Previous studies have suggested that high pressure may induce chemical activity in noble gases (He and Xe), resulting in the emergence of high-pressure compounds containing these elements. By using first-principles theory and crystal structural prediction methods, we propose that six unconventional stoichiometries, namely, ${\mathrm{Na}}_2\mathrm{Xe}$, NaXe, ${\mathrm{Na}}_2{\mathrm{Xe}}_3, {\mathrm{NaXe}}_2, {\mathrm{NaXe}}_3$, and ${\mathrm{NaXe}}_4$, can be stabilized at pressures ranging from 48 to 400 GPa, which is the highest pressure considered in this study. All the predicted Xe-containing compounds exhibit metallic properties with strong ionic Na–Xe bonds. Further $abinitio$ molecular dynamics simulations show that NaXe, ${\mathrm{NaXe}}_3$, and ${\mathrm{NaXe}}_4$ remain in the solid state under extreme conditions, such as those present in the Earth's mantle, at pressures up to 135 GPa and temperatures up to 5000 K. This suggests that Na–Xe compounds might be possible constituents inside the Earth's mantle. These findings not only enhance our understanding of the Earth's interior, but also provide insights into Xe chemistry.

In this paper, we present a simple interpolation methodology for spectroscopic time series based on conventional interpolation techniques (random forests) implemented in widely available libraries. We demonstrate that our existing library of simulations is sufficient for training, producing interpolated spectra that respond sensitively to varied ejecta parameter, postmerger time, and viewing angle inputs. We compare our interpolated spectra to the AT2017gfo spectral data and find parameters similar to our previous inferences using broadband light curves. However, the spectral observations have significant systematic short-wavelength residuals relative to our models, which we cannot explain within our existing framework. In line with previous studies, we consider the contribution of a third component as a radioactive heating source characterized by light, slow-moving, lanthanide-free ejecta with $M_{\mathrm{th}}=0.003M_{\odot }, v_{\mathrm{th}}=0.05\mathrm{c}$, and ${\kappa }_{\mathrm{th}}=1{\mathrm{cm}}^2/\mathrm{g}$. When included as part of our radiative transfer simulations, our choice of third component reprocesses blue photons into lower energies, having the opposite effect and further accentuating the blue-underluminosity disparity in our simulations. As such, we are unable to overcome short-wavelength deficits at later times using an additional radioactive heating component, indicating the need for a more sophisticated modeling treatment.

Non-Hermitian (NH) Hamiltonians have been shown to exhibit unique signatures, including the NH skin effect and an exponential spectral sensitivity with respect to boundary conditions. Here, we investigate as to what extent these remarkable phenomena, recently predicted and observed in a broad range of settings, may also occur in closed correlated fermionic systems that are governed by a Hermitian many-body Hamiltonian. There, an effectively NH quasiparticle description naturally arises in the Green's function formalism due to interparticle scattering that represents an inherent source of dissipation. As a concrete platform we construct an extended interacting Su-Schrieffer-Heeger (SSH) model subject to varying boundary conditions, which we analyze using exact diagonalization and nonequilibrium Green's function methods. That way, we clearly identify the presence of the aforementioned NH phenomena in the quasiparticle properties of this Hermitian model system.

Employing currently available quantum technology, we design and implement a nonclassically correlated SWAP heat engine that allows to achieve an efficiency above the standard Carnot limit. Such an engine also boosts the amount of extractable work, in a wider parameter window, with respect to engine's cycle in the absence of initial quantum correlations in the working substance. The boosted efficiency arises from a trade-off between the entropy production and the consumption of quantum correlations during the full thermodynamic cycle. We derive a generalized second-law limit for the correlated cycle and implement a proof-of-principle demonstration of the engine efficiency enhancement by effectively tailoring the thermal engine on a cloud quantum processor.

The use of single electron spins in quantum dots as qubits requires detailed knowledge about the processes involved in their initialization and operation as well as their relaxation and decoherence. In optical schemes for such spin qubits, spin-flip Raman as well as Auger processes play an important role, in addition to environment-induced spin relaxation. In this paper, we demonstrate how to quantitatively access all the spin-related processes in one go by monitoring the charge fluctuations of the quantum dot. For this, we employ resonance fluorescence and analyze the charge fluctuations in terms of waiting-time distributions and full counting statistics characterized by factorial cumulants.

