Rydberg atoms possess strong electric-dipole transitions and tunable energy levels, making them promising candidates for microwave to optical conversion on integrated superconducting atom chips. Achieving strong coupling of the atoms to, e.g., the microwave field of an on-chip resonator requires placing the atoms within tens of micrometers from the chip surface. However, inhomogeneous stray electric fields originating from the surface can induce position-dependent Stark forces, resulting in atomic motion and leading to time-dependent shifts of the Rydberg energy levels. We experimentally investigate these effects using time-of-flight and spectroscopic techniques, observing substantial level shifts and signal loss attributable to field-induced atomic motion. A theoretical model incorporating an exponentially decaying surface field with a superimposed bias accurately reproduces the observed dynamics. To mitigate the level shift, we introduce a Stark echo sequence that dynamically reverses the force. This approach suppresses the atomic motion and maintains the atomic resonance. The method relies solely on global field control and is compatible with atom-resonator coupling architectures, providing a robust strategy for preserving coherence of Rydberg atoms in inhomogeneous electric fields near surfaces.

We develop a finite-temperature Gaussian-state formulation of quantum energy teleportation in the one-dimensional harmonic chain. For Gibbs states, the optimized measurement-feedback protocol reduces to thermal two-point functions. In the single-site protocol, the extracted energy is governed by a single correlator, which makes the thermodynamic and near-critical limits analytically tractable. At fixed finite temperature, the extracted energy is exponentially screened with distance and is controlled by a thermal correlation length for both critical and noncritical $\alpha$. In the zero-temperature critical limit taken after the thermodynamic limit, we derive the exact asymptotic law $E_{\mathrm{ext}}\sim d^{-4}$. Numerical results confirm both regimes and resolve the crossover responsible for the apparent drift of the effective decay exponent at intermediate distances. We also analyze squeezed Gaussian measurements and show that they modify the extraction prefactor: $p$ squeezing enhances the extracted energy, whereas $q$ squeezing suppresses it without changing the large-distance scaling.

Continuous-time quantum walks on a lattice spread ballistically and converge to a limiting distribution for the rescaled position. On the hard-wall half line the boundary reflects the walker but does not change the bulk dispersion, so the ballistic front remains set by the maximal group velocity. We ask how close one can get to this front when the initial state is constrained to occupy only the first $M$ sites. We show that optimizing the moment-generating function of the limiting-velocity distribution over this finite-support class reduces to the principal eigenvalue of an explicit $M\times M$ Hermitian matrix, which yields the optimal state by direct diagonalization. For large $M$, a near-front scaling limit produces a continuum description that controls the entire peak region. In particular, the maximal mean drift approaches the front with an inverse-square deficit in $M$ and a constant prefactor ${\pi }^2/4$. Numerical results verify both the finite-$M$ spectral formulation and the predicted scaling.

Quantum imaginarity is an important resource in quantum information theory, associated with the operational role of complex numbers in quantum mechanics. Here we investigate how imaginarity behaves under coherent superposition of orthogonal pure states. For orthonormal components, we express the geometric imaginarity in terms of a conjugation-overlap matrix. We characterize these matrices as complex symmetric contractions and determine the minimum dimension required for their realization. In the two-component setting, we derive the exact feasible region of the off-diagonal conjugation overlap and a sharp bound on its modulus. Moreover, the conjugation-overlap matrix of an orthonormal qubit pair is unitary, yielding the full range attainable by varying the relative phase. For multicomponent superpositions, we identify the exact condition for attaining maximal imaginarity in superpositions of real components and show that pairwise compatibility is insufficient for global realizability, although pairwise constraints still yield lower bounds. When only the diagonal conjugation overlaps are specified, the attainable imaginarity values form a closed interval whose end points can be determined by convex optimization. Our results show that the imaginarity of a superposition depends not only on the imaginarities of its components but also on their relative phases and the global compatibility of their conjugation overlaps.

