Quantizing a single, spinless, nonrelativistic particle constrained to a moving surface, and requiring that Schrödinger's equation is recovered, implies that the surface should be advected by the Madelung velocity field. Moreover, the surface-height gradient, weighted by the squared modulus of the wave function, should have zero net outward flux across closed paths. These constraints determine a phase-coincident companion solution to Schrödinger's equation, which allows us to construct an orthogonal unoccupied state. By supposing that surface fluctuations may induce rare transitions into this state, we motivate an empirical test of de Broglie's double-solution theory. The associated Fermi-golden-rule rate is obtained from first-order perturbation theory in the fluctuation amplitude.

To uncover the mechanism behind dynamical quantum phase transitions (DQPTs), we employ initial-state engineering by tuning the effective inverse temperature $\beta$ of the coherent Gibbs state in the one-dimensional XY model. We find that DQPTs arising from interphase quenches are topologically protected, originating from the topological mismatch between the initial state and the postquench Hamiltonian, whereas those triggered by intraphase quenches are topologically independent. Despite this distinction, both types of DQPTs are governed by a unified geometric condition: A DQPT occurs when the Bloch vector of a given momentum mode becomes orthogonal to the postquench Hamiltonian axis, causing the mode-resolved Loschmidt amplitude to vanish at critical times. We show that the effective inverse temperature $\beta$ of the coherent Gibbs state acts as a geometric knob that continuously rotates the initial Bloch vector. For interphase quenches, the topological mismatch guarantees this orthogonality for any $\beta$, making topological protection a natural consequence of this geometric picture. For intraphase quenches, the orthogonality condition reveals a particularly insightful limit: at $\beta =0$, DQPTs can occur even without any quench; as $\beta$ increases, the initial Bloch vector rotates smoothly, and this rotation must be compensated for by a corresponding rotation of the Hamiltonian axis, precisely achieved by the external quench. This interplay gives rise to two critical modes that emerge from opposite Brillouin-zone boundaries, migrate inward with increasing $\beta$, and eventually coalesce and annihilate at a finite critical inverse temperature. These results establish a unified geometric description of DQPTs and elucidate how intraphase critical modes can arise and persist in the absence of any topological protection.

Quantum Fisher information (QFI) provides powerful entanglement criteria, but existing formulations are all related to the global QFI of the full composite state. We first define the block-diagonal postmeasurement ensemble obtained by local projective measurements on one subsystem of a bipartite state. Then we show that the QFI of the block-diagonal postmeasurement ensemble can decompose into the QFI of the unmeasured subsystem and the classical Fisher information of the measurement outcomes. For separable states the sum of the subsystem QFI and the classical Fisher information admits an upper bound expressed solely in terms of local variances; violation of this bound signals entanglement. Compared with Tóth's global spin-squeezing criterion [Phys. Rev. A 85, 022322 (2012)], our witness detects entanglement over a wider parameter range for high-dimensional systems. The dimensional advantage and reduced experimental cost make the subsystem QFI a practical entanglement witness.

Phase sensing with entangled multiqubit states in the presence of noise is a central theme of modern quantum metrology. The present work investigates Dicke-state superposition probes for quantum phase sensing under parameter encoding generated by one- and two-body interaction Hamiltonians. Under linear collective-spin encoding, near-optimal Dicke superposition states are shown to exhibit significantly enhanced robustness against phase damping noise compared with Greenberger-Horne-Zeilinger (GHZ), $W$-superposition, and balanced Dicke states, while maintaining favorable metrological performance under realistic decoherence channels. For two-body interactions, optimal probe states maximizing the quantum Fisher information are identified. Their noise resilience and metrological scaling behavior under phase damping, amplitude damping, and global depolarizing channels are analyzed. The associated near-optimal Dicke superposition states are found to exhibit improved resilience to phase damping for the system sizes considered. These results establish tailored near-optimal Dicke-state superposition probes as versatile and noise-resilient resources for Heisenberg and super-Heisenberg quantum phase sensing governed by one- and two-body interactions.

