We investigate the propagation of spin excitations in a one-dimensional ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this system is soundlike, the dispersion of transverse spin excitations is quadratic, making a direct application of the Luttinger liquid theory impossible. By using a combination of different analytic methods we derive the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion. The result has an unusual structure associated with a crossover from the regime of trapped spin wave to an open regime and does not have analogues in known low-energy universality classes of quantum 1D systems.

We prove a generalized version of the no-broadcasting theorem, applicable to essentially any nonclassical finite-dimensional probabilistic model satisfying a no-signaling criterion, including ones with “superquantum” correlations. A strengthened version of the quantum no-broadcasting theorem follows, and its proof is significantly simpler than existing proofs of the no-broadcasting theorem.

Through exact numerical diagonalization for small numbers of atoms, we show that it is possible to access quantum Hall states in harmonically confined Bose gases at rotation frequencies well below the centrifugal limit by applying a repulsive Gaussian potential at the trap center. The main idea is to reduce or eliminate the effective trapping frequency in regions where the particle density is appreciable. The critical rotation frequency required to obtain the bosonic Laughlin state can be fixed at an experimentally accessible value by choosing an applied Gaussian whose amplitude increases linearly with the number of atoms while its width increases as the square root.

A local Schrödinger equation (LSE) method is proposed for solving the Schrödinger equation (SE) of general atoms and molecules without doing analytic integrations over the complement functions of the free ICI (iterative-complement-interaction) wave functions. Since the free ICI wave function is potentially exact, we can assume a flatness of its local energy. The variational principle is not applicable because the analytic integrations over the free ICI complement functions are very difficult for general atoms and molecules. The LSE method is applied to several 2 to 5 electron atoms and molecules, giving an accuracy of ${10}^{-5}$ Hartree in total energy. The potential energy curves of ${\mathrm{H}}_2$ and LiH molecules are calculated precisely with the free ICI LSE method. The results show the high potentiality of the free ICI LSE method for developing accurate predictive quantum chemistry with the solutions of the SE.

Magnetic resonance measurements of migration and irreversible dynamics in the capillary shear flow of a Brownian suspension are presented. The results demonstrate the presence of phenomena typically associated with concentrated noncolloidal systems and indicate the role of many body hydrodynamics in dilute Brownian suspension transport. The application of concepts from chaos theory and nonequilibrium statistical mechanics is demonstrated.

We describe a new type of Fourier transform (FT) interferometer in which the tunable optical delay between the two arms is realized by using a continuously variable slow-light medium instead of a moving arm as in a conventional setup. The spectral resolution of such a FT interferometer exceeds that of a conventional setup of comparable size by a factor equal to the maximum group index of the slow-light medium. The scheme is experimentally demonstrated by using a rubidium atomic vapor cell as the tunable slow-light medium, and the spectral resolution is enhanced by a factor of approximately 100.

We study the statistics of return intervals between events above a certain threshold in multifractal data sets without linear correlations. We find that nonlinear correlations in the record lead to a power-law (i) decay of the autocorrelation function of the return intervals, (ii) increase in the conditional return period, and (iii) decay in the probability density function of the return intervals. We show explicitly that all the observed quantities depend both on the threshold value and system size, and hence there is no simple scaling observed. We also demonstrate that this type of behavior can be observed in real economic records and can be used to improve considerably risk estimation.

In the study of transport in inhomogeneous systems it is common to construct transport equations invoking the inhomogeneous Fick law. The validity of this approach requires that at least two ingredients be present in the system. First, finite characteristic length and time scales associated with the dominant transport process must exist. Second, the transport mechanism must satisfy a microscopic symmetry: global reversibility. Global reversibility is often satisfied in nature. However, many complex systems exhibit a lack of finite characteristic scales. In this Letter we show how to construct a generalization of the inhomogeneous Fick law that does not require the existence of characteristic scales while still satisfying global reversibility.

Waveguides can be employed to test nonlinear effects in electrodynamics. We solve Born-Infeld equations for TE waves in a rectangular waveguide. We show that the energy velocity acquires a dependence on the amplitude, and harmonic components appear as a consequence of the nonlinear behavior.

A Fermi-Bose mapping method is used to determine the exact ground states of several models of mixtures of strongly interacting ultracold gases in tight waveguides, which are generalizations of the Tonks-Girardeau (TG) gas (1D Bose gas with point hard cores) and fermionic Tonks-Girardeau (FTG) gas (1D spin-aligned Fermi gas with infinitely strong zero-range attractions). We detail the case of a Bose-Fermi mixture with TG boson-boson (BB) and boson-fermion (BF) interactions. Exact results are given for density profiles in a harmonic trap, single-particle density matrices, momentum distibutions, and density-density correlations. Since the ground state is highly degenerate, we analyze the splitting of the ground manifold for large but finite BB and BF repulsions.