Quantum information processing, communication, and sensing networks are being developed with various qubit platforms that use different encoding schemes. Connecting quantum network nodes to distribute entanglement requires matching photon qubit basis encoding. In this work we implement an interconversion protocol which converts photon qubit encoding from the polarization basis to the time-bin basis, transmits the photons through a transport fiber with large fluctuations in polarization, and converts back to polarization encoding for ease of measurement. This interconversion scheme faithfully transmits a polarization Bell state across the transport fiber by converting sources of infidelity to changes in transmission rate. These results illustrate a practical approach for interfacing distinct qubit platforms to enable modular and flexible operation in heterogeneous quantum networks.

We present fully correlated calculations of angularly resolved one- and two-photon photoionization delays in ${\mathrm{H}}_2\mathrm{O}$ for different ionization channels and light-polarization directions. By solving the time-dependent Schrödinger equation in full dimensionality, we obtain molecular-frame photoelectron angular distributions, Wigner delays, and two-photon photoionization delays for the three lowest cationic states of water. The comparison between Wigner and two-photon delays reveals that the interaction with the infrared (IR) field strongly reshapes the angular dependence of the delays, leading to pronounced anisotropies and directional asymmetries that are absent in the one-photon delays. Within a given sideband, the resulting angular variations can reach up to $\approx 80$ as for a fixed vibrational state, while differences between vibrational levels of the residual cation at a fixed emission angle are typically limited to $\approx 15$ as. The continuum-continuum contribution induced by the IR field is found to strongly depend on the photoelectron emission direction and molecular orientation, indicating that isotropic approximations commonly employed for atomic targets are not generally adequate for molecular systems. These results highlight the importance of orientation-resolved measurements for accessing the full complexity of molecular photoionization dynamics.

The Aharonov-Bohm (AB) effect remains a cornerstone of fundamental and applied physics. In this work, we utilize the AB caging effect originated from an effective magnetic field induced by multiorbital interactions, creating an all flat band (FB) lattice system. Normally, FB states are known for being compact in space and having a zero tail; therefore, their mobility in a linear environment is generally understood as impossible. We propose a Floquet driving protocol in an all-FB photonic system to fully control the dynamics of localized photonic states. The modulation of the Hamiltonian along the propagation coordinate allows the translation of compact states in the direction of constructive interference, resulting in an effective stroboscopic quantum walk-like effect. We find that the traveling states exist in chiral pairs. We experimentally implement the Floquet driven protocol using femtosecond laser written photonic waveguides and demonstrate directional control of the propagation, determined by the relative phase of the input condition.

The secondary rainbow, a classic fold caustic, presents a long-standing challenge in wave theory because standard semiclassical approximations predict unphysical intensity nulls near the Brewster angle. We resolve this Brewster-caustic confluence by developing a uniform asymptotic theory that integrates complex angular momentum theory with the Chester-Friedman-Ursell expansion. By incorporating first-order amplitude gradients, our framework regularizes these polarization-dependent caustics, effectively decoupling the macroscopic caustic envelope from high-frequency Mie diffraction. Validated for relative refractive indexes $1.18<N<2$, this size-parameter-independent $O\left(1\right)$ computational framework bridges classical meteorological optics with modern singular optics, providing a robust analytical foundation for polarimetric inverse scattering.

We revisit quantum $\varphi$-synchronization in a dissipatively coupled cavity-magnon system and formulate the calculation within one consistent system-bath model. A Hermitian photon-magnon interaction of strength $g$ is supplemented by a common Markov channel $L_c=\sqrt{2\mathrm{\Gamma }}(a-im)$. Interference between coherent and dissipative coupling produces the asymmetric rates ${\lambda }_1=g-\mathrm{\Gamma }$ and ${\lambda }_2=g+\mathrm{\Gamma }$, while the same channel necessarily supplies correlated input noise. We derive the quantum Langevin equations from the input-output model and show explicitly that the reduced adjoint Lindblad map is not an operator-algebra homomorphism; canonical commutators are instead preserved by the full Langevin dynamics, including the input fields. For the linear Gaussian system, a quantum Itô product calculation gives the closed second-moment equation $\dot{V}=AV+V{A}^{\mathsf{T}}+D$, with a nondiagonal diffusion matrix fixed by the common bath. This construction answers how the higher-order moments are obtained without raising a first-moment solution to a power. At resonance the drift spectrum has an exceptional point at ${\mathrm{\Gamma }}_{\mathrm{EP}}=\sqrt{g^2-{(\kappa -\gamma )}^2/4}$. For $g/\kappa =2$, $\gamma /\kappa =0.1$, a vacuum common bath, and a magnon-bath occupation $n_m=10$, the fluctuation measure $S_q^{\varphi }$ increases from 0.256 at $\mathrm{\Gamma }=0$ to 0.672 at the exceptional point; the full measure, which also retains the mean-amplitude mismatch, increases from 0.243 to 0.632. A thermal-bath control shows that this improvement is caused by reservoir engineering rather than by spectral coalescence alone. The exceptional point is therefore an experimentally identifiable spectral marker of the strong-dissipation regime, not an independent source of noiseless topological enhancement.

