We theoretically investigate the influence of molecular alignment on elliptically polarized high-order harmonic generation (HHG) from ${\mathrm{H}}_2^{+}$ driven by an orthogonally polarized two-color laser field by numerically solving the three-dimensional time-dependent Schrödinger equation. Our findings indicate that the alignment of ${\mathrm{H}}_2^{+}$ along the laser propagation direction $(R\parallel z)$ leads to an enhancement in both the harmonic intensity and ellipticity compared with alignment along the laser polarization direction $(R\parallel x)$. Increasing the frequency ratio enhances both the ionization and recollision probabilities, thereby increasing the harmonic intensity. Furthermore, the relative phase enables control over the harmonic intensity, ellipticity, and quantum-path selection. We further demonstrate that the relative phase induces asymmetry in the electric field waveform, leading to a redshift of the harmonic spectrum that is closely associated with the enhancement of harmonic ellipticity. Finally, we synthesize a near-circularly polarized attosecond pulse train with an ellipticity of 0.99. Our study provides an effective route for experimentally controlling the polarization and intensity of molecular HHG.

We derive the canonical-ensemble scaling of Tan's contact for $N$ harmonically trapped Tonks-Girardeau bosons at finite temperature in the large-$N$ limit. The leading scaling coefficient reproduces the local-density-approximation result and is obtained from a contour-integral representation of the canonical partition function followed by a saddle-point reduction to a phase-space integral with a self-consistent scaled chemical potential. The subleading coefficient is the central object of this work: it admits an explicit representation in terms of universal phase-space integrals of the Fermi factor, having closed-form Sommerfeld and virial limits, and is identified with the canonical-versus-grand-canonical ensemble difference at fixed mean particle number. In the high-temperature Boltzmann regime the ratio of subleading to leading coefficients collapses to a universal value, traceable to the Poissonian particle-number statistics of the dilute grand-canonical gas. We construct Padé approximants for both scaling functions that interpolate uniformly between the low-temperature Sommerfeld and high-temperature virial regimes; for the subleading coefficient we report a form that is uniformly accurate on our working range of temperatures and asymptotically correct beyond. The scaling law is verified against canonical contour-integration data across the full temperature range, and the experimental visibility of the ensemble correction is quantified: for the mesoscopic particle numbers and temperatures of current one-dimensional experiments it reaches the several-percent level.

Upstream motion, a typical form of nonequilibrium dynamics, is generally exhibited by active matter that is closely correlated with nonreciprocal interactions. This classic picture is likely to be extended into the quantum regime, benefiting from recent advances that endowed the interactions of quantum entities with a nonreciprocal feature. In this work, we demonstrate the upstream motion of a swimmer—a narrow optical beam—in a quantum fluid of light. The swimmer undergoes nonreciprocal mutual interactions with the optical fluid, acquiring a counterintuitive recoil inverted relative to that in equilibrium systems. Experimental validation via an optical platform enabling nonreciprocal light-light interactions confirms the upstream motion. Our findings further reveal that the maximum upstream capability is achieved at moderate fluid-flow velocity and density. Our results unveil another quantum form of active behavior induced by nonreciprocal interactions, providing key inspiration for achieving the goal of designing novel quantum devices with active functionalities.

Quantum-optical simulations of inhomogeneous media typically rely on a global eigenmode basis that must be recomputed for each geometry. We show that, for lossless, nondispersive media, the dynamics can instead be formulated without such a basis. From the source-free Maxwell equations we identify a self-adjoint real-space generator of single-photon dynamics and directly construct bosonic field operators, a single-particle Hamiltonian, and a Liouville–von Neumann equation for the single-photon density matrix. A finite integration technique discretization transfers this operator structure to the numerical grid while preserving self-adjointness. This ensures unitary evolution and exact photon-number conservation up to projection accuracy and machine precision. Numerical examples demonstrate single-photon propagation in a dielectric waveguide and reproduce the two-photon Hong-Ou-Mandel dip in a 50-50 coupler. The few-photon dynamics in this formulation is fully determined by the bosonic symmetry of the state space and the linear single-particle propagation, without explicit photon-photon interaction terms. The approach therefore enables direct quantum-optical simulation of inhomogeneous and geometrically complex photonic structures.

