We introduce a new platform for quantum simulation of many-body systems based on nonspherical atoms or molecules with zero dipole moments but possessing a significant value of electric quadrupole moments. We consider a quadrupolar Fermi gas trapped in a 2D square optical lattice, and show that the peculiar symmetry and broad tunability of the quadrupole-quadrupole interaction results in a rich phase diagram encompassing unconventional BCS and charge density wave phases, and opens up a perspective to create a topological superfluid. Quadrupolar species, such as metastable alkaline-earth atoms and homonuclear molecules, are stable against chemical reactions and collapse and are readily available in experiment at high densities.

B diffusion measurements are used to probe the basic nature of self-interstitial point defects in Ge. We find two distinct self-interstitial forms—a simple one with low entropy and a complex one with entropy $\sim 30k$ at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket—we name it a morph. Computational modeling suggests that morphs exist in both self-interstitial and vacancylike forms, and are crucial for diffusion and defect dynamics in Ge, Si, and probably many other crystalline solids.

It has been widely assumed that Se terminates the surface of the topological insulator, bismuth selenide. Although some Se is initially at the surface after cleaving at 80 K, low energy ion scattering reveals a complete Bi termination at room temperature. Density functional theory shows that a Bi bilayer atop the bulk-terminated structure is energetically favorable. It is thus proposed that a thermally activated process induces a spontaneous termination change after cleaving. This has profound implications on the electrical transport and long-term stability of such materials and devices.

Interfacing photonic and solid-state qubits within a hybrid quantum architecture offers a promising route towards large scale distributed quantum computing. Ideal candidates for coherent qubit interconversion are optically active spins, magnetically coupled to a superconducting resonator. We report on an on-chip cavity QED experiment with magnetically anisotropic ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystals and demonstrate collective strong coupling of rare-earth spins to a lumped element resonator. Moreover, the electron spin resonance and relaxation dynamics of the erbium spins are detected via direct microwave absorption, without the aid of a cavity.

We derive the ac dielectric loss in glasses due to resonant processes created by two-level systems and a swept electric field bias. It is shown that at sufficiently large ac fields and bias sweep rates, the nonequilibrium loss tangent created by the two fields approaches a universal maximum determined by the bare linear dielectric permittivity. In addition, this nonequilibrium loss tangent is derived for a range of bias sweep rates and ac amplitudes. A predicted loss function can be understood in a Landau-Zener theory and used to extract the two-level system density, dipole moment, and relaxation rate.

Inelastic neutron scattering measurements of individual phonon lifetimes and dispersion at 295 and 1200 K have been used to probe anharmonicity and thermal conductivity in $\mathrm{U}{\mathrm{O}}_2$. They show that longitudinal optic phonon modes carry the largest amount of heat, in contrast to past simulations and that the total conductivity demonstrates a quantitative correspondence between microscopic and macroscopic phonon physics. We have further performed first-principles simulations for $\mathrm{U}{\mathrm{O}}_2$ showing semiquantitative agreement with phonon lifetimes at 295 K, but larger anharmonicity than measured at 1200 K.

We study a family of binary state, socially inspired contagion models which incorporate imitation limited by an aversion to complete conformity. We uncover rich behavior in our models whether operating with either probabilistic or deterministic individual response functions on both dynamic and fixed random networks. In particular, we find significant variation in the limiting behavior of a population’s infected fraction, ranging from steady state to chaotic. We show that period doubling arises as we increase the average node degree, and that the universality class of this well-known route to chaos depends on the interaction structure of random networks rather than the microscopic behavior of individual nodes. We find that increasing the fixedness of the system tends to stabilize the infected fraction, yet disjoint, multiple equilibria are possible depending solely on the choice of the initially infected node.

We propose a procedure to generate dynamical networks with bursty, possibly repetitive and correlated temporal behaviors. Regarding any weighted directed graph as being composed of the accumulation of paths between its nodes, our construction uses random walks of variable length to produce time-extended structures with adjustable features. The procedure is first described in a general framework. It is then illustrated in a case study inspired by a transportation system for which the resulting synthetic network is shown to accurately mimic the empirical phenomenology.

Intensive theoretical studies have recently predicted that a Bose-Einstein condensate will exhibit a variety of novel properties if spin-orbit coupling is present. However, an unambiguous fact has also been pointed out: Rashba coupling destroys a condensate of noninteracting bosons even in high dimensions. Therefore, a conceptually important question arises as to whether or not a condensate exists in the presence of interaction and a general type of spin-orbit coupling. Here we show that interaction qualitatively changes the ground state of bosons under Rashba spin-orbit coupling. Any infinitesimal repulsion forces bosons either to condense at one or two momentum states or to form a superfragmented state that is a superposition of infinite numbers of fragmented condensates. The superfragmented state is unstable against the anisotropy of spin-orbit coupling in systems with large numbers of particles, leading to the revival of a condensate in current experiments.

We develop a systematic method of performing corrected gate operations on an array of exchange-coupled singlet-triplet qubits in the presence of both fluctuating nuclear Overhauser field gradients and charge noise. The single-qubit control sequences we present have a simple form, are relatively short, and form the building blocks of a corrected cnot gate when also implemented on the interqubit exchange link. This is a key step towards enabling large-scale quantum computation in a semiconductor-based architecture by facilitating error reduction below the quantum error correction threshold for both single-qubit and multiqubit gate operations.

