We report the observation of optomechanical strain applied to thermal and quantum degenerate ${}^{87}\mathrm{Rb}$ atomic clouds when illuminated by an intense, far detuned homogeneous laser beam. In this regime the atomic cloud acts as a lens that focuses the laser beam. As a backaction, the atoms experience a force opposite to the beam deflection, which depends on the atomic cloud density profile. We experimentally demonstrate the basic features of this force, distinguishing it from the well-established scattering and dipole forces. The observed strain saturates, ultimately limiting the momentum impulse that can be transferred to the atoms. This optomechanical force may effectively induce interparticle interactions, which can be optically tuned.

Coulometric measurements on salt-water-immersed nanoporous carbon electrodes reveal, at a fixed voltage, a charge decrease with increasing temperature. During far-out-of-equilibrium charging of these electrodes, calorimetry indicates the production of both irreversible Joule heat and reversible heat, the latter being associated with entropy changes during electric double layer (EDL) formation in the nanopores. These measurements grant experimental access—for the first time—to the entropic contribution of the grand potential; for our electrodes, this amounts to roughly 25% of the total grand potential energy cost of EDL formation at large applied potentials, in contrast with point-charge model calculations that predict 100%. The coulometric and calorimetric experiments show a consistent picture of the role of heat and temperature in EDL formation and provide hitherto unused information to test against EDL models.

We observe and explain theoretically a dramatic evolution of the Dzyaloshinskii-Moriya interaction (DMI) in the series of isostructural weak ferromagnets, ${\mathrm{MnCO}}_3$, ${\mathrm{FeBO}}_3$, ${\mathrm{CoCO}}_3$, and ${\mathrm{NiCO}}_3$. The sign of the interaction is encoded in the phase of the $x$-ray magnetic diffraction amplitude, observed through interference with resonant quadrupole scattering. We find very good quantitative agreement with first-principles electronic structure calculations, reproducing both sign and magnitude through the series, and propose a simplified “toy model” to explain the change in sign with $3d$ shell filling. The model gives insight into the evolution of the DMI in Mott and charge transfer insulators.

We experimentally investigate the quantum criticality and Tomonaga-Luttinger liquid (TLL) behavior within one-dimensional (1D) ultracold atomic gases. Based on the measured density profiles at different temperatures, the universal scaling laws of thermodynamic quantities are observed. The quantum critical regime and the relevant crossover temperatures are determined through the double-peak structure of the specific heat. In the TLL regime, we obtain the Luttinger parameter by probing sound propagation. Furthermore, a characteristic power-law behavior emerges in the measured momentum distributions of the 1D ultracold gas, confirming the existence of the TLL.

Quantum physics in one spatial dimension is remarkably rich, yet even with strong interactions and disorder, surprisingly tractable. This is due to the fact that the low-energy physics of nearly all one-dimensional systems can be cast in terms of the Luttinger liquid, a key concept that parallels that of the Fermi liquid in higher dimensions. Although there have been many theoretical proposals to use linear chains and ladders of Josephson junctions to create novel quantum phases and devices, only modest progress has been made experimentally. One major roadblock has been understanding the role of disorder in such systems. We present experimental results that establish the insulating state of linear chains of submicron Josephson junctions as Luttinger liquids pinned by random offset charges, providing a one-dimensional implementation of the Bose glass, strongly validating the quantum many-body theory of one-dimensional disordered systems. The ubiquity of such an electronic glass in Josephson-junction chains has important implications for their proposed use as a fundamental current standard, which is based on synchronization of coherent tunneling of flux quanta (quantum phase slips).

The pulsar $\mathrm{J}1023+0038$ rotates with a frequency $\nu \approx 592\mathrm{Hz}$ and has been observed to transition between a radio state, during which it is visible as a millisecond radio pulsar, and a low-mass x-ray binary (LMXB) state, during which accretion powered x-ray pulsations are visible. Timing during the two phases reveals that during the LMXB phase the neutron star is spinning down at a rate of $\dot{\nu }\approx -3\times {10}^{-15}\mathrm{Hz}/\mathrm{s}$, which is approximately 27% faster than the rate measured during the radio phase, $\dot{\nu }\approx -2.4\times {10}^{-15}\mathrm{Hz}/\mathrm{s}$, and is at odds with the predictions of accretion models. We suggest that the increase in spin-down rate is compatible with gravitational wave emission, particularly with the creation of a “mountain” during the accretion phase. We show that asymmetries in pycnonuclear reaction rates in the crust can lead to a large enough mass quadrupole to explain the observed spin-down rate, which thus far has no other self-consistent explanation. We also suggest two observational tests of this scenario, involving radio timing at the onset of the next millisecond radio pulsar phase, when the mountain should dissipate, and accurate timing during the next LMXB phase to track the increase in torque as the mountain builds up. Another possibility is that an unstable $r$ mode with an amplitude $\alpha \approx 5\times {10}^{-8}$ may be present in the system.