Quantum measurements inevitably disturb the state being measured and this disturbance, together with measurement incompatibility, plays a crucial role in the sequential sharing of nonlocality. While the information-disturbance trade-off for a single measurement is well understood, its interplay with measurement incompatibility remains relatively unexplored. Here, we investigate this interplay in the sequential sharing of three forms of tripartite nonlocality: standard, genuine, and no-signaling genuine. By deriving incompatibility trade-off relations among the measurements performed by the three observers, we show that the role of measurement incompatibility differs qualitatively across three forms of nonlocality. Standard tripartite nonlocality can be demonstrated even when one party performs compatible measurements, rendering unbounded sequential sharing essentially trivial. In contrast, genuine tripartite nonlocality cannot be realized when any two parties perform nearly compatible measurements, precluding unbounded sharing. For no-signaling–genuine nonlocality, however, the incompatibility trade-off allows the critical measurement unsharpness to be arbitrarily small, along with another party's measurement to be almost compatible, so that the minimum measurement-induced disturbance required to demonstrate nonlocality can also be made arbitrarily small, preserving sufficient quantum correlations for unbounded sequential sharing. We further show that in this regime, the feasibility of unbounded sequential sharing depends sensitively on the Kraus realization implementing the measurement. Our results demonstrate that measurement incompatibility alone does not fully determine the limits of sequential multipartite nonlocality; instead, the minimum measurement-induced disturbance required to achieve nonlocality plays an equally decisive operational role.

Quantum state transfer between distant nodes is essential for distributed quantum information processing. Existing protocols are typically optimized for specific coupling regimes, such as adiabatic dark-state transfer in the single-mode limit and pitch-and-catch schemes in the multimode regime, leaving the crossover between them without a simple and unified control strategy. Here, we identify a minimal two-parameter control framework that enables high-fidelity quantum state transfer across this single-mode–to–multimode crossover in a multimode quantum channel. Using a pulse-shaped pitch-and-catch protocol controlled only by the pulse ramp rate and the emission-absorption delay, we achieve transfer fidelities exceeding $99.9\%$, extending pitch-and-catch protocols toward the single-mode limit without requiring dark-state protection or complex pulse design. We further demonstrate robustness against dissipation, disorder, detuning, and imperfect initialization under experimentally realistic conditions. These results provide a simple and broadly applicable framework for state transfer in multimode quantum channels, with relevance to circuit-QED and hybrid quantum-acoustic systems.

Hybrid entanglement between discrete-variable (DV) and continuous-variable (CV) optical qubits is a fascinating area of quantum science and technology, because such hybrid entanglement is a key resource for building hybrid quantum networks and interconnecting quantum processors employing different qubit encodings. In this work, we propose a scheme to create a hybrid Greenberger-Horne-Zeilinger–type (GHZ-type) entangled state of a single DV optical qubit and $n$ CV optical qubits, utilizing $(n+1)$ microwave cavities coupled to a superconducting flux qutrit. The two logic states of a DV optical qubit here are represented by the vacuum state and the single-photon state of a cavity, while the two logic states of a CV optical qubit are indicated by the two coherent states of a cavity. The GHZ state preparation protocol requires only a few basic operations, significantly reducing circuit resources by utilizing a single flux qutrit as the coupler. Since the third energy level of the qutrit remains unpopulated during the operation, decoherence from higher levels is significantly suppressed. Moreover, the total operation time is independent of the number of microwave cavities, and the GHZ state is deterministically generated since no measurement is made. As an example, our numerical simulation demonstrates that high-fidelity generation of a hybrid four-cavity GHZ state is feasible with present circuit quantum electrodynamics (QED) technology. This proposal is quite universal and can be applied to other physical systems, such as microwave or optical cavities, which are coupled to an artificial or a natural atom.