We consider spin-$1/2$ fermions of mass $m$ with interactions near the unitary limit. In an applied periodic potential of amplitude $V$ and period $a_L$, and with a density of an even integer number of fermions per unit cell, there is a second-order quantum phase transition between superfluid and insulating ground states at a critical $V=V_c$. We compute the universal ratio $V_{c}m{a}_L^2/{\hslash }^2$ at $N=\infty$ in a model with Sp($2N$) spin symmetry. The insulator interpolates between a band insulator of fermions and a Mott insulator of fermion pairs. We discuss implications for recent experiments.

A Brownian particle moving in the vicinity of a generic potential minimum under the influence of dissipation and thermal noise from two different heat baths is shown to act as a minimal heat engine, generating a systematic torque onto the physical object at the origin of the potential and an opposite torque onto the medium generating the dissipation.

We study the effects of dissipation on a disordered quantum phase transition with $O(N)$ order-parameter symmetry by applying a strong-disorder renormalization group to the Landau-Ginzburg-Wilson field theory of the problem. We find that Ohmic dissipation results in a nonperturbative infinite-randomness critical point with unconventional activated dynamical scaling while super-Ohmic damping leads to conventional behavior. We discuss applications to the superconductor-metal transition in nanowires and to the Hertz theory of the itinerant antiferromagnetic transition.

We construct a unifying theory of geometric effects in mesoscopic stochastic kinetics. We demonstrate that the adiabatic pump and the reversible ratchet effects, as well as similar new phenomena in other domains, such as in epidemiology, all follow from very similar geometric phase contributions to the effective action in the stochastic path integral representation of the moment generating function. The theory provides the universal technique for identification, prediction, and calculation of pumplike phenomena in an arbitrary mesoscopic stochastic framework.

We propose and analyze a probabilistic scheme to entangle two spatially separated topological qubits in a $p_x+i{p}_y$ superfluid using controlled collisions between atoms in movable dipole traps and unpaired atoms inside vortex cores in the superfluid. We discuss how to test the violation of Bell’s inequality with the generated entanglement. A set of universal quantum gates is shown to be implementable deterministically using the entanglement despite the fact that the entangled states can be created only probabilistically.

We present a general framework for understanding carrier-envelope phase (CEP) effects in a quantum system interacting with an intense, short laser pulse. We establish a simple connection between the CEP and the wave function that can be exploited to obtain the full CEP dependence of an observable given the wave function at a single CEP. Within this framework, all CEP effects are interpreted as interference between different photon amplitudes which, in turn, can be used to put limits on the pulse lengths and intensities required to see significant CEP effects.

We demonstrate superradiant conversion between a two-mode collective atomic state and a single-mode light field in an elongated cloud of Bose-condensed atoms. Two off-resonant write beams induce superradiant Raman scattering, producing two independent coherence gratings with different wave vectors in the cloud. By applying phase-matched read beams after a controllable delay, the gratings can be selectively converted into the light field also in a superradiant way. Because of the large optical density and the small velocity width of the condensate, a high conversion efficiency of $>70\%$ and a long storage time of $>120\mu \mathrm{s}$ were achieved.

We show that the formalism of tensor-network states, such as the matrix-product states (MPS), can be used as a basis for variational quantum Monte Carlo simulations. Using a stochastic optimization method, we demonstrate the potential of this approach by explicit MPS calculations for the transverse Ising chain with up to $N=256$ spins at criticality, using periodic boundary conditions and $D\times D$ matrices with $D$ up to 48. The computational cost of our scheme formally scales as $N{D}^3$, whereas standard MPS approaches and the related density matrix renormalization group method scale as $N{D}^5$ and $N{D}^6$, respectively, for periodic systems.

We propose a real-space renormalization group (RG) transformation for quantum systems on a $D$-dimensional lattice. The transformation partially disentangles a block of sites before coarse-graining it into an effective site. Numerical simulations with the ground state of a 1D lattice at criticality show that the resulting coarse-grained sites require a Hilbert space dimension that does not grow with successive RG transformations. As a result we can address, in a quasi-exact way, tens of thousands of quantum spins with a computational effort that scales logarithmically in the system’s size. The calculations unveil that ground state entanglement in extended quantum systems is organized in layers corresponding to different length scales. At a quantum critical point, each relevant length scale makes an equivalent contribution to the entanglement of a block.

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.