level magic monotone, of the noise channel and the APEP of the resulting circuit, which may provide insight for designing efficient nonlocal nonstabilizerness factories.

We study the classical compilation of quantum circuits for the preparation of matrix product states (MPS), which are quantum states of low entanglement with an efficient classical description. Our algorithm represents a near-term alternative to previous sequential approaches by reverse application of a disentangler, which can be found by minimizing bipartite entanglement measures after the application of a layer of parametrized disentangling gates. Since a successful disentangler is expected to decrease the bond dimension on average, such a layer-by-layer optimization remains classically efficient even for deep circuits. Additionally, as the Schmidt coefficients of all bonds are locally accessible through the canonical $\mathrm{\Gamma }\text{−}\mathrm{\Lambda }$ form of an MPS, the optimization algorithm can be heavily parallelized. We discuss guarantees and limitations to trainability and show numerical results for ground states of one-dimensional, local Hamiltonians as well as artificially spread out entanglement among multiple qubits using error-correcting codes.

Typical stabilizer codes aim to solve the general problem of fault-tolerance without regard for the structure of a specific system. By incorporating a broader representation-theoretic perspective, we provide a generalized framework that allows the code designer to take this structure into account. For any representation of a finite group, we produce a quantum code with a code space invariant under the group action, providing passive error mitigation against errors belonging to the image of the representation. Furthermore, errors outside this scope are detected and diagnosed by performing a projective measurement onto the isotypic components corresponding to irreducible representations of the chosen group, effectively generalizing syndrome extraction to symmetry-resolved quantum measurements. We show that all stabilizer codes are a special case of this construction, including qudit stabilizer codes, and show that there is a natural one logical qubit code associated to the dihedral group. Thus we provide a unifying framework for existing codes while simultaneously facilitating symmetry-aware codes tailored to specific systems.

Assessing the security of lattice-based cryptography against near-term quantum attacks is crucial to the development of postquantum cryptography. Existing quantum algorithms for the shortest-vector problem (SVP) typically reformulate the problem as a search for the first excited state of a single fully-connected quantum Ising model. However, as the quantum system scales with the problem size, determining the first excited state becomes intractable due to the exponentially increased complexity for large-scale SVP instances. In this paper we propose a variational quantum Korkin-Zolotarev (VQKZ) algorithm that substantially reduces the qubit requirement for solving the SVP. Specifically, by decomposing the original SVP into a series of subproblems on sublattices, the VQKZ algorithm can significantly expand the scale of problems solvable by near-term quantum devices compared with existing methods. Our numerical simulations demonstrate that for solving $q$-ary lattice-based SVP problems, the VQKZ algorithm outperforms existing methods in terms of both the solution vector length and the number of qubits required.

We investigate the decay dynamics of a three-level artificial atom, a superconducting transmon qubit, weakly coupled to a continuum of modes in a broadband one-dimensional cavity. Using the resolvent formalism, we derive analytical expressions for the resonance frequency shifts and widths, which are then evaluated numerically for a Gaussian density of states. We identify two distinct dynamical regimes, differentiated by the ratio of the qubit's coupling strength to the continuum bandwidth. When this ratio is much less than one, the system exhibits a Markovian regime in which the resonance width is practically independent of energy within the continuum band. As the ratio increases, the system transitions to a non-Markovian regime where the resonance width becomes strongly energy dependent. In this regime, the qubit interacts with the continuum faster than the continuum can erase the information from the qubit's past. Furthermore, we demonstrate that the coupling between the transmon's second level and its ground state significantly influences the decay dynamics of the third level. The interaction between these two levels opens a fast two-photon decay channel, which broadens the transmon's second level.