We investigate enantiodetection for both a single cyclic three-level chiral molecule and a mixture of a finite number of chiral molecules by monitoring the steady-state intracavity photon number in a cavity-QED platform. Our scheme exploits the intrinsic global $\pi$-phase difference between opposite enantiomers to engineer destructive or constructive interference pathways, enabling a direct readout of enantiomeric excess with an error below $5\%$ and exhibiting robustness against energy-level dissipation. To capture mesoscopic many-molecule effects beyond mean field while avoiding brute-force master-equation simulations, we employ a generalized discrete truncated Wigner approximation, which is well suited for systems with many yet a finite number of molecules. These results pave the way for implementing enantiodetection in realistic quantum-optical settings.

Nonreciprocal transport at the few-photon level is important for integrated quantum optics and quantum information processing. Unlike conventional small atoms, giant atoms interact with a waveguide through multiple discrete coupling points, allowing photons to accumulate phases along different coupling paths. In this paper, we theoretically investigate few-photon diode effects in a one-dimensional waveguide chirally coupled to a dissipative giant atom. By solving the Schrödinger equation, we obtain analytical solutions for both single-photon and two-photon scattering processes. Our results show that the two-point coupling structure of the giant atom allows diode effects to occur in multiple frequency regions, rather than only near resonance. By tuning the distance $L$ between the two coupling points, one can modify the propagation phase and the interference condition. This provides a geometric way to control the operating frequency range of the diode effect. For the chiral coupling configuration considered here, the optimal diode performance is obtained when the atom-waveguide coupling rate $\mathrm{\Gamma }$ and the dissipation rate $\kappa$ satisfy $\mathrm{\Gamma }/\kappa =1$. The two-photon diode effect further shows a clear dependence on $\mathrm{\Gamma }/\kappa$. For $\mathrm{\Gamma }/\kappa \gg 1$, the nonreciprocal response mainly appears in the bound-state-dominated region. In contrast, for $\mathrm{\Gamma }/\kappa \ll 1$, the transport tends to become reciprocal. These results indicate that nonlocal giant-atom coupling, chiral coupling, and dissipation can work together to realize frequency-tunable few-photon nonreciprocal transport.

Vacuum fluctuations of quantum fields provide an unavoidable environment for any quantum system coupled to it. We study the interplay between boundary conditions and acceleration in determining decoherence of a two-level Unruh-DeWitt detector coupled to a scalar field in a cylindrical cavity. We show that the decoherence rate closely follows the emission profile, and exhibits Purcell-like enhancement for both inertial and uniformly accelerated detectors. The acceleration induces an effective smearing of the resonant density of states, diluting the resonance enhancement for large accelerations while replacing the inertial off-resonant decay with an oscillatory behavior for small accelerations. For moderate accelerations, this interplay between cavity-induced and acceleration-assisted effects results in an extended region of cavity parameters where decoherence is strongly suppressed, particularly in regimes where the inertial detector otherwise experience strong decoherence. Thus, contrary to naive expectations, the Unruh thermality in a suitably engineered cavity can enhance rather than degrade quantum coherence, providing a very uncharacteristic feature of quantum fields in noninertial frames.