We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy ${\mathrm{\Omega }}_o/{\mathrm{\Omega }}_i=(r_o/r_i{)}^{-3/2}$. In this quasi-Keplerian regime, a nonmagnetic system would be Rayleigh stable for all Reynolds numbers Re, and the resulting purely azimuthal flow incapable of kinematic dynamo action for all magnetic Reynolds numbers $\mathrm{R}\mathrm{m}$. For $\mathrm{Re}={10}^4$ and $\mathrm{R}\mathrm{m}={10}^5$, we demonstrate the existence of a finite-amplitude dynamo, whereby a suitable initial condition yields mutually sustaining turbulence and magnetic fields, even though neither could exist without the other. This dynamo solution results in significantly increased outward angular momentum transport, with the bulk of the transport being by Maxwell rather than Reynolds stresses.

Quantum statistics have a profound impact on the properties of systems composed of identical particles. At the most elementary level, Bose and Fermi quantum statistics differ in the exchange phase, either 0 or $\pi$, which the wave function acquires when two identical particles are exchanged. In this Letter, we demonstrate that the exchange phase can be directly probed with a pair of massive particles by physically exchanging their positions. We present two protocols where the particles always remain spatially well separated, thus ensuring that the exchange contribution to their interaction energy is negligible and that the detected signal can only be attributed to the exchange symmetry of the wave function. We discuss possible implementations with a pair of trapped atoms or ions.

On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per $8.0\times {10}^4\mathrm{years}$. We infer the component masses of the binary to be between 0.86 and $2.26M_{\odot }$, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range $1.17–1.60M_{\odot }$, with the total mass of the system $2.74_{-0.01}^{+0.04}{M}_{\odot }$. The source was localized within a sky region of $28{\mathrm{deg}}^2$ (90% probability) and had a luminosity distance of $40_{-14}^{+8}\mathrm{Mpc}$, the closest and most precisely localized gravitational-wave signal yet. The association with the $\gamma$-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short $\gamma$-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation, and cosmology.

We demonstrate the deterministic generation of multipartite entanglement based on scalable methods. Four qubits are encoded in ${}^{40}{\mathrm{Ca}}^{+}$, stored in a microstructured segmented Paul trap. These qubits are sequentially entangled by laser-driven pairwise gate operations. Between these, the qubit register is dynamically reconfigured via ion shuttling operations, where ion crystals are separated and merged, and ions are moved in and out of a fixed laser interaction zone. A sequence consisting of three pairwise entangling gates yields a four-ion Greenberger-Horne-Zeilinger state $|\psi ⟩=(1/\sqrt{2})(|0000⟩+|1111⟩)$, and full quantum state tomography reveals a state fidelity of 94.4(3)%. We analyze the decoherence of this state and employ dynamic decoupling on the spatially distributed constituents to maintain 69(5)% coherence at a storage time of 1.1 sec.

Topological semimetals can be classified by the connectivity and dimensionality of the band crossings in momentum space. The band crossings of a Dirac, Weyl, or an unconventional fermion semimetal are zero-dimensional (0D) points, whereas the band crossings of a nodal-line semimetal are one-dimensional (1D) closed loops. Here we propose that the presence of perpendicular crystalline mirror planes can protect three-dimensional (3D) band crossings characterized by nontrivial links such as a Hopf link or a coupled chain, giving rise to a variety of new types of topological semimetals. We show that the nontrivial winding number protects topological surface states distinct from those in previously known topological semimetals with a vanishing spin-orbit interaction. We also show that these nontrivial links can be engineered by tuning the mirror eigenvalues associated with the perpendicular mirror planes. Using first-principles band structure calculations, we predict the ferromagnetic full Heusler compound ${\mathrm{Co}}_2\mathrm{MnGa}$ as a candidate. Both Hopf link and chainlike bulk band crossings and unconventional topological surface states are identified.

We study experimentally and theoretically discrete solitons in crystalline structures consisting of several tens of laser-cooled ions confined in a radio frequency trap. Resonantly exciting localized, spectrally gapped vibrational modes of the soliton, a nonlinear mechanism leads to a nonequilibrium steady state of the continuously cooled crystal. We find that the propagation and the escape of the soliton out of its quasi-one-dimensional channel can be described as a thermal activation mechanism. We control the effective temperature of the soliton’s collective coordinate by the amplitude of the external excitation. Furthermore, the global trapping potential permits controlling the soliton dynamics and realizing directed transport depending on its topological charge.

We investigate the stability of the many-body localized phase for a system in contact with a single ergodic grain modeling a Griffiths region with low disorder. Our numerical analysis provides evidence that even a small ergodic grain consisting of only three qubits can delocalize a localized chain as soon as the localization length exceeds a critical value separating localized and extended regimes of the whole system. We present a simple theory, consistent with De Roeck and Huveneers’s arguments in [Phys. Rev. B 95, 155129 (2017)] that assumes a system to be locally ergodic unless the local relaxation time determined by Fermi’s golden rule is larger than the inverse level spacing. This theory predicts a critical value for the localization length that is perfectly consistent with our numerical calculations. We analyze in detail the behavior of local operators inside and outside the ergodic grain and find excellent agreement of numerics and theory.

