Topological edge states in systems of two (or more) dimensions offer scattering-free transport, exhibiting robustness to inhomogeneities and disorder. In a different domain, time-modulated systems, such as photonic time crystals, offer nonresonant amplification drawing energy from the modulation. Combining these concepts, we explore topological systems that vary periodically in both time and space, manifesting the best of both worlds. We present topological phases and topological edge states in photonic space-time crystals—materials in which the refractive index varies periodically in both space and time, displaying band gaps in both frequency and momentum. The topological nature of this system leads to topological invariants that govern the phase between refracted and reflected waves generated from both the spatial and the temporal interfaces. The 2D (1D space + 1D time) nature of this system leads to propagating edge states, and a unique edge state that grows exponentially in amplitude while following the space-time edge.

Several physical variables and fluid systems exhibit memory effects arising from their internal dynamics and interactions with external forcings. Various existing techniques are either complex or face limitations due to the usual nonlinear nature of the time series, typically overestimating memory timescales. We overcome this by considering a nonparametric, model-free framework grounded in information theory, with methodological modifications to estimate memory timescales. We show that there is a good agreement between the estimated memory and the known Markov order of some synthetic time series. Leveraging this method, we analyzed observational and reanalysis datasets of soil moisture (SM) time series over India’s core monsoon zone and quantified SM memory. Results indicate that SM behaves as a finitary, higher order Markov process, revealing a memory timescale of $\sim 35\mathrm{days}$ on core monsoon zone. The proposed treatment offers methodological simplicity and generalization beyond conventional linear approaches for analyzing stationary time series.

High-order harmonic generation by the diffraction of an intense Laguerre-Gaussian (LG) laser beam through a small aperture is studied. It is found that the 2D peripheral electron dynamics at the boundary of the diffraction aperture can facilitate complex interplay between the spin and orbital angular momentum interaction, which leads to distinct selection rules for LG pulses with different polarization states. In particular, when the driver is linearly polarized, each harmonic beam contains multiple LG modes with different topological charges. The number of modes equals to the harmonic order and the total angular momentum is conserved during this process. A theory is derived and validated by simulations, which can predict the harmonic topological charges as well as their relative intensities for LG drivers with different polarization states. Our Letter provides fundamental insight into the behavior of light in nonlinear optics and paves the way toward high-intensity UV or x-ray pulses carrying controllable orbital angular momentum that can serve as versatile tools at frontiers of various scientific fields.

Motivated by recent experimental realization of a Bose-Einstein condensate (BEC) of dipolar molecules, we develop superfluid transport theory for a dissipative BEC to show that a weak uniform two-body loss can induce phase rigidity, leading to superfluid transport of bosons without repulsive interactions. A generalized $f$-sum rule is shown to hold for a dissipative superfluid as a consequence of weak U(1) symmetry. We also demonstrate that dissipation enhances the stability of a molecular BEC with dipolar interactions. Possible experimental signatures of dissipative superfluidity are discussed.

Quantization of particle transport lies at the heart of topological physics. In Thouless pumps—dimensionally reduced versions of the integer quantum Hall effect—quantization is dictated by the integer winding of single-band Wannier states. Here, we show that repulsive interactions can drive a transition from an integer- to a fractional-quantized Thouless pump (at fixed integer filling) by stabilizing a crystal of multiband Wannier states, each with fractional winding. We numerically illustrate the concept in few-particle systems and show that a dynamical Hartree-Fock ansatz can quantitatively reproduce the pumping phase diagram.

Building on recent advancements in altermagnetism, we develop a highly frustrated magnetic model with Kitaev-like interactions that integrates key aspects of both quantum spin liquids and altermagnets. While the ground state is a gapless quantum spin liquid, our analysis indicates that an altermagnetic local order emerges upon the introduction of additional interactions that gap the excitation spectrum and give rise to a ${\mathbb{Z}}_2$ topological order. This magnetically fragmented topological altermagnet has fractionalized fermionic excitations with momentum-dependent splitting, in stark contrast to both standard altermagnets and Kitaev spin liquids. In addition, we discover two more altermagnetic phases, including a pseudoaltermagnet that exhibits splitting in the absence of a local order and a half-altermagnet that possesses only one type of fractionalized excitation, similar to a half-metal. We discuss experimental approaches for detecting these phases, including layer-dependent spin and heat transport. Our results highlight the rich physics that can arise due to the interplay between altermagnetism and fractionalized excitations in quantum magnets.

Spatial nonhomogeneities can synchronize clusters of spatially extended oscillators in different frequency plateaus. Motivated by physiological rhythms, we fully characterize the phase diagram of a Ginzburg-Landau (GL) model with a gradient of frequencies. For large gradients and diffusion, the rest state is stable, and the linear spectrum around it maps onto the non-Hermitian Bloch-Torrey equation. When complex pairs of eigenvalues turn unstable, precursors of plateaus grow, separated by defects where the GL amplitude vanishes. Nonlinear effects either saturate the amplitude of plateaus or lead to a phase-locked state, with saddle-node bifurcations separating the two regimes. In the region of plateaus, we trace the formation of defects to a nonlinear renormalization of the diffusivity, and determine the scaling of their number and length vs dynamical parameters.