We investigate the time evolution of the second-order Rényi entropy (RE) for bosons in a one-dimensional optical lattice following a sudden quench of the hopping amplitude $J$. Specifically, we examine systems that are quenched into the strongly correlated Mott-insulating (MI) regime with $J/U\ll 1$ ($U$ denotes the strength of the on-site repulsive interaction) from the MI limit with $J=0$. In this regime, the low-energy excited states can be effectively described by fermionic quasiparticles known as doublons and holons. They are excited in entangled pairs through the quench dynamics. By developing an effective theory, we derive a direct relation between the RE and correlation functions associated with doublons and holons. This relation allows us to analytically calculate the RE and obtain a physical picture for the RE, both in the ground state and during time evolution through the quench dynamics, in terms of doublon-holon pairs. In particular, we show that the RE is proportional to the population of doublon-holon pairs that span the boundary of the subsystem. Our quasiparticle picture introduces some remarkable features that are absent in previous studies on the dynamics of entanglement entropy in free-fermion models. It provides with valuable insights into the dynamics of entanglement entropy in strongly-correlated systems.

Systems with lattice geometry can be renormalized exploiting their coordinates in metric space, which naturally define the coarse-grained nodes. By contrast, complex networks defy the usual techniques, due to their small-world character and lack of explicit geometric embedding. Current network renormalization approaches require strong assumptions (e.g., community structure, hyperbolicity, scale-free topology), thus remaining incompatible with generic graphs and ordinary lattices. Here we introduce a graph renormalization scheme valid for any hierarchy of heterogeneous coarse-grainings, thereby allowing for the definition of “block-nodes” across multiple scales. This approach identifies a class of scale-invariant networks characterized by a necessary and specific dependence on additive hidden variables attached to nodes, plus optional dyadic factors. If the hidden variables are annealed, they lead to realistic scale-free networks with assortativity and finite local clustering, even in the sparse regime and in the absence of geometry. If they are quenched, they can guide the renormalization of real-world networks with node attributes and distance-dependence or communities. As an application, we derive an accurate multiscale model of the International Trade Network applicable across arbitrary geographic partitions. These results highlight a deep conceptual distinction between scale-free and scale-invariant networks, and they provide a geometry-free route to renormalization.

High-harmonic generation sources can produce coherent, broadband radiation at extreme-ultraviolet and soft-x-ray wavelengths. The wavefronts of the generated high-order harmonics are influenced by the incident laser field, the generation conditions, and geometry. These influences depend on harmonic wavelength, which may result in wavelength-dependent focusing properties and spatiotemporal couplings that can affect attosecond physics experiments. We experimentally demonstrate and characterize these chromatic effects in high-harmonic generation by measuring the spectrally resolved high-harmonic wavefronts as a function of generation conditions. We find that the high-harmonic generation process can have significant intrinsic chromatic aberration, particularly for converging incident laser fields. Furthermore, we identify regimes where chromatic effects can be minimized, and show that analytical single-atom models allow accurate predictions of harmonic wavefronts produced by a specific driving field.

Graph states are special entangled states advantageous for many quantum technologies, including quantum error correction, multiparty quantum communication, and measurement-based quantum computation. Yet, their fidelity is often disrupted by various errors, most notably qubit loss. In general, given an entangled state, Bell inequalities can be used to certify whether quantum entanglement remains despite errors. Here, we study the robustness of graph states to loss in terms of their Bell violation. Considering the recently proposed linearly scalable Bell operators by Baccari et al. [Phys. Rev. Lett. 124, 020402 (2020)], we use the stabilizer formalism to derive a formula for the extent by which the Bell violation of a given graph state is decreased with qubit loss. Our analysis allows one to determine which graph topologies are tolerable to qubit loss as well as pinpointing the Achilles' heel of each graph, namely the sets of qubits whose loss jeopardizes the Bell violation. Our results serve as an analytical tool for optimizing experiments and protocols involving graph states in realistically lossy systems. An experimental demonstration of a Bell violation in our noise-tolerant graphs is within reach using state of the art technology.

In the presence of strong electronic spin correlations, the hyperfine interaction imparts long-range coupling between nuclear spins. Efficient protocols for the extraction of such complex information about electron correlations via magnetic response are not well known. Here we study how machine learning can extract material parameters and help interpret magnetic response experiments. A low-dimensional representation that classifies the strength and range of the interaction is discovered by unsupervised learning. Supervised learning generates models that predict the spatial extent of electronic correlations and the total interaction strength. Our work demonstrates the utility of artificial intelligence in the development of new probes of quantum systems, with applications to experimental studies of strongly correlated materials.

