We present direct observation of a coherent spin precession of an individual ${\mathrm{Mn}}^{2+}$ ion, having both electronic and nuclear spins equal to $5/2$, embedded in a CdTe quantum dot and placed in a magnetic field. The spin state evolution is probed in a time-resolved pump-probe measurement of absorption of the single dot. The experiment reveals subtle details of the large-spin coherent dynamics, such as nonsinusoidal evolution of states occupation, and beatings caused by the strain-induced differences in energy levels separation. Sensitivity of the large-spin impurity on the crystal strain opens the possibility of using it as a local strain probe.

We implement all single-qubit operations with fidelities significantly above the minimum threshold required for fault-tolerant quantum computing, using a trapped-ion qubit stored in hyperfine “atomic clock” states of ${}^{43}{\mathrm{Ca}}^{+}$. We measure a combined qubit state preparation and single-shot readout fidelity of 99.93%, a memory coherence time of $T_2^{*}=50\sec$, and an average single-qubit gate fidelity of 99.9999%. These results are achieved in a room-temperature microfabricated surface trap, without the use of magnetic field shielding or dynamic decoupling techniques to overcome technical noise.

A search for excited states of the $B_c^{\pm }$ meson is performed using $4.9{\mathrm{fb}}^{-1}$ of 7 TeV and $19.2{\mathrm{fb}}^{-1}$ of 8 TeV $pp$ collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay $B_c^{\pm }\to J/\psi {\pi }^{\pm }$. The state appears in the $m(B_c^{\pm }{\pi }^{+}{\pi }^{-})-m(B_c^{\pm })-2m({\pi }^{\pm })$ mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is $6842\pm 4\pm 5\mathrm{MeV}$, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second $S$-wave state of the $B_c^{\pm }$ meson, $B_c^{\pm }(2S)$.

We find in a canonical chaotic system, the kicked spin-$1/2$ rotor, a Planck’s quantum($h_e$)-driven phenomenon bearing a close analogy to the integer quantum Hall effect but of chaos origin. Specifically, the rotor’s energy growth is unbounded (“metallic” phase) for a discrete set of critical values of $h_e$, but otherwise bounded (“insulating” phase). The latter phase is topological and characterized by a quantum number (“quantized Hall conductance”). The number jumps by unity whenever $h_e$ passes through each critical value as it decreases. Our findings indicate that rich topological quantum phenomena can emerge from chaos.

The popular bar prank known in colloquial English as beer tapping consists in hitting the top of a beer bottle with a solid object, usually another bottle, to trigger the foaming over of the former within a few seconds. Despite the trick being known for a long time, to the best of our knowledge, the phenomenon still lacks scientific explanation. Although it seems natural to think that shock-induced cavitation enhances the diffusion of ${\mathrm{CO}}_2$ from the supersaturated bulk liquid into the bubbles by breaking them up, the subtle mechanism by which this happens remains unknown. Here, we show that the overall foaming-over process can be divided into three stages where different physical phenomena take place in different time scales: namely, the bubble-collapse (or cavitation) stage, the diffusion-driven stage, and the buoyancy-driven stage. In the bubble-collapse stage, the impact generates a train of expansion-compression waves in the liquid that leads to the fragmentation of preexisting gas cavities. Upon bubble fragmentation, the sudden increase of the interface-area-to-volume ratio enhances mass transfer significantly, which makes the bubble volume grow by a large factor until ${\mathrm{CO}}_2$ is locally depleted. At that point buoyancy takes over, making the bubble clouds rise and eventually form buoyant vortex rings whose volume grows fast due to the feedback between the buoyancy-induced rising speed and the advection-enhanced ${\mathrm{CO}}_2$ transport from the bulk liquid to the bubble. The physics behind this explosive process sheds insight into the dynamics of geological phenomena such as limnic eruptions.

