The pairing gap for ${}^{53}\mathrm{Ca}$ obtained from new experimental data on the masses of ${}^{52–54}\mathrm{Ca}$ has the smallest value yet observed. This is explained in the framework of the nuclear shell model with schematic and realistic Hamiltonians as being due to shell gaps around the low-$j$ orbital $1p_{1/2}$. Minima in the pairing gaps for all nuclei are shown and discussed.

The existence of bound states of the system ($\alpha$, $e$, $e$, $e$) in a magnetic field $B$ is studied using the variational method. It is shown that for $B\gtrsim 0.13\mathrm{a}.\mathrm{u}.$ this system gets bound with total energy below the one of the ($\alpha$, $e$, $e$) system. It manifests the existence of the stable ${\mathrm{He}}^{-}$ atomic ion. Its ground state is a spin doublet ${}^2(-1{)}^{+}$ at $0.74\mathrm{a}.\mathrm{u}.\gtrsim B\gtrsim 0.13\mathrm{a}.\mathrm{u}.$ and it becomes a spin quartet ${}^4(-3{)}^{+}$ for larger magnetic fields. For $0.8\mathrm{a}.\mathrm{u}.\gtrsim B\gtrsim 0.7\mathrm{a}.\mathrm{u}.$ the ${\mathrm{He}}^{-}$ ion has two (stable) bound states ${}^2(-1{)}^{+}$ and ${}^4(-3{)}^{+}$.

The dissociation of an ${\mathrm{H}}_2^{+}$ molecular-ion beam by linearly polarized, carrier-envelope-phase-tagged 5 fs pulses at $4\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ with a central wavelength of 730 nm was studied using a coincidence 3D momentum imaging technique. Carrier-envelope-phase-dependent asymmetries in the emission direction of ${\mathrm{H}}^{+}$ fragments relative to the laser polarization were observed. These asymmetries are caused by interference of odd and even photon number pathways, where net zero-photon and one-photon interference predominantly contributes at ${\mathrm{H}}^{+}+\mathrm{H}$ kinetic energy releases of 0.2–0.45 eV, and net two-photon and one-photon interference contributes at 1.65–1.9 eV. These measurements of the benchmark ${\mathrm{H}}_2^{+}$ molecule offer the distinct advantage that they can be quantitatively compared with ab initio theory to confirm our understanding of strong-field coherent control via the carrier-envelope phase.

Quantum transmission lines are central to superconducting and hybrid quantum computing. In this work we show how coupling them to a left-handed transmission line allows circuit QED to reach a new regime: multimode ultrastrong coupling. Out of the many potential applications of this novel device, we discuss the preparation of multipartite entangled states and the simulation of the spin-boson model where a quantum phase transition is reached up to finite size effects.

We experimentally demonstrate optomechanical motion and force measurements near the quantum precision limits set by the quantum Cramér-Rao bounds. Optical beams in coherent and phase-squeezed states are used to measure the motion of a mirror under an external stochastic force. Utilizing optical phase tracking and quantum smoothing techniques, we achieve position, momentum, and force estimation accuracies close to the quantum Cramér-Rao bounds with the coherent state, while the estimation using squeezed states shows clear quantum enhancements beyond the coherent-state bounds.

We study the dynamics of successive slip events at a frictional interface with finite-element simulations. Because of the viscous properties of the material, the stress concentrations created by the arrest of precursory slip are not erased by the propagation of the following rupture but reappear with the relaxation of the material. We show that the amplitude of the stress concentrations follows an exponential decay, which is controlled by the bulk material properties. These results highlight the importance of viscosity in the heterogeneous stress state of a frictional interface and reveal the “memory effect” that affects successive ruptures.

We show that if the three-dimensional self-avoiding walk (SAW) is conformally invariant, then one can compute the hitting densities for the SAW in a half-space and in a sphere. We test these predictions by Monte Carlo simulations and find excellent agreement, thus providing evidence that the SAW is conformally invariant in three dimensions.

Optical excitations of BiTeI with large Rashba spin splitting have been studied in an external magnetic field ($B$) applied parallel to the polar axis. A sequence of transitions between the Landau levels (LLs), whose energies are in proportion to $\sqrt{B}$ were observed, being characteristic of massless Dirac electrons. The large separation energy between the LLs makes it possible to detect the strongest cyclotron resonance even at room temperature in moderate fields. Unlike in 2D Dirac systems, the magnetic field induced rearrangement of the conductivity spectrum is directly observed.