We study how universality classes of $O(N)$-symmetric models depend continuously on the dimension $d$ and the number of field components $N$. We observe, from a renormalization group perspective, how the implications of the Mermin-Wagner-Hohenberg theorem set in as we gradually deform theory space towards $d=2$. For a fractal dimension in the range $2<d<3$, we find, for any $N\ge 1$, a finite family of multicritical effective potentials of increasing order. Apart from the $N=1$ case, these disappear in $d=2$ consistently with the Mermin-Wagner-Hohenberg theorem. Finally, we study $O(N=0)$-universality classes and find an infinite family of these in two dimensions.

The inclusive breakup for the ${}^{11}\mathrm{Li}+{}^{208}\mathrm{Pb}$ reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of ${}^9\mathrm{Li}$ following the ${}^{11}\mathrm{Li}$ dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of $B(E1)$ distribution close to the threshold. Four-body continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the ${}^{11}\mathrm{Li}$ continuum at low excitation energy.

We discovered that chiral nanoneedles fabricated by vortex laser ablation can be used to visualize the helicity of an optical vortex. The orbital angular momentum of light determines the chirality of the nanoneedles, since it is transferred from the optical vortex to the metal. Only the spin angular momentum of the optical vortex can reinforce the helical structure of the created chiral nanoneedles. We also found that optical vortices with the same total angular momentum (defined as the sum of the orbital and spin angular momenta) are degenerate, and they generate nanoneedles with the same chirality and spiral frequency.

Levitated nanospheres in optical cavities open a novel route to study many-body systems out of solution and highly isolated from the environment. We show that properly tuned optical parameters allow for the study of the nonequilibrium dynamics of composite nanoparticles with nonisotropic optical friction. We find optically induced ordering and nematic transitions with nonequilibrium analogs to liquid crystal phases for ensembles of dimers.

Azopolymer films exposed to nonuniform illumination exhibit a phenomenon of light-induced mass transport, leading to the formation of permanent relief patterns on the film surface. Its underlying microscopic mechanism remains unclear, despite many years of research effort. Here we introduce a model of the mass migration process based on anisotropic light-driven molecular diffusion. A key ingredient of our model is an enhanced molecular diffusion in proximity of the free polymer surface, which is essential for explaining, in particular, the recently observed spiral-shaped reliefs resulting from vortex-beam illumination.

We report local spectra of the near-field thermal emission recorded by a Fourier transform infrared spectrometer, using a tungsten tip as a local scatterer coupling the near-field thermal emission to the far field. Spectra recorded on silicon carbide and silicon dioxide exhibit temporal coherence due to thermally excited surface waves. Finally, we evaluate the ability of this spectroscopy to probe the frequency dependence of the electromagnetic local density of states.

We present a unified study of the effect of periodic, quasiperiodic, and disordered potentials on topological phases that are characterized by Majorana end modes in one-dimensional $p$-wave superconducting systems. We define a topological invariant derived from the equations of motion for Majorana modes and, as our first application, employ it to characterize the phase diagram for simple periodic structures. Our general result is a relation between the topological invariant and the normal state localization length. This link allows us to leverage the considerable literature on localization physics and obtain the topological phase diagrams and their salient features for quasiperiodic and disordered systems for the entire region of parameter space.

We perform calculations of the 3D finite-temperature homogeneous electron gas in the warm-dense regime ($r_s\equiv (3/4\pi n{)}^{1/3}{a}_0^{-1}=1.0–40.0$ and $\Theta \equiv T/T_F=0.0625–8.0$) using restricted path-integral Monte Carlo simulations. Precise energies, pair correlation functions, and structure factors are obtained. For all densities, we find a significant discrepancy between the ground state parametrized local density approximation and our results around $T_F$. These results can be used as a benchmark for developing finite-temperature density functionals, as well as input for orbital-free density function theory formulations.

The explanation of heavy-fermion superconductivity is a long-standing challenge to theory. It is commonly thought to be connected to nonlocal fluctuations of either spin or charge degrees of freedom and therefore of unconventional type. Here we present results for the Kondo-lattice model, a paradigmatic model to describe heavy-fermion compounds, obtained from dynamical mean-field theory which captures local correlation effects only. Unexpectedly, we find robust $s$-wave superconductivity in the heavy-fermion state. We argue that this novel type of pairing is tightly connected to the formation of heavy quasiparticle bands and the presence of strong local spin fluctuations.

Two level systems that can be reliably controlled and measured hold promise as qubits both for metrology and for quantum information science. Since a fluctuating environment limits the performance of qubits in both capacities, understanding environmental coupling and dynamics is key to improving qubit performance. We show measurements of the level splitting and dephasing due to the voltage noise of a GaAs singlet-triplet qubit during exchange oscillations. Unexpectedly, the voltage fluctuations are non-Markovian even at high frequencies and exhibit a strong temperature dependence. This finding has impacts beyond singlet-triplet qubits since nearly all solid state qubits suffer from some kind of charge noise. The magnitude of the fluctuations allows the qubit to be used as a charge sensor with a sensitivity of $2\times {10}^{-8}e/\sqrt{\mathrm{Hz}}$, 2 orders of magnitude better than a quantum-limited rf single electron transistor. Based on these measurements, we provide recommendations for improving qubit coherence, allowing for higher fidelity operations and improved charge sensitivity.