In quantum logic spectroscopy, internal transitions of trapped ions and molecules can be probed by measuring the motional displacement caused by an applied light field of variable frequency. This provides a solution to “needle-in-a-haystack” problems, such as the search for narrow clock transitions in highly charged ions, recently discussed by Chen et al. [Phys. Rev. Appl. 22, 054059 (2024)]. The main bottleneck is the search speed over a frequency bandwidth, which can be increased by enhancing the sensitivity of displacement detection. In this work, we explore two complementary improvements: the use of squeezed motional states, explained using an analytical phase-space model, and optimal statistical postprocessing of data using a hypothesis-testing framework. We demonstrate that each method independently provides a substantial boost to search speed. Their combination effectively mitigates state preparation and measurement errors, improving the search speed by an order of magnitude and fully leveraging the quantum enhancement offered by squeezing.

We report a precision characterization of the ${}^{2}F_{5/2}$ state in ${}^{171}\mathrm{Yb}^{+}$, including its energy relative to the ${}^{2}D_{3/2}$ state, lifetime, hyperfine splitting, and Landé $g_J$ factor. The state is probed via the ${}^{2}D_{3/2}\to {}^{2}F_{5/2}$ transition at 1161.8 nm, driven by a diode laser. We stabilize and accurately measure its frequency using an optical frequency comb, referenced to a stable 1140-nm laser and an active hydrogen maser. The ${}^{2}F_{5/2}$ state in ${\mathrm{Yb}}^{+}$ with an observed lifetime of 589(53) $\mu \mathrm{s}$ offers the potential for additional degrees of freedom for quantum information processing and testing quantum many-body calculations in ${}^{171}\mathrm{Yb}^{+}$.

In recent years, quantum reception technology has achieved significant progress in microwave detection. However, most existing studies focus on energy-level resonance conditions, while research on the influence of frequency detuning is relatively scarce. Based on the four-level heterodyne Rydberg-atom receiver system, this paper establishes a theoretical model using the two-dimensional Fourier transform to analyze the correlation between frequency detuning and system response. Through theoretical simulation, the system response under different detuning conditions is quantitatively obtained, and the model is verified by experiment. This study expands the understanding of frequency detuning in Rydberg-atom receivers and provides guidance for designing their parameters in complex environments.

We report a channel-resolved study of intense-field Coulomb explosion in the HCl dimer, induced by a linearly polarized 6-fs laser pulse and analyzed through an ensemble of ${\mathrm{H}}^{+}$ and ${\mathrm{Cl}}^{+}$ ion trajectories. Three primary fragmentation pathways emerge: a minor three-body channel alongside two four-body channels—one proceeding sequentially and one near simultaneously—involving the dissociation of both monomers. The principal finding is that pathway selection is strongly correlated with the extent of ionization during the laser pulse, which is in turn critically sensitive to the orientation of the dimer with respect to the laser polarization direction. Higher early-time ionization predisposes the system toward near-simultaneous four-body breakup, whereas lower ionization favors sequential and three-body fragmentation; for low-ionization cases, a fragment-resolved charge metric further differentiates three-body and sequential behavior. These charge-dependent trends consistently map onto experimentally accessible observables: the simultaneous mechanism dominates the high-energy tail of the kinetic energy release (KER) of the fragment ions and populates distinct regions of the emission-angle distributions, while sequential events concentrate at lower KER. Overall, early-time charge evolution provides a unifying explanation for channel branching and for the channel-resolved fragmentation signatures.

Periodically driven quantum systems, known as Floquet systems, provide a versatile platform for engineering novel topological phases absent in static settings. However, dynamically characterizing these nonequilibrium topological invariants remains a challenge. Here, we develop a Floquet perturbation theory in the extended Hilbert space to analytically describe the center-of-mass (c.m.) dynamics of a wave packet. When applied to the driven Su-Schrieffer-Heeger model, our theory reveals that the c.m. exhibits multifrequency Zitterbewegung oscillations whose spectral composition and phase are directly tied to the system's Floquet band structure. Crucially, we find that band inversions at topological phase transitions imprint distinct signatures on the c.m. dynamics, including the emergence of low-frequency modes and phase shifts of the oscillatory trajectory. These dynamical signatures offer a practical protocol for detecting Floquet topological invariants, which we demonstrate for both high-frequency and strongly driven regimes. Our work establishes c.m. dynamics as a simple and experimentally accessible probe for exploring topological phase transitions in Floquet systems.

