Inverse Anderson localizations in lower dimensions predict that, as the hopping rates increase, all localized eigenmodes transition to extended states. Here, through the implementation of a mosaic quasiperiodic photonic waveguide lattice, we experimentally demonstrate a distinctive scenario, where the intermediate-energy eigenmodes become extended, while the low- or high-energy eigenmodes remain localized, leading to the emergence of energy-dependent Anderson localization transitions and mobility edge phases. Our experiment is enabled by developing an adiabatic procedure to prepare the photonic lattice into the zero-energy, lower and upper middle-energy, and ground and highest excited eigenmodes and subsequently measuring their localization properties. Moreover, we also experimentally investigate nonequilibrium quench dynamics for photons and show that photonic Loschmidt echoes can identify the appearance of mobility edge phases. Our study thus opens new avenues for investigating energy-dependent photonic Anderson localizations and harnessing photons to explore intriguing nonequilibrium physics.

We study a model of self-propelled particles interacting with their $k$ nearest neighbors through polar alignment. By exploring its phase space as a function of two nondimensional parameters (alignment strength $g$ and Péclet number Pe), we identify two distinct order-disorder transitions. One occurs at a low critical $g$ value independent of Pe, has no significant density-order coupling, and is consistent with the transition previously predicted by the mean-field approach. Up to the system sizes studied, it appears continuous. The other is discontinuous, depends on a combined control parameter involving Pe and $g$ that controls the alignment strength, and results from the formation of small, dense, highly persistent clusters of particles that follow metric-like dynamics. These dense clusters form at a critical value of the combined control parameter $\mathrm{Pe}/g^{\alpha }$, with $\alpha \approx 1.5$, which appears to be valid for different alignment-based models. Our study shows that models of active particles with metric-free interactions can produce characteristic length scales and self-organize into metric-like collective states that undergo metric-like transitions.

Quantum cryptographic conferencing (QCC) allows sharing secret keys among multiple distant users and plays a crucial role in quantum networks. Because of the fragility and low generation rate of genuine multipartite entangled states required in QCC, realizing and extending QCC with the entanglement-based protocol is challenging. Measurement-device-independent (MDI) QCC, which removes all detector side channels, is a feasible long-distance quantum communication scheme to practically generate multipartite correlation with multiphoton projection measurement. Here we experimentally realize the three-user MDI QCC protocol with four-intensity decoy-state method, in which we employ the polarization encoding and the Greenberger-Horne-Zeilinger state projection measurement. Our work demonstrates the experimental feasibility of the MDI QCC, which lays the foundation for the future realization of quantum networks with multipartite communication tasks.

We propose a novel approach using neural networks (NNs) to differentiate between cosmological models, and implemented lime as an interpretability approach to identify the key features influencing our model’s decisions. We show the potential of NNs to enhance the extraction of meaningful information from cosmological large-scale structure data, based on current galaxy-clustering survey specifications, for the cosmological constant and cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model and the Hu-Sawicki $f(R)$ model. We find that the NN can successfully distinguish between $\mathrm{\Lambda }\mathrm{C}\mathrm{D}\mathrm{M}$ and the $f(R)$ models, by predicting the correct model with approximately 97% overall accuracy, thus demonstrating that NNs can maximize the potential of current and next generation surveys to probe for deviations from general relativity.

The type IIB matrix model is a promising nonperturbative formulation of superstring theory, which may elucidate the emergence of ($3+1$)-dimensional space-time. However, the partition function is divergent due to the Lorentz symmetry, which is represented by a noncompact group. This divergence has been regularized conventionally by introducing some infrared cutoff, which breaks the Lorentz symmetry. Here we point out, in a simple model, that Lorentz-invariant observables become classical as one removes the infrared cutoff and that this “classicalization” is actually an artifact of the Lorentz symmetry breaking cutoff. In order to overcome this problem, we propose a natural way to “gauge-fix” the Lorentz symmetry in a fully nonperturbative manner. Thus, we arrive at a new definition of the type IIB matrix model, which also enables us to perform numerical simulations in such a way that the time evolution can be extracted from the generated configurations.