We prove the invariance of scalar Feynman graphs of any planar topology under the Yangian level-one momentum symmetry given certain constraints on the propagator powers. The proof relies on relating this symmetry to a planarized version of the conformal simplices of Bzowski, McFadden, and Skenderis. In particular, this proves a momentum-space analogue of the position-space conformal condition on propagator powers. When combined with the latter, the invariance under the level-one momentum implies full Yangian symmetry of the considered graphs. These include all scalar Feynman integrals for which a Yangian symmetry was previously demonstrated at the level of examples, e.g., the fishnet or loom graphs, as well as generalizations to graphs with massive propagators.

The overlaps between integrable matrix product states (MPSs) and Bethe states are important in both the nonequilibrium statistical physics and the AdS/CFT duality. We present the general MPS overlap formula. The result is a product of a ratio of Gaudin determinants and a prefactor. The Gaudin determinants depend on the spin chain but not on the MPS. The MPS dependent prefactor is given for all integrable MPSs of the ${\mathfrak{gl}}_N$, ${\mathfrak{o}}_N$, and ${\mathfrak{sp}}_N$ symmetric spin chains with arbitrary representations.

Slow relaxation processes spanning widely separated timescales pose fundamental challenges for probing steady-state properties and engineering functional quantum systems, such as quantum heat engines and quantum computing devices. We introduce a protocol that enables significant acceleration of relaxation in general Markovian open quantum systems by temporarily coupling the system to a reset channel, inspired by the Mpemba effect. Crucially, this acceleration persists even when the slowest decaying Lindbladian modes form complex-conjugate pairs. Unlike previous approaches, which typically target a single mode, our protocol may suppress multiple relaxation modes simultaneously. This framework provides a versatile and experimentally feasible tool for controlling relaxation timescales, with broad implications for quantum thermodynamics, computation, and state preparation.

The Hadamard test is one of the pillars on which quantum algorithm development rests and, at the same time, is naturally suited for the intermediate regime between the current era of noisy quantum devices and complete fault tolerance. Its applications use measurements of the auxiliary qubit to extract information but disregard the system register completely. Concomitantly, but independently of this development, advances in quantum learning theory have enabled the efficient representation of quantum states via classical shadows. This Letter shows that, strikingly, putting both lines of thought into a new context results in substantial improvements to the Hadamard test on a single auxiliary readout qubit, by suitably exploiting classical shadows on the remaining $n$-qubit work register. We argue that this combination inherits the best of both worlds and discuss statistical phase estimation as a vignette application. At the same time, the framework is more general and applicable to a wide range of other algorithms. There, we can use the Hadamard test to estimate energies on the auxiliary qubit, while classical shadows on the system register provide access to additional features such as (i) the fidelity of the initial state with certain pure quantum states, (ii) the initial state’s energy, and (iii) how pure and how close the initial state is to an eigenstate of the Hamiltonian. Finally, we also discuss how anticontrolled unitaries can further augment this framework and explain how this Letter settles the exploitation of the Hadamard test for intermediate applications.

A search for the rare decay $D^0\to {\mu }^{+}{\mu }^{-}$ is reported using proton-proton collision events at $\sqrt{s}=13.6\mathrm{TeV}$ collected by the CMS detector in 2022–2023, corresponding to an integrated luminosity of $64.5{\mathrm{fb}}^{-1}$. This is the first analysis to use a newly developed inclusive dimuon trigger, expanding the scope of the CMS flavor physics program. The search uses $D^0$ mesons obtained from $D^{*+}\to D^0{\pi }^{+}$ decays. No significant excess is observed. A limit on the branching fraction of $\mathcal{B}(D^0\to {\mu }^{+}{\mu }^{-})<2.4\times {10}^{-9}$ at 95% confidence level is set. This is the most stringent upper limit set on any flavor changing neutral current decay in the charm sector.

A search for an invisible particle, $X$, with a mass between 0 and $0.96\mathrm{GeV}/c^2$, is performed in the process $J/\psi \to \varphi +X$ using $(8774.0\pm 39.4)\times {10}^{6}J/\psi$ events collected with the BESIII detector from 2017 to 2019. The $\varphi$ meson is fully reconstructed and an efficient veto of photons and neutral and charged hadrons up to twice the $K_L^0$ mass is applied to the rest of the event and the recoil mass against the $\varphi$ is obtained precisely from the kinematic constraint in the event. No significant signal over the expected background is observed in the investigated region and the upper limit on the inclusive branch fraction of $J/\psi \to \varphi +X$ is determined to be $7.0\times {10}^{-8}$ at 90% confidence level. Upper limits at a 90% confidence level are also given for this branch fraction as a function of the invisible particle mass, varying from $4\times {10}^{-9}$ to $4\times {10}^{-8}$ over the investigated mass range. Additionally, a 90% confidence level upper limit on the branch fraction of $\eta \to \text{invisible}$ is determined to $2.4\times {10}^{-5}$, which improves the previous best results by more than 4 times. The analysis technique in this Letter offers a clean window to search for sub-GeV invisible particles, which can be adapted for other $J/\psi$ decays and direct $e^{+}{e}^{-}$ annihilation experiments in future studies, and improve the sensitivity by orders of magnitude.