We derive the effective heat current density operator for the strong-coupling regime of Mott insulators. Similarly to the case of the electric current density, the leading contribution to this effective operator is proportional to the local scalar spin chirality ${\widehat{\chi }}_{jkl}={\mathbf{S}}_l·({\mathbf{S}}_j\times {\mathbf{S}}_k)$. This common form of the effective heat and electric current density operators leads to a novel cross response in Mott insulators. A heat current induces a distribution of orbital magnetic moments in systems containing loops of an odd number of hopping terms. The relative orientation of the orbital moments depends on the particular lattice of magnetic ions. This subtle effect arises from the symmetries that the heat and electric currents have in common.

Relaxation of soft modes (e.g., charge density in gated semiconductor heterostructures, spin density in the presence of magnetic field) slowed down by disorder may lead to giant enhancement of energy transfer (cooling power) between overheated electrons and phonons at low bath temperature. We show that in strongly disordered systems with time-reversal symmetry broken by external or intrinsic exchange magnetic field the cooling power can be greatly enhanced. The enhancement factor as large as ${10}^2$ at magnetic field $B\sim 10\mathrm{T}$ in 2D InSb films is predicted. A similar enhancement is found for the ultrasound attenuation.

We present indications of thermalization and cooling of quasiparticles, a precursor for quantum condensation, in a plasmonic nanoparticle array. We investigate a periodic array of metallic nanorods covered by a polymer layer doped with an organic dye at room temperature. Surface lattice resonances of the array—hybridized plasmonic-photonic modes—couple strongly to excitons in the dye, and bosonic quasiparticles which we call plasmon-exciton polaritons (PEPs) are formed. By increasing the PEP density through optical pumping, we observe thermalization and cooling of the strongly coupled PEP band in the light emission dispersion diagram. For increased pumping, we observe saturation of the strong coupling and emission in a new weakly coupled band, which again shows signatures of thermalization and cooling.

Europium nitride is semiconducting and contains nonmagnetic ${\mathrm{Eu}}^{3+}$, but substoichiometric EuN has Eu in a mix of $2+$ and $3+$ charge states. We show that at ${\mathrm{Eu}}^{2+}$ concentrations near 15%–20% EuN is ferromagnetic with a Curie temperature as high as 120 K. The ${\mathrm{Eu}}^{3+}$ polarization follows that of the ${\mathrm{Eu}}^{2+}$, confirming that the ferromagnetism is intrinsic to the EuN which is, thus, a novel diluted magnetic semiconductor. Transport measurements shed light on the likely exchange mechanisms.

We measure the quasistatic friction force acting on intruders moving downwards into a granular medium. By utilizing different intruder geometries, we demonstrate that the force acts locally normal to the intruder surface. By altering the hydrostatic loading of grain contacts by a sub-fluidizing airflow through the bed, we demonstrate that the relevant frictional contacts are loaded by gravity rather than by the motion of the intruder itself. Lastly, by measuring the final penetration depth versus airspeed and using an earlier result for inertial drag, we demonstrate that the same quasistatic friction force acts during impact. Altogether this force is set by a friction coefficient, hydrostatic pressure, projectile size and shape, and a dimensionless proportionality constant. The latter is the same in nearly all experiments, and is surprisingly greater than one.

We investigate jammed granular matter in a slowly rotating drum partially filled with granular material and find a state of polydirectional stability. In this state, the material responds elastically to small stresses in a wide angular interval while it responds by plastic deformation when subjected to small stresses outside this interval of directions. We describe the evolution of the granulate by means of a rate equation and find quantitative agreement with the experiment. The state of polydirectional stability complements the fragile state, where the material responds elastically to small applied stresses only in a certain direction but even very small stresses in any other direction would lead to plastic deformations. Similar to fragile matter, polydirectionally stable matter is created in a dynamic process by self-organization.

Using the techniques of optical microscopy and particle tracking, we measure the correlated diffusion in a monolayer of uniform silica spheres dispersed at a water-air interface. It is found that the correlated motion of the interfacial particles can be well described by two universal response functions, the normalized longitudinal and transverse diffusion coefficients ${\tilde{D}}_{\parallel }(r/r_0)$ and ${\tilde{D}}_{\perp }(r/r_0)$, where $r$ is the interparticle distance and $r_0=a({\lambda }_S/a{)}^{3/2}$ is a new scaling length, which depends on both the Saffman length ${\lambda }_S$ and particle radius $a$. The obtained response functions characterize the crossover behavior of the colloidal monolayers from the subphase-dominated three-dimensional hydrodynamics at low surface coverage to the monolayer-dominated 2D hydrodynamics at high concentrations. The surface viscosity ${\eta }_s^{(2)}$ of the colloidal monolayer obtained by two-particle rheology compares well with the one-particle measurements.

