Despite recent advances in quantum repeater networks, entanglement distribution on a continental scale remains prohibitively difficult and resource intensive. Using satellites to distribute maximally entangled photons (Bell pairs) between distant stations is an intriguing alternative. Quantum satellite networks are known to be viable for quantum key distribution, but the question of if such a network is feasible for fault tolerant distributed quantum computation (FTDQC) has so far been unaddressed. In this paper we determine a closed form expression for the rate at which logical Bell pairs can be produced between distant surface code encoded qubits using a satellite network to supply imperfect physical Bell pairs. With generous parameter assumptions, our results show that FTDQC with satellite networks over statewide distances (500–999 km) is possible up to a collective clock rate on the order of 1 MHz, while continental (1000–4999 km) and transcontinental ($5000+$ km) distances run on the order of 10 kHz and 100 Hz, respectively.

The notion of scale-invariant dynamics is well established at late times in quantum chaotic systems, as illustrated by the emergence of a ramp in the spectral form factor (SFF). Building on the results of the preceding Letter [Phys. Rev. Lett. 131, 060404 (2023)], we explore features of scale-invariant dynamics of survival probability and SFF at criticality, i.e., at eigenstate transitions from quantum chaos to localization. We show that, in contrast to the quantum chaotic regime, the quantum dynamics at criticality do not only exhibit scale invariance at late times, but also at much shorter times that we refer to as mid-time dynamics. Our results apply to both quadratic and interacting models. Specifically, we study Anderson models in dimensions three to five and power-law random banded matrices for the former, and the quantum sun model and the ultrametric model for the latter, as well as the Rosenzweig-Porter model.

Atomic interferometers measure forces and acceleration with exceptional precision. The conventional approach to atomic interferometry is to launch an atomic cloud into a ballistic trajectory and perform the wave-packet splitting in momentum space by Raman transitions. This places severe constraints on the possible atomic trajectory, positioning accuracy, and probing duration. Here, we propose and analyze an alternative atomic interferometer that uses micro-optical traps (optical tweezers) to manipulate and control the motion of atoms. This interferometer allows long probing time, submicrometer positioning accuracy, and utmost flexibility in the shaping of the atomic trajectory. The cornerstone of the tweezer interferometer consists of the coherent atomic splitting and combining schemes. We present two adiabatic schemes with two or three tweezers that are robust in the presence of experimental imperfections and work simultaneously with many vibrational states. The latter property allows for multiatom interferometry in a single run. We also highlight the advantage of using fermionic atoms to obtain single-atom occupation of vibrational states and to eliminate mean-field shifts. We examine the impact of tweezer intensity noise and demonstrate that, when constrained by shot noise, the interferometer can achieve a relative accuracy better than ${10}^{-11}$ in measuring Earth's gravitational acceleration. The submicrometer resolution and extended measurement duration offer promising opportunities for exploring fundamental physical laws in new regimes. We discuss two applications well suited for the unique capabilities of the tweezer interferometer: the measurement of gravitational forces and the study of Casimir-Polder forces between atoms and surfaces. Crucially, our proposed tweezer interferometer is within the reach of current technological capabilities.

Branched flow governs the transition from ballistic to diffusive motion of waves and conservative particle flows in spatially correlated random or complex environments. It occurs in many physical systems from micrometer to interstellar scales. In living matter systems, however, this transport regime is usually suppressed by dissipation and noise. In this article, we demonstrate that, nonetheless, noisy active random walks, characterizing many living systems such as foraging animals and chemotactic bacteria, can show a regime of branched flow. To this end we model the dynamics of trail-forming ants, and we use it to derive a scaling theory of branched flows in active random walks in random bias fields in the presence of noise. We also show how trail patterns, formed by the interaction of ants by depositing pheromones along their trajectories, can be understood as a consequence of branched flow.

Subcontinuum gas conduction is an essentially important phenomenon in disparate fields of applications ranging from aerospace vehicles to biomedical sensors, and has been the focus of many computational studies over the past decades. These studies predicted that the energy exchange mechanisms are driven by gas-surface interactions, strongly dependent on the gas and surface characteristics. Despite its fundamental and practical importance, thermal transport via gas conduction at noncontinuum regimes mostly remains experimentally unverified. Here, we report precision measurements of subcontinuum gas conduction within parallel microcavities and elucidate its dependence on the gas and surface characteristics. More importantly, we demonstrate a systematic approach for extracting the energy accommodation coefficient (EAC), which is necessary to establish gas-surface scattering kernels or develop diffusive-specular solutions to the Boltzmann transport equation. EACs are also required for calculating the temperature jump coefficient in near-continuum conditions to solve classical hydrodynamical equations. We show a correction to the kinetic theory in the transition to near-continuum regimes (particularly for nonmonatomic gases) by extracting a physical parameter representing the intermolecular collisions within the Knudsen layer. Our results agree well with the kinetic theory predictions and are expected to inform the development of technologies such as thermal switches, gas sensors, and light-driven actuators.

