We study, in the framework of open quantum systems, the geometric phase acquired by a uniformly accelerated two-level atom undergoing nonunitary evolution due to its coupling to a bath of fluctuating vacuum electromagnetic fields in the multipolar scheme. We find that the phase variation due to the acceleration can be in principle observed via atomic interferometry between the accelerated atom and the inertial one, thus providing an evidence of the Unruh effect.

A weak measurement consists of coupling a system to a probe in such a way that constructive interference generates a large output. So far, only the average output of the probe and its variance were studied. Here, the characteristic function for the moments of the output is provided. The outputs considered are not limited to the eigenstates of the pointer or of its conjugate variable, so the results apply to any observable $\widehat{o}$ of the probe. Furthermore, a family of well-behaved complex quantities, the normal weak values, is introduced, in terms of which the statistics of the weak measurement can be described. It is shown that, within a good approximation, the whole statistics of weak measurement is described by a complex parameter, the weak value, and a real one.

Quantum mechanics is a nonlocal theory, but not as nonlocal as the no-signalling principle allows. However, there exist quantum correlations that exhibit maximal nonlocality: they are as nonlocal as any nonsignalling correlation and thus have a local content, quantified by the fraction $p_L$ of events admitting a local description, equal to zero. We exploit the known link between the Kochen-Specker and Bell theorems to derive a maximal violation of a Bell inequality from every Kochen-Specker proof. We then show that these Bell inequalities lead to experimental bounds on the local content of quantum correlations that are significantly better than those based on other constructions. We perform the experimental demonstration of a Bell test originating from the Peres-Mermin Kochen-Specker proof, providing an upper bound on the local content $p_L\lesssim 0.22$.

Recent experiments have demonstrated ququart state-independent quantum contextuality and qutrit state-dependent quantum contextuality. So far, the most basic form of quantum contextuality pointed out by Kochen and Specker, and Bell, has eluded experimental confirmation. Here we present an experimentally feasible test to observe qutrit state-independent quantum contextuality using single photons in a three-path setup. In addition, we show that if the same measurements are performed on two entangled qutrits, rather than sequentially on the same qutrit, then the noncontextual inequality becomes a Bell inequality. We show that this connection also applies to other recently introduced noncontextual inequalities.

Most entanglement verification is examined in either the completely characterized or the totally device-independent scenario. The assumptions imposed by these extreme cases are often either too weak or too strong for real experiments. Here we investigate this detection task in the intermediate regime where there is partial knowledge of the measured observables, considering cases like orthogonal, sharp, or only dimension-bounded measurements. We show that for all these assumptions it is not necessary to violate a corresponding Bell inequality in order to detect entanglement. We derive strong detection criteria that can be directly evaluated for experimental data and which are robust against large classes of calibration errors. The conditions are even capable of detecting bound entanglement under the sole assumption of dimension-bounded measurements.

In this paper, we investigate the behavior of bipartite entanglement of fermionic systems when one of the parties is traveling with a uniform acceleration. For the ordering problem in fermionic systems, we apply the recent result of Montero and Martín-Martínez [Phys. Rev. A 83, 052306 (2011)]. Based on the approach, we consider both pure and mixed entangled states, and we show that the behavior in terms of the entanglement measure (negativity) allows one to obtain physical results, i.e., its convergence in the infinite acceleration. The behavior shows that the ordering employed is relevant to derive physical results for fermionic entanglement. This also corrects the previous analysis of Martín-Martínez and Fuentes.

It is believed that the presence of anticrossings with exponentially small gaps between the lowest two energy levels of the system Hamiltonian can render adiabatic quantum optimization inefficient. Here, we present a simple adiabatic quantum algorithm designed to eliminate exponentially small gaps caused by anticrossings between eigenstates that correspond with the local and global minima of the problem Hamiltonian. In each iteration of the algorithm, information is gathered about the local minima that are reached after passing the anticrossing nonadiabatically. This information is then used to penalize pathways to the corresponding local minima by adjusting the initial Hamiltonian. This is repeated for multiple clusters of local minima as needed. We generate 64-qubit random instances of the maximum independent set problem, skewed to be extremely hard, with between ${10}^5$ and ${10}^6$ highly degenerate local minima. Using quantum Monte Carlo simulations, it is found that the algorithm can trivially solve all of the instances in $\sim$10 iterations.

We present quantum simulations of a vibrating hydrogen molecule H${}_2$ and address the issue of electron correlation. After appropriately setting the frame and the observer plane, we were able to determine precisely the number of electrons and nuclei which actually flow by evaluating electronic and nuclear fluxes. This calculation is repeated for three levels of quantum chemistry, for which we account for no correlation, Hartree-Fock, static correlation, and dynamic correlation. Exciting each of these systems with the same amount of energy, we show that the electron correlation can be revealed with the knowledge of quantum fluxes. This is evidenced by a clear sensitivity of these fluxes to electron correlation. In particular, we find that this correlation remarkably enhances more electronic yield than the nuclear one. It turns out that less electrons accompany the nuclei in Hartree-Fock than in the correlation cases.

