We investigate excitation transfer in an engineered cavity-QED transport architecture consisting of an $N$-site donor ring coupled coherently to a central acceptor and driven by a single quantized photon mode. The system evolves under a Lindblad master equation including spontaneous loss and pure dephasing. In the ordered symmetric limit, the dynamics reduce exactly to a photon–bright-mode–acceptor trimer, allowing closed-form analytic expressions for transfer efficiencies and mode-resolved losses. We demonstrate that near-unity efficiency arises from photon-mediated hybridization that generates a dark transport channel in which ring population is strongly suppressed. This cavity-induced mechanism bypasses dissipative dark modes of the ring and is distinct from conventional excitonic transport or environmentally assisted quantum transport. Static disorder in photon and ring coupling activates lossy ring modes through hybridization, while intraring coupling primarily shifts spectral crossings and can restore efficiency by separating dissipative channels. The model is interpreted as a tunable quantum-optical transport device. Our analytic reduction provides clear design principles for engineered quantum transport networks operating in cavity-QED platforms.

We theoretically propose a scheme for the generation of $n$-phonon and photon-phonon pair bundle emissions in a cavity magnomechanics system. By utilizing the Barnett effect under resonant driving, $n$-phonon and photon-phonon super Rabi oscillations can be achieved. Through the system's dissipative channels, the intracavity multiquanta states are released as bunched $n$-phonon and photon-phonon pair emissions. These different bundle emissions can be readily controlled via the Barnett effect, allowing the desired functionality to be selected simply by tuning the direction of the static magnetic field. Featuring high purity, compactness, and flexible controllability, our system holds great promise for applications in quantum information processing and on-chip quantum communication.

This work studies a $\mathcal{PT}$-symmetric non-Hermitian spin-boson model consisting of a non-Hermitian two-level system coupled to a continuous bosonic bath. The static properties of the system are analyzed through a projection method derived from the displacement operator. We find that only a single exceptional point (EP) emerges, in contrast to non-Hermitian spin-boson models with finite modes, which typically exhibit multiple EPs. Notably, only a single real eigenvalue is found before the EP, which differs markedly from typical non-Hermitian systems where a pair of real eigenvalues precedes the EP. The time evolution of observables is further investigated via the Dirac–Frenkel time-dependent variational principle. Compared to its Hermitian counterpart, the non-Hermitian model exhibits distinct dynamical signatures, most notably the emergence of oscillations with periodic amplified amplitude. In the $\mathcal{PT}$-unbroken phase, the system exhibits sustained oscillatory dynamics with suppressed decoherence, whereas in the $\mathcal{PT}$-broken phase, additional dissipative channels accelerate decoherence and drive rapid convergence toward a stable steady state. These results shed light on how $\mathcal{PT}$ symmetry protects coherent light–matter interactions in non-Hermitian quantum systems.

Entanglement in continuous-variable Gaussian systems is a key resource, and common reservoirs can both suppress and generate correlations. Existing work focused on preentangled states or Markovian baths, leaving open whether separable squeezed inputs entangle in structured environments or under modulation. We study two bosonic modes coupled to a common reservoir, each initialized in a separable squeezed vacuum. The dynamics are analyzed utilizing Gaussian covariance methods, evolved under approximate non-Markovian quantum state diffusion (QSD), finite-temperature pseudomode embeddings, and Bures-based non-Markovian diagnostics. We identify three mechanisms absent in Markovian dynamics: (1) A detuning condition that freezes entanglement trajectories across reservoir correlation times; (2) birth, death, and revival of entanglement from orthogonal inputs; and (3) integer-locked beating with square-wave oscillations produced by periodic detuning. All mechanisms persist at finite temperature, with deviations bounded within $5\%$ in cryogenic regimes and $20\%$ at moderate occupations. These deviation bounds align with cryogenic cavity, phononic, and optomechanical platforms, where structured spectral densities and detuning modulation are already accessible. Structured reservoirs are shown to emerge as tunable entanglement resources for continuous-variable quantum technologies.

