We report bounds on local Lorentz invariance (LLI) violation in Cs and Hg. The limits are obtained through the observation of the spin-precession frequencies of ${}^{199}$Hg and ${}^{133}$Cs atoms in their ground states as a function of the orientation of an applied magnetic field with respect to the fixed stars. We measure the amplitudes of the dipole couplings to a preferred direction in the equatorial plane to be 19(11) nHz for Hg and 9(5) μHz for Cs. The upper bounds established here improve upon previous bounds by about a factor of 4. The improvement is primarily due to mounting the apparatus on a rotating table. Bounds are established on several terms in the standard model extension including the first bounds on the spin couplings of the neutron and proton to the $z$ direction: ${\tilde{b}}_z^n<7\times {10}^{-30}$ GeV and ${\tilde{b}}_z^p<7\times {10}^{-29}$ GeV.

In this work, we calculate the exact asymptotic quantum correlations between two interacting nonresonant harmonic oscillators in a common Ohmic bath. We derive analytical formulas for the covariances, fully describing any Gaussian stationary state of the system, and use them to study discord and entanglement in the strong- and weak-dissipation regimes. We discuss the rich structure of the discord of the stationary separable states arising in the strong-dissipation regime. Also under strong dissipation, when the modes are not mechanically coupled, these may entangle only through their interaction with the common environment. Interestingly enough, this stationary entanglement assisted by dissipation is only present within a finite band of frequencies and increases with the dissipation rate. Robust entanglement between detuned oscillators is also observed at low temperature.

We develop a general framework for the construction of probabilities for the time of arrival in quantum systems. The time of arrival is identified with the time instant when a transition in the detector's degrees of freedom takes place. Thus, its definition is embedded within the larger issue of defining probabilities with respect to time for general quantum transitions. The key point in our analysis is that we manage to reduce the problem of defining a quantum time observable to a mathematical model where time is associated to a transition from a subspace of the Hilbert space of the total system to its complementary subspace. This property makes it possible to derive a general expression for the probability for the time of transition, valid for any quantum system, with the only requirement that the time of transition is correlated with a definite macroscopic record. The framework developed here allows for the consideration of any experimental configuration for the measurement of the time of arrival, and it also applies to relativistic systems with interactions described by quantum field theory. We use the method in order to describe time-of-arrival measurements in high-energy particle reactions and for a rigorous derivation of the time-integrated probabilities in particle oscillations.

The quantum decay of noninteracting many particles to a common continuum is theoretically investigated in the framework of a multilevel Friedrichs-Lee model, and the role of the particle statistics on the fractional decay and Fano resonances is highlighted. In particular it is shown that, according to the Pauli exclusion principle, fractional decay and trapping found for a single particle due to destructive quantum interference among different decay paths can be inhibited for fermions, but not for bosons. Examples are provided for the decay dynamics of electrons in quantum dots side-coupled to a quantum wire.

We present an efficient entanglement concentration protocol (ECP) for electron spins based on quantum-dot and microcavity coupled systems. In our ECP, each two-electron spin system in a partially entangled state can be concentrated with the assistance of an ancillary quantum dot and a single photon, not two copies of two-electron spin systems. With current and near-future technology, the locally maximal entanglement of electron spins can be achieved, and our ECP can be used in long-distance quantum communications.

A non-trace-preserving map describing a probabilistic but heralded noiseless linear amplifier has recently been proposed and experimentally demonstrated. Here, we exhibit another remarkable feature of this peculiar transformation, namely its ability to serve as a universal single-mode squeezer regardless of the quadrature that is initially squeezed. Hence, it acts as a heralded phase-insensitive optical squeezer, conserving the signal-to-noise ratio just as a phase-sensitive optical amplifier but for all quadratures at the same time, which may offer interesting perspectives in quantum optical communications. Although this ability to squeeze all quadratures seemingly opens a way to instantaneous signaling by circumventing the quantum no-cloning theorem, we explain the subtle mechanism by which such a causality violation is forbidden, even on an heralded basis.

The collective response of matter is ubiquitous and widely exploited, e.g., in plasmonic, optical, and electronic devices. Here we trace on an attosecond time scale the birth of collective excitations in a finite system and find distinct features in this regime. Combining quantum chemical computation with quantum kinetic methods, we calculate the time-dependent light absorption and refraction in fullerene that serve as indicators for the emergence of collective modes. We explain the numerically calculated transient features by an analytical model and point out the relevance for ultrafast photonic and electronic applications. A scheme is proposed to measure the predicted effects via the emergent attosecond metrology.

We demonstrate loading of ions into a surface-electrode trap (SET) from a remote, laser-cooled source of neutral atoms. We first cool and load $\sim$${10}^6$ neutral ${}^{88}$Sr atoms into a magneto-optical trap from an oven that has no line of sight with the SET. The cold atoms are then pushed with a resonant laser into the trap region where they are subsequently photoionized and trapped in an SET operated at a cryogenic temperature of 4.6 K. We present studies of the loading process and show that our technique achieves ion loading into a shallow (15 meV depth) trap at rates as high as 125 ions/s while drastically reducing the amount of metal deposition on the trap surface as compared with direct loading from a hot vapor. Furthermore, we note that due to multiple stages of isotopic filtering in our loading process, this technique has the potential for enhanced isotopic selectivity over other loading methods. Rapid loading from a clean, isotopically pure, and precooled source may enable scalable quantum-information processing with trapped ions in large, low-depth surface-trap arrays that are not amenable to loading from a hot atomic beam.