High-fidelity spin readout is a crucial component for quantum information processing with optically interfaced solid-state spins. Here, we propose and investigate two theoretical protocols for fast single-shot readout of cavity-coupled single T center electronic spins. For fluorescence-based readout, we selectively couple one of the T center spin-conserving transitions to a single-mode photonic cavity, exploiting the enhancement of the fluorescence emission and cyclicity. For reflection-based readout, we leverage the spin-dependent cavity reflection contrast to generate the qubit readout signal. We show that the cavity reflection approach enables high-fidelity spin readout even when the T center only has a modest cyclicity. With realistic system parameters, such as cavity quality factor $Q=2\times {10}^5$ and T-center optical linewidth $\mathrm{\Gamma }/2\pi =100\mathrm{MHz}$, we calculate a single-shot readout fidelity exceeding 99% within 10 $\mu \mathrm{s}$ for both spin readout protocols.

Multiphoton resonances provide an important manifestation of counterrotating interactions in light-matter systems. These resonances, however, are sensitive to detuning errors, making the phenomena challenging to experimentally observe. In this manuscript, we introduce an optimization strategy to address this problem. By using an optimized parameter segmented sequence, the sensitivity to quasistatic detuning errors of the high-order quantum state transfers can be substantially relaxed. We prove the versatility of our strategy against frequency detunings by demonstrating the evolution of two specific models. In both cases, the parameter window for maintaining a high state-transfer fidelity is substantially expanded. We further analyze the output photon flux of the optimized system and, taking the three-photon resonance as an example, demonstrate that the system remains capable of generating a stable output photon flux even in the presence of detuning errors.

The open anisotropic quantum Rabi model (QRM) is studied in this work, with an explicit $A^2$ term incorporated. It is shown that, in the presence of cavity loss, anisotropy allows the steady-state superradiant transition to occur even when the $A^2$ term prohibits the transition in the isotropic case. The $A^2$ term reshapes and enriches the known steady-state phase diagram of the open anisotropic QRM, leading to an asymmetric structure composed of normal, superradiant, and bistable phases. In particular, the nonequilibrium tricritical points are generally separated from the merger point of the two critical branches that bound the superradiant region. Isolated bistable regions also emerge, and the number and positions of tricritical points are reduced. Notably, the anomalous photon-number fluctuation scaling is associated with the merger of the two critical branches, rather than with the tricritical points. These results clarify the role of the $A^2$ term contribution in the steady-state structure of the open anisotropic QRM and provide a refined extension of the previously known dissipative phase diagram, offering a useful theoretical reference for future studies of related open light-matter systems.

Encoding continuous-variable quantum information in the optical domain has recently enabled the generation of large entangled states, yet robust implementation remains a challenge. Here we present a straightforward protocol for generating multipartite entanglement based on spontaneous parametric down-conversion in a circular array of quadratic nonlinear waveguides. We provide a rigorous theoretical framework, including comprehensive derivations of the propagation equations and the identification of regimes where analytical solutions are possible. Crucially, our approach identifies the pump and detection configurations required to sustain and measure multipartite full inseparability across arbitrary propagation distances and for any number of waveguides $N=4n$. This regime, elusive to standard numerical methods, represents a key requirement for scalable quantum protocols. Our scheme is inherently robust as it relies on phase-matched propagation eigenmodes, making it resilient against variations in sample length, coupling, and nonlinearity.

Optical asynchronous light-intensity transmission (OALT) is a counterintuitive nonlinear phenomenon where output field intensity declines with increasing input intensity. In this work we theoretically establish a controllable, all-optical, and passive OALT mechanism in an atom-cavity coupling system via disruptive inverted-S-shaped bistability (ISB). Solving the stationary input-output relation for a driven-dissipative Tavis-Cummings model predicts an OALT phase in the reflection field that is distinct from traditional monostable and bistable regimes. The demonstration of controllable optical negative differential transmission, which is governed by disruptive ISB, confirms an efficient OALT response. Our findings suggest a promising paradigm for self-adaptive optical protection systems and self-stabilized generation of quantum light sources.