Gaussian boson sampling (GBS) provides a route toward demonstrating quantum computational advantage. However, optical loss, which reduces the entanglement in the system, can render GBS results classically simulable. We propose a nonlinear photonic architecture based on optical parametric amplifiers (OPAs) arranged in an interferometer network. This active configuration amplifies quantum correlations within the circuit while preserving the #$P$-hard Hafnian structure of the output probabilities. Using logarithmic negativity, we numerically show that entanglement scales linearly with both the OPA gain and network depth in the lossless limit and maintains linear scaling with the number of modes under realistic loss rate. These scaling behaviors suggest that classical simulation in lossy scenarios remains computationally intractable. The decomposition of the output into a core state and a random Gaussian displacement shows that the SU(1,1) network outperforms the SU(2) network when loss is present. Our results demonstrate that OPA-boosted GBS preserves computational hardness in noisy environments, offering a more effective implementations of near-term photonic quantum computers.

We present a systematic method for constructing universal composite phase gates with a continuously tunable target phase. Using a general Cayley-Klein parametrization of the single-pulse propagator, we design gates from an even number of nominal $\pi$ pulses and derive analytic phase families by canceling, order by order in a small deviation parameter, the leading contributions to the undesired off-diagonal element of the composite propagator, independently of the dynamical phase. The resulting sequences provide intrinsic robustness against generic control imperfections and parameter fluctuations and remain valid for arbitrary pulse shapes. Numerical simulations in a standard two-level model confirm high-order error suppression and demonstrate broad, flat high-fidelity plateaus over wide ranges of simultaneous pulse-area and detuning errors, highlighting the efficiency of the proposed universal composite phase gates for resilient phase control in quantum information processing.

The Harrow-Hassidim-Lloyd (HHL) algorithm remains a paradigmatic quantum routine for solving linear systems and a widely used benchmark in theoretical and experimental studies. Several circuit-level variants have been proposed to simplify its implementation, including constructions in which the clock register is factorized via Hadamard gates to reduce circuit depth and entanglement. In this work, we show that this commonly deployed modification can fundamentally alter the asymptotic behavior of the algorithm and may fail to converge in the limit of large clock size due to persistent phase interference effects. This phenomenon is not a finite-size artifact and compromises the correctness guarantees of the factorized-clock implementation. We provide an analytic characterization of the underlying mechanism and demonstrate that a minimal and experimentally feasible modification suffices to restore convergence while preserving the practical advantages of the simplified circuit. Our results clarify an overlooked correctness issue in a widely used HHL implementation pattern and delineate the conditions under which simplified realizations faithfully reproduce the intended algorithmic behavior.

Reliable quantum storage in practice relies on precise calibration of key parameters, notably the global detuning, while inevitably being subject to the combined influence of multiple disorder sources. In this work, a comprehensive model for an electromagnetically induced transparency protocol is considered, in which coupling disorder and detuning disorder are incorporated simultaneously. After quantitatively analyzing the control dynamics, a highly precise phase-detuning relation to improve calibration accuracy is obtained. Building on this result, a Berry-phase-based control strategy is proposed to mitigate the degradation caused by the global detuning. We further reveal that there exists a joint effect simultaneously induced by different disorder sources, which can substantially reshape the decoherence. Finally, an effective notion of storage capacity is introduced and a general time-capacity relation is obtained, providing guidance for subsequent experimental optimization and device design.

The well-known graphical representation called the Lu-Fano plot was originally developed for multichannel Rydberg spectroscopy, especially in quantum-defect theory. The present study shows some of the limitations of this traditional Lu-Fano plot that are desirable to improve on, when there are closely split ionization thresholds, as in many current generation quantum information applications involving hyperfine-split thresholds, or when there are more than two ionization threshold energies. The modified representation introduced here is especially simplifying in the situation where one is exploring the bound states lying very far below those closely split thresholds. Moreover, it overcomes one limitation, namely, that in contrast with the traditional Lu-Fano plot, the modified representation developed here can be utilized for problems where there are more than two ionization thresholds. An example application to Rydberg series of the manganese atom illuminates its use in a practical problem.