We study the metastability and decay of multiply charged superflow in a ring-shaped atomic Bose-Einstein condensate. Supercurrent corresponding to a giant vortex with topological charge up to $q=10$ is phase imprinted optically and detected both interferometrically and kinematically. We observe $q=3$ superflow persisting for up to a minute and clearly resolve a cascade of quantized steps in its decay. These stochastic decay events, associated with vortex-induced $2\pi$ phase slips, correspond to collective jumps of atoms between discrete $q$ values. We demonstrate the ability to detect quantized rotational states with $>$99$\%$ fidelity, which allows a detailed quantitative study of time-resolved phase-slip dynamics. We find that the supercurrent decays rapidly if the superflow speed exceeds a critical velocity in good agreement with numerical simulations, and we also observe rare stochastic phase slips for superflow speeds below the critical velocity.

We study the expansion of repulsively interacting Bose-Einstein condensates (BECs) in shallow one-dimensional potentials. We show for these systems that the onset of wave chaos in the Gross-Pitaevskii equation (GPE), that is, the onset of exponential separation in Hilbert space of two nearby condensate wave functions, can be used as an indication for the onset of depletion of the BEC and the occupation of excited modes within a many-body description. Comparison between the multiconfigurational time-dependent Hartree for bosons method and the GPE reveals a close correspondence between the many-body effect of depletion and the mean-field effect of wave chaos for a wide range of single-particle external potentials. In the regime of wave chaos the GPE fails to account for the fine-scale quantum fluctuations because many-body effects beyond the validity of the GPE are non-negligible. Surprisingly, despite the failure of the GPE to account for the depletion, coarse-grained expectation values of the single-particle density such as the overall width of the atomic cloud agree very well with the many-body simulations. The time-dependent depletion of the condensate could be investigated experimentally, for example, via decay of coherence of the expanding atom cloud.

We show that the interaction between vortices and sound waves in atomic Bose-Einstein condensates can be elucidated in a double-well trap: With one vortex in each well, the sound emitted by each precessing vortex can be driven into the opposing vortex (if of the same polarity). This cross talk leads to a periodic exchange of energy between the vortices which is long range and highly efficient. The increase in vortex energy (obtained by simulations of the Gross-Pitaevskii equation) is experimentally observable as a migration of the vortex to higher density over just a few precession periods. Similar effects can be controllably engineered by introducing a precessing localized obstacle into one well as an artificial generator of sound, thereby demonstrating the parametric driving of energy into a vortex.

We study quantum spin mixing in a mixture of two spin-1 condensates including coherent interspecies mixing processes, using condensates of ${}^{87}$Rb and ${}^{23}$Na atoms in the ground lower hyperfine $F=1$ manifold as prototype examples. Adopting the single spatial mode approximation for each of the two spinor condensates, we find the mixing dynamics reduce to that of three coupled nonrigid pendulums with clear physical interpretation. With suitably prepared initial states, the spin mixing dynamics allow for the determination of interspecies singlet-pairing as well as spin-exchange interaction parameters.

We propose an efficient scheme for realizing squeezing for both an atomic ensemble and a cavity field via adiabatic evolution of the dark state of the atom-cavity system. Controlled symmetry breaking of the Hamiltonian ensures a unique dark state for the total system, in which the atomic system or cavity mode is squeezed depending upon the choice of the detunings. Since the generation of the atomic squeezed state requires neither the cavity mode nor the atomic system to be excited, the decoherence effects are effectively suppressed. The scheme is insensitive to the uncertainty in the atomic number and imperfect timing, and the time needed for the generation of the desired squeezed state decreases as the size of the system grows. The required experimental techniques are within the scope of what can be obtained in the present cavity QED setups.

We construct families of symmetric, antisymmetric, and asymmetric solitary modes in one-dimensional bichromatic lattices with the second-harmonic-generating (${\chi }^{\left(2\right)}$) nonlinearity concentrated at a pair of sites placed at distance $l$. The lattice can be built as an array of optical waveguides. Solutions are obtained in an implicit analytical form, which is made explicit in the case of adjacent nonlinear sites, $l=1$. The stability is analyzed through the computation of eigenvalues for small perturbations and verified by direct simulations. In the cascading limit, which corresponds to a large mismatch $q$, the system becomes tantamount to the recently studied single-component lattice with two embedded sites carrying the cubic nonlinearity. The modes undergo qualitative changes with the variation of $q$. In particular, at $l⩾2$, the symmetry-breaking bifurcation, which creates asymmetric states from symmetric ones, is supercritical and subcritical for small and large values of $q$, respectively, while the bifurcation is always supercritical at $l=1$. In the experiment, the corresponding change of the phase transition between the second and first kinds may be implemented by varying the mismatch, via the wavelength of the input beam. The existence threshold (minimum total power) for the symmetric modes vanishes exactly at $q=0$, which suggests a possibility to create the solitary mode using low-power beams. The stability of solution families also changes with $q$.