We theoretically propose a scheme to achieve multisideband phonon blockade in a modulated circuit quantum acoustodynamics system, in which a high-overtone bulk acoustic-wave resonator is piezoelectrically coupled to a transmon qubit. By periodically modulating the qubit frequency, we theoretically demonstrate a Floquet-engineered Jaynes-Cummings interaction that can extend the conventional blockade condition from single-phonon resonance to multisideband resonance in the strong-coupling regime. Under weak-driving conditions, we first show the phonon blockade at the zeroth-order sideband due to the strong anharmonicity of the dressed-state energy levels and characterize the blockade performance by combining the second-order correlation function $g^{\left(2\right)}\left(0\right)$ and the single-phonon population $P_1$. Crucially, it is revealed that the detuning between the phonon mode and the qubit can lead to a trade-off between $g^{\left(2\right)}\left(0\right)$ and $P_1$ by altering the dressed-state energy-level structure and composition and thus can be used to manipulate the purity and brightness of the single-phonon source. Then we extend the phonon blockade to multiple tunable Floquet sidebands and analyze the influence of the system parameters on the phonon blockade. The proposed scheme enables the manipulation of the phonon blockade at multiple distinct frequencies without modifying the intrinsic system parameters, which reduces the experimental complexity and improves the operational flexibility, thereby facilitating the potential applications of circuit quantum acoustodynamics systems in emerging quantum technologies.

We consider the generation of photonic graph states in a linear optics setting where sequential nondeterministic fusion measurements are used to build large graph states out of small linear clusters and develop a framework to optimize the building process using graph-theoretic characterizations of fusion networks. We present graph-state generation protocols for linear cluster resource states and type-I/type-II fusions which are adaptive to fusion failure, that is, they reuse leftover graph states in the remaining building process. To estimate hardware costs, we interpret our protocols as finite Markov processes. This viewpoint allows us to cast the expected number of fusion measurements until success as a first passage problem. We then deploy a pipeline of polynomial algorithms to optimize arbitrary graph states, extract fusion networks, and find beneficial orderings of fusions. We check the effectiveness of these algorithms by verifying that the corresponding mean first passage times are decreased. We evaluate our pipeline for different initial resource states and fusion mechanisms with varying success probabilities. Results show reductions in the fusion overhead by several orders of magnitude when compared to simple repeat until success protocols and by up to $40\%$ when compared to state-of-the-art graph-state generation protocols, especially for realistic fusion success probabilities between 50% and 75%.

We investigate the dissociative ionization of 1,3-butadiene (${\mathrm{C}}_4{\mathrm{H}}_6$) induced by 1-MeV/u ${\mathrm{C}}^{4+}$ ions using a cold-target recoil-ion momentum spectroscopy, with a specific focus on the three-body channels involving ${\mathrm{H}}_2{}^{+}$ formation. With triplet-ion coincidence measurement, the dissociation channels ${{\mathrm{H}}_2}^{+} + {\mathrm{CH}}_2{}^{+} + {\mathrm{C}}_3{\mathrm{H}}_2{}^{+}$ and ${\mathrm{H}}_2{}^{+} + {\mathrm{CH}}_3{}^{+} + {\mathrm{C}}_3{\mathrm{H}}^{+}$ are directly identified, whereas the ${{\mathrm{H}}_2}^{+} + {\mathrm{C}}_2{\mathrm{H}}^{+} + {\mathrm{C}}_2{\mathrm{H}}_3{}^{+}$ and ${{\mathrm{H}}_2}^{+} + {\mathrm{C}}_2{{\mathrm{H}}_2}^{+} + {\mathrm{C}}_2{\mathrm{H}}_2{}^{+}$ channels are not well separated in the time-of-flight correlation map. These two three-body channels are disentangled by analyzing the correlation between kinetic energy release versus dissociation angle. Using Dalitz plots, Newton diagrams, and the native frame method, the sequential pathways with ${\mathrm{H}}_2{}^{+}$ emitted first are identified for all four channels. In addition, the ${{\mathrm{H}}_2}^{+} + {\mathrm{CH}}_2{}^{+} + {\mathrm{C}}_3{{\mathrm{H}}_2}^{+}$ channel exhibits a sequential pathway with ${\mathrm{CH}}_2{}^{+}$ emitted first, whereas the ${\mathrm{H}}_2{}^{+} + {\mathrm{C}}_2\mathrm{H}{}^{+} + {\mathrm{C}}_2{\mathrm{H}}_3{}^{+}$ channel also proceeds via a concerted mechanism. $Ab initio$ potential-energy surface calculations are performed to illuminate the intrinsic state and hydrogen-site selectivity governing ${\mathrm{H}}_2{}^{+}$ formation. These results provide insight into the mechanisms and dynamics of ${\mathrm{H}}_2{}^{+}$ formation in the three-body fragmentation processes of hydrocarbon molecules.