A conjugate topological photonic crystal (CTPC) is designed to achieve highly efficient optical bistability. By exploiting the conjugate topological edge state supported by the CTPC, the structure exhibits a markedly reduced bistability threshold, reaching the level of a few microwatts per meter in simulations. Meanwhile, the conjugate design enables high transmission, giving the device a clear advantage in high-contrast optical switching applications. Furthermore, we examine its robustness against fabrication-induced structural perturbations and analyze the effects of the incident angle and the number of periods on the bistable behavior. Moreover, the optical bistability is employed as a nonlinear activation function in all-optical neural-network computing, leading to improved accuracy in image-recognition tasks. These results provide important theoretical support for the conjugate topological photonic crystals and demonstrate their promise for developing highly robust, low-power all-optical neural networks.

We propose a scheme to realize nonreciprocal dark modes in a coupled optomagnonic system consisting of a yttrium iron garnet (YIG) cavity and a silica cavity. Through magnon-induced Brillouin scattering, we establish a chiral optomagnonic coupling which leads to a dark mode occurring only under one propagation direction. Owing to the chiral dark mode, the system supports a nonreciprocal optical transmission channel that exhibit distinct transparency windows for leftward and rightward propagation. The system also supports an asymmetric quantum state transfer channel. Specifically, an optical quantum state prepared in one circulating direction can be coherently transferred to the magnon mode with high fidelity, while the mode in the opposite direction cannot be transferred due to the absence of the dark mode. We further identify the parameter regimes of coupling strength and dissipation that ensure high-quality state transfer. Our works introduce chiral dark modes as a quantum resource with applications in unidirectional quantum communication and quantum memory.

The Whittaker-Shannon decomposition provides a temporally localized description of squeezed light, making it applicable in the continuous-wave limit and leading to a definition of squeezing strength based on the number of photon pairs at a time. We show examples of its usefulness by calculating quadrature variance in a homodyne detection scheme, coincidence detection probabilities in the continuous-wave limit, and analyzing the Hong-Ou-Mandel effect for strongly squeezed light. Quadrature uncertainty falls farther below the shot noise limit when squeezing is strong, but effects due to correlations between photon pairs are most significant with weak squeezing. Our analysis extends previous results to more general scenarios, and we leverage the Whittaker-Shannon formalism to interpret them based on the temporal properties of photon pairs.

Exceptional points are singularities in the spectrum of non-Hermitian systems in which several eigenvectors are linearly dependent and their eigenvalues are equal to each other. Usually it is assumed that the order of the exceptional point is limited by the number of degrees of freedom of a non-Hermitian system. In this paper, we refute this common opinion and show that non-Markovian effects can lead to dynamics characteristic of systems with exceptional points of higher orders than the number of degrees of freedom in the system. This takes place when the energy returns from the reservoir to the system such that the dynamics of the system are divided into intervals in which it is described by the product of the exponential and a polynomial function of ever-increasing order. We demonstrate that by choosing the observation time, it is possible to observe exceptional points of arbitrary high orders with the same system parameters.

We investigate the two-port scattering process in non-Hermitian dimer models via quantum measurements using external leads. We focus on two exemplary dimer models that preserve parity-time symmetry via spatial gain-loss balance and exhibit nonreciprocity due to directional hopping. The scattering matrix is constructed using the biorthogonality of the left and right scattering states of the Hamiltonian, allowing us to calculate the reflection and transmission probabilities. Our analysis compares the reflection and transmission coefficients derived from the left, right, and combined scattering states, revealing that, unlike in Hermitian systems, the non-Hermitian scattering process does not adhere to unitarity when considering only the right scattering states. Furthermore, non-Hermitian scattering can enhance the reflection and transmission probabilities, with distinct physical contributions arising from complex eigenvalues and the nonorthogonality of eigenstates, which can be isolated and analyzed separately in different minimal models. Our results clarify how biorthogonality restores generalized unitarity and identify distinct physical origins of enhanced transport in $\mathcal{PT}$-symmetric and nonreciprocal dimers, providing insights into quantum transport in non-Hermitian systems.