Fermionic atoms in a large-scale, homogeneous optical lattice provide an ideal quantum simulator for investigating the fermionic Hubbard model, yet achieving this remains challenging. Here, by developing a hybrid potential that integrates a flat-top optical lattice with an optical box trap, we successfully realize the creation of three-dimensional, homogeneous fermionic Hubbard gases across approximately $8\times {10}^5$ lattice sites. This homogeneous system enables us to capture a well-defined energy band occupation that aligns perfectly with the theoretical calculations for a zero-temperature, ideal fermionic Hubbard model. Furthermore, by employing novel radio-frequency spectroscopy, we precisely measure the doublon fraction $D$ as a function of interaction strength $U$ and temperature $T$, respectively. The crossover from metal to Mott insulator is detected, where $D$ smoothly decreases with increasing $U$. More importantly, we observe a nonmonotonic temperature dependence in $D$, revealing the Pomeranchuk effect and the development of extended antiferromagnetic correlations.

Biphotons and single photons with narrow bandwidths and long coherence times are essential to the realization of long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). In this Letter, we manipulate the biphoton wave functions of the spontaneous four-wave mixing in a two-level atomic ensemble with a single-laser pump scheme. Our innovative experimental approach enables the generation of biphotons with a sub-MHz bandwidth of 0.36 MHz, a record spectral brightness of $2.28\times {10}^7{\mathrm{s}}^{-1}{\mathrm{mW}}^{-1}{\mathrm{MHz}}^{-1}$, and a temporally symmetric wave packet at moderate optical depth. The strong nonclassical cross-correlation of the biphotons also enables the observation of heralded sub-MHz-linewidth single photons with a pronounced single-photon nature. The generation of sub-MHz-linewidth biphotons and single photons with a two-level atomic ensemble not only finds applications in quantum repeaters and large cluster states for LDQC and LOQC but also opens up the opportunity to miniaturize the biphoton or single-photon sources for chip-scale quantum technologies.

The ability to process and store information on surrounding nuclear spins is a major requirement for group-IV color center-based repeater nodes. We demonstrate coherent control of a ${}^{13}\mathrm{C}$ nuclear spin strongly coupled to a negatively charged germanium-vacancy center in diamond with coherence times beyond 2.5 s at mK temperatures, which is the longest reported for group-IV defects. Detailed analysis allows us to model the system’s dynamics, extract the coupling parameters, and characterize noise. We estimate an achievable memory time of 18.1 s with heating limitations considered, paving the way to successful applications as a quantum repeater node.

Smith-Purcell radiation (SPR) is an electromagnetic radiation generated by the motion of free electrons in close to a periodic structure. Over the past 70 years, there has been significant interest in the generation of light in three-dimensional (3D) free space through SPR. Here, by using the interaction between moving electrons and a designed metallic nanoaperture array, the observation of two-dimensional (2D) SPR, e.g., the plasmon polaritons propagating on metal surfaces, is presented. This phenomenon was confirmed using cathodoluminescence under grazing incidence, by decoupling 2D SPR with specially designed optical grating into far field. Moreover, by utilizing the phased array radar effect in 2D, the radiation direction of 2D SPR is demonstrated to be manipulated by rotating the aperture orientation. This work not only expands our understanding of SPR from the 3D to 2D, but also provides a practical approach for controlling the propagation of 2D SPR.

The emerging field of free-electron quantum optics enables electron-photon entanglement and holds the potential for generating nontrivial photon states for quantum information processing. Although recent experimental studies have entered the quantum regime, rapid theoretical developments predict that qualitatively unique phenomena only emerge beyond a certain interaction strength. It is thus pertinent to identify the maximal electron-photon interaction strength and the materials, geometries, and particle energies that enable one to approach it. We derive an upper limit to the quantum vacuum interaction strength between free electrons and single-mode photons, which illuminates the conditions for the strongest interaction. Crucially, we obtain an explicit energy selection recipe for electrons and photons to achieve maximal interaction at arbitrary separations and identify two optimal regimes favoring either fast or slow electrons over those with intermediate velocities. We validate the limit by analytical and numerical calculations on canonical geometries and provide near-optimal designs indicating the feasibility of strong quantum interactions. Our findings offer fundamental intuition for maximizing the quantum interaction between free electrons and photons and provide practical design rules for future experiments on electron-photon and electron-mediated photon-photon entanglement. They should also enable the evaluation of key metrics for applications such as the maximum power of free-electron radiation sources and the maximum acceleration gradient of dielectric laser accelerators.

