Recent results in $d+\mathrm{Au}$ and $p+\mathrm{Pb}$ collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from $p+\mathrm{Pb}$, $d+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ or $t+\mathrm{Au}$ collisions at the same $\sqrt{s_{NN}}$ . Using a Monte Carlo Glauber simulation we find that a ${}^3\mathrm{He}$ or triton projectile, with a realistic wave function description, induces a significant intrinsic triangular shape to the initial medium. If the system lives long enough, this survives into a significant third-order flow moment $v_3$ even with viscous damping. By comparing systems with one, two, and three initial hot spots, one could disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools for answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

It is observed that the exact interacting ground-state electronic energy of interest may be obtained directly, in principle, as a simple sum of orbital energies when a universal density-dependent term is added to $w([\rho ];\mathit{r})$, the familiar Hartree plus exchange-correlation component in the Kohn-Sham effective potential. The resultant shifted potential, $\overline{w}([\rho ];\mathit{r})$, actually changes less on average than $w([\rho ];\mathit{r})$ when the density changes, including the fact that $\overline{w}([\rho ];\mathit{r})$ does not undergo a discontinuity when the number of electrons increases through an integer. Thus, the approximation of $\overline{w}([\rho ];\mathit{r})$ represents an alternative direct approach for the approximation of the ground-state energy and density.

The coherent evolution of an electron hole in a photoionized molecule represents an unexplored facet of charge transfer phenomena occurring in complex systems. Using ultrafast extreme ultraviolet spectroscopy, we investigate the real-time dynamics of an electron hole wave packet created near a conical intersection in ${\mathrm{CO}}_2$. We resolve the oscillation of the electron hole density between $\sigma$ and $\pi$ character, driven by the coupled bending and asymmetric stretch vibrations of the molecule. We also quantify the mixing between electron hole configurations and find that the wave packet coherence diminishes with time due to thermal dephasing.

Deterministic photon-photon interactions are a long-standing goal in optical science. Using an atomic ensemble inside a cavity, we demonstrate the mutual cross modulation of two continuous light beams at the level of individual photons. The originally uncorrelated beams derived from independent lasers become anticorrelated, as evidenced by an equal-time cross-correlation function $g^{(2)}=0.89(1)$, showing that one photon in one beam extinguishes a photon in the other beam with a probability of 11(1)%. With further technical improvements, our approach should enable the nondestructive continuous detection of traveling optical photons.

We propose an experimental arrangement to image, with attosecond resolution, transient surface plasmonic excitations. The required modifications to state-of-the-art setups used for attosecond streaking experiments from solid surfaces only involve available technology. Buildup and lifetimes of surface plasmon polaritons can be extracted and local modulations of the exciting optical pulse can be diagnosed in situ.

Current experimental realizations of the quantum anomalous Hall phase in both electronic and photonic systems have been limited to a Chern number of one. In photonics, this corresponds to a single-mode one-way edge waveguide. Here, we predict quantum anomalous Hall phases in photonic crystals with large Chern numbers of 2, 3, and 4. These new topological phases were found by simultaneously gapping multiple Dirac and quadratic points. We demonstrate a continuously tunable power splitter as a possible application of multimode one-way waveguides. All our findings are readily realizable at microwave frequencies.

Topological superfluids usually refer to a superfluid state which is gapped in the bulk but metallic at the boundary. Here we report that a gapless, topologically nontrivial superfluid with an inhomogeneous Fulde-Ferrell pairing order parameter can emerge in a two-dimensional spin-orbit coupled Fermi gas, in the presence of both in-plane and out-of-plane Zeeman fields. The Fulde-Ferrell pairing—induced by the spin-orbit coupling and in-plane Zeeman field—is responsible for this gapless feature. This exotic superfluid has a significant Berezinskii-Kosterlitz-Thouless transition temperature and has robust Majorana edge modes against disorder owing to its topological nature.

We explore the 32 crystallographic point groups and identify topological phases of matter with robust surface modes. For $n=3,4$, and 6 of the $C_{nv}$ groups, we find the first-known 3D topological insulators without spin-orbit coupling, and with surface modes that are protected only by point groups; i.e., the relevant symmetries are purely crystalline and do not include time reversal. To describe these $C_{nv}$ systems, we introduce the notions of (a) a halved mirror chirality, an integer invariant which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent Chern number, the traditional Thouless–Kohmoto–Nightingale–den Nijs invariant generalized to bent 2D manifolds. We find that a Weyl semimetallic phase intermediates two gapped phases with distinct halved chiralities. In addition to electronic systems without spin-orbit coupling, our findings also apply to intrinsically spinless systems such as photonic crystals and ultracold atoms.

We investigate the evolution of the electronic structure of fused silica in a dense plasma regime using time-resolved x-ray absorption spectroscopy. We use a nanosecond (ns) laser beam to generate a strong uniform shock wave in the sample and a picosecond (ps) pulse to produce a broadband x-ray source near the Si $K$ edge. By varying the delay between the two laser beams and the intensity of the ns beam, we explore a large thermodynamical domain with densities varying from 1 to $5\mathrm{g}/{\mathrm{cm}}^3$ and temperatures up to 5 eV. In contrast to normal conditions where silica is a well-known insulator with a wide band gap of 8.9 eV, we find that shocked silica exhibits a pseudogap as a semimetal throughout this thermodynamical domain. This is in quantitative agreement with density functional theory predictions performed using the generalized gradient approximation.