We characterize sets of fractional orbital angular momentum (OAM) modes of a light beam using unitary-invariant properties encoded by two-mode overlaps. Using basis-independent coherence and dimension witnesses, we experimentally certify, on a triple of fractional modes, both the presence of coherence and that the states necessarily span a space of dimension 3. We propose and implement a practical, fast experimental method to extract two-mode overlaps requiring only a single intensity image per interference pair. These results lay the groundwork for using fractional OAM states in high-dimensional quantum information protocols.

The sub-Planck structures in phase space are extremely fragile interference patterns that serve as distinctive quantum signatures, with applications in precision metrology and quantum sensing. While such structures have been frequently studied with coherent-state superposition, their emergence in squeezed states, among the most fundamental and experimentally accessible nonclassical states, remains comparatively unexplored. In this work, we introduce a class of superposition of squeezed states that are inherently devoid of sub-Planck structure. We further investigate their engineering through non-Gaussian operations of photon addition and subtraction. Our analytical and numerical results reveal that these operations, well-known to enhance nonclassicality, induce clear sub-Planck structures, which for any even or odd component number beyond $M>2$ can exhibit isotropic structures and enhanced sensitivity. Here, isotropy becomes a feature of quantum resource rather than of the geometry, providing more flexibility in engineering quantum states for precision metrology. These isotropic features become more pronounced with an increasing number of squeezed components and an increasing number of photons added or subtracted. Moreover, photon addition is shown to produce finer and more pronounced interference fringes than photon subtraction, leading to stronger sensitivity to small displacements in phase space. As a notable outcome, we identify the four-component squeezed state as the squeezed counterpart of the original compass state and demonstrate that unlike the anisotropic compass state, it exhibits nearly isotropic sub-Planck structures together with enhanced quantum sensitivity. These findings not only advance the fundamental understanding of quantum phase-space engineering but also position the engineered squeezed superposition as a versatile platform for quantum sensing and precision parameter estimation beyond the standard quantum limit.

We study the properties of a generalized Dicke-Ising model realized with an array of Rydberg atoms, driven by microwave electric fields, and coupled to an optical cavity. As this platform allows for a precisely tunable anisotropy parameter, the model exhibits a rich landscape of phase transitions and critical phenomena, induced by the interplay of rotating-wave, counterrotating-wave, and Ising interactions. We develop an improved quantum Monte Carlo algorithm based on the stochastic series expansion that explicitly tracks the Fock state of the quantum cavity. In the superradiant (SR) phase, this allows us to determine, through data collapse, the scaling laws of the photon number. We also demonstrate the vanishing of parity symmetry in finite-size simulations and show that the Rydberg blockade leads to a significant suppression of cavity occupation. Notably, stronger quantum fluctuations induced by the counterrotating wave terms slightly favor the superradiant solid (SRS) phase over the solid-1/2 state. Finally, we confirm that the SR phase transition and the transition from the solid-1/2 to the SRS are second-order. In contrast, the transitions from the solid-1/2 or SRS to the SR phase are both first-order for any value of the normalized anisotropy parameter.

In continuous-variable quantum information, nonclassicality and non-Gaussianity serve as valuable resources for achieving quantum advantages in various quantum information processing tasks. For a judicious use of non-Gaussian resources, identifying and characterizing non-Gaussianity is a crucial prerequisite. In this work, we develop efficient criteria for detecting non-Gaussianity and quantum non-Gaussianity of single-mode non-Gaussian states, the latter being a stricter nonclassical notion of non-Gaussianity, by probing only a few points in phase space. Our approach draws on the observation that the fluctuation of the Wigner function profile is relatively constrained for the case of Gaussian states. Our criteria are thus effective for identifying non-Gaussian states whose Wigner functions have sharp changes or peaks. We demonstrate the detection of non-Gaussianity as well as quantum non-Gaussianity through prototypical examples such as mixtures of Fock states and Gottesman-Kitaev-Preskill states.