We report on the first experimental observation of bright matter wave solitons for ${}^{87}\mathrm{Rb}$ atoms with repulsive atom-atom interaction. This counterintuitive situation arises inside a weak periodic potential, where anomalous dispersion can be realized at the Brillouin zone boundary. If the coherent atomic wave packet is prepared at the corresponding band edge, a bright soliton is formed inside the gap. The strength of our system is the precise control of preparation and real time manipulation, allowing the systematic investigation of gap solitons.

We realize an interferometer with an atomic Fermi gas trapped in an optical lattice under the influence of gravity. The single-particle interference between the eigenstates of the lattice results in macroscopic Bloch oscillations of the sample. The absence of interactions between fermions allows a time-resolved study of many periods of the oscillations, leading to a sensitive determination of the acceleration of gravity. The experiment proves the superiority of noninteracting fermions with respect to bosons for precision interferometry and offers a way for the measurement of forces with microscopic spatial resolution.

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of $N$ atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble’s Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as $N^{1/6}$ compared to the atomic shot noise level.

We consider the BCS-BEC (Bose-Einstein-condensate) crossover for a system of trapped Fermi atoms at finite temperature, both below and above the superfluid critical temperature, by including fluctuations beyond mean field. We determine the superfluid critical temperature and the pair-breaking temperature as functions of the attractive interaction between Fermi atoms, from the weak- to the strong-coupling limit (where bosonic molecules form as bound-fermion pairs). Density profiles in the trap are also obtained for all temperatures and couplings.

We study the ground states of rotating Bose gases when interactions are affected by a nearby Feshbach resonance. We show that exact ground states at high angular momentum can be found analytically for a general model for the resonant interactions. We identify parameter regimes where the exact ground states are exotic fractional quantum Hall states, the excitations of which obey nonabelian exchange statistics.

The atomic masses of the $\alpha$ particle and ${}^4\mathrm{He}$ have been measured by means of a Penning trap mass spectrometer which utilizes a frequency-shift detector to observe single-ion cyclotron resonances in an extremely stable 6.0 T magnetic field. The present resolution of this instrument approaches 0.01 ppb [10 ppt (parts per trillion)] and is limited primarily by the effective stability ($<5\mathrm{ppt}/\mathrm{h}$) of the magnet over hundreds of hours of observation. The leading systematic shift [at $-202(9)\mathrm{ppt}$] is due to the image charge located in the trap electrodes. The new value for the atomic mass of the $\alpha$ particle is $4001506179.147(64)\mathrm{nu}$ and the corresponding value for the mass of ${}^4\mathrm{He}$ is $4002603254.153(64)\mathrm{nu}$ ($\mathrm{nu}={10}^{-9}\mathrm{u}$). The 16 ppt uncertainty is at least 20 times smaller than any previous determination.

The elastic oscillations of the vortex lattice of a cold Bose gas (Tkachenko modes) are shown to play a crucial role in the saturation of the compressibility sum rule, as a consequence of the hybridization with the longitudinal degrees of freedom. The presence of the vortex lattice is responsible for a $q^2$ behavior of the static structure factor at small wave vectors $q$, which implies the absence of long range order in 2D configurations at zero temperature. Sum rules are used to calculate the Tkachenko frequency in the presence of harmonic trapping. Results are derived in the Thomas-Fermi regime and compared with experiments as well as with previous theoretical estimates.

Arbitrary atomic Bell states with two trapped ions are generated in a deterministic and preprogrammed way. The resulting entanglement is quantitatively analyzed using various measures of entanglement. For this, we reconstruct the density matrix using single qubit rotations and subsequent measurements with near-unity detection efficiency. This procedure represents the basic building block for future process tomography of quantum computations. As a first application, the temporal decay of entanglement is investigated in detail. We observe ultralong lifetimes for the Bell states ${\Psi }_{\pm }$, close to the fundamental limit set by the spontaneous emission from the metastable upper qubit level and longer than all reported values by 3 orders of magnitude.

We propose a method for generating shock waves in Bose-Einstein condensates by rapidly increasing the value of the nonlinear coefficient using Feshbach resonances. We show that in a cigar-shaped condensate there exist primary (transverse) and secondary (longitudinal) shock waves. We analyze how the shocks are generated in multidimensional scenarios and describe the related phenomenology.

