Measurement is integral to quantum information processing and communication; it is how information encoded in the state of a system is transformed into classical signals for further use. In quantum optics, measurements are typically destructive, so that the state is not available afterwards for further steps. Here we show how to measure the presence or absence of the vacuum in a quantum optical field without destroying the state, implementing the ideal projections onto the respective subspaces. This not only enables sequential measurements, useful for quantum communication, but it can also be adapted to create novel states of light via bare raising and lowering operators.

The low-energy monochromatic neutron emission from an ${}^{88}\mathrm{Y}/\mathrm{Be}$ source can be exploited to mimic the few ${\mathrm{keV}}_{\mathrm{nr}}$ nuclear recoils expected from low-mass weakly interacting massive particles and coherent scattering of neutrinos off nuclei. Using this source, a $\lesssim 10\%$ quenching factor is measured for sodium recoils below $24{\mathrm{keV}}_{\mathrm{nr}}$ in NaI[Tl]. This is considerably smaller than the 30% typically adopted in the interpretation of the DAMA/LIBRA dark matter experiment, resulting in a marked increase of its tension with other searches, under the standard set of phenomenological assumptions. The method is illustrated for other target materials (superheated and noble liquids).

We quantize spherically symmetric vacuum gravity without gauge fixing the diffeomorphism constraint. Through a rescaling, we make the algebra of Hamiltonian constraints Abelian, and therefore the constraint algebra is a true Lie algebra. This allows the completion of the Dirac quantization procedure using loop quantum gravity techniques. We can construct explicitly the exact solutions of the physical Hilbert space annihilated by all constraints. New observables living in the bulk appear at the quantum level (analogous to spin in quantum mechanics) that are not present at the classical level and are associated with the discrete nature of the spin network states of loop quantum gravity. The resulting quantum space-times resolve the singularity present in the classical theory inside black holes.

We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas.

Abelian Chern-Simons-Maxwell theory can emerge from the bosonization of the ($2+1$)-dimensional Thirring model that describes interacting Dirac fermions. Here we show how the Thirring model manifests itself in the low energy limit of a two-dimensional tight-binding model of spinless fermions. To establish that, we employ a modification of Haldane’s model, where the “doubling” of fermions is rectified by adiabatic elimination. Subsequently, fermionic interactions are introduced that lead to the analytically tractable Thirring model. By local density measurements of the lattice fermions we can establish that for specific values of the couplings the model exhibits the confining ($2+1$)-dimensional QED phase or a topological ordered phase that corresponds to the Chern-Simons theory. The implementation of the model as well as the measurement protocol are accessible with the current technology of cold atoms in optical lattices.

We develop a general quantum theory for reactive collisions involving power-law potentials ($-1/r^n$) valid from the ultracold up to the high-temperature limit. Our quantum defect framework extends the conventional capture models to include the nonuniversal case when the short-range reaction probability $P^{\mathrm{re}}<1$. We present explicit analytical formulas as well as numerical studies for the van der Waals ($n=6$) and polarization ($n=4$) potentials. Our model agrees well with recent merged beam experiments on Penning ionization, spanning collision energies from 10 mK to 30 K [Henson et al., Science 338, 234 (2012)].

We present experiments in which the laterally confined flow of a surfactant film driven by controlled surface tension gradients causes the subtended liquid layer to self-organize into an inner upstream microduct surrounded by the downstream flow. The anomalous interfacial flow profiles and the concomitant backflow are a result of the feedback between two-dimensional and three-dimensional microfluidics realized during flow in open microchannels. Bulk and surface particle image velocimetry data combined with an interfacial hydrodynamics model explain the dependence of the observed phenomena on channel geometry.