The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon $3d^{9}4p^5$ core-valence double ionization of Kr and subsequent Auger decay to triply charged states associated with the $4s^{2}4p^3$ and $4s^{1}4p^4$ configurations. The photon energy used was $h\nu =150$ eV. Multiconfiguration Dirac-Fock calculations were performed both for the doubly ionized intermediate states and the triply ionized final states. The intermediate states of Kr${}^{2+}$ are observed between 120 and 125 eV, whereas the final states of Kr${}^{3+}$ are observed between 74- and 120-eV ionization energy. Assignments of all structures are made based on the present numerical results. The calculated Auger rates give a detailed explanation of the relative line strengths observed.

Rydberg-valence (RV) mixing and doublet-quartet (DQ) interchannel coupling in the core-excited states of triplet open-shell O${}_2$ are experimentally and theoretically unveiled through the resonant inelastic x-ray scattering around the O $1s\to {\sigma }_u^{*}$ resonance. Ab initio calculations explain complicated excitation energy dependence of the spectral profile by the interplay of the DQ interchannel coupling under the presence of the RV mixing. Complicated intermediate states with valence and/or Rydberg character are successfully analyzed through the filtering of pure valence and pure Rydberg final states.

In the recent work of S. Sharma et al. (e-print arXiv:0912.1118), a single-electron spectrum associated with the natural orbitals was defined as the derivative of the total energy with respect to the occupation numbers at half filling for the orbital of interest. This idea reproduces the bands of various periodic systems using the appropriate functional quite accurately. In the present work we apply this approximation to the calculation of the ionization potentials and electron affinities of molecular systems using various functionals within the reduced-density-matrix functional theory. We demonstrate that this approximation is very successful in general and in particular for certain functionals it performs better than the direct determination of the ionization potentials and electron affinities through the calculation of positive and negative ions respectively. The reason for this is identified to be the inaccuracy that arises from different handling of the open- and closed-shell systems.

We determine the sensitivity to a possible variation of the proton-to-electron mass ratio $\mu$ for torsion-wagging-rotation transitions in the ground state of methylamine (${\mathrm{CH}}_3{\mathrm{NH}}_2$). Our calculation uses an effective Hamiltonian based on a high-barrier tunneling formalism combined with extended-group ideas. The $\mu$ dependence of the molecular parameters that are used in this model are derived, and the most important ones of these are validated using the spectroscopic data of different isotopologues of methylamine. We find a significant enhancement of the sensitivity coefficients due to energy cancellations between internal rotational, overall rotational, and inversion energy splittings. The sensitivity coefficients of the different transitions range from $-19$ to $+24$. The sensitivity coefficients of the 78.135, 79.008, and 89.956 GHz transitions that were recently observed in the disk of a $z=0.89$ spiral galaxy located in front of the quasar PKS 1830-211 [S. Muller et al., Astron. Astrophys. 535, A103 (2011)] were calculated to be $-0.87$ for the first two and $-1.4$ for the third transition. From these transitions a preliminary upper limit for a variation of the proton to electron mass ratio of $\Delta \mu /\mu <9\times {10}^{-6}$ is deduced.

We have studied interspecies scattering in an ultracold mixture of ${}^{87}$Rb and ${}^{133}$Cs atoms, both in their lowest-energy spin states. The three-body loss signatures of 30 incoming $s$- and $p$-wave magnetic Feshbach resonances over the range 0 to 667 G have been cataloged. Magnetic field modulation spectroscopy was used to observe molecular states bound by up to 2.5 $\text{MHz}\times h$. We have created RbCs Feshbach molecules using two of the resonances. Magnetic moment spectroscopy along the magnetoassociation pathway from 197 to 182 G gives results consistent with the observed and calculated dependence of the binding energy on magnetic field strength. We have set up a coupled-channel model of the interaction and have used direct least-squares fitting to refine its parameters to fit the experimental results from the Feshbach molecules, in addition to the Feshbach resonance positions and the spectroscopic results for deeply bound levels. The final model gives a good description of all the experimental results and predicts a large resonance near 790 G, which may be useful for tuning the interspecies scattering properties. Quantum numbers and vibrational wave functions from the model can also be used to choose optimal initial states of Feshbach molecules for their transfer to the rovibronic ground state using stimulated Raman adiabatic passage.