Unspeakable coherence is a key feature separating quantum and classical physics. Modeled as asymmetry with respect to a continuous transformation generated by a physically relevant observable, such as the Hamiltonian or angular moment, unspeakable coherence has been shown to be the relevant notion of coherence for achieving quantum advantage in the tasks of metrology, reference frame alignment, and work extraction, among others. A question of both practical and foundational value is: Given some copies of a state with low coherence, can we prepare a more coherent state via coherence nonincreasing operations? Here, we study this question in the minimal limiting case: Given two uncorrelated copies of a coherent state, can one, via globally coherence nonincreasing unitaries, increase the coherence in a subsystem? We fully solve this problem for qubits, identifying the optimal unitaries and revealing the existence of bound coherence. This is then used to create a completely constructive multiqubit coherence enhancement protocol, where only effective-qubit unitaries are used. Unexpectedly, in this protocol, we show that there exist states for which the ratio of the input-output coherence can be amplified unboundedly. Extending beyond qubits, we derive two fundamental upper bounds on the amount of local coherence that can be increased and prove a no-go theorem showing that certain global correlations cannot be converted to local coherence.

Quantum teleportation is a quintessential quantum communication protocol that enables the transmission of an arbitrary quantum state between two distant parties without physically transmitting the state with the help of shared entanglement and limited classical communication. We show that it is possible to relax the entanglement requirement in quantum teleportation if we have access to a certain strain of superposition of quantum processes. Two types of superposition of quantum processes are generally considered in the literature: superposition of paths identified with quantum maps and superposition of indefinite causal orders of the maps. We find that when the superposition of paths is incorporated in the protocol, quantum teleportation with unit fidelity becomes possible—with nonzero probability of $1/4$—even when the two parties share certain classes of separable states, including pure product states. In contrast, the assistance of superposition of indefinite causal order of quantum maps in teleportation protocol does not enable any quantum advantage for shared pure product states. Furthermore, we show that separable Werner states can also yield a quantum advantage in quantum teleportation assisted by the superposition of paths. Finally, we establish that the presence of quantum coherence in the control qubit is both necessary and sufficient to achieve a quantum advantage in quantum teleportation assisted by the superposition of paths. The results potentially uncover yet another role of quantum superposition, in general, in teleportation versus entanglement.

Trotter errors in digitized quantum dynamics arise from approximating time-ordered evolution under noncommuting Hamiltonian terms with a product formula. In the adiabatic regime, such errors are known to exhibit long-time self-healing [Phys. Rev. Lett. 131, 060602 (2023)], where discretization effects are effectively suppressed. Here we show that self-healing persists at finite evolution times once nonadiabatic errors induced by finite-speed ramps are compensated. Using counterdiabatic driving to cancel diabatic transitions and isolate discretization effects, we study both noninteracting and interacting spin models and characterize the finite-time scaling with the Trotter steps and the total evolution time. In the instantaneous eigenbasis of the driven (gapped) Hamiltonian, the leading digital error maps to an effective harmonic perturbation whose dominant Fourier component yields an analytic upper bound on the finite-time Trotter error and reveals the phase-cancellation mechanism underlying self-healing. Our results establish finite-time self-healing as a generic feature of digitized counterdiabatic protocols, clarify its mechanism beyond the long-time adiabatic limit, and provide practical guidance for high-fidelity state preparation on gate-based quantum processors.

Coordination in distributed systems is often hampered by communication latency, which degrades performance. Quantum entanglement offers fundamentally stronger correlations than classically achievable without communication. Crucially, these correlations manifest instantaneously upon measurement, irrespective of the physical distance separating the systems. We investigate the application of shared entanglement to a dual-work optimization problem in a distributed system comprising two servers. The system must process both a continuously available, preemptible baseline task and incoming customer requests arriving in pairs. System performance is characterized by the trade-off between baseline task throughput and customer waiting time. We present a rigorous analytical model demonstrating that when the baseline task throughput function is strictly convex, rewarding longer uninterrupted processing periods, entanglement-assisted routing strategies achieve Pareto-superior performance compared to optimal communication-free classical strategies. We prove this advantage through queueing-theoretic analysis, nonlocal game formulation, and computational certification of classical bounds. We complement these formal results with simulations indicating that the advantage persists when arrivals are independent across routers and grows under bursty traffic. Our results suggest distributed scheduling and coordination as a candidate application domain for near-term entanglement-based quantum networks.