Ghost projection is the reversed process of computational classical ghost imaging that allows any desired image to be synthesized using a linear combination of illuminating patterns. Typically, physical attenuating masks are used to produce these illuminating patterns. A mask-free alternative form of ghost projection is explored here, where the illuminations are a set of caustic-laden diffraction patterns known as diffraction catastrophes. These are generated by focusing a coherent beam with a spatially modulated phase having random Zernike-polynomial aberrations. We demonstrate, via simulation, that a suitable linear combination of such random focal-field intensity patterns can be used as a basis to synthesize arbitrary images. In our proof-of-concept ghost-projection synthesis, the positive weighting coefficients in the decomposition are proportional to exposure times for each focal-field diffraction catastrophe. Potential applications include dynamic on-demand beam shaping of focused fields, aberration correction, and lithography.

In a two-membrane cavity optomechanical setup, two semitransparent membranes placed within an optical Fabry-Pérot cavity lead to a nontrivial dependence of the frequency of a mode of the optical cavity on the membranes' positions, which is due to interference. However, the system dynamics is typically described by a radiation-pressure-force treatment in which the frequency shift is expanded, stopping at first order in the membrane displacements. In this paper, we study the full dynamics of the system obtained by considering the exact nonlinear dependence of the optomechanical interaction between two membranes' vibrational modes and the driven cavity mode. We then compare this dynamics with the standard treatment based on the Hamiltonian linear interaction, and we find the conditions under which the two dynamics may significantly depart from each other. In particular, we see that a parameter regime exists in which the customary first-order treatment provides distinct and incorrect predictions for the synchronization of two self-sustained mechanical limit cycles and for Gaussian entanglement of the two membranes in the case of two-tone driving.

We investigate the induced modulation instability in second-harmonic generation beyond the early stage of the linearized growth of the modulation. We find a regime of recurrence (quasiperiodic conversion and back-conversion between the pump and the modulation) which is genuine of the parametric conversion process in quadratic media. Such recurrence is mainly driven by a process of nondegenerate downconversion, showing no analogy to the cascading regime which mimics the cubic (Kerr) nonlinearities. We consider two different steady states, i.e., a pure second-harmonic and a mixed fundamental and second-harmonic state. Both exhibit this dynamics, which we show to be amenable to a description in terms of reduced frequency-truncated models. The comparison with full numerical simulations of the starting model proves the validity and robustness of the reduced models in characterizing, in a simple and elegant way, a wide range of modulationally unstable steady states.

Isotope shifts have emerged as a sensitive probe of new bosons that couple to electrons and neutrons, and of nuclear structure. The recent Hz- or even sub-Hz-level isotope shift measurements across different elements call for a global assessment of all available data. In this work, we present the fit framework kifit that enables a combined analysis of isotope shift data from several elements, taking into account correlations. We provide a thorough comparison of analytical methods and the fit to analyze linear and nonlinear King plots and quantify their uncertainties. Finally, we provide recommendations for future measurements that could enhance the sensitivity to new physics and offer new insights into nuclear structure.

Quantum entanglement is a foundational resource in quantum information science, underpinning applications across physics. However, detecting and quantifying entanglement remains a significant challenge. In this article, we introduce a variational quantum algorithm inspired by Uhlmann's theorem to quantify the Bures entanglement of general quantum states, a method that naturally extends to other quantum resources, including genuine multipartite entanglement, quantum discord, quantum coherence, and total correlations, while also enabling reconstruction of the closest free states. The algorithm requires a polynomial number of ancillary qubits and circuit depth relative to the system size, dimensionality, and free-state cardinality, making it scalable for practical implementations. Thus, it provides a versatile framework for quantifying quantum resources, demonstrated here through several applications.

Developing quantum algorithms adaptive to specific constraints of near-term devices is an essential step towards practical quantum advantage. In a recent work [Phys. Rev. Lett. 131, 103601 (2023)], we show cold atoms in an optical cavity can be built as a universal quantum optimizer with programmable all-to-all interactions, and the effective Hamiltonian for atoms directly encodes number partitioning problems (NPPs). Here, we numerically investigate the performance of quantum annealing (QA) and quantum approximate optimization algorithm (QAOA) to find the solution of NPP that is encoded in the ground state of atomic qubits. We find the success probability of the standard QA decays rapidly with the problem size. The optimized annealing path or inhomogeneous driving fields only lead to mild improvement on the success probability. Similarly, the QAOA always gets trapped in a false local minimum, and there is no significant performance improvement as we increase the depth of the quantum circuit. To overcome the difficulty of solving NPPs, we propose an adaptive variational quantum algorithm (VQA) whose ansatz differs from that of the QAOA by releasing the parameter freedom of the NPP Hamiltonian. Through numerical simulations, we find that our adaptive VQA can achieve rather high success probability within very small circuit depth. It is thus worth paying the extra optimization cost of additional parameters for improving performance compared to the QAOA. Therefore, our adaptive VQA provides a promising choice for programmable atom-cavity systems to demonstrate competitive computational power within its quantum coherence time.