Shubnikov-de Haas (SdH) oscillations are the fingerprint of the Landau and Zeeman splitting level structure on the resistivity in presence of a moderate magnetic field before full quantization is manifest in the integer quantum Hall effect. These oscillations have served as a paradigmatic experimental probe and tool for extracting key semiconductor parameters such as carrier density, effective mass $m^{*}$, Zeeman splitting with g factor $g^{*}$, quantum scattering time, and Rashba $\alpha$ and Dresselhaus $\beta$ spin-orbit (SO) coupling parameters. Analytical descriptions of the SdH oscillations are available for some special cases, but no analytical solution could be found for the vast majority of parameter space with all three terms present, usually relevant for experiments. Despite over 50 years of experiments and many theoretical models, which were put forth, this has seriously hampered the analysis and interpretation of experimental data. Here, we bridge this gap by providing an analytical formulation for the SdH oscillations of 2D electron gases (2DEGs) with simultaneous Rashba, Dresselhaus, and Zeeman interactions over a very broad range of parameter space. We use a Poisson summation formula for the density of states of the 2DEG, which affords a complete yet simple description of the oscillatory behavior of its magnetoresistivity. Our analytical and numerical calculations allow us to extract the beating frequencies, quantum lifetimes, and also to understand the role of higher harmonics in the SdH oscillations. More importantly, we derive a simple condition for beating-free SdH oscillations for all harmonics in 2DEGs $\alpha /\beta ={[(1-\tilde{\mathrm{\Delta }})/(1+\tilde{\mathrm{\Delta }})]}^{1/2}$, where $\tilde{\mathrm{\Delta }}\propto g^{*}{m}^{*}$ is a material parameter given by the ratio of the Zeeman and Landau level splitting. This condition is notably different from that of the persistent spin helix at $\alpha /\beta =1$ for materials with large $g^{*}{m}^{*}$ such as InAs or InSb. We also predict beatings in the higher harmonics of the SdH oscillations and elucidate the inequivalence of the SdH response of Rashba-dominated ($\alpha >\beta$) vs Dresselhaus-dominated ($\alpha <\beta$) 2DEGs in semiconductors with substantial $g^{*}$. We find excellent agreement with recent available experimental data of Dettwiler et al. [Phys. Rev. X 7, 031010 (2017)], and Beukman et al. [Phys. Rev. B 96, 241401(R) (2017)]. The formalism builds the foundation for a generation of quantum transport experiments in quantum materials with unprecedented physical insight and material parameter extraction.

Biological systems must be robust for stable functioning against perturbations, but robustness alone is insufficient. The ability to switch between appropriate states (phenotypes) in response to different conditions is essential for biological functions, as observed in allosteric enzymes and motor proteins. How are robustness and plasticity simultaneously acquired through evolution? In an attempt to answer this question, we examine the evolution of genotypes that realize plastic switching between two endpoint phenotypes upon external inputs as well as stationary expressions of phenotypes. Here, we introduce a statistical physics model consisting of spins, with active sites and regulatory sites, which are distinct from each other. In our model, we represent the phenotype and genotype as spin configurations and spin-spin interactions, respectively. The fitness for selection is given by the spin configuration, whose behavior is governed by the genotypes. Specifically, the fitness for selection is given so that it takes a higher value as more active sites take two requested spin configurations depending on the states of the regulatory sites. The remaining spins do not directly affect the fitness, but they interact with other spins. We numerically evolve the matrices of spin-spin interactions (genotypes) by changing them with mutations and selection of those with higher fitness. Our numerical simulations show that characteristic genotypes with higher fitness evolve slightly above the phase transition temperature between replica-symmetric and replica-symmetry-breaking phase in spin-glass theory. These genotypes shape the two spin configurations separately depending on the regulation. Each phenotype is primarily represented by the first or second eigenmode of the genotypes. Smooth switching between the two phenotypes is achieved by following a one-dimensional quarter-circle that connects them. Upon changes in regulations, spin configurations are attracted to this path, which allows for robust and plastic switching between the two phenotypes. The statistical physics analysis based on the two eigenmodes shows that the free energy landscape has a valley along the one-dimensional quarter-circle switching path. Robust attraction to the path is achieved through the evolution of the interactions within nonactive and nonregulatory spin sites, which themselves do not contribute to fitness. Our findings indicate that the compatibility between robustness and plasticity is acquired by the evolution of low dimensionality in the phenotype space, which will be relevant to the understanding of the robust function of protein as well as material design.