Theoretical studies of dielectronic recombination, a very important process for both atomic and plasma physics, are carried out for low-ionized Er-like W. The dielectronic recombination (DR) of the Er-like ion W${}^{6+}$ proceeds via electron capture into the intermediate autoionizing states of the Tm-like ion W${}^{5+}$ followed by the radiative decay to singly-excited bound states. In particular, energy levels, radiative transition probabilities, and autoionization rates for [Cd]$4f^{14}5p^{5}5l^{\prime }nl$, [Cd]$4f^{14}5p^{5}6l^{\prime \prime }nl$, [Cd]$4f^{13}5p^{6}5l^{\prime }nl$, and [Cd]$4f^{13}5p^{6}6l^{\prime \prime }nl$ ($l^{\prime }=d,f,g$, $l^{\prime \prime }=s,p,d,f,g$, $n=5–7$) states in Tm-like tungsten (W${}^{5+}$) are calculated using the relativistic many-body perturbation theory and relativistic all-order single-double method as well as the Hartree-Fock-relativistic method (cowan code). Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines. DR rate coefficients are determined for the singly-excited [Cd]$4f^{14}5p^{6}nl$ ($n=5–7$) and nonautoionizing doubly-excited [Cd]$4f^{14}5p^{5}5d^2$, [Cd]$4f^{13}5p^{6}5d^2$, [Cd]$4f^{13}5p^{6}6s^2$, [Cd]$4f^{13}5p^{6}5d6s$, and [Cd]$4f^{13}5p^{6}5d6p$ states. Also, contributions from the autoionizing doubly-excited [Cd]$4f^{14}5p^{5}5l^{\prime }nl$, [Cd]$4f^{14}5p^{5}6l^{\prime \prime }nl$, [Cd]$4f^{13}5p^{6}5l^{\prime }nl$, and [Cd]$4f^{13}5p^{6}6l^{\prime \prime }nl$ states (with $n$ up to 100), which are very important for calculating total DR rates, are estimated. Synthetic dielectronic satellite spectra from Tm-like W are simulated in a broad spectral range from 140 to 1200 Å. These relativistic calculations provide recommended values critically evaluated for their accuracy for a number of W${}^{5+}$ ion properties useful for a variety of applications, including for fusion applications.

We study numerically pump-probe schemes for monitoring electron-nuclear motion in a dissociating molecule using a midinfrared, intense few-femtosecond probe laser pulse which generates molecular high-order harmonics (MHOHG) from a coherent superposition of electron-nuclear wave packets prepared by a weak femtosecond UV pump pulse from an initial bound state. We show that by varying the time delay between the intense probe pulse and the UV pump pulse by a few hundred attoseconds one alters the MHOHG signal intensity by many orders of magnitude. The periodicity of the MHOHG intensity variations as function of the time delay is equal to the period of the electron oscillation in the coherent superposition which varies with internuclear distance. We use the strong field approximation (SFA) and three-step model to explain this high sensitivity of the harmonic intensity to pulse delay time and to the overlap of nuclear wave packets. We also solve numerically the three-dimensional (3D) time-dependent Schrödinger equation describing harmonic generation for a hydrogen atom prepared in a superposition of its two lowest atomic states, in order to investigate the dependence of the same effect (in a simpler system but in 3D) on the probe-pulse carrier-envelope phase (CEP) and on the probe duration. We also relate these strong effects in the intensity of harmonics to the correlation between the velocity of the recolliding electron wave packet and the electron velocity in the coherent superposition of the electron bound states.

A femtosecond degenerate four-wave mixing (fs-DFWM) technique for probing the alignment of molecules is described. The rotational wave packet generated by a strong pump beam modulates the nonresonant third-order susceptibility of the gas and this modulation is observed using a noncollinear background-free setup. As a demonstration of the technique, we measure the alignment of a linear molecule (nitrogen), a symmetric top (benzene), and an asymmetric top (iodobenzene) in a supersonic jet. The measured signal is shown to agree well with calculations of the nonresonant third-order susceptibility from the solution of the time-dependent Schrödinger equation. The pump-DFWM measurement scheme can be used with dilute jet-cooled targets, allows arbitrary pump pulses to be used, and is rapid enough to be incorporated into a feedback optimization loop. The scheme can easily be made polarization-sensitive, indicating the possibility of measuring and optimizing three-dimensional alignment of asymmetric-top molecules.

We study the flow of a one-dimensional Bose-Einstein condensate incident onto a narrow obstacle. We consider a configuration in which a dispersive shock is formed and propagates upstream away from the obstacle while the downstream flow reaches a supersonic velocity, generating a sonic horizon. Conditions for obtaining this regime are explicitly derived and the accuracy of our analytical results is confirmed by numerical simulations.

Correlation properties in ultracold Fermi gas with negative scattering length and its impact on the three-body recombination is analyzed. We find that Cooper pairing enhances the recombination rate in contrast to the decrease of this rate accompanying Bose-Einstein condensation in a Bose gas. This trend is characteristic for all interval of temperatures $T<T_C$.

We study fast expansions of cold atoms in a three-dimensional Gaussian-beam optical trap. Three different methods to avoid final motional excitation are compared: inverse engineering using Lewis-Riesenfeld invariants, which provides the best overall performance, a bang-bang approach, and a fast adiabatic approach. We analyze the excitation effect of anharmonic terms, radial-longitudinal coupling, and radial-frequency mismatch. In the inverse-engineering approach these perturbations can be suppressed or mitigated by increasing the laser beam waist.

We demonstrate that the static structure factor, momentum distribution, and density distribution provide clear signatures of the emergence of Wigner crystal for the fermionic dipolar gas with strongly repulsive dipole-dipole interactions trapped in one-dimensional optical lattices. Our numerical evidences are based on the exact diagonalization of the microscopic effective lattice Hamiltonian of few particles interacting with long-range interactions. As a comparison, we also study the system with only nearest-neighbor interactions, which displays quite different behavior from the dipolar system in the regime of strong repulsion.