The quantum interaction between free electrons and photons is fundamental to free-electron-based light sources and free-electron quantum optics applications. A large coupling between free electrons and photons is generally desired. In this Letter, I obtain the upper bound for the quantum coupling between free electrons and photons. The upper bound has a straightforward expression and can be applied to a broad range of optical materials, especially widely used low-loss photonic materials. The upper bound depends on the optical medium, the free-electron velocity, and the separation between the free electron and the optical medium. With simple structures, the numerically calculated coupling coefficient can reach $\sim 99\%$ of the upper bound. This study provides simple and practical guidance to reach the strong coupling between free electrons and photons.

We experimentally demonstrate the real-time detection and control of correlated charge tunneling in a dynamically driven quantum dot. Specifically, we measure the joint distribution of waiting times between tunneling charges and show that the waiting times for holes may be strongly correlated due to the periodic drive and the Coulomb interactions on the dot, although the electron waiting times are not. Our measurements are in excellent agreement with a theoretical model that allows us to develop a detailed understanding of the correlated tunneling events. We also demonstrate that the degree of correlations can be controlled by the drive. Our experiment paves the way for systematic real-time investigations of correlated electron transport in low-dimensional nanostructures.

Lattice deformations in graphene couple to the low-energy electronic degrees of freedom as effective scalar and gauge fields. Using molecular dynamics simulations, we show that the optical component of the displacement field, i.e., the relative motion of different sublattices, contributes at equal order as the acoustic component and effectively screens the pseudogauge fields. In particular, we consider twisted bilayer graphene and corrugated monolayer graphene. In both cases, optical lattice displacements significantly reduce the overall magnitude of the pseudomagnetic fields. For corrugated graphene, optical contributions also reshape the pseudomagnetic field and significantly modify the electronic bands near charge neutrality. Previous studies based on continuum elasticity, which ignores this effect, have therefore systematically overestimated the strength of the strain-induced pseudomagnetic field. Our results have important consequences for the interpretation of experiments and design of straintronic applications.

In the extreme quantum limit, when the Landau level filling factor $\nu <1$, the dominant electron-electron interaction in low-disorder two-dimensional electron systems leads to exotic many-body phases. The ground states at even-denominator $\nu =1/2$ and $1/4$ are typically Fermi seas of composite fermions carrying two and four flux quanta, surrounded by the Jain fractional quantum Hall states (FQHSs) at odd-denominator fillings $\nu =p/(2p\pm 1)$ and $\nu =p/(4p\pm 1)$, where $p$ is an integer. For $\nu <1/5$, an insulating behavior, which is generally believed to signal the formation of a pinned Wigner crystal, is seen. Our experiments on ultra-high-quality, dilute, GaAs two-dimensional electron systems reveal developing FQHSs at $\nu =p/(6p\pm 1)$ and $\nu =p/(8p\pm 1)$, manifested by magnetoresistance minima superimposed on the insulating background. In stark contrast to $\nu =1/2$ and $1/4$, however, we observe a pronounced, sharp minimum in magnetoresistance at $\nu =1/6$ and a somewhat weaker minimum at $\nu =1/8$, suggesting developing FQHSs, likely stabilized by the pairing of composite fermions that carry six and eight flux quanta. Our results signal the unexpected entry, in ultra-high-quality samples, of FQHSs at even-denominator fillings $1/6$ and $1/8$, which are likely to harbor non-Abelian anyon excitations.

