We study synthetic temporal networks whose evolution is determined by stochastically evolving node variables—synthetic analogues of, e.g., temporal proximity networks of mobile agents. We quantify the long-timescale correlations of these evolving networks by an autocorrelative measure of network-structural memory. Several distinct patterns of autocorrelation arise, including power-law decay and exponential decay, depending on the choice of node-variable dynamics and connection probability function. Our methods are also applicable in wider contexts; our temporal network models are tractable mathematically and in simulation, and our long-term memory quantification is analytically tractable and straightforwardly computable from temporal network data.

Variational quantum algorithms are gaining attention as an early application of noisy intermediate-scale quantum (NISQ) devices. One of the main problems of variational methods lies in the phenomenon of barren plateaus, present in the optimization of variational parameters. Adding geometric inductive bias to the quantum models has been proposed as a potential solution to mitigate this problem, leading to a new field called geometric quantum machine learning. In this work, an equivariant architecture for variational quantum classifiers is introduced to create a label-invariant model for image classification with $C_4$ rotational label symmetry. The equivariant circuit is benchmarked against two different architectures, and it is experimentally observed that the geometric approach boosts the model's performance. Finally, a classical equivariant convolution operation is proposed to extend the quantum model for the processing of larger images, employing the resources available in NISQ devices.

We consider a prototypical problem of Bayesian inference for a structured spiked model: a low-rank signal is corrupted by additive noise. While both information-theoretic and algorithmic limits are well understood when the noise is a Gaussian Wigner matrix, the more realistic case of structured noise still remains challenging. To capture the structure while maintaining mathematical tractability, a line of work has focused on rotationally invariant noise. However, existing studies either provide suboptimal algorithms or are limited to a special class of noise ensembles. In this paper, using tools from statistical physics (replica method) and random matrix theory (generalized spherical integrals) we establish the characterization of the information-theoretic limits for a noise matrix drawn from a general trace ensemble. Remarkably, our analysis unveils the asymptotic equivalence between the rotationally invariant model and a surrogate Gaussian one. Finally, we show how to saturate the predicted statistical limits using an efficient algorithm inspired by the theory of adaptive Thouless-Anderson-Palmer (TAP) equations.

With the realization of controlled quantum systems, exploring excitations beyond the resonant case opens new possibilities. We investigate an extended Jaynes-Cummings model in which two nondegenerate photon modes are coupled off resonantly to a quantum emitter. This allows us to identify few-photon scattering mechanisms that lead to a full inversion of the emitter while transferring off-resonant photons from one mode to another. This behavior is connected to recent measurements of a two-level emitter scattering two off-resonant photons simultaneously. Furthermore, our results can be understood as a quantized analog of the recently developed off-resonant quantum control scheme known as swing-up of quantum emitter (SUPER). Our intuitive formalism gives deeper insight into the interaction of a two-level emitter with off-resonant light modes with the prospect of novel photonic applications.

The nonlinear Schrödinger equation (NLSE) in one spatial dimension has stationary solutions similar to those of the linear Schrödinger equation (LSE) as well as more exotic solutions such as solitary waves and quantum droplets. Here, we present a newly discovered conformal duality which unifies the stationary and time-dependent traveling-wave solutions of the one-dimensional cubic-quintic NLSE, the cubic NLSE and LSE. Any two systems that are classified by the same single number called the cross ratio are related by this symmetry. Notably, the conformal duality can also be adapted in Newtonian mechanics and serves as a powerful tool for investigating physical systems that otherwise cannot be directly accessed in experiments. Further, we show that the conformal symmetry is a valuable resource to substantially improve NLSE parameter estimation from noisy empirical data by introducing an optimization afterburner. The new method therefore has far reaching practical applications for nonlinear physical systems.