The radiolysis of water molecules by ionizing radiation leads to the production of various reactive species, which play a critical role in the indirect killing of cancer cells. In radiotherapy (RT) techniques involving nuclear reactions, both radiolysis-induced radical generation and nuclear reaction processes are present within the irradiated environment. However, the interaction between these two mechanisms remains poorly understood, limiting further optimization of RT. In this work, the effect of the ${}^{15}\mathrm{N}(p,\alpha ){}^{12}\mathrm{C}$ reaction on the kinetic energy release of water fragmentation and on the kinetic energy (KE) of the generated radicals is investigated using a point-charge model. It is found that the charge state $q$ and flight velocity $v$ of the nuclear reaction products are the primary influencing factors. Additionally, lighter and more distant radicals produced by the nuclear reaction are observed to obtain higher KEs. These radicals may influence the local spatial distribution of reactive species and their interaction with nearby biomolecules. A feasibility analysis indicates that such effects can be experimentally measured using a cold target recoil ion momentum spectroscopy. The primary motivation of this study is to provide atomic- and molecular-level insights into how nuclear reactions influence water fragmentation in RT, laying a foundation for future experimental and biological investigations.

We present a method to compute interacting Wannier functions in an optical superlattice for cold atom gas experiments. We start from a noninteracting Wannier function obtained from the band projected position operator method and perform Trotter method to compute the interacting Wannier function. Then, we use this function to compute the on-site interaction strength in a superlattice, compare the result to a measurement, and find good agreement between simulation and data.

The nonequilibrium dynamics of an impurity immersed with a finite velocity into a one-dimensional system of weakly interacting bosons is studied within the framework of the time-dependent Gross-Pitaevskii equation. We uncover and characterize different regimes of relaxation dynamics. We find that the final impurity velocity remains constant in a large interval of sufficiently big and realistic initial velocities. The underlying physical mechanism is the emission of the dispersive density shock waves that carry away the excess of the initial impurity momentum, while locally the system remains in the same stationary state. In contrast, a heavy impurity with the same coupling constant relaxes differently and the regime of constant final velocity disappears. Furthermore, a fast heavy impurity exhibits damped velocity oscillations in time before reaching a stationary state. This process is accompanied by the oscillations of the local depletion of the boson density around the impurity, until their positions coincide and they continue the motion together. Decreasing the impurity-boson coupling or increasing the strength of repulsion between bosons, the oscillations get amplified. In the case of a heavy impurity with the mass bigger than the critical one, the ground-state energy as a function of momentum exhibits cusps and metastable branches. We show that they manifest themselves by a soliton emission, a considerable slowing down of the relaxation, and a change of the impurity direction of motion with respect to the initial one.

Single-photon scattering in waveguide-QED systems plays a pivotal role in quantum information processing and communication. We introduce a time-dependent variational approach employing a modified multiple Davydov Ansatz to simulate single-photon dynamics in one-dimensional waveguide-QED systems within the strong-coupling regime. The method is benchmarked across three configurations: a single qubit, two distant qubits, and a ladder-type qutrit coupled to the waveguide. For the single- and two-qubit cases, the variational results exhibit excellent agreement with those derived from a transformed rotating-wave approximation (TRWA). The accuracy of our approach is further verified by an analysis of the local-in-time error, which remains small even under strong coupling, indicating its potential superiority over TRWA in specific regimes. In addition, by contrasting our results with the rotating-wave approximation, we elucidate the significant influence of counter-rotating couplings on scattering dynamics. Our findings establish this variational method as a reliable and versatile tool for investigating single-photon scattering in diverse waveguide-QED systems, particularly in regimes where traditional approximations falter.

We experimentally demonstrate a violation of local realism with highly spatially multimode polarization-entangled two-photon states produced by spontaneous parametric down-conversion (SPDC) pumped by a spatially incoherent light source—a light-emitting diode (LED). While existing studies have observed such a violation only by postselecting the LED-pumped SPDC photons into a single spatial detection mode, we achieve a Clauser-Horne-Shimony-Holt inequality violation of $S=2.532\pm 0.069>2$ using a spatially multimode detection setup that collects nearly 4080 SPDC spatial modes. These results indicate that coherent pump sources, such as lasers, are not required for SPDC-based entanglement generation. Our work could enable novel and practical sources of entangled photons for quantum technologies such as device-independent quantum key distribution and quantum-enhanced sensing.

