Cross-platform verification, a critical undertaking in the realm of early-stage quantum computing, endeavors to characterize the similarity of two imperfect quantum devices executing identical algorithms, utilizing minimal measurements. While the random measurement approach has been instrumental in this context, the quasiexponential computational demand with increasing qubit count hurdles its feasibility in large-qubit scenarios. To bridge this knowledge gap, here we introduce an innovative multimodal learning approach, recognizing that the formalism of data in this task embodies two distinct modalities: measurement outcomes and classical description of compiled circuits on explored quantum devices, both containing unique information about the quantum devices. Building upon this insight, we devise a multimodal neural network to independently extract knowledge from these modalities, followed by a fusion operation to create a comprehensive data representation. The learned representation can effectively characterize the similarity between the explored quantum devices when executing new quantum algorithms not present in the training data. We evaluate our proposal on platforms featuring diverse noise models, encompassing system sizes up to 50 qubits. The achieved results demonstrate an improvement of 3 orders of magnitude in prediction accuracy compared to the random measurements and offer compelling evidence of the complementary roles played by each modality in cross-platform verification. These findings pave the way for harnessing the power of multimodal learning to overcome challenges in wider quantum system learning tasks.

Ionizing radiation interactions in matter can trigger a cascade of processes that underpin long-lived damage in the medium. To date, however, a lack of suitable methodologies has precluded our ability to understand the role that material nanostructure plays in this cascade. Here, we use transient photoabsorption to track the lifetime of free electrons (${\tau }_c$) in bulk and nanostructured ${\mathrm{SiO}}_2$ (aerogel) irradiated by picosecond-scale (${10}^{-12}\mathrm{s}$) bursts of x rays and protons from a laser-driven accelerator. Optical streaking reveals a sharp increase in ${\tau }_c$ from $<1\mathrm{ps}$ to $>50\mathrm{ps}$ over a narrow average density (${\rho }_{\mathrm{av}}$) range spanning the expected phonon-fracton crossover in aerogels. Numerical modeling suggests that this discontinuity can be understood by a quenching of rapid, phonon-assisted recovery in irradiated nanostructured ${\mathrm{SiO}}_2$. This is shown to lead to an extended period of enhanced energy density in the excited electron population. Overall, these results open a direct route to tracking how low-level processes in complex systems can underpin macroscopically observed phenomena and, importantly, the conditions that permit them to emerge.

Motivated by the recently reported signatures of superconductivity in trilayer ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ under pressure, we comprehensively study this system using ab initio and random-phase approximation techniques. Without electronic interactions, the Ni $d_{3z^2-r^2}$ orbitals show a bonding-antibonding and nonbonding splitting behavior via the O $p_z$ orbitals inducing a “trimer” lattice in ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, analogous to the dimers of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. The Fermi surface consists of three electron sheets with mixed $e_g$ orbitals, and a hole and an electron pocket made up of the $d_{3z^2-r^2}$ orbital, suggesting a Ni two-orbital minimum model. In addition, we find that superconducting pairing is induced in the $s^{\pm }$-wave channel due to partial nesting between the $\mathbf{M}=(\pi ,\pi )$ centered pockets and portions of the Fermi surface centered at the $\mathbf{\Gamma }=(0,0)$ point. With changing electronic density $n$, the $s^{\pm }$ instability remains leading and its pairing strength shows a domelike behavior with a maximum around $n=4.2$ ($\sim 6.7\%$ electron doping). The superconducting instability disappears at the same electronic density as that in the new 1313 stacking ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, correlated with the vanishing of the hole pocket that arises from the trilayer sublattice, suggesting that the high-$T_c$ superconductivity of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ does $not$ originate from a trilayer and monolayer structure. Furthermore, we confirm the experimentally proposed spin state in ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ with an in-plane ($\pi$, $\pi$) order and antiferromagnetic coupling between the top and bottom Ni layers, and spin zero in the middle layer.