Optical systems are a promising platform for realizing universal quantum computation. However, photons do not naturally interact, presenting a major challenge for implementing efficient and deterministic multiqubit gates. Here, we propose a coupling scheme between photons and Rydberg atoms that induces strong effective photon-photon interactions with a negligibly small imaginary component. Leveraging this coherent photonic nonlinearity and combining it with the stationary light approach, we design a deterministic two-photon controlled-not gate with significantly improved fidelity compared to previous schemes. This approach could enable additional avenues for universal quantum computation and quantum information processing based on optical systems.

We present a quantum computation approach in which computation is guided by positive-operator-valued-measure (POVM) measurements following a given computation path in multisteps. In this approach, one ancillary qubit is coupled to a register of working qubits, and a POVM measurement is implemented effectively on the working qubits by applying a unitary operation on the whole system followed by a projective measurement performed on the ancillary qubit. Each step of the computation is a repeat-until-success procedure such that the desired state of the step is obtained deterministically on the working qubits via POVM measurements. The principle of deferred measurement states that measurements can always be moved from an intermediate stage of a quantum circuit to the end of the circuit without affecting the efficiency of the computation. We demonstrate that in our approach, by introducing intermediate measurements on the ancillary qubit in the computation process, both the number of qubits and unitary operations can be reduced polynomially, compared to the case where the intermediate measurements are deferred to the end of the computation. We also provide a method for implementation of the approach.

We initiate an investigation into a notion of state complexity for discrete-variable quantum systems. Specifically, we propose an information-theoretic quantifier for the complexity of quantum states within the stabilizer formalism of quantum computation. This is achieved by leveraging the symmetric Jordan product (associated with classicality) and the skew-symmetric Lie product (linked to quantumness) between the square root of the quantum state and the Heisenberg-Weyl displacement operators. We reveal fundamental properties of this quantifier and demonstrate that state complexity is closely related to the nonstabilizerness of quantum states via the $L^4$-norm of their characteristic functions. By the way, we characterize the maximally mixed states, the stabilizer states, and the symmetric informationally complete positive operator valued measure fiducial states from the perspective of state complexity.

We propose the first continuous-variable (CV) unclonable encryption scheme, extending the paradigm of quantum encryption of classical messages to CV systems. In our construction, a classical message is first encrypted classically and then encoded using an error-correcting code. Each bit of the codeword is mapped to a CV mode by creating a coherent state which is squeezed in the $q$ or $p$ quadrature direction, with a small displacement that encodes the bit. The squeezing directions are part of the encryption key. We prove unclonability in the framework introduced by Broadbent and Lord, via a reduction of the cloning game to a CV monogamy-of-entanglement game. Furthermore, we demonstrate that our scheme can be readily implemented with current technology. By incorporating realistic imperfections such as channel noise and detector inefficiencies, we show that the protocol remains robust under these conditions.

A protocol for identifying controlled-not (cnot) gates versus single-qubit-only gates in universal quantum circuits using randomized input states was recently shown to be intimately connected to the quantum resource of state texture. Here, we revisit this gate identification protocol and demonstrate that a more general fidelity-based formulation succeeds for nearly all laboratory bases. We then examine a broader family of quantum resource theories, where a distinct resource theory can be defined for each choice of reference pure state, establishing core resource-theoretic requirements without the computational shortcut offered by the “grand sum” employed in the original formulation of state texture. By extending from single “resourceless” states to convex sets via a convex-roof construction, we recover single-qubit measures of known resource theories such as imaginarity and coherence. Finally, we introduce a family of “fixed-point resource theories” that includes fixed-point instances of the theories of state texture, genuine coherence, purity, and athermality. For these fixed-point resource theories we show that under free operations the fidelity-based lower bound is weakly monotonic, while specific violations of strong monotonicity are found for the convex-roof logarithmic measure.