We define and study a long-range version of the xx model, arising as the free-fermion point of the xxz-type Haldane-Shastry (HS) chain. It has a description via nonunitary fermions, based on the free-fermion Temperley-Lieb algebra, and may also be viewed as an alternating $\mathfrak{g}\mathfrak{l}(1|1)$ spin chain. Even and odd lengths behave very differently; we focus on odd length. The model is integrable, and we explicitly identify two commuting Hamiltonians. While nonunitary, their spectrum is real by PT symmetry. One Hamiltonian is chiral and quadratic in fermions, while the other is parity invariant and quartic. Their one-particle spectra have two linear branches, realizing a massless relativistic dispersion on the lattice. The appropriate fermionic modes arise from “quasi-translation” symmetry, which replaces ordinary translation symmetry. The model exhibits exclusion statistics, like the isotropic HS chain, with even more “extended symmetry” and larger degeneracies.

The doped Hubbard model is one of the paradigmatic platforms to engineer exotic quantum many-body states, including charge-ordered states, strange metals, and unconventional superconductors. While undoped and doped correlated phases have been experimentally realized in a variety of twisted van der Waals materials, experiments in monolayer materials, and in particular $1T$ transition metal dichalcogenides, have solely reached the conventional insulating undoped regime. Correlated phases in monolayer two-dimensional materials have much higher associated energy scales than their twisted counterparts, making doped correlated monolayers an attractive platform for high temperature correlated quantum matter. Here, we demonstrate the realization of a doped Mott phase in a van der Waals dichalcogenide $1T\text{−}{\mathrm{NbSe}}_2$ monolayer. The system is electron doped due to electron transfer from a monolayer van der Waals substrate via proximity, leading to a correlated triangular lattice with both half-filled and fully filled sites. We analyze the distribution of the half-filled and filled sites and show the arrangement is unlikely to be controlled by disorder alone, and we show that the presence of competing nonlocal many-body correlations would account for the charge correlations found experimentally. Our results establish $1T\text{−}{\mathrm{NbSe}}_2$ as a potential monolayer platform to explore correlated doped Mott physics in a frustrated lattice.

Modeling ion correlations in inhomogeneous polymers and soft matters with spatially varying ionic strength or dielectric permittivity remains a great challenge. Here, we develop a new theory that systematically incorporates electrostatic fluctuations into the self-consistent field theory for polymers. The theory is applied to polyelectrolyte brushes to explain abnormal phenomena observed in recent experiments. We show that ion correlations induce a nonmonotonic change of the brush height: collapse followed by reexpansion. The scaling analysis elucidates the origin as the competition between the repulsive osmotic pressure due to translational entropy and the attraction induced by ion correlations. We also clarify the absence of causal relationship between the brush collapse-reexpansion and the inversion of the surface electrostatic potential. Furthermore, strong ion correlations can trigger microphase separation, either in the lateral direction as pinned micelles or in the normal direction as oscillatory layers. Our theoretical predictions are in good agreement with the experimental results reported in the literature.

Understanding the structural dynamics of many-particle glassy systems remains a key challenge in statistical physics. Over the last decade, glassy dynamics has also been reported in biological tissues, but is far from being understood. It was recently shown that vertex models of dense biological tissue exhibit very atypical, sub-Arrhenius dynamics, and here we ask whether such atypical structural dynamics of vertex models are related to unusual elastic properties. It is known that at zero temperature these models have an elasticity controlled by their underconstrained or isostatic nature, but little is known about how their elasticity varies with temperature. To address this question we investigate the 2D Voronoi model and measure the temperature dependence of the intermediate-time plateau shear modulus and the bulk modulus. We find that unlike in conventional glass formers, these moduli increase monotonically with temperature until the system fluidizes. We further show that the structural relaxation time can be quantitatively linked to the plateau shear modulus $G_p$, i.e. $G_p$ modulates the typical energy barrier scale for cell rearrangements. This suggests that the anomalous, structural dynamics of the 2D Voronoi model originates in its unusual elastic properties. Based on our results, we hypothesize that underconstrained systems might more generally give rise to a new class of “ultrastrong” glass formers.

A search is presented for an extended Higgs sector with two new particles, $X$ and $\varphi$, in the process $X\to \varphi \varphi \to (\gamma \gamma )(\gamma \gamma )$. Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected with the CMS detector, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. No evidence of such resonances is seen. Upper limits are set on the production cross section for $m_X$ between 300 and 3000 GeV and $m_{\varphi }/m_X$ between 0.5% and 2.5%, representing the most sensitive search in this channel.