We show that the Wigner-Bargmann program of grounding nonrelativistic quantum mechanics in the unitary projective representations of the Galilei group can be extended to include all noninertial reference frames. The key concept is the Galilean line group, the group of transformations that ties together all accelerating reference frames, and its representations. These representations are constructed under the natural constraint that they reduce to the well-known unitary, projective representations of the Galilei group when the transformations are restricted to inertial reference frames. This constraint can be accommodated only for a class of representations with a sufficiently rich cocycle structure. Unlike the projective representations of the Galilei group, these cocycle representations of the Galilean line group do not correspond to central extensions of the group. Rather, they correspond to a class of nonassociative extensions, known as loop prolongations, that are determined by three-cocycles. As an application, we show that the phase shifts due to the rotation of Earth that have been observed in neutron interferometry experiments and the rotational effects that lead to simulated magnetic fields in optical lattices can be rigorously derived from the representations of the loop prolongations of the Galilean line group.

While the slogan “no measurement without disturbance” has established itself under the name of the Heisenberg effect in the consciousness of the scientifically interested public, a precise statement of this fundamental feature of the quantum world has remained elusive, and serious attempts at rigorous formulations of it as a consequence of quantum theory have led to seemingly conflicting preliminary results. Here we show that despite recent claims to the contrary [L. Rozema et al, Phys. Rev. Lett. 109, 100404 (2012)], Heisenberg-type inequalities can be proven that describe a tradeoff between the precision of a position measurement and the necessary resulting disturbance of momentum (and vice versa). More generally, these inequalities are instances of an uncertainty relation for the imprecisions of any joint measurement of position and momentum. Measures of error and disturbance are here defined as figures of merit characteristic of measuring devices. As such they are state independent, each giving worst-case estimates across all states, in contrast to previous work that is concerned with the relationship between error and disturbance in an individual state.

Quantum state tomography is currently the standard tool for verifying that a state prepared in the lab is close to an ideal target state, but up to now there have been no rigorous methods for evaluating the precision of the state preparation in tomographic experiments. We propose a new estimator for quantum state tomography, and prove that the (always physical) estimates will be close to the true prepared state with a high probability. We derive an explicit formula for evaluating how high the probability is for an arbitrary finite-dimensional system and explicitly give the one- and two-qubit cases as examples. This formula applies for any informationally complete sets of measurements, arbitrary finite number of data sets, and general loss functions including the infidelity, the Hilbert-Schmidt, and the trace distances. Using the formula, we can evaluate not only the difference between the estimated and prepared states, but also the difference between the prepared and target states. This is the first result directly applicable to the problem of evaluating the precision of estimation and preparation in quantum tomographic experiments.

We propose an efficiently measurable lower bound on quantum process fidelity of $N$-qubit controlled-$Z$ gates. This bound is determined by average output state fidelities for $N$ partially conjugate product bases. A distinct advantage of our approach is that only fidelities with product states need to be measured while keeping the total number of measurements much smaller than what is necessary for full quantum process tomography. As an application, we use this method to experimentally estimate quantum process fidelity $F$ of a three-qubit linear optical quantum Toffoli gate and we find that $F\ge 0.83$. We also demonstrate the entangling capability of the gate by preparing Greenberger-Horne-Zeilinger-type three-qubit entangled states from input product states.

We report on the first measurement of inclusive $J/\psi$ elliptic flow $v_2$ in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ in the rapidity range $2.5<y<4.0$. The dependence of the $J/\psi$ $v_2$ on the collision centrality and on the $J/\psi$ transverse momentum is studied in the range $0\le p_T<10\mathrm{GeV}/c$. For semicentral Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$, an indication of nonzero $v_2$ is observed with a largest measured value of $v_2=0.116\pm 0.046(\mathrm{stat})\pm 0.029(\mathrm{syst})$ for $J/\psi$ in the transverse momentum range $2\le p_T<4\mathrm{GeV}/c$. The elliptic flow measurement complements the previously reported ALICE results on the inclusive $J/\psi$ nuclear modification factor and favors the scenario of a significant fraction of $J/\psi$ production from charm quarks in a deconfined partonic phase.