Quantum sensing has highly practical potential applications in fields ranging from fundamental physics and quantum communication to biophysics and bioengineering. However, achieving high fidelity and control of entangled qubits that enables sensing beyond the quantum limit is still a challenging endeavor. In this paper, we present an alternative approach to quantum sensing, which we call open-system quantum sensing, where we exploit a generalization of the Pauli exclusion principle to sense the openness of a multiqubit quantum system from only measurement of the qubit occupations. Qubit occupations of a pure state obey generalized Pauli exclusion constraints that define a convex set known as the Pauli polytope, and hence violation of one of these constraints—a facet of the polytope—reveals a mixed state from the interaction of a quantum system with its environment without performing full-state tomography. We examine experimental ultrafast spectroscopic data from the photosynthetic light-harvesting complex in green sulfur bacteria and show that we can sense and decode the relaxation of the complex due to environmental noise. More generally, we can apply open-system quantum sensing with any general multiqubit quantum system, where it provides a unique, visual approach that promises enhanced sensitivity and fidelity.

Tissue growth underpins a wide array of biological and developmental processes, and numerical modeling of growing systems has been shown to be a useful tool for understanding these processes. However, the phenomena that can be captured are often limited by the size of systems that can be modeled. Here, we address this limitation by introducing a lattice Boltzmann method (LBM) for a growing system that is able to efficiently model hydrodynamic length scales. The model incorporates a bounce-back approach to describing the growing front of a tissue, which we use to investigate the dynamics of the interface of growing model tissues. We find that the interface grows with scaling in agreement with the Kardar-Parisi-Zhang (KPZ) universality class when growth in the system is bulk driven. Interestingly, we also find the emergence of a previously unreported hydrodynamic instability when proliferation is restricted to the tissue edge. We then develop an analytical theory to show that the instability arises due to a coupling between the number of cells actively proliferating and the position of the interface.

The ground state of an atom interacting with the electromagnetic field in the ultrastrong coupling regime is composed of virtual photons entangled with the atom. We propose a method to promote to real the entire photonic state, while preserving the entanglement with the atom. The process can be reversed, and the entangled state can be restored in the vacuum. We consider a four-level atom, with two of these levels ultrastrongly coupled to a cavity mode. The process is obtained by making use of either an ideal ultrafast pulse or a more realistic multitone $\pi$ pulse that drives only the atom. An experimental realization of this proposal will not only enable the investigation of the exotic phenomena of emission of particles from the vacuum, but will also prove that quantum superposition states can be extracted from the vacuum. Moreover, it will allow one to inspect the ground state in the ultrastrong coupling regime, and to generate on-demand entangled states for quantum information processing.

Precise control of hyperfine matterwaves via Raman excitations is instrumental to a class of atom-based quantum technology. We investigate the Raman matterwave control technique for alkaline-like atoms in an intermediate regime characterized by the single-photon detuning where a choice can be made to balance the Raman excitation power efficiency with the control speed, excited-state adiabatic elimination, and spontaneous-emission suppression requirements. Within the regime, rotations of atomic spinors by the Raman coupling are biased by substantial light shifts. Taking advantage of the fixed bias angle, we show that composite biased rotations can be optimized to enable precise ensemble spinor matterwave control within nanoseconds, even for multiple Zeeman pseudospins defined on the hyperfine ground states and when the laser illumination is strongly inhomogeneous. Our scheme fills a technical gap in light pulse atom interferometry for achieving high-speed Raman spinor matterwave control with moderate laser power.

Finite simplex lattice models are used in different branches of science, e.g., in condensed-matter physics, when studying frustrated magnetic systems and non-Hermitian localization phenomena; or in chemistry, when describing experiments with mixtures. An $n$-simplex represents the simplest possible polytope in $n$ dimensions, e.g., a line segment, a triangle, and a tetrahedron in one, two, and three dimensions, respectively. In this work, we show that various fully solvable, in general non-Hermitian, $n$-simplex lattice models with open boundaries can be constructed from the high-order field-moments space of quadratic bosonic systems. Namely, we demonstrate that such $n$-simplex lattices can be formed by a dimensional reduction of highly degenerate iterated polytope chains in $(k>n)$-dimensions, which naturally emerge in the field-moments space. Our findings indicate that the field-moments space of bosonic systems provides a versatile platform for simulating real-space $n$-simplex lattices exhibiting non-Hermitian phenomena, and it yields valuable insights into the structure of many-body systems exhibiting similar complexity. Among a variety of practical applications, these simplex structures can offer a physical setting for implementing the discrete fractional Fourier transform, an indispensable tool for both quantum and classical signal processing.