Atomic Bose-Einstein condensates confined to a dual-ring trap support Josephson vortices as topologically stable defects in the relative phase. We propose a test of the scaling laws for defect formation by quenching a Bose gas to degeneracy in this geometry. Stochastic Gross-Pitaevskii simulations reveal a $-1/4$ power-law scaling of defect number with quench time for fast quenches, consistent with the Kibble-Zurek mechanism. Slow quenches show stronger quench-time dependence that is explained by the stability properties of Josephson vortices, revealing the boundary of the Kibble-Zurek regime. Interference of the two atomic fields enables clear long-time measurement of stable defects and a direct test of the Kibble-Zurek mechanism in Bose-Einstein condensation.

We report neutron diffraction measurements on $\mathrm{U}({\mathrm{Ru}}_{0.96}{\mathrm{Rh}}_{0.04}{)}_2{\mathrm{Si}}_2$ single crystal under pulsed high magnetic fields up to 30 T applied along the tetragonal $c$ axis. The high-field experiments revealed that the field-induced phase II above 26 T corresponds to a commensurate up-up-down ferrimagnetic structure characterized by the wave vector $\mathit{q}=(2/3,0,0)$ with the magnetic moments parallel to the $c$ axis, which naturally explains the one-third magnetization plateau and the substantially changed Fermi surface in phase II. This $a$-axis modulated magnetic structure indicates that the phase II near the hidden order phase is closely related to the characteristic incommensurate magnetic fluctuations at ${\mathbf{Q}}_1=(0.6,0,0)$ in the pure system ${\mathrm{URu}}_2{\mathrm{Si}}_2$, in contrast to the pressure-induced antiferromagnetic order at ${\mathbf{Q}}_0=(1,0,0)$.

Symmetric electron-hole bilayer systems have been studied at zero temperature using the diffusion quantum Monte Carlo method. A flexible trial wave function is used that can describe fluid, excitonic, and biexcitonic phases. We calculate condensate fractions and pair correlation functions for a large number of densities $r_s$ and layer separations $d$. At small $d$ we find a one-component fluid phase, an excitonic fluid phase, and a biexcitonic fluid phase, and the transitions among them appear to be continuous. At $d=0$, excitons appear to survive down to about $r_s=0.5\mathrm{a}.\mathrm{u}.$, and biexcitons form at $r_s>2.5\mathrm{a}.\mathrm{u}.$

Despite the great interest organic spintronics has recently attracted, there is only a partial understanding of the fundamental physics behind electron spin relaxation in organic semiconductors. Mechanisms based on hyperfine interaction have been demonstrated, but the role of the spin-orbit interaction remains elusive. Here, we report muon spin spectroscopy and time-resolved photoluminescence measurements on two series of molecular semiconductors in which the strength of the spin-orbit interaction has been systematically modified with a targeted chemical substitution of different atoms at a particular molecular site. We find that the spin-orbit interaction is a significant source of electron spin relaxation in these materials.

The spectrum of a segment of InAs nanowire, confined between two superconducting leads, was measured as function of gate voltage and superconducting phase difference using a third normal-metal tunnel probe. Subgap resonances for odd electron occupancy—interpreted as bound states involving a confined electron and a quasiparticle from the superconducting leads, reminiscent of Yu-Shiba-Rusinov states—evolve into Kondo-related resonances at higher magnetic fields. An additional zero-bias peak of unknown origin is observed to coexist with the quasiparticle bound states.

We have used low-energy implanted muons as a volume sensitive probe of the magnetic properties of ${\mathrm{EuO}}_{1-x}$ thin films. We find that static and homogeneous magnetic order persists up to the elevated $T_{\mathrm{C}}$ in the doped samples, and the muon signal displays the double dome feature also observed in the sample magnetization. Our results appear incompatible with either the magnetic phase separation or bound magnetic polaron descriptions previously suggested to explain the elevated $T_{\mathrm{C}}$, but are compatible with an RKKY-like interaction mediating magnetic interactions above 69 K.

Thermal transport measurements have been made on the spin-ice material ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ in an applied magnetic field with both the heat current and the field parallel to the [111] direction for temperatures from 50 mK to 1.2 K. A large magnetic field $>6\mathrm{T}$ is applied to suppress the magnetic contribution to the thermal conductivity in order to extract the lattice conductivity. The low field thermal conductivity thus reveals a magnetic field dependent contribution to the conductivity which both transfers heat and scatters phonons. We interpret these magnetic excitations as monopolelike excitations and describe their behavior via existing Debye-Hückel theory.