We present measurements on a metastable state in ${\mathrm{Th}}^{2+}$ with the electronic configuration $6d^2{}^{3}P_0\left(5090{\mathrm{cm}}^{-1}\right)$. This is motivated by the prospect of using the state in laser excitation of the low-energy ${}^{229}\mathrm{Th}$ nuclear resonance independent from the leading hyperfine interactions. The $6d^2{}^{3}P_0$ state has no dipole-allowed radiative decay channel and is connected to the second ground state $6d^2{}^3{F}_2\left(63{\mathrm{cm}}^{-1}\right)$ through an electric quadrupole transition only. We populate the state by laser excitation at 484 nm via a higher excited level and detect its population in laser-induced fluorescence. The isotope shift of the $J=0$ level between ${}^{232}\mathrm{Th}^{2+}$ and ${}^{229}\mathrm{Th}^{2+}$ is determined as a measure of the interaction of electronic and nuclear charge distributions. The lifetime of the level in our ion trap with buffer gas is limited by collisional mixing with the nearby state $5f6d{}^{3}G_3\left(5060{\mathrm{cm}}^{-1}\right)$. In ultrahigh vacuum, it could serve as a hyperfine-free nuclear clock that is largely immune to field-induced frequency shifts via the electron shell.

Purely quantum phenomena such as dynamical localization (DL) can be observed in a molecular rotor subjected to a periodic train of short and intense laser pulses in the gas phase. Using requantized classical molecular dynamics simulations, we investigate the impact of collisional effects for ${\mathrm{O}}_2$ molecules. We consider different trains of kicks for which the system exhibits quantum resonance, DL, or Bloch oscillations under collision-free conditions. Within achievable experimental conditions, we demonstrate that, as the gas pressure increases, all the dynamics become progressively similar, leading to a quantum-to-classical transition. We study how decoherence induced by intermolecular collisions reduces the quantum interferences through loss of memory. These findings pave the way for future experimental investigations and further theoretical studies of the influence of dissipation on quantum effects in rotational dynamics.

We propose an analog quantum simulation of chiral magnetic dynamics using ultracold atoms in an optical superlattice. The massive Schwinger model in the zero gauge coupling limit maps onto the Rice-Mele model, with the fermion mass and topological angle encoded in the superlattice parameters. We study the real-time dynamics of the vector current following two quench protocols that drive continuous chirality injection and chirality relaxation. Simulations with realistic superlattice parameters and experimental noise demonstrate clear mass dependence of the current dynamics in both protocols, robust against experimental imperfections. The vector current may be directly measurable via single-bond-resolved detection, establishing cold atom superlattices as a viable platform for probing nonequilibrium chiral phenomena.

Perfect chiral circulation, the sequential transfer of a quantum state around a closed loop with unit fidelity, has been achieved in specific few-site systems, yet the universal physical conditions underlying this phenomenon remain unclear. We prove that discrete translational invariance and an equidistant energy spectrum together constitute the necessary and sufficient conditions for perfect chiral circulation. With this criterion established, an exact closed-form Hamiltonian valid for arbitrary $N$-site rings naturally follows. In the minimal three-site ring, we demonstrate two physically distinct realizations: Floquet engineering of a driven open chain that restores translational invariance by equalizing the couplings and correlated doublon dynamics in an anyon-Hubbard model where fractional statistics intrinsically provide the synthetic flux that renders the spectrum equidistant. Our results establish unified physical criteria for perfect chiral circulation, with potential applications in diverse platforms such as superconducting circuits, cold atoms, classical electrical circuits, and photonic synthetic dimensions, and further extend this framework beyond spatial transport by incorporating internal degrees of freedom such as spin.