There are two renowned theories of superfluidity in liquid ${}^4\mathrm{He}$, quite different and each with specific domains of application. In the first, the Landau theory, superflow follows from the existence of a well-defined collective mode supported by dense liquid ${}^4\mathrm{He}$, the phonon-roton mode. In the second, superflow is a manifestation of Bose-Einstein condensation (BEC) and phase coherence in the liquid. We present combined measurements of superfluidity, BEC and phonon-roton (P-R) modes in liquid ${}^4\mathrm{He}$ confined in the porous medium MCM-41. The results integrate the two theories by showing that well-defined P-R modes exist where there is BEC. The two are common properties of a Bose condensed liquid and either can be used as a basis of a theory of superfluidity. In addition, the confinement and disorder suppresses the critical temperature for superfluidity, $T_c$, below that for BEC creating a localized BEC “phase” consisting of islands of BEC and P-R modes. This phase is much like the pseudogap phase in the cuprate superconductors.

The pinch-off behavior of yield stress fluids is investigated using droplet and liquid-bridge breakup experiments. Contrary to expectations, the neck thinning behavior depends strongly on the way the breakup experiment is carried out. This nonuniversal behavior can be explained through an analysis of the thinning dynamics as well as the shapes of the fluid necks. Recent nonlocal models for the rheology of yield stress fluids are found to be compatible with the results presented.

The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior of the magnetoresistance in ${\mathrm{WTe}}_2$ was identified.

Grover’s quantum search and its generalization, quantum amplitude amplification, provide a quadratic advantage over classical algorithms for a diverse set of tasks but are tricky to use without knowing beforehand what fraction $\lambda$ of the initial state is comprised of the target states. In contrast, fixed-point search algorithms need only a reliable lower bound on this fraction but, as a consequence, lose the very quadratic advantage that makes Grover’s algorithm so appealing. Here we provide the first version of amplitude amplification that achieves fixed-point behavior without sacrificing the quantum speedup. Our result incorporates an adjustable bound on the failure probability and, for a given number of oracle queries, guarantees that this bound is satisfied over the broadest possible range of $\lambda$.

Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present-day variation of fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of ${}^{171}{\mathrm{Yb}}^{+}$. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of $6\times 10^{-16}$. Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, $\dot{\mu }/\mu =0.2(1.1)\times 10^{-16}{\mathrm{yr}}^{-1}$, along with an improved constraint on time variation of the fine structure constant, $\dot{\alpha }/\alpha =-0.7(2.1)\times 10^{-17}{\mathrm{yr}}^{-1}$.

Accurate measurements of different transition frequencies between atomic levels of the electronic and hyperfine structure over time are used to investigate temporal variations of the fine structure constant $\alpha$ and the proton-to-electron mass ratio $\mu$. We measure the frequency of the ${}^2{S}_{1/2}\to {}^2{F}_{7/2}$ electric octupole ($E3$) transition in ${}^{171}{\mathrm{Yb}}^{+}$ against two caesium fountain clocks as $f(E3)=642121496772645.36\mathrm{Hz}$ with an improved fractional uncertainty of $3.9\times 10^{-16}$. This transition frequency shows a strong sensitivity to changes of $\alpha$. Together with a number of previous and recent measurements of the ${}^2{S}_{1/2}\to {}^2{D}_{3/2}$ electric quadrupole transition in ${}^{171}{\mathrm{Yb}}^{+}$ and with data from other elements, a least-squares analysis yields $(1/\alpha )(d\alpha /dt)=-0.20(20)\times 10^{-16}/\mathrm{yr}$ and $(1/\mu )(d\mu /dt)=-0.5(1.6)\times 10^{-16}/\mathrm{yr}$, confirming a previous limit on $d\alpha /dt$ and providing the most stringent limit on $d\mu /dt$ from laboratory experiments.

It has been claimed that the electroweak vacuum may be unstable during inflation due to large fluctuations of the order $H$ in the case of a high inflationary scale as suggested by BICEP2. We compute the standard model Higgs effective potential including UV-induced curvature corrections at one-loop level. We find that for a high inflationary scale a large curvature mass is generated due to renormalization group running of nonminimal coupling $\xi$, which either stabilizes the potential against fluctuations for ${\xi }_{\mathrm{EW}}\gtrsim 6\times 10^{-2}$, or destabilizes it for ${\xi }_{\mathrm{EW}}\lesssim 2\times 10^{-2}$ when the generated curvature mass is negative. Only in the narrow intermediate region may the effect of the curvature mass be significantly smaller.

