Superconducting qubits are an attractive platform for quantum computing since they have demonstrated high-fidelity quantum gates and extensibility to modest system sizes. Nonetheless, an outstanding challenge is stabilizing their energy-relaxation times, which can fluctuate unpredictably in frequency and time. Here, we use qubits as spectral and temporal probes of individual two-level-system defects to provide direct evidence that they are responsible for the largest fluctuations. This research lays the foundation for stabilizing qubit performance through calibration, design, and fabrication.

The typical values and fluctuations of time-integrated observables of nonequilibrium processes driven in steady states are known to be characterized by large deviation functions, generalizing the entropy and free energy to nonequilibrium systems. The definition of these functions involves a scaling limit, similar to the thermodynamic limit, in which the integration time $\tau$ appears linearly, unless the process considered has long-range correlations, in which case $\tau$ is generally replaced by ${\tau }^{\xi }$ with $\xi \ne 1$. Here, we show that such an anomalous power-law scaling in time of large deviations can also arise without long-range correlations in Markovian processes as simple as the Langevin equation. We describe the mechanism underlying this scaling using path integrals and discuss its physical consequences for more general processes.

We study quasiparticle excitations for quantum spin chains with long-range interactions using variational matrix product state techniques. It is confirmed that the local quasiparticle ansatz is able to capture those excitations very accurately, even when the correlation length becomes very large and in the case of topological nontrivial excitation such as spinons. It is demonstrated that the breaking of the Lieb-Robinson bound follows from the appearance of cusps in the dispersion relation, and evidence is given for a crossover between different quasiparticles as the long-range interactions are tuned.

Following up on our earlier work [K. A. Meissner and H. Nicolai, Phys. Rev. D 91, 065029 (2015)] where we showed how to amend a scheme originally proposed by M. Gell-Mann to identify the 48 spin-$\frac{1}{2}$ fermions of $N=8$ supergravity that remain after complete breaking of $N=8$ supersymmetry with the $3\times 16$ quarks and leptons of the standard model, we further generalize the construction to account for the full ${\mathrm{SU}(3)}_c\times {\mathrm{SU}(2)}_w\times \mathrm{U}(1{)}_Y$ assignments, with an additional family symmetry ${\mathrm{SU}(3)}_f$. Our proposal relies in an essential way on embedding the SU(8) $R$ symmetry of $N=8$ supergravity into the (infinite-dimensional) “maximal compact” subgroup $K(E_{10})$ of the conjectured maximal duality symmetry $E_{10}$. As a by-product, it predicts fractionally charged and possibly strongly interacting massive gravitinos. It also indicates how $E_{10}$ and $K(E_{10})$ can supersede supersymmetry as a guiding principle for unification.

We conducted a search for an exotic spin- and velocity-dependent interaction for polarized electrons with an experimental approach based on a high-sensitivity spin-exchange relaxation-free (SERF) magnetometer, which serves as both a source of polarized electrons and a magnetic-field sensor. The experiment aims to sensitively detect magnetic-fieldlike effects from the exotic interaction between the polarized electrons in a SERF vapor cell and unpolarized nucleons of a closely located solid-state mass. We report experimental results on the interaction with 82 h of data averaging, which sets an experimental limit on the coupling strength around ${10}^{-19}$ for the axion mass $m_a\lesssim {10}^{-3}\mathrm{eV}$, within the important axion window.

We report a measurement of the lifetime of the ${\mathrm{\Omega }}_c^0$ baryon using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected by the LHCb experiment. The sample consists of about $1000{\mathrm{\Omega }}_b^{-}\to {\mathrm{\Omega }}_c^0{\mu }^{-}{\overline{\nu }}_{\mu }X$ signal decays, where the ${\mathrm{\Omega }}_c^0$ baryon is detected in the $p{K}^{-}{K}^{-}{\pi }^{+}$ final state and $X$ represents possible additional undetected particles in the decay. The ${\mathrm{\Omega }}_c^0$ lifetime is measured to be ${\tau }_{{\mathrm{\Omega }}_c^0}=268\pm 24\pm 10\pm 2\mathrm{fs}$, where the uncertainties are statistical, systematic, and from the uncertainty in the $D^{+}$ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.

Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum ($k_F$). A fundamental characteristic of SRC pairs is having large relative momenta as compared to $k_F$, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton ($pp$) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the $A(e,e^{\prime }pp)$ reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to $170\mathrm{MeV}/c$, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.

We demonstrate the generation of metastable krypton in the long-lived $1s^5$ state using laser excitation. The atoms are excited through a two-photon absorption process into the $2p^6$ state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.

We study how a suspended liquid film is deformed by an external flow en route to forming a bubble through experiments and a model. We identify a family of nonminimal but stable equilibrium shapes for flow speeds up to a critical value beyond which the film inflates unstably, and the model accounts for the observed nonlinear deformations and forces. A saddle-node or fold bifurcation in the solution diagram suggests that bubble formation at high speeds results from the loss of equilibrium and at low speeds from the loss of stability for overly inflated shapes.

We report on the first multilocation electron temperature ($T_e$) and flow measurements in an ignition hohlraum at the National Ignition Facility using the novel technique of mid-$Z$ spectroscopic tracer “dots.” The measurements define a low resolution “map” of hohlraum plasma conditions and provide a basis for the first multilocation tests of particle and energy transport physics in a laser-driven x-ray cavity. The data set is consistent with classical heat flow near the capsule but reduced heat flow near the laser entrance hole. We evaluate the role of kinetic effects, self-generated magnetic fields, and instabilities in causing spatially dependent heat transport in the hohlraum.