Thermal management in coupled quantum systems is essential, given the inherent fragility of quantum states and correlations. In this work, we theoretically investigate thermal reconfiguration by manipulating the steady-state phonon currents and phonon numbers in an optomechanical array. The system consists of $N$ cells, each containing an optical cavity coupled to a mechanical resonator. Each resonator is coupled to an independent thermal bath, its temperature increasing with the site index. This setup creates a temperature gradient that induces a steady-state phonon current flowing from the hotter region to the colder region of the array. The direction of the phonon current can be manipulated by introducing a synthetic gauge field, which is achieved by modulating the driving laser with a site-dependent phase. This modulation results in a phase-dependent linearized optomechanical coupling. Counterintuitively, the direction of the phonon current can be reversed to flow against the temperature gradient by tuning the synthetic phase. When the direction is reversed, the total steady-state phonon number is further reduced. This indicates that thermal reconfiguration can be realized via the introduction of a synthetic phase. Our results provide a phase-controlled mechanism with potential applications in thermal management for quantum information processing.

We consider the combined effect of a Duffing nonlinearity and the optomechanical interaction on the cavity density of states (DOS), which is directly observable in optomechanically induced transparency (OMIT) experiments. Both nonlinearities introduce the same type of interaction between polaritons, producing a distinct feature in the optical response. We derive the resonant condition that enhances the nonlinear scattering between polaritons and study the parameter dependence of the cavity DOS in detail. This allows us to characterize the typical strength and optimal conditions for observing the quantum effects of the Duffing nonlinearity in OMIT experiments.

A system, comprising a qubit pair coupled to a common cavity, is studied with the aim of establishing qubit entanglement. This study is a continuation of an earlier publication [Phys. Rev. A 111, 043705 (2025)], where a similar model was investigated for an initially vacuum cavity. In the present paper, a cavity with a finite initial occupancy is considered and the effect of asymmetric qubit-cavity couplings is investigated. For a closed system scenario, the ratio of the qubit-cavity couplings shows a minimum value below which no maximally entangled qubit state is available. The threshold value is shown to depend critically on the initial number of photons present in the cavity. It is shown that a greater photon number prefers symmetric couplings for generating maximal entanglement. For a driven-dissipative case steady-state entanglement is shown to depend nonmonotonically on the qubit drive. For a moderate drive, steady-state entanglement decreases with decreasing coupling symmetry, leading to a regime of “no entanglement.” Interestingly, as the symmetry is further decreased, steady-state entanglement again becomes finite. The Intricate interplay of drive, dissipation, and coupling asymmetry is shown to be pivotal for steady-state entanglement generation.

We study two distinct diagnostics of bipartite quantum channels: the average fidelity between a desired state and noisy output across different classes of input states, and generation of entanglement from pure product input states, quantified by well-defined entangling power. These diagnostics are generally independent, but together they provide a more complete description of bipartite channels. We show that the fidelity averaged over any local-unitary orbit with fixed Schmidt coefficients for equal local dimensions is completely determined by the average input-output fidelity and its restriction to product inputs. We also introduce concurrence- and negativity-based entangling power for two-qubit channels, prove their convexity and monotonicity under local postprocessing, and show that, unlike the previously proposed linear-entropy quantity, they vanish for all separable channels. Representative separable and nonseparable channels are investigated. Finally, we generalize our definitions of entangling power to nonproduct inputs, and provide an analytical lower bound for the concurrence-based entanglement variation, showing its effectiveness with specific examples.

We present a protocol using neural networks to simultaneously optimize the quantum error-correcting code space and the corresponding recovery map in the framework of continuous-time quantum error correction. Given a Hilbert space and a noise process—potentially correlated across both space and time—the protocol identifies the optimal recovery strategy, measured by the average logical state fidelity. This approach enables the discovery of recovery schemes tailored to arbitrary device-level noise.