The thermodynamic behavior of Markovian open quantum systems can be described at the level of fluctuations by using continuous monitoring approaches. However, practical applications require assessing imperfect detection schemes, where the definition of main thermodynamic quantities becomes subtle and universal fluctuation relations are unknown. Here, we fill this gap by deriving a universal fluctuation relation that links thermodynamic entropy production and information-theoretical irreversibility along single trajectories in inefficient monitoring setups. This relation provides as a corollary an irreversibility estimator of dissipation using imperfect detection records that lower bounds the underlying entropy production at the level of visible trajectories. We illustrate our findings with a driven-dissipative two-level system following quantum jump trajectories and discuss the experimental applicability of our results for thermodynamic inference.

Numerous biological and microscale systems exhibit synchronization in noisy environments. The theory of such noisy oscillators and their synchronization has been developed and experimentally demonstrated, but inferring the noise intensity and phase response is not always straightforward. In this paper, we propose a useful formula that enables us to infer the noise intensity and phase response of a noisy oscillator synchronized with periodic external forcing. Through asymptotic approximations for small noise, we show that noisy synchronous oscillators satisfy a simple relationship among the noise intensity and measurable quantities, i.e., the stationary distribution of the oscillation phase and stationary probability current obtained as the average phase velocity, which is verified through systematic numerical analysis. The proposed formula facilitates a unified analysis and design of synchronous oscillators in weakly noisy environments.

Ferrite-free circulators that are passive and readily integratable on a chip are highly sought-after in quantum technologies based on superconducting circuits. In our previous work, we implemented such a circulator using a three-Josephson-junction loop that exhibited unambiguous nonreciprocity and signal circulation, but required junction energies to be within $1\%$ of design values. This tolerance is tighter than standard junction fabrication methods provide, so we propose and demonstrate a design improvement that relaxes the required junction fabrication precision, allowing for higher device performance and fabrication yield. Specifically, we introduce large direct capacitive couplings between the waveguides, which based on the modeling we describe here, requires less stringent junction fabrication tolerance. We implement the design, and measure enhanced “circulation fidelity” above $97\%$, with optimized on-resonance insertion loss of 0.2 dB, isolation of 18 dB, and power reflectance of $-15\mathrm{dB}$, in good agreement with model calculations.

The synthesis of heavy elements in supernovae is affected by low-energy $(n,p)$ and $(p,n)$ reactions on unstable nuclei, yet experimental data on such reaction rates are scarce. The SECAR (SEparator for CApture Reactions) recoil separator at FRIB (Facility for Rare Isotope Beams) was originally designed to measure astrophysical reactions that change the mass of a nucleus significantly. We used a novel approach that integrates machine learning with ion-optical simulations to find an ion-optical solution for the separator that enables the measurement of $(p,n)$ reactions, despite the reaction leaving the mass of the nucleus nearly unchanged. A new measurement of the ${}^{58}\mathrm{Fe}(p,n){}^{58}\mathrm{Co}$ reaction in inverse kinematics with a $3.66\pm 0.12$ MeV/nucleon ${}^{58}\mathrm{Fe}$ beam (corresponding to $3.69\pm 0.12$ MeV proton energy in normal kinematics) yielded a cross-section of $20.3\pm 6.3$ mb and served as a proof of principle experiment for the new technique demonstrating its effectiveness in achieving the required performance criteria. This novel approach paves the way for studying astrophysically important $(p,n)$ reactions on unstable nuclei produced at FRIB.

Coupling a system to two different baths can lead to novel phenomena escaping the constraints of thermal equilibrium. In quantum materials inside optical cavities, this feature can be exploited as electrons and cavity photons are easily pulled away from their mutual equilibrium, even in the steady state. This offers new routes for a noninvasive control of material properties and functionalities. We show that the absence of thermal equilibrium between electrons and photons leads to reduced symmetries of the steady-state electronic distribution function. Moreover, by defining an effective temperature from the on-shell distribution function, we find a nonmonotonic behavior as a function of cavity frequency, consistent with recent experimental findings. Finally, we show that, the nonthermal behavior leads to qualitative modifications of the materials properties, as the standard Sommerfeld expansion for observables is modified by a leading-order correction linearly proportional to the temperature difference between the two baths and to the frequency derivative of the electron damping.