Bilayer graphene is susceptible to a family of unusual broken symmetry states with spin and valley dependent layer polarization. We report on a microscopic study of the domain walls in these systems, demonstrating that they have interesting microscopic structure related to the topological character of the ordered states. We use our results to show that the metal-insulator transition temperature in bilayer graphene is reduced from mean-field estimates by thermal excitation of domain walls.

Vortices trapped in thin-film superconducting microwave resonators can have a significant influence on the resonator performance. Using a variable-linewidth geometry for a weakly coupled resonator, we are able to observe the effects of a single vortex trapped in the resonator through field cooling. For resonant modes where the vortex is near a current antinode, the presence of even a single vortex leads to a measurable decrease in the quality factor and a dispersive shift of the resonant frequency. For modes with the vortex located at a current node, the presence of the vortex results in no detectable excess loss and, in fact, produces an increase in the quality factor. We attribute this enhancement to a reduction in the density of nonequilibrium quasiparticles in the resonator due to their trapping and relaxation near the vortex core.

We demonstrate a coupled cavity realization of a Bose-Hubbard dimer to achieve quantum-limited amplification and to generate frequency entangled microwave fields with squeezing parameters well below $-12\mathrm{dB}$. In contrast to previous implementations of parametric amplifiers, our dimer can be operated both as a degenerate and as a nondegenerate amplifier. The large measured gain-bandwidth product of more than 250 MHz for the nondegenerate operation and the saturation at input photon numbers as high as 2000 per $\mu s$ are both expected to be improvable even further, while maintaining wide frequency tunability of about 2 GHz. Featuring flexible control over all relevant system parameters, the presented Bose-Hubbard dimer based on lumped element circuits has significant potential as an elementary cell in nonlinear cavity arrays for quantum simulations.

The recent computation on the full threshold contributions to Higgs boson production at next to next to next to leading order (${\mathrm{N}}^3\mathrm{L}\mathrm{O}$) in QCD contains valuable information on the soft gluons resulting from virtual and real emission partonic subprocesses. We use those from the real emissions to obtain the corresponding soft gluon contributions to Drell-Yan production and determine the missing $\delta (1-z)$ part of the ${\mathrm{N}}^3\mathrm{L}\mathrm{O}$. The numerical impact of threshold effects demonstrates the importance of our results in the precision study with the Drell-Yan process at the LHC.

Symmetries in nature offer very simple descriptions of complex systems. Partial Dynamical Symmetries (PDS) can considerably broaden their relevance. To present the first extensive test of a PDS for nuclei, we compare an SU(3) PDS to gamma to ground band $B(E2)$ values for 47 deformed nuclei. The parameter-free PDS is found to be quite successful, but with characteristic discrepancies, suggesting that symmetry remnants are more pervasive than heretofore realized. Furthermore, the SU(3) PDS gives new insights into collective models (e.g., interacting boson approximation). If these reproduce the PDS, they reflect finite size effects, while differences from the PDS point to SU(3) configuration mixing.

We present a theoretical study of noise-induced quantum coherences in a model three-level $V$-type system interacting with incoherent radiation, an important prototype for a wide range of physical systems ranging from trapped ions to biomolecules and quantum dots. By solving the quantum optical equations of motion, we obtain analytic expressions for the noise-induced coherences and show that they exhibit an oscillating behavior in the limit of large excited level spacing $\mathrm{\Delta }$ ($\mathrm{\Delta }/\gamma \gg 1$, where $\gamma$ is the radiative decay width). Most remarkably, we find that in the opposite limit of small level spacing $\mathrm{\Delta }/\gamma \ll 1$, appropriate for large molecules, (a) the coherences can survive for an extremely long time $\tau =(2/\gamma )(\mathrm{\Delta }/\gamma {)}^{-2}$ before eventually decaying to zero, and (b) coherences at short times can be substantial. We further show that the long-lived coherences can survive environmental relaxation and decoherence, suggesting implications to the design of quantum heat engines and to incoherent light excitation of biological systems.

We demonstrate that 60-keV electron irradiation drives the diffusion of threefold-coordinated Si dopants in graphene by one lattice site at a time. First principles simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely than the direct bond inversion. Our results thus provide a model of nondestructive and atomically precise structural modification and detection for two-dimensional materials.

Numerically exact results of hopping charge transport in disordered organic semiconductors show for uncorrelated and dipole-correlated Gaussian energy disorder a universal, power-law, and non-power-law dependence, respectively, of the relative conductance fluctuations on the size of the considered region. Data collapse occurs upon scaling with a characteristic length having a power-law temperature dependence. Below this length, which can be as high as 100 nm for correlated disorder in a realistic case, fluctuations dominate and a continuum description of charge transport breaks down.