We theoretically investigate the stability and dynamics of self-channeled beams that form via nonlocal optomechanical interactions in dual-nanoweb microstructured fibers. These beams represent a class of spatial soliton.

We show that a quantum clock can not be teleported without prior synchronization between sender and receiver: every protocol using a finite amount of entanglement and an arbitrary number of rounds of classical communication will necessarily introduce an error in the teleported state of the clock. Nevertheless, we show that entanglement can be used to achieve synchronization with precision higher than any classical correlation allows, and we give the optimized strategy for this task. The same results hold also for arbitrary continuous quantum reference frames, which encode general unspeakable information, information that can not be encoded into a number, but instead requires a specific physical support, such as a clock or a gyroscope, to be conveyed.

Quantum-mechanical interference with far-off-resonance neighboring states is found to cause systematic shifts for the measurements of the 2 ${}^{3}P$ fine-structure intervals. The shifts depend on the type of experiment used to measure the intervals. Here the shifts are calculated for measurements using a single microwave pulse and for measurements using the Ramsey method of separated oscillatory fields. The shifts are small, but are large enough to affect the continuing program of determining the fine-structure constant from a comparison between accurate experimental measurements and theoretical calculations of the interval energies. The separated-oscillatory-field shifts are found to be much smaller than the single-pulse shifts.

We derive exact general relations between various observables for $N$ spin-1/2 fermions with zero-range or short-range interactions, in continuous space or on a lattice, in two or three dimensions, in an arbitrary external potential. Some of our results generalize known relations between the large-momentum behavior of the momentum distribution, the short-distance behaviors of the pair distribution function and of the one-body density matrix, the norm of the regular part of the wave function, the derivative of the energy with respect to the scattering length or to time, and the interaction energy (in the case of finite-range interactions). The expression relating the energy to a functional of the momentum distribution is also generalized. Moreover, we find expressions (in terms of the regular part of the wave function) for the derivative of the energy with respect to the effective range $r_e$ in three dimensions (3D), and to the effective range squared in two dimensions (2D). They express the fact that the leading corrections to the eigenenergies due to a finite-interaction range are linear in the effective range in 3D (and in its square in 2D) with model-independent coefficients. There are subtleties in the validity condition of this conclusion, for the 2D continuous space (where it is saved by factors that are only logarithmically large in the zero-range limit) and for the 3D lattice models (where it applies only for some magic dispersion relations on the lattice that sufficiently weakly break Galilean invariance and that do not have cusps at the border of the first Brillouin zone; an example of such relations is constructed). Furthermore, the subleading short-distance behavior of the pair distribution function and the subleading $1/k^6$ tail of the momentum distribution are related to $\partial E/\partial r_e$ [or to $\partial E/\partial \left(r_e^2\right)$ in 2D]. The second-order derivative of energy with respect to the inverse (or the logarithm in the two-dimensional case) of the scattering length is found to be expressible for any eigenstate in terms of the eigen-wave-function's regular parts; this implies that, at thermal equilibrium, this second-order derivative, taken at fixed entropy, is negative. Applications of the general relations are presented: We compute corrections to exactly solvable two-body and three-body problems and find agreement with available numerics; for the unitary gas in an isotropic harmonic trap, we determine how the finite-$1/a$ and finite-range energy corrections vary within each energy ladder (associated with the SO(2,1) dynamical symmetry) and we deduce the frequency shift and the collapse time of the breathing mode; for the bulk unitary gas, we compare to fixed-node Monte Carlo data, and we estimate the deviation from the Bertsch parameter due to the finite interaction-range in typical experiments.

We perform an ab initio analysis of the temperature dependence of the phase coherence length of finite-temperature, quasi-one-dimensional Bose gases measured in the experiments of Richard et al. [Phys. Rev. Lett. 91, 010405 (2003)] and Hugbart et al. [Eur. Phys. J. D 35, 155 (2005)], finding very good agreement across the entire observed temperature range ($0.8<T/T_{\phi }<28$). Our analysis is based on the one-dimensional stochastic Gross-Pitaevskii equation, modified to self-consistently account for transverse, quasi-one-dimensional effects, thus making it a valid model in the regime where $\mu$ is approximately equal to a few $\hslash {\omega }_{\perp }$. We also numerically implement an alternative identification of $T_{\phi }$, based on direct analysis of the distribution of phases in a stochastic treatment.

We investigate the effect of Pauli blocking on universal two- and three-body states in the medium. Their corresponding energies are extracted from the poles of two- and three-body in-medium scattering amplitudes. Compared to the vacuum, the binding of dimer and trimer states is reduced by the medium effects. In two-body scattering, the well-known physics of Cooper pairs is recovered. In the three-body sector, we find a class of positive energy poles which can be interpreted as Cooper triples.