We present an exact solution of the relativistic Boltzmann equation for a system undergoing boost-invariant longitudinal and azimuthally symmetric transverse flow (“Gubser flow”). The resulting exact nonequilibrium dynamics is compared to first and second order relativistic hydrodynamic approximations for various shear viscosity to entropy density ratios. This novel solution can be used to test the validity and accuracy of different hydrodynamic approximations in conditions similar to those generated in relativistic heavy-ion collisions.

When intense laser beams overlap in plasmas, the refractive index modulation created by the beat wave via the ponderomotive force can lead to optical wave mixing phenomena similar to those used in crystals and photorefractive materials. A new comprehensive analytical description of the modification of the polarization state of laser beams crossing at arbitrary angles in a plasma is presented. It is shown that a laser-plasma system can be used to provide full control of the polarization state of a separate “probe” laser beam; simple analytical estimates and practical considerations are provided for the design of novel photonics devices such as laser-plasma polarizers and wave plates.

The average result of a weak measurement of some observable $A$ can, under postselection of the measured quantum system, exceed the largest eigenvalue of $A$. The nature of weak measurements, as well as the presence of postselection and hence possible contribution of measurement disturbance, has led to a long-running debate about whether or not this is surprising. Here, it is shown that such “anomalous weak values” are nonclassical in a precise sense: a sufficiently weak measurement of one constitutes a proof of contextuality. This clarifies, for example, which features must be present (and in an experiment, verified) to demonstrate an effect with no satisfying classical explanation.

Controlled transfer of orbital angular momentum to an exciton-polariton Bose-Einstein condensate spontaneously created under incoherent, off resonant excitation conditions is a long-standing challenge in the field of microcavity polaritonics. We demonstrate, experimentally and theoretically, a simple and efficient approach to the generation of nontrivial orbital angular momentum states by using optically induced potentials—chiral polaritonic lenses. These lenses are produced by a structured optical pump with a spatial distribution of intensity that breaks the chiral symmetry of the system.

We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the “holes” in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling.

An intense phase-controlled orthogonally polarized two-color ultrashort laser pulse is used to singly ionize and dissociate ${\mathrm{H}}_2$ into a neutral hydrogen atom and a proton. Emission-direction and kinetic-energy dependent asymmetric dissociation of ${\mathrm{H}}_2$ is observed as a function of the relative phase of the orthogonally polarized two-color pulse. Significant asymmetric proton emission is measured in the direction between two polarization axes. Our numerical simulations of the time-dependent Schrödinger equation reproduce many of the observed features. The asymmetry is attributed to the coherent superposition of two-dimensional nuclear wave packets with opposite parities, which have the same energies and overlap in the same emission directions.

We produce ultracold dense trapped samples of ${}^{87}\mathrm{Rb}{}^{133}\mathrm{Cs}$ molecules in their rovibrational ground state, with full nuclear hyperfine state control, by stimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We observe the onset of hyperfine-changing collisions when the magnetic field is ramped so that the molecules are no longer in the hyperfine ground state. A strong quadratic shift of the transition frequencies as a function of applied electric field shows the strongly dipolar character of the RbCs ground-state molecule. Our results open up the prospect of realizing stable bosonic dipolar quantum gases with ultracold molecules.

We demonstrate that application of an increasing shear field on a glass leads to an intriguing dynamic first-order transition in analogy with equilibrium transitions. By following the particle dynamics as a function of the driving field in a colloidal glass, we identify a critical shear rate upon which the diffusion time scale of the glass exhibits a sudden discontinuity. Using a new dynamic order parameter, we show that this discontinuity is analogous to a first-order transition, in which the applied stress acts as the conjugate field on the system’s dynamic evolution. These results offer new perspectives to comprehend the generic shear-banding instability of a wide range of amorphous materials.