The generation and preservation of entanglement is a central goal in quantum technology. Traditionally, dissipation in quantum systems is thought to be detrimental to entanglement, however dissipation can also be utilized as a means of generating entanglement between quantum spins that are not directly interacting. In particular, entanglement can be generated between two qubits, or multiqubit systems via a collective coupling to a reservoir. In this work, we explore multiple spin domains pairwise coupled to different reservoirs and show that entanglement can be generated between spins which are not coupled to each other, or even coupled to the same reservoir.

The spin Edelstein effect has proven to be a promising phenomenon to generate spin polarization from a charge current in systems without inversion symmetry. In recent years, a current-induced orbital magnetization, called the orbital Edelstein effect, has been predicted for various systems with broken inversion symmetry, using the atom-centered approximation and the modern theory of orbital magnetization. In this paper, we study the current-induced spin and orbital magnetization for a bilayer system with Rashba interaction, using the modern theory of orbital magnetization and Boltzmann transport theory in the relaxation time approximation. We find that the spin Edelstein effect is significantly larger than the orbital contribution. Furthermore, the orbital Edelstein response can be enhanced, suppressed, and even reversed, depending on the relation of the effective Rashba parameters of each layer. A sign change of the orbital polarization is related to an interchange of the corresponding layer localization of the states.

A strong ultraviolet pumping laser propagating through the atmosphere could activate the medium and produce the forward and backward coherent air lasing. In this work, we present the theoretical analyses of forward and backward lasing dynamics in the long gain medium consisting of oxygen atoms. By numerically solving the semiclassical Maxwell-Bloch equations, we demonstrate that the atom density, the gain medium length, and the collisional decoherence rate substantially regulate the forward and backward air laser radiation at 845 nm. Especially, our study points out that lower atom density and moderate collisional decoherence rate are favorable for the backward radiation amplification in a long medium, since such conditions balance the competing processes of forward and backward radiation fields. The simulation shows that long medium backward air lasing becomes challenging in the oxygen atom system via double-photon pump, because the amplification can only occur around $z=0$, and the amplified backward radiation does not carry the spectral information of atoms throughout the medium. On the other hand, certain mechanisms such as variation of backward-seeding delay could possibly alleviate the suppression of backward amplification.

Few-layer (FL) transition metal dichalcogenides have been found to exhibit discrete subbands, called van der Waals quantum well (vdWQW) states, resulting from out-of-plane quantum confinement. In this study, we reveal the twisted-resonant tunneling characteristics of a vdWQW device using a three-layer (3L) $\mathrm{W}{\mathrm{Se}}_2/h$-BN/3L-$\mathrm{W}{\mathrm{Se}}_2$ junction with different twist angles ${\theta }_{\mathrm{tunnel}}$ between the two 3L $\mathrm{W}{\mathrm{Se}}_2$ flakes. Using an ambipolar graphene contact to $\mathrm{W}{\mathrm{Se}}_2$, two primary vdWQW states of 3L $\mathrm{W}{\mathrm{Se}}_2$ located in the conduction band (CB) and valence band (VB) were investigated. We found that while the current peak positions due to the electron resonant tunneling between the CB-QW states significantly change with ${\theta }_{\mathrm{tunnel}}$ having a periodicity of ${60}^{\circ }$, the hole resonant tunneling between the VB-QW states exhibits no ${\theta }_{\mathrm{tunnel}}$ dependence; these are due to different angular dispersions of two vdWQWs. The results highlight the different twistronic properties of CB and VB vdWQWs in FL $\mathrm{W}{\mathrm{Se}}_2$.

We formulate a theoretical approach to describe photon vortex production in synchrotron/cyclotron radiation from a helical moving electron under a uniform magnetic field in the relativistic quantum framework. In quantum theory, electron orbitals in a magnetic field are under Landau states. The Landau level density increases with decreasing the magnetic field strength, and it is practically impossible to calculate exactly the synchrotron radiation in possible magnetic fields in the laboratory. We present a method to calculate it by using asymptotic formulations of the emission amplitudes under the condition of $L_i-L_f\ll L_i$, where $L_i$ and $L_f$ are the initial and final Landau numbers, respectively. The wave function of the generated photon is the eigenstate of the $z$ component of the total angular momentum (zTAM) when the magnetic field is parallel to the $z$ axis. The approximation is applicable for photon vortex production of several tens $\hslash$ of zTAM. We also calculate numerically the energy spectra and spatial distribution of photon vortices in magnetic field strengths of 10 and 20 T using electrons with energies of 150 MeV and 8 GeV and Larmor radii of 10 and 100 µm for the helical motion. Although the Landau number becomes up to ${10}^8$ in these conditions, the radiations could be calculated using the approximation. The results indicate that it is possible to produce predominantly photon vortices with a fixed zTAM when we control the energy and entrance trajectory of electrons and the structure of a magnetic field. The present formula contributes to the prediction and verification of photon vortex generation.