Transmission through potential barriers is a fundamental problem in quantum mechanics. While semiclassical methods can approximate certain aspects of transmission, they fail to capture the intrinsically quantum interference associated with Wigner-function negativity. We numerically study the transmission of displaced Fock states through an inverted-oscillator barrier, with and without a Kerr nonlinearity that offers a potential route to experimental realization. These states allow only an approximate classical description since their characteristic Wigner-function negativity is absent in phase space. The semiclassical simulation reproduces the overall transmission, but deviates from exact results and fails to capture short-time plateaus that arise when regions of Wigner-function negativity cross the barrier. With the Kerr nonlinearity, reflections from nonlinear boundaries drive interference into classically forbidden regions, an effect that is inaccessible to semiclassical approaches. We find that these interference effects do not alter the maximum transmission probability, which is bounded by the initial positive-energy fraction and therefore already encoded in the phase-space structure of the Fock states. Because Fock states cannot be faithfully represented within classical phase space, the transmission through a barrier reveals the fundamental limitations of semiclassical approaches.

We develop a recursive perturbative expansion for the time-convolutionless generator of an open quantum system in a generalized Lindblad form. This formulation provides a systematic approach to derive the generator at arbitrary order while preserving a Lindblad-like structure, without imposing assumptions on the system or environment beyond an initially uncorrelated state. The generator is written, at all orders, in a canonical form, which also corresponds to the minimal dissipation condition, which uniquely specifies the decomposition of the generator into Hamiltonian and dissipative contributions. To validate the method and show its effectiveness in addressing non-Markovian dynamics and strong-coupling effects, we compute the generator explicitly up to fourth order.

Nonorientable manifolds, such as the Möbius strip and the Klein bottle, defy conventional geometric intuition through their periodic boundary condition with a twist. As a result, topological defects on nonorientable manifolds give rise to novel physical phenomena. We study the adiabatic transport of exceptional points (EPs) along nonorientable closed loops and uncover distinct topological responses arising from the lack of global orientation. Notably, we demonstrate that the winding number associated with encircling an EP depends sensitively on the loop orientation, leading to inequivalent results for clockwise and counterclockwise encirclement; this feature is unique to nonorientable manifolds. Orientation-dependent geometric quantities cannot be consistently defined due to the absence of a global orientation. However, when a boundary is introduced, such quantities become well defined within the local interior, even though the global manifold remains nonorientable. We further demonstrate the adiabatic evolution of EPs and the emergence of orientation-sensitive observables in a Klein Brillouin zone, described by an effective non-Hermitian Hamiltonian that preserves momentum-space glide symmetry. Finally, we numerically implement these ideas in a microdisk cavity with embedded scatterers using synthetic momenta.

The performance of error correction in the surface code can be enhanced by leveraging the knowledge of the noise model for physical qubits. To provide accurate noise information to the decoder in parallel with quantum computation, an adaptive estimation of the noise model based on syndrome measurement statistics is an effective approach. While noise-model estimation based on syndrome measurement statistics is well established for Pauli noise, it remains unexplored for more complex and realistic scenarios such as amplitude damping, which cannot be represented as a Pauli channel. In this paper, we propose Bayesian inference methods for general noise models, integrating a tensor network simulator of surface code, which can efficiently simulate various noise models, with Monte Carlo sampling techniques. For stationary noise, we propose a method based on the Markov chain Monte Carlo. For time-varying noise, which is a more realistic scenario, we introduce another method based on the sequential Monte Carlo. We present numerical results of applying our proposed methods to various noise models, such as static, time-varying, and nonuniform cases, and evaluate their performance in detail.

We address the control of the dynamics of both population and coherence phase in an open two-level quantum system employing a single external control field. The system dynamics is described by a Markovian master equation that takes into account dephasing and thermal noise. The control is engineered by inverting the underlying equations of motion, which yields an analytical expression for the control field in terms of user-specified time-dependent functions for the population and coherence phase. Our approach allows us to dictate not only the initial and final populations and phases, but the full dynamics of these quantities. The chosen functions for population and phase have to conform to certain constraints indicated in our analysis. Our methodology also reveals the possible transitions for given initial conditions and environmental noise parameters.

We derive exact analytical expressions for the quantum capacity of a broad subclass of generalized dephasing channels of the form $\mathrm{\Lambda }\left(\rho \right)=(1-x)\rho +xD\left(\rho \right)$, where $D\left(\rho \right)$ represents a structured decoherence process. These channels are degradable for all noise parameters and in arbitrary dimensions, yielding closed-form single-letter capacity formulas. Our analysis includes fully decohering, block-decohering, and weakly decohering channels, the latter involving coherence preservation within overlapping subspaces. Surprisingly, even under maximal decoherence, the channel may retain nonzero capacity due to residual coherence structure. These results reveal a quantitative role for decoherence-free and partially coherent subspaces in preserving quantum information, offering guidance for encoding strategies in quantum memories and fault-tolerant quantum communication systems.