The theory of dynamical diffraction (DD) in perfect crystals is the backbone of high-precision neutron and x-ray diffraction experiments, enabling accurate determination of crystal-structure factors and the realization of perfect-crystal interferometers. In practice, however, real crystals exhibit deformations and imperfections, including surface roughness, defects, temperature gradients, angled crystal faces, and curvature, that degrade interferometer performance and are difficult to model using conventional DD theory, particularly in complex geometries. To address these challenges, a quantum information (QI) model for DD has been under development, with demonstrated experimental agreement both for ideal crystals and in the presence of some imperfections such as surface roughness and defects. Here, we present a unified quantum walk model that is now suitable for reproducing a broad range of established DD effects. We demonstrate this by incorporating several diverse internal crystal effects influencing DD intensity distributions, including linear temperature gradients, the DD Talbot effect, and angled or miscut crystals. These results establish the QI model as a comprehensive and flexible framework for experimental analysis, as well as for the design of next-generation perfect-crystal neutron interferometers and neutron optical components, such as condensing monochromators.

In phase-randomized weak coherent pulse (WCP) implementations of the quantum key distribution (QKD) BB84 protocol, the decoy method is often used to compensate BB84's vulnerability against photon number splitting attacks. However, this typically introduces extra complexities and requirements on experimental devices. In this paper, we are therefore interested in phase-randomized WCP implementations without the decoy method. We examine the performance of three QKD protocols with different classical announcement structures, namely, BB84, SARG04, and No Public Announcement of Basis (NPAB) BB84, using numerical security proof techniques. Key rates are computed using the openqkd security software [J. Burniston et al., software openqkdsecurity, ver. 2.0.2 (2024)]. We compare secure key rates of the three protocols in asymptotic and finite-size regimes for lossy and noisy channels. The three protocols show different relative advantages depending on the channel behavior. Canonical BB84 shows robustness against errors and depolarization, SARG04 demonstrates resilience against high-loss channels, and NPAB BB84 shows potential advantages against physical misalignment between QKD devices.

Entanglement distillation is the process of converting noisy entangled states into maximally entangled pure states via local operations and classical communication. A long-standing, unresolved question is which entangled states are amenable to distillation, known as the distillability problem. For Bell-diagonal qutrit states with a Weyl structure, combining two existing results shows that violating the positive partial transpose (PPT) criterion is both necessary and sufficient for one-copy distillability. However, these results do not identify a Schmidt-rank-2 witness that maximizes robustness to white noise. To address this limitation, we present a noise-robust entanglement-distillation scheme for all non-PPT Bell-diagonal qutrit states with a Weyl structure. Specifically, we construct a Schmidt-rank-2 eigenvector of the partially transposed density matrix associated with its unique, threefold degenerate negative eigenvalue. This feature makes the derived entanglement distillation protocol resilient to white-noise effects on the quantum states. Our results thus make noisy entangled qutrit pairs more accessible for future quantum technologies.

We investigate the private capacity of quantum channels using the recently proposed quantum convolution theory for discrete-variable quantum systems. We focus on the role played by magic resources in this framework. First, for a broad class of convolutional channels, we find that the private capacity is zero if the fixed environmental state is a stabilizer state. Moreover, we show that the private capacity can be nonzero for some magic environmental states. For pure environmental states, we further prove that the private capacity of a discrete beam-splitter channel is upper bounded by twice the modified relative entropy of magic of the environment. In addition, if the environmental state exhibits a certain symmetric structure, even if it is magic, the corresponding private capacity will also vanish for a class of convolutional channels. Together, these results show that environmental magic is necessary but not sufficient for positive private capacity in the channel class considered here, while also providing a quantitative upper bound on the achievable private rate.

We analyze the WAHUHA Floquet protocol recently applied to arrays of Rydberg atoms and derive beyond-leading-order corrections in the high-frequency expansion of the effective spin theory. We find that an appropriate choice of the pulses times can enforce an approximate symmetry corresponding to the conservation of the total magnetization. The interaction channels emerging from higher-order Floquet terms affect three-body bound states (trimers), which gain a significant mobility. We estimate the corresponding enhancement in one-dimensional spin chains and conclude that their dynamics is within experimental reach. Detrimental effects due to the proliferation of particles outside of the trimer magnetization sector are found to occur and spread on timescales slower than the trimer propagation. We further show that long-range interactions enhance trimer propagation and that two-dimensional triangular geometries can host energetically isolated trimer bands, providing a possible route to reduce resonant mixing with higher-magnetization sectors. Our results establish a concrete route to realizing mobile multiparticle bound states in Floquet-engineered Rydberg platforms.