We explore the dynamics of quantum spin systems in two and three dimensions using an exact mapping to classical stochastic processes. In recent work, we explored the effectiveness of sampling around the mean-field evolution as determined by a stochastically averaged Weiss field. Here, we show that this approach can be significantly extended by sampling around the instantaneous Weiss field associated with each stochastic trajectory taken separately. This trajectory-resolved approach incorporates sample to sample fluctuations and allows for longer simulation times. We demonstrate the utility of this approach for quenches in the two-dimensional and three-dimensional quantum Ising model. We show that the method is particularly advantageous in situations where the average Weiss field vanishes, but the trajectory-resolved Weiss fields are nonzero. We discuss the connection to the gauge-P phase-space approach, where the trajectory-resolved Weiss field can be interpreted as a gauge degree of freedom.

Core-periphery is a key feature of large-scale networks underlying a wide range of social, biological, and transportation phenomena. Nodes in the core have an influential position in the network, and thus, the periphery can be under structural disadvantage if the groups are aligned with external attributes such as gender or economic status. Despite its prevalence in empirical data, it is unclear whether core-periphery is a consequence of fundamental network evolution processes. While preferential attachment can create degree heterogeneity indistinguishable from core-periphery, it does not explain why cores and peripheries are aligned with some external node attribute, i.e., why specific groups of nodes gain dominance and become cores. We show that even small amounts of assortative attachment, e.g., homophily in social networks, can break the symmetric effect of preferential attachment and that the interplay of the two mechanisms leads to one of the groups emerging as a prominent core. A systematic analysis of the phase space of the proposed model reveals the levels of assortative and preferential attachment necessary for a group to become either core or periphery. We find that relative group size is significant, with minority groups typically having a disadvantage on becoming the core for similar assortative attachment levels among groups. We also find that growing networks are less prone to develop core-periphery than dynamically evolving networks and that these two network evolution mechanisms lead to different types of core-periphery structures. Analyzing five empirical networks, our findings suggest that core nodes are highly assortative, illustrating the potential of our model as a tool for designing and analyzing interventions on evolving networks.

We investigate the properties of a two-dimensional spinor microcavity polariton system driven by a linearly polarized continuous pump. In particular, we establish the role of the elementary excitations, namely, the so-called half-vortices and full vortices; these objects carry a quantum rotation only in one of the two, or both, spin components, respectively. Our numerical analysis of the steady state shows that it is only the half-vortices that are present in the vortex-antivortex pairing and dissociation responsible for the Berezinskii-Kosterlitz-Thouless transition. These are the relevant elementary excitations close to the critical point. However, by exploring the phase-ordering dynamics following a sudden quench across the transition we prove that full vortices become the relevant excitations away from the critical point in a deep quasi-ordered state at late times. The time scales for half-vortices binding into full vortices are much faster than the vortex-antivortex annihilations.

Efficient preparation of spin-squeezed states is important for quantum-enhanced metrology. Current protocols for generating strong spin squeezing rely on either high dimensionality or long-range interactions. A key challenge is how to generate considerable spin squeezing in one-dimensional systems with only nearest-neighbor interactions. Here, we develop variational spin-squeezing algorithms to solve this problem. We consider both digital and analog quantum circuits for these variational algorithms. After the closed optimization loop of the variational spin-squeezing algorithms, the generated squeezing can be comparable to the strongest squeezing created from two-axis twisting. By analyzing the experimental imperfections, the variational spin-squeezing algorithms proposed in this paper are feasible in recently developed noisy intermediate-scale quantum computers.

Learning the properties of dynamical quantum systems underlies applications ranging from nuclear magnetic resonance spectroscopy to quantum device characterization. A central challenge in this pursuit is the learning of strongly interacting systems, where conventional observables decay quickly in time and space, limiting the information that can be learned from their measurement. In this work, we introduce a new class of observables into the context of quantum learning—the out-of-time-order correlator—which we show can substantially improve the learnability of strongly interacting systems by virtue of displaying informative physics at large times and distances. We identify two general scenarios in which out-of-time-order correlators provide a significant learning advantage: (i) when experimental access to the system is spatially restricted, for example, via a single “probe” degree of freedom, and (ii) when one desires to characterize weak interactions whose strength is much less than the typical interaction strength. We numerically characterize these advantages across a variety of learning problems, and find that they are robust to both read-out error and decoherence. Motivated by these physical scenarios, we introduce several learning tasks—including Clifford tomography, and learning the connectivity of an unknown unitary—in which out-of-time-order experiments have a provable exponential advantage over any learning protocol involving only time-ordered operations.