Copper and boron seldom engage in reaction at ambient pressure. The few reports on copper-doped boron compounds that exist in the literature often lack definitive stoichiometry. Here, we report successful synthesis of ${\mathrm{Cu}}_{2-\delta }{\mathrm{B}}_{25}$ single crystals ($\delta \sim 0.03$, indicating Cu understoichiometry) via a high-pressure melting method using copper and $\beta$-rhombohedral boron as precursors. Crystals thus synthesized are characterized by a tetragonal boron sublattice, within which Cu atoms are either partially or fully situated at different interstices between ${\mathrm{B}}_{12}$ icosahedra. The crystals possess a high Vickers hardness of 26.5 GPa and an unusually high electrical conductivity of $1.19\times {10}^5\mathrm{S}/\mathrm{m}$—the highest conductivity among the icosahedron-based borides. Hall measurements reveal a notable $p\text{−}n$ conduction type transition around 30 GPa. This transition, alongside the remarkable conductivity, is potentially modulated by the copper content and its valence states within the structure. The synthesis of ${\mathrm{Cu}}_{2-\delta }{\mathrm{B}}_{25}$ not only broadens the spectrum of hard materials but also opens new avenues for innovative modulation of electronic properties in boron-rich compounds, with promising technological implications.

We present the first results from a proof-of-concept search for dark sectors via invisible decays of pseudoscalar $\eta$ and ${\eta }^{\prime }$ mesons in the NA64h experiment at the CERN SPS. Our novel technique uses the charge-exchange reaction of 50 GeV ${\pi }^{-}$ on nuclei of an active target as the source of neutral mesons. The $\eta ,{\eta }^{\prime }\to \text{invisible}$ events would exhibit themselves via a striking signature—the complete disappearance of the incoming beam energy in the detector. No evidence for such events has been found with $2.9\times {10}^9$ pions on target accumulated during one day of data taking. This allows us to set a stringent limit on the branching ratio $\mathrm{Br}({\eta }^{\prime }\to \text{invisible})<2.1\times {10}^{-4}$ improving the current bound by a factor of $\simeq 3$. We also set a limit on $\mathrm{Br}(\eta \to \text{invisible})<1.1\times {10}^{-4}$ comparable with the existing one. These results demonstrate the great potential of our approach and provide clear guidance on how to enhance and extend the sensitivity for dark sector physics from future searches for invisible neutral meson decays.

Two-dimensional coherent terahertz spectroscopy (2DCS) emerges as a valuable tool to probe the nature, couplings, and lifetimes of excitations in quantum materials. It thus promises to identify unique signatures of spin liquid states in quantum magnets by directly probing properties of their exotic fractionalized excitations. Here, we calculate the second-order 2DCS of the Kitaev honeycomb model and demonstrate that distinct spin liquid fingerprints appear already in this lowest-order nonlinear response ${\chi }_{yzx}^{(2)}({\omega }_1,{\omega }_2)$ when using crossed light polarizations. We further relate the off-diagonal 2DCS peaks to the localized nature of the matter Majorana excitations trapped by ${\mathbb{Z}}_2$ flux excitations and show that 2DCS thus directly probes the inverse participation ratio of Majorana wave functions. By providing experimentally observable features of spin liquid states in the 2D spectrum, our Letter can guide future 2DCS experiments on Kitaev magnets.

The unconventional superconductor ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ (critical temperature $T_{\mathrm{c}}\approx 0.4\mathrm{K}$) displays an exceptionally rare magnetic-field-induced transition between two distinct superconducting (SC) phases, proposed to be states of even and odd parity of the SC order parameter, which are enabled by a locally noncentrosymmetric structure. The superconductivity is preceded by a phase transition of unknown origin at $T_0=0.5\mathrm{K}$. Electronic low-temperature properties of ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ show pronounced non-Fermi-liquid behavior, indicative of a proximity to a quantum critical point (QCP). The role of quantum fluctuations and normal state orders for the superconductivity in a system with staggered Rashba interaction is currently an open question, pertinent to explaining the occurrence of the two-phase superconductivity. In this work, using measurements of resistivity and specific heat under hydrostatic pressure, we show that the $T_0$ order vanishes completely at a modest pressure of $P_0\approx 0.5\mathrm{GPa}$, revealing a QCP. In line with the quantum criticality picture, the linear temperature dependence of the resistivity at $P_0$ evolves into a Fermi-liquid quadratic dependence as quantum critical fluctuations are suppressed by increasing pressure. Furthermore, the domelike behavior of $T_{\mathrm{c}}$ around $P_0$ implies that the fluctuations of the $T_0$ order are involved in the SC pairing mechanism.