We develop a semiempirical model to describe the creation of an electron plasma in matter at extreme conditions, as excited by high-intensity, extreme ultraviolet (EUV) or x-ray radiation pulses currently available at free-electron laser (FEL) facilities. In typical FEL experiments, EUV and x-ray pulses are used to investigate highly excited states of matter produced by optical pump pulses. The pump pulses, promoting electrons from delocalized valence band states, excite the system often through multiphoton absorption processes and/or shock wave propagation. Instead, the use of FEL radiation as a pump allows triggering electron transitions from bound, core states to nearly free levels above the Fermi energy, promptly generating a highly excited state, toward the warm dense matter regime. We model such an excitation process starting from the optical properties of the analyzed materials and first-principle considerations, with the aim of motivating further studies in this scheme. We apply our model to predict the differences in the plasma creation process in insulators and metals, at varying exciting pulse wavelength and fluence, and we interpret the results in terms of the different nature of the investigated systems. Furthermore, we explore the effect of the finite core hole lifetime on the plasma formation and relaxation dynamics. We show the model is suited for the interpretation of real experimental data obtained from a prototypical insulating crystal (LiF) in a EUV FEL pump–optical transmission probe experiment.

We propose a laboratory accelerated test method for study of the atmospheric neutron radiation effects by using a compact laser-driven spallation neutron source (LDSNS). The LDSNS is obtained by injecting a GeV quasimonoenergetic proton beam accelerated by light-sail (LS) radiation pressure of intense lasers into a lead target. According to the LS scaling law, proton energy spectra can be regulated by adjusting the laser and foil target parameters, so that the neutron spectra at various atmospheric altitudes are well reproduced. Integrated PIC and MC simulations have verified the scheme (for that at altitude 12 km, laser intensity of ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ is required) and shown that the neutron fluence per laser shot is as high as $1.73\times {10}^8\mathrm{n}/{\mathrm{cm}}^2$, equivalent to 3.7 year flux accumulation in atmosphere. Using the G4SEE toolkit, we estimate that the HM628128 SRAM may undergo an average of ten single event upsets per shot for the proposed laboratory test.

We study the statistical physics of the classical Ising model in the so-called $\alpha$-Rényi ensemble, a finite-temperature thermal state approximation that minimizes a modified free energy based on the $\alpha$-Rényi entropy. We begin by characterizing its critical behavior in mean-field theory in different regimes of the Rényi index $\alpha$. Next, we re-introduce correlations and consider the model in one and two dimensions, presenting analytical arguments for the former and devising a Monte Carlo approach to the study of the latter. Remarkably, we find that while mean-field predicts a continuous phase transition below a threshold index value of $\alpha \sim 1.303$ and a first-order transition above it, the Monte Carlo results in two dimensions point to a continuous transition at all $\alpha$. We conclude by performing a variational minimization of the $\alpha$-Rényi free energy using a recurrent neural network (RNN) Ansatz where we find that the RNN performs well in two dimensions when compared to the Monte Carlo simulations. Our work highlights the potential opportunities and limitations associated with the use of the $\alpha$-Rényi ensemble formalism in probing the thermodynamic equilibrium properties of classical and quantum systems.

We introduce a device-independent two-prover scheme in which a classical verifier can use a simple untrusted quantum measurement device (the client device) to securely delegate a quantum computation to an untrusted quantum server. To do this, we construct a parallel self-testing protocol to perform device-independent remote state preparation of $n$ qubits and compose this with the unconditionally secure universal verifiable blind quantum computation (VBQC) scheme of Fitzsimons and Kashefi [Phys. Rev. A 96, 012303 (2017)]. Our self-test achieves a multitude of desirable properties for the application we consider, giving rise to practical and fully device-independent VBQC. It certifies parallel measurements of all cardinal and intercardinal directions in the $XY$ plane as well as the computational basis, uses few input questions (of size logarithmic in $n$ for the client and a constant number communicated to the server) and requires only single-qubit measurements to be performed by the client device.