We analyze instabilities of the collinear up-up-down state of a two-dimensional quantum spin-$S$ spatially anisotropic triangular lattice antiferromagnet in a magnetic field. We find, within the large-$S$ approximation, that near the end point of the plateau, the collinear state becomes unstable due to the condensation of two-magnon bound pairs rather than single magnons. The two-magnon instability leads to a novel two-dimensional vector chiral phase with alternating spin currents but no magnetic order in the direction transverse to the field. This phase breaks a discrete $Z_2$ symmetry but preserves a continuous $U(1)$ one of rotations about the field axis. It possesses orbital antiferromagnetism and displays a magnetoelectric effect.

We report the dramatic effect of applied pressure and magnetic field on the layered intermetallic compound ${\mathrm{Pr}}_{0.5}{\mathrm{Y}}_{0.5}{\mathrm{Mn}}_2{\mathrm{Ge}}_2$. In the absence of pressure or magnetic field this compound displays interplanar ferromagnetism at room temperature and undergoes an isostructural first order magnetic transition (FOMT) to an antiferromagnetic state below 158 K, followed by another FOMT at 50 K due to the reemergence of ferromagnetism as praseodymium orders ($T_C^{\mathrm{Pr}}$). The application of a magnetic field drives these two transitions towards each other, whereas the application of pressure drives them apart. Pressure also produces a giant magnetocaloric effect such that a threefold increase of the entropy change associated with the lower FOMT (at $T_C^{\mathrm{Pr}}$) is seen under a pressure of 7.5 kbar. First principles calculations, using density functional theory, show that this remarkable magnetic behavior derives from the strong magnetoelastic coupling of the manganese layers in this compound.

We experimentally demonstrate control of the rate of spontaneous emission in a tunable hybrid photonic system that consists of two canonical building blocks for spontaneous emission control, an optical antenna and a mirror, each providing a modification of the local density of optical states (LDOS). We couple fluorophores to a plasmonic antenna to create a superemitter with an enhanced decay rate. In a superemitter analog of the seminal Drexhage experiment we probe the LDOS of a nanomechanically approached mirror. Because of the electrodynamic interaction of the antenna with its own mirror image, the superemitter traces the inverse of the LDOS enhancement provided by the mirror, in stark contrast to a bare source, whose decay rate is proportional to the mirror LDOS.

We report a femtosecond transient spectroscopy study in the near to middle infrared range, 0.8–0.35 eV photon energy, on graphene and few layer graphene single flakes. The spectra show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations, we assign the photoinduced absorption features to intersubband transitions as the number of layers is increased. Interestingly, the intersubband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these intersubband transitions reflects the lifetime of the hot carriers and provides an elegant method to access it in this important class of semimetals.

Quasiparticle dynamics on the topological surface state of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, and superconducting ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$ are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of $\sim 3$ and $\sim 15–20\mathrm{meV}$ associated with an exceptionally large coupling constant $\lambda$ of $\sim 3$, which is one of the strongest ever reported for any material. This result is compatible with the recent observation of a strong Kohn anomaly in the surface phonon dispersion of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, but it appears that the theoretically proposed “spin-plasmon” excitations realized in helical metals are also playing an important role. Intriguingly, the $\sim 3\mathrm{meV}$ mode coupling is found to be enhanced in the superconducting state of ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$.

The spin current pumped by a precessing ferromagnet into an adjacent normal metal has a constant polarization component parallel to the precession axis and a rotating one normal to the magnetization. The former is now routinely detected as a dc voltage induced by the inverse spin Hall effect (ISHE). Here we compute ac ISHE voltages much larger than the dc signals for various material combinations and discuss optimal conditions to observe the effect. The backflow of spin is shown to be essential to distill parameters from measured ISHE voltages for both dc and ac configurations.