One of the main challenges in device-independent quantum key distribution (DIQKD) is achieving the required Bell violation over long distances, as the channel losses result in low overall detection efficiencies. Recent works have explored the concept of certifying nonlocal correlations over extended distances through the use of a local Bell test. Here, an additional quantum device is placed in close proximity to one party, using short-distance correlations to verify nonlocal behavior at long distances. However, existing works have either not resolved the question of DIQKD security against active attackers in this setup, or used methods that do not yield tight bounds on the key rates. In this work, we introduce a general formulation of the key rate computation task in this setup that can be combined with recently developed methods for analyzing standard DIQKD. Using this method, we show that if the short-distance devices exhibit sufficiently high detection efficiencies, positive key rates can be achieved in the long-distance branch with lower detection efficiencies as compared to standard DIQKD setups. This highlights the potential for improved performance of DIQKD over extended distances in scenarios where short-distance correlations are leveraged to validate quantum correlations.

We introduce the task of shadow process simulation, where the goal is to simulate the estimation of the expectation values of arbitrary quantum observables at the output of a target physical process. When the sender and receiver share random bits or other no-signaling resources, we show that the performance of shadow process simulation exceeds that of conventional process simulation protocols in a variety of scenarios including communication, noise simulation, and data compression. Remarkably, we find that there exist scenarios where shadow simulation provides increased statistical accuracy without any increase in the number of required samples.

We report results from an analysis aimed at detecting the trispectrum of the kinematic Sunyaev-Zel’dovich (kSZ) effect by combining data from the South Pole Telescope (SPT) and Herschel-SPIRE experiments over a $100{\mathrm{deg}}^2$ field. The SPT observations combine data from the previous and current surveys, namely SPTpol and SPT-3G, to achieve depths of 4.5, 3, and $16\mathrm{\mu }\mathrm{K}\text{−}\mathrm{arcmin}$ in bands centered at 95, 150, and 220 GHz. For SPIRE, we include data from the 600 and 857 GHz bands. We reconstruct the velocity-induced large-scale correlation of the small-scale kSZ signal with a quadratic estimator that uses two cosmic microwave background (CMB) temperature maps, constructed by optimally combining data from all the frequency bands. We reject the null hypothesis of a zero trispectrum at $10.3\sigma$ level. However, the measured trispectrum contains contributions from both the kSZ and other undesired components, such as CMB lensing and astrophysical foregrounds, with kSZ being sub-dominant. We use the agora simulations to estimate the expected signal from CMB lensing and astrophysical foregrounds. After accounting for the contributions from CMB lensing and foreground signals, we do not detect an excess kSZ-only trispectrum and use this nondetection to set constraints on reionization. By applying a prior based on observations of the Gunn-Peterson trough, we obtain an upper limit on the duration of reionization of $\mathrm{\Delta }{z}_{\mathrm{re},50}<4.5$ (95% confidence level). We find these constraints are fairly robust to foregrounds assumptions. This trispectrum measurement is independent of, but consistent with, Planck’s optical depth measurement. This result is the first constraint on the epoch of reionization using the non-Gaussian nature of the kSZ signal.

Previous works have argued that future gravitational-wave detectors will be able to probe the properties of astrophysical environments where binaries coalesce, including accretion disks, but also dark matter structures. Most analyses have resorted to a Newtonian modeling of the environmental effects, which are not suited to study extreme-mass-ratio inspirals immersed in structures of ultralight bosons. In this Letter, we use relativistic perturbation theory to consistently study these systems in spherical symmetry. We compute the flux of scalar particles and the rate at which orbital energy is dissipated via gravitational radiation and depletion of scalars, i.e., dynamical friction. Our results confirm that the Laser Interferometer Space Antenna will be able to probe ultralight dark matter structures by tracking the phase of extreme-mass-ratio inspirals.