Dissociative electron attachment to N-ethylacetamide is investigated using velocity map imaging with a tunable electron beam. Previously reported ion-yield spectra reveal two prominent resonant features near 5.5 and 8.8 eV across all observed anion channels. Surprisingly, no distinct structure is observed in the intermediate 6–7-eV energy region, where smaller amides typically exhibit an additional resonance associated with amide-bond cleavage. For N-ethylacetamide, the absence of a clear feature in this energy region indicates that any corresponding transient negative-ion state does not contribute significantly to dissociation. The momentum distributions obtained in the present work reveal distinct dissociation dynamics for different channels. The ${\mathrm{CH}}_3{}^{-}$ fragment at 5.5 eV exhibits an anisotropic distribution, indicating a direct dissociation process with finite kinetic-energy release. In contrast, the ${\mathrm{NH}}^{-}$ fragment at 8.8 eV shows an isotropic distribution with near-zero kinetic energy, which suggests a three-body dissociation process. These results demonstrate that the observed resonances correspond to qualitatively different dissociation mechanisms and suggest that the intermediate resonance, if present, does not drive efficient or direct fragmentation in N-ethylacetamide.

Relativistic effects have a profound impact on the electronic structure of the heaviest elements, and consequently on their chemical and physical properties. In order to investigate these effects, we developed an ion mobility spectrometer equipped with a cryogenic drift tube to measure the reduced mobilities of the ions of monoatomic lanthanides and actinides. As a benchmark, we conducted the first systematic study of lutetium cations (${\mathrm{Lu}}^{+}$) drifting in helium at 298 K, resolving ground and metastable electronic states using electronic state chromatography. We compared the state-specific mobilities with predictions based on state-of-the-art ab initio calculations, and they show very good agreement. Our work paves the way for atomic structure studies in the region of the superheavy elements and provides a powerful experimental approach for exploring ion-neutral interactions and electronic configuration effects in heavy element systems.

We present a purely theoretical, fully analytical momentum-space description of “superkick” momentum transfer to a two-level atom driven by a tightly focused, circularly polarized Laguerre-Gaussian vortex beam. Using the short-time excitation amplitude ${\psi }_e(\mathbf{r},t)\propto E_z\left(\mathbf{r}\right){\psi }_g\left(\mathbf{r}\right)$ and an exact Fourier-transform treatment in the near-focus regime, we derive closed-form expressions for the excited-state wave function ${\tilde{\psi }}_e\left(\mathbf{K}\right)$ and its momentum distribution $|{\tilde{\psi }}_e{\left(\mathbf{K}\right)|}^2$. This framework yields direct superkick diagnostics such as peak displacement and transverse-momentum moments, and enables a systematic comparison between opposite-handedness and same-handedness configurations, as well as a paraxial reference case. We show that tight focusing, through the longitudinal-field enhancement, strongly increases the near-axis excitation and makes superkick signatures most prominent in the opposite-handedness configuration, whereas the same-handedness and paraxial reference cases retain related transverse superkick structure but carry much smaller near-axis probability weight.

We provide a fully analytical derivation of Anderson's orthogonality catastrophe for the one dimensional Fermi polaron integrable model, describing a system of $N$ spin-up fermions, with fixed density $n=N/L$, interacting with a single spin-down fermion via an attractive contact potential. The proof combines the determinant representations of the norm of the many-body wave function and of its scalar product with the noninteracting ground state, obtained from the Bethe-ansatz solution, with the special properties of Cauchy matrices. We derive the leading asymptotics of the two determinants in the thermodynamic limit and show that the quasiparticle residue $Z$ decays algebraically, $Z=W{N}^{-\theta }$. We confirm that the Anderson exponent $\theta$ is equal to $2{\delta }_F^2/{\pi }^2$, where ${\delta }_F$ is the Bethe-ansatz phase shift at the Fermi edge. We also derive the asymptotic behavior of the prefactor $W$ at strong coupling and compare it against exact numerics.