A simple method for generating single-spike hard x-ray pulses in free-electron lasers (FELs) has been developed at the Linac Coherent Light Source (LCLS). This is realized by nonlinear bunch compression using 20-pC bunch charge, demonstrated in the hard x-ray regime at 5.6 and 9 keV, respectively. Measurements show about half of the FEL shots containing a single-spike spectrum. At 5.6-keV photon energy, the single-spike shots have a mean pulse energy of about $10\mu \mathrm{J}$ with 70% intensity fluctuation and the pulse full width at half maximum is evaluated to be at 200-as level.

We report on a “giant” quantum Hall effect plateau in a graphene-based field-effect transistor where graphene is capped by a layer of the van der Waals crystal InSe. The giant quantum Hall effect plateau arises from the close alignment of the conduction band edge of InSe with the Dirac point of graphene. This feature enables the magnetic-field- and electric-field-effect-induced transfer of charge carriers between InSe and the degenerate Landau level states of the adjacent graphene layer, which is coupled by a van der Waals heterointerface to the InSe.

We describe the first precision measurement of the electron’s electric dipole moment ($d_e$) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on ${}^{180}\mathrm{Hf}{}^{19}{\mathrm{F}}^{+}$ in its metastable ${{}^3\mathrm{\Delta }}_1$ electronic state, we obtain $d_e=(0.9\pm 7.7_{\mathrm{stat}}\pm 1.7_{\mathrm{syst}})\times {10}^{-29}e\mathrm{cm}$, resulting in an upper bound of $|d_e|<1.3\times {10}^{-28}e\mathrm{cm}$ (90% confidence). Our result provides independent confirmation of the current upper bound of $|d_e|<9.4\times {10}^{-29}e\mathrm{cm}$ [J. Baron et al., New J. Phys. 19, 073029 (2017)], and offers the potential to improve on this limit in the near future.

On August 14, 2017 at 10∶30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of $\lesssim 1$ in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are $30.5_{-3.0}^{+5.7}{M}_{\odot }$ and $25.3_{-4.2}^{+2.8}{M}_{\odot }$ (at the 90% credible level). The luminosity distance of the source is $540_{-210}^{+130}\mathrm{Mpc}$, corresponding to a redshift of $z=0.11_{-0.04}^{+0.03}$. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from $1160{\mathrm{deg}}^2$ using only the two LIGO detectors to $60{\mathrm{deg}}^2$ using all three detectors. For the first time, we can test the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.

By dual gating a few-layer ${\mathrm{MoS}}_2$ flake, we induce spatially separated electronic states showing superconductivity and Shubnikov–de Haas (SdH) oscillations. While the highly confined superconductivity forms at the $K/K^{\prime }$ valleys of the topmost layer, the SdH oscillations are contributed by the electrons residing in the $Q/Q^{\prime }$ valleys of the rest of the bottom layers, which is confirmed by the extracted Landau level degeneracy of 3, electron effective mass of $0.6m_e$, and carrier density of $5\times {10}^{12}{\mathrm{cm}}^{-2}$. Mimicking conventional heterostructures, the interaction between the heteroelectronic states can be electrically manipulated, which enables “bipolarlike” superconducting transistor operation. The off-on-off switching pattern can be continuously accessed at low temperatures by a field effect depletion of carriers with a negative back gate bias and the proximity effect between the top superconducting layer and the bottom metallic layers that quenches the superconductivity at a positive back gate bias.

We present a method of detecting sequence defects by supercoiling DNA with magnetic tweezers. The method is sensitive to a single mismatched base pair in a DNA sequence of several thousand base pairs. We systematically compare DNA molecules with 0 to 16 adjacent mismatches at 1 M monovalent salt and 3.6 pN force and show that under these conditions, a single plectoneme forms and is stably pinned at the defect. We use these measurements to estimate the energy and degree of end-loop kinking at defects. From this, we calculate the relative probability of plectoneme pinning at the mismatch under physiologically relevant conditions. Based on this estimate, we propose that DNA supercoiling could contribute to mismatch and damage sensing in vivo.

The linear growth of operators in local quantum systems leads to an effective light cone even if the system is nonrelativistic. We show that the consistency of diffusive transport with this light cone places an upper bound on the diffusivity: $D\lesssim v^2{\tau }_{\text{eq}}$. The operator growth velocity $v$ defines the light cone, and ${\tau }_{\text{eq}}$ is the local equilibration time scale, beyond which the dynamics of conserved densities is diffusive. We verify that the bound is obeyed in various weakly and strongly interacting theories. In holographic models, this bound establishes a relation between the hydrodynamic and leading nonhydrodynamic quasinormal modes of planar black holes. Our bound relates transport data—including the electrical resistivity and the shear viscosity—to the local equilibration time, even in the absence of a quasiparticle description. In this way, the bound sheds light on the observed $T$-linear resistivity of many unconventional metals, the shear viscosity of the quark-gluon plasma, and the spin transport of unitary fermions.