We show that the planar, charged black hole in asymptotically anti–de Sitter spacetime, dual to the strongly coupled quark-gluon plasma thermal state of large $N$, $\mathrm{SU}(N)$, $\mathcal{N}=4$ super Yang-Mills at finite chemical potential undergoes a third-order phase transition in the grand canonical ensemble to a hairy black hole of type IIB supergravity. The hairy phase is another strongly coupled fluid with a conformal equation of state and can be interpreted as another kind of quark-gluon plasma. This new quark-gluon plasma has less entropy and, therefore, seems to characterize some form of smooth hadronization. The locus of the transition in terms of the critical values of the “baryon” chemical potential ${\mu }_c$ and the temperature $T_c$ is ${\mu }_c=2\pi T_c$.

Periodically driven systems have emerged as a useful technique to engineer the properties of quantum systems, and are in the process of being developed into a standard toolbox for quantum simulation. An outstanding challenge that leaves this toolbox incomplete is the manipulation of the states dressed by strong periodic drives. The state-of-the-art in Floquet control is the adiabatic change of parameters. Yet, this requires long protocols conflicting with the limited coherence times in experiments. To achieve fast control of nonequilibrium quantum matter, we generalize the notion of variational counterdiabatic driving away from equilibrium focusing on Floquet systems. We derive a nonperturbative variational principle to find local approximations to the adiabatic gauge potential for the effective Floquet Hamiltonian. It enables transitionless driving of Floquet eigenstates far away from the adiabatic regime. We discuss applications to two-level, Floquet band, and interacting periodically driven models. The developed technique allows us to capture nonperturbative photon resonances and obtain high-fidelity protocols that respect experimental limitations like the locality of the accessible control terms.

Divalent atoms provide excellent means for advancing control in Rydberg atom-based quantum simulation and computing due to the second optically active valence electron available. Particularly promising in this context are circular Rydberg atoms, for which long-lived ionic core excitations can be exploited without suffering from detrimental autoionization. Here, we report the implementation of electric quadrupole coupling between the metastable $4{\mathrm{D}}_{3/2}$ level and a very high-$n$ ($n=79$) circular Rydberg qubit, realized in doubly excited ${}^{88}\mathrm{Sr}$ atoms prepared from an optical tweezer array. We measure the kHz-scale differential level shift on the circular Rydberg qubit via beat-node Ramsey interferometry comprising spin echo. Observing this coupling requires coherent interrogation of the Rydberg states for more than $100\mathrm{\mu }\mathrm{s}$, which is assisted by tweezer trapping and circular state lifetime enhancement in a black-body radiation suppressing capacitor. Further, we find no noticeable loss of qubit coherence under continuous photon scattering on the ion core, paving the way for laser cooling and imaging of Rydberg atoms. Our results demonstrate access to weak electron-electron interactions in Rydberg atoms and expand the quantum simulation toolbox for optical control of highly excited circular state qubits via ionic core manipulation.

The polarization control of micro- and nanolasers is an important topic in nanophotonics. Up to now, the simultaneous generation of two distinguishable orthogonally polarized lasing modes from a single organic microlaser remains a critical challenge. Here, we demonstrate simultaneously orthogonally polarized dual lasing from a microcavity filled with an organic single crystal exhibiting selective strong coupling. We show that the non-Hermiticity due to polarization-dependent losses leads to the formation of real and imaginary Fermi arcs with exceptional points. Simultaneous orthogonally polarized lasing becomes possible thanks to the eigenstate mixing by the photonic spin-orbit coupling at the imaginary Fermi arcs. Our work provides a novel way to develop linearly polarized lasers and paves the way for the future fundamental research in topological photonics, non-Hermitian optics, and other fields.