We develop a self-supervised ensemble learning (SSEL) method to accurately classify distinct types of phase transitions by analyzing the fluctuation properties of machine learning outputs. Employing the 2D Potts model and the 2D Clock model as benchmarks, we demonstrate the capability of SSEL in discerning first-order, second-order, and Berezinskii-Kosterlitz-Thouless transitions, using in situ spin configurations as the input features. Furthermore, we show that the SSEL approach can also be applied to investigate quantum phase transitions in 1D Ising and 1D $XXZ$ models upon incorporating quantum sampling. We argue that the SSEL model simulates a special state function with higher-order correlations between physical quantities, and hence provides richer information than previous machine learning methods. Consequently, our SSEL method can be generally applied to the identification/classification of phase transitions even without explicit knowledge of the underlying theoretical models.

Electron-hole bound pairs, or excitons, are common excitations in semiconductors. They can spontaneously form and condense into a new insulating ground state—the so-called excitonic insulator—when the energy of electron-hole Coulomb attraction exceeds the band gap. In the presence of electron-phonon coupling, a periodic lattice distortion often concomitantly occurs. However, a similar structural transition can also be induced by electron-phonon coupling itself, therefore hindering the clean identification of bulk excitonic insulators (e.g., which instability is the driving force of the phase transition). Using high-resolution synchrotron x-ray diffraction and angle-resolved photoemission spectroscopy, we identify key electron-phonon coupling effects in a leading excitonic insulator candidate ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$. These include an extensive unidirectional lattice fluctuation and an electronic pseudogap in the normal state, as well as a negative electronic compressibility in the charge-doped broken-symmetry state. In combination with first principles and model calculations, we use the normal state electronic spectra to quantitatively determine the electron-phonon interaction vertex $g$ and interband Coulomb interaction $V$ in the minimal lattice model, the solution to which captures the experimental observations. Moreover, we show how the Coulomb and electron-phonon coupling effects can be unambiguously separated based on the solution to quantified microscopic models. Finally, we discuss how the strong lattice fluctuations enabled by low dimensionality relate to the unique electron-phonon interaction effects beyond the textbook Born-Oppenheimer approximation..

We measure electron transport through point contacts in an electron gas in AlGaAs/GaAs heterostructures and graphene for a range of temperatures, magnetic fields, and electron densities. We find a magnetoconductance peak around $B=0$. With increasing temperature, the width of the peak increases monotonically, while its amplitude first increases and then decreases. For GaAs point contacts the peak is particularly sharp at relatively low temperatures $T\approx 1.5\mathrm{K}$: the curve rounds on a scale of a few tens of microteslas, hinting at length scales of several millimeters for the corresponding scattering processes. We propose a model based on the transition between different transport regimes with increasing temperature: from ballistic transport to few electron-electron scatterings to hydrodynamic superballistic flow to hydrodynamic Poiseuille-like flow. The model is in qualitative and, in many cases, quantitative agreement with the experimental observations.

The scalar spin chirality is a three-body physical observable that plays an outstanding role both in classical magnetism, characterizing non-co-planar spin textures, and in quantum magnetism, as an order parameter for chiral spin liquids. In quantum information, the scalar spin chirality is a witness of genuine tripartite entanglement. Here we propose an indirect measurement scheme, based on the Hadamard test, to estimate the scalar spin chirality for general quantum states. We apply our method to study chirality in two types of quantum states: generic one-magnon states of a ferromagnet, and the ground state of a model with competing symmetric and antisymmetric exchange. We show a single-shot determination of the scalar chirality is possible for chirality eigenstates, via quantum phase estimation with a single auxiliary qutrit. Our approach provides a unified theory of chirality in classical and quantum magnetism.

Mergoassociation of two ultracold atoms to form a weakly bound molecule can occur when two optical traps that each contain a single atom are merged. Molecule formation occurs at an avoided crossing between a molecular state and the lowest motional state of the atom pair. We develop the theory of mergoassociation for pairs of nonidentical nonspherical traps. We develop a coupled-channel approach for the relative motion of the two atoms and present results for pairs of cylindrically symmetrical traps as a function of their anisotropy. We focus on the strength of the avoided crossing responsible for mergoassociation. We also develop an approximate method that gives insight into the dependence of the crossing strength on aspect ratio.