Free-energy simulation methods are applied toward the calculation of cluster integrals that appear in diagrammatic methods of statistical mechanics. In this approach, Monte Carlo sampling is performed on a number of molecules equal to the order of the integral, and configurations are weighted according to the absolute value of the integrand. An umbrella-sampling average yields the value of the cluster integral in reference to a known integral. Virial coefficients, up to the sixth for the Lennard-Jones model and the fifth for the SPCE model of water, are calculated as a demonstration.

An electric field enhanced by a metallic nanoprobe has locally induced coherent anti-Stokes Raman scattering (CARS) of adenine molecules in a nanometric DNA network structure. Owing to the third-order nonlinearity, the excitation of the CARS polarization is extremely confined to the end of the tip apex, resulting in a spatial resolution far beyond the diffraction limit of light. Our tip-enhanced CARS microscope visualized the DNA network structure at a specific vibrational frequency ($\sim 1337\mathrm{c}{\mathrm{m}}^{\mathrm{-}\mathrm{1}}$) corresponding to the ring-breathing mode of diazole of adenine molecules.

We report on a momentum-position realization of the EPR paradox using direct detection in the near and far fields of the photons emitted by collinear type-II phase-matched parametric down conversion. Using this approach we achieved a measured two-photon momentum-position variance product of $0.01{\hslash }^2$, which dramatically violates the bounds for the EPR and separability criteria.

Under assumptions on initial wave-packet spreads and particle interactions, different mass particles scattering off one another will have the product ${\sigma }_i^2{m}_i$ converge to a common value, where ${\sigma }_i$ is the spread and $m_i$ is the mass of the $i$th particle. When this relation is satisfied, kinematic entanglement vanishes.

The competition between chain entropy and bending rigidity in compact polymers can be addressed within a lattice model introduced by Flory in 1956 [Proc. R. Soc. London A 234, 60 (1956)]. It exhibits a transition between an entropy dominated disordered phase and an energetically favored crystalline phase. The nature of this order-disorder transition has been debated ever since the introduction of the model. Here we present exact results for the Flory model in two dimensions relevant for polymers on surfaces, such as DNA adsorbed on a lipid bilayer. We predict a continuous melting transition and compute exact values of critical exponents at the transition point.

In the course of high-precision measurements of the relation between the superflow current $J$ through a weak link in ${}^3\mathrm{He}\mathrm{\text{−}}B$ and the difference in order parameter phase between each side of the link $\phi$ in a flexible wall Helmholtz resonator equipped with a rotation pickup loop, we have observed the signature of a stable textural defect that sustains a change of the phase by $\pi$ across it. “Cosmiclike” solitons, proposed by Salomaa and Volovik and hitherto thought unstable, can constitute such a defect.

In this Letter it is shown that exact decoherence to minimal uncertainty Gaussian pointer states is generic for free quantum particles coupled to a heat bath. More specifically, the Letter is concerned with damped free particles linearly coupled under product initial conditions to a heat bath at arbitrary temperature, with arbitrary coupling strength and spectral densities covering the Ohmic, sub-Ohmic, and supra-Ohmic regime. Then it is true that there exists a time $t_c$ such that for times $t>t_c$ the state can always be exactly represented as a mixture (convex combination) of particular minimal uncertainty Gaussian states, regardless of and independent from the initial state. This exact “localization” is hence not a feature specific to high temperature and weak damping limit, but is a generic property of damped free particles.

We model collisionless collective conversion of a degenerate Fermi gas of atoms into bosonic molecules via a Feshbach resonance, treating the bosonic molecules as a classical field and seeding the pairing amplitudes with random phases. A dynamical instability of the Fermi sea against association with molecules drives the conversion. The model qualitatively reproduces several experimental observations [Regal et al., Nature (London) 424, 47 (2003)]. We predict that the initial temperature of the Fermi gas sets the limit for the efficiency of atom-molecule conversion.

We show that the quantum Zeno and anti-Zeno effects are realizable for macroscopic quantum tunneling by current-bias modulation in Josephson junctions (and their analogs in atomic condensates).

While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement—analogous to the one used in quantum optics—we show how to extract higher-order correlation functions from individual “photographs” of the atomic sample. As a possible application, we apply the method to detect a subtle phase coherence in mesoscopic superpositions.

We describe an apparatus that can measure the instantaneous angular displacement and torque applied to a quartz particle which is angularly trapped. Torque is measured by detecting the change in angular momentum of the transmitted trap beam. The rotational Brownian motion of the trapped particle and its power spectral density are used to determine the angular trap stiffness. The apparatus features a feedback control that clamps torque or other rotational quantities. The torque sensitivity demonstrated is ideal for the study of known biological molecular motors.