We compute the thermal conductivity and electrical resistivity of solid hcp Fe to pressures and temperatures of Earth’s core. We find significant contributions from electron-electron scattering, usually neglected at high temperatures in transition metals. Our calculations show a quasilinear relation between the electrical resistivity and temperature for hcp Fe at extreme high pressures. We obtain thermal and electrical conductivities that are consistent with experiments considering reasonable error. The predicted thermal conductivity is reduced from previous estimates that neglect electron-electron scattering. Our estimated thermal conductivity for the outer core is $77\pm 10\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ and is consistent with a geodynamo driven by thermal convection.

In ferromagnetic superconductors, like URhGe, superconductivity coexists with magnetism near zero field, but then reappears in a finite field range, where the system also displays mass enhancement in the normal state. We present the theoretical understanding of this nonmonotonic behavior. We explore the multiband nature of URhGe and associate reentrant superconductivity and mass enhancement with the topological transition (Lifshitz) in one of the bands in a finite magnetic field. We find excellent agreement between our theory and a number of experimental results for URhGe, such as weakly first-order reentrant transition, the dependence of superconducting $T_c$ on a magnetic field, and the field dependence of the effective mass, the specific heat, and the resistivity in the normal state. Our theory can be applied to other ferromagnetic multiband superconductors.

We identify a structural one-body force field that sustains spatial inhomogeneities in nonequilibrium overdamped Brownian many-body systems. The structural force is perpendicular to the local flow direction, it is free of viscous dissipation, it is microscopically resolved in both space and time, and it can stabilize density gradients. From the time evolution in the exact (Smoluchowski) low-density limit, Brownian dynamics simulations, and a novel power functional approximation, we obtain a quantitative understanding of viscous and structural forces, including memory and shear migration.

We study a one-dimensional system of strongly correlated bosons on a dynamical lattice. To this end, we extend the standard Bose-Hubbard Hamiltonian to include extra degrees of freedom on the bonds of the lattice. We show that this minimal model exhibits phenomena reminiscent of fermion-phonon models. In particular, we discover a bosonic analog of the Peierls transition, where the translational symmetry of the underlying lattice is spontaneously broken. This provides a dynamical mechanism to obtain a topological insulator in the presence of interactions, analogous to the Su-Schrieffer-Heeger model for electrons. We characterize the phase diagram numerically, showing different types of bond order waves and topological solitons. Finally, we study the possibility of implementing the model using atomic systems.

We present a simple effective field theory formulation of a general family of single-field flux monodromy models for which strong coupling effects at large field values can flatten the potential and activate higher-derivative operators. Both of these effects can suppress the tensor amplitude. These models are radiatively and nonperturbatively stable and can sustain $\gtrsim 60$ $e$ folds of inflation. The dynamics combines features of both large-field chaotic inflation and $k$ inflation. Reducing the tensor-scalar ratio below the observational bound $r\lesssim 0.1$ while keeping the scalar spectral index $n_s$ within experimental bounds either yields equilateral non-Gaussianity $f_{\mathrm{NL}}^{\mathrm{eq}}\simeq \mathcal{O}(1)$, close to the current observational bounds, or gives very small $r$.

The first measurements of the forward-backward asymmetry of the dimuon pair ($A_{\mathrm{FB}}$), the triple-product asymmetry ($A_{2\varphi }$), and the charge-parity-conjugation asymmetry ($A_{CP}$), in $D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ and $D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-}$ decays are reported. They are performed using data from proton-proton collisions collected with the LHCb experiment from 2011 to 2016, corresponding to a total integrated luminosity of $5{\mathrm{fb}}^{-1}$. The asymmetries are measured to be $A_{\mathrm{FB}}(D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})=(3.3\pm 3.7\pm 0.6)\%$, $A_{2\varphi }(D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})=(-0.6\pm 3.7\pm 0.6)\%$, $A_{CP}(D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})=(4.9\pm 3.8\pm 0.7)\%$, $A_{\mathrm{FB}}(D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-})=(0\pm 11\pm 2)\%$, $A_{2\varphi }(D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-})=(9\pm 11\pm 1)\%$, $A_{CP}(D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-})=(0\pm 11\pm 2)\%$, where the first uncertainty is statistical and the second systematic. The asymmetries are also measured as a function of the dimuon invariant mass. The results are consistent with the standard model predictions.

rf spectroscopy is one of the most powerful probing techniques in the field of ultracold gases. We report on a novel rf spectroscopy scheme with which we can detect very weak signals of only a few atoms. Using this method, we extended the experimentally accessible photon-energies range by an order of magnitude compared to previous studies. We directly verify a universal property of fermions with short-range interactions which is a power-law scaling of the rf spectrum tail all the way up to the interaction scale. We also determine, with high precision, the trap average contact parameter for different interaction strength. Finally, we employ our technique to precisely measure the binding energy of Feshbach molecules in an extended range of magnetic fields. These data are used to extract a new calibration of the Feshbach resonance between the two lowest energy levels of ${}^{40}\mathrm{K}$.

Cavity-enhanced single photon sources exhibit mode-locked biphoton states with comblike correlation functions. Our ultrabright source additionally emits single photon pairs as well as two-photon NOON states, dividing the output into an even and an odd comb, respectively. With even-comb photons we demonstrate revivals of the typical nonclassical Hong-Ou-Mandel interference up to the 84th dip, corresponding to a path length difference exceeding 100 m. With odd-comb photons we observe single photon interference fringes modulated over twice the displacement range of the Hong-Ou-Mandel interference.