We investigate the dissociation dynamics of hydrogen molecular ions driven by nonclassical light by solving the time-dependent Schrödinger equation. The driving field is composed of horizontally polarized 400 nm coherent light and vertically polarized 800 nm quantum squeezed light. Our results reveal that the photon quantum fluctuations encoded in the squeezing parameter influence the kinetic energy release spectra and modulate the relative yields of competing dissociation channels. In particular, the photon-number statistics and phase uncertainty introduced by the quadrature-squeezed light can selectively enhance or suppress specific dissociation pathways. These findings highlight the potential of quantum light as a tunable resource for manipulating and probing the molecular dynamics. This Letter has implications on ultrafast chemistry with quantum light.

Optomechanical systems subjected to environmental noise give rise to rich physical phenomena. We investigate entanglement between a mechanical oscillator and the reflected coherent optical field in a general, not necessarily Markovian environment. For the input optical field, we consider stationary Gaussian states and frequency-dependent squeezing. We demonstrate that for a coherent laser drive, either unsqueezed or squeezed in a frequency-independent manner, optomechanical entanglement is destroyed after a threshold that depends only on the environmental noises—independent of the coherent coupling between the oscillator and the optical field, or the squeeze factor. In this way, we have found a universal entangling-disentangling transition. We also show that for a configuration in which the oscillator and the reflected field are separable, entanglement cannot be generated by incorporating frequency-dependent squeezing in the optical field.

The manipulation of visible and near-infrared light at the single-photon level plays a key role in quantum communication systems where information is encoded into photonic degrees of freedom. In practical implementations, it is important to achieve this manipulation with high speeds, low loss, and low noise. In this Letter, we propose the use of terahertz electric fields as a pump source for electro-optic modulation of single photons in bulk media. We demonstrate spectral modulations of single photons in the form of frequency translation and bandwidth manipulations as the terahertz field imparts linear and quadratic phases on the photons at various time delays within 1 ps. Our results show frequency translations exceeding 500 GHz at multi-THz modulation speeds and loss levels of $\approx 1\mathrm{dB}$, complementing the current state-of-the-art electro-optic modulation techniques limited to speeds up to 100 GHz. The proposed approach leverages recent developments in terahertz generation techniques, introducing new avenues to manipulate nonclassical light in an unexplored regime for quantum photonics.

We demonstrate the parametric modulation of a double quantum dot charge dipole coupled to a cavity, at the cavity frequency, achieving an amplified readout signal compared to conventional dispersive protocols. Our findings show that the observed cavity field displacement originates from dipole radiation within the cavity, rather than from a longitudinal coupling mechanism, yet exhibits the same signatures while relying on a transverse coupling. By carefully tuning the phase and amplitude of the intracavity field, we achieve a $\pi$-phase shift between two dipole states, resulting in a substantial enhancement of the signal-to-noise ratio. In addition to its applications in quantum dot based qubits in circuit QED architectures, this protocol could serve as a new promising tool for probing exotic electronic states in mesoscopic circuits embedded in cavities.

Strongly correlated photons play a crucial role in modern quantum technologies. Here, we investigate the probability of generating strongly correlated photons in a chain of $N$ qubits coupled to a one-dimensional waveguide. We found that disorder in the transition frequencies can induce photon antibunching and especially nearly perfect photon blockade events in the transmission and reflection outputs. As a comparison, in ordered chains, strongly correlated photons cannot be generated in the transmission output, and only weakly antibunched photons are found in the reflection output. The occurrence of nearly perfect photon blockade events stems from the disorder-induced nearly completely destructive interference of photon scattering paths. Our Letter highlights the impact of disorder on photon correlation generation and suggests that disorder can enhance the potential for achieving strongly correlated photons.

Low-energy electrons, with their large scattering cross sections and exceptional sensitivity to electric fields, have attracted considerable attention for probing ultrafast surface structural and electronic dynamics, particularly through techniques such as low-energy electron diffraction and imaging. However, the significant dispersion of low-energy electron pulses during transport poses a critical challenge to achieving high temporal resolution in time-resolved experiments. In this Letter, we present an at-the-source compression method for low-energy electron pulses using terahertz surface waves on a micrometer-sized tip cathode. Simultaneous electron acceleration and compression have been achieved directly at the emitter surface within a few tens of micrometers. A low-energy (1.5 keV) electron beam with near femtocoulomb charge is temporally compressed by a factor of 3.5, producing 74-femtosecond (FWHM) electron bunches. The quality of the compressed electron bunches is validated through high-quality diffraction patterns of few-layer graphene and projection imaging of a copper mesh. Furthermore, the compressed electrons are applied to investigate the transient electric field propagation generated by photoexcited charged particles on metal surfaces, demonstrating the enhanced temporal resolution. This advancement presents the most compact solution for an electron gun that integrates electron generation, acceleration, and compression into a unified system, paving the way for investigating surface dynamics and complex material phenomena with unprecedented precision.