We report a collision-induced Raman band by room temperature gas mixtures of sulfur hexafluoride and nitrogen. The band is centered at the sum of the frequencies of the symmetric-stretching ${\nu }_1$ transition of ${\mathrm{SF}}_6$ and the fundamental transition of ${\mathrm{N}}_2$, and its intensity scales as the product of the partial densities of the gases. The observed process is evidence of double incoherent Raman scattering (DRS) by ${\mathrm{SF}}_6-{\mathrm{N}}_2$, in which both molecules simultaneously undergo two Raman-allowed transitions. The band was found to be almost fully depolarized, in agreement with previous observations in other systems and with theoretical predictions. Its integrated intensity is about one-third higher than the total area predicted by the leading-order dipole-induced dipole model. This discrepancy suggests that DRS is a practical means of assessing the quality of intermolecular potential models, which, in the case of ${\mathrm{SF}}_6-{\mathrm{N}}_2$, is still believed to be not good enough. Our work is expected to open the door to a multitude of studies involving complicated processes encountered in nonpolar gases and their mixtures, which are of direct relevance to atmospheric research.

Diatomic potentials for krypton are computed and also probed experimentally. For a probe-laser wavelength near $811$ nm, several strong dipole-dipole interactions produce purely-long-range potential wells in the singly excited manifold of ($s+p$) potentials and in the doubly excited manifold of ($p+p$) and ($s+d$) potentials. Evidence of resonant photoassociation into bound states of these potential wells is observed in the emission of ions and ultraviolet photons from a magneto-optically trapped krypton cloud.

We derive calculations on the statistics of a heralded single-photon source based on parametric photon-pair generation. These calculations highlight fundamental and practical limits for these sources and show which physical parameters can be optimized to improve the quality of a real source.

We derive a quantum linear Boltzmann equation from first principles to describe collisional friction, diffusion, and decoherence in a unified framework. In doing so, we discover that the previously celebrated quantum contribution to position diffusion is not a true physical process, but rather an artifact of the use of a coarse-grained time scale necessary to derive Markovian dynamics.

We study the energy level shift of a static two-level atom interacting with a massless scalar field in a thermal bath with the presence of a plane boundary, which gives rise to the Casimir-Polder force. We separately calculate contributions of both thermal fluctuations and radiation reaction using the formalism suggested by J. Dalibard, J. Dupont-Roc, and C. Cohen-Tannoudji [J. Phys. (France) 43, 1617 (1982); 45, 673 (1984)] and analyze in detail the behaviors of the total energy level shifts in three distinct distance regimes in both the low- and high-temperature limits. A comparison of our results with those of a uniformly accelerated atom reveals that uniformly accelerated atoms, in general, do not behave the same as static ones in a thermal bath at the Unruh temperature in terms of the atomic energy level shifts.

Almost all Bell inequality experiments to date have used postselection and therefore relied on the fair sampling assumption for their interpretation. The standard form of the fair sampling assumption is that the loss is independent of the measurement settings, so the ensemble of detected systems provides a fair statistical sample of the total ensemble. This is often assumed to be needed to interpret Bell inequality experiments as ruling out hidden-variable theories. Here we show that it is not necessary; the loss can depend on measurement settings, provided the detection efficiency factorizes as a function of the measurement settings and any hidden variable. This condition implies that Tsirelson’s bound must be satisfied for entangled states. On the other hand, we show that it is possible for Tsirelson’s bound to be violated while the Clauser-Horne-Shimony-Holt (CHSH)-Bell inequality still holds for unentangled states, and present an experimentally feasible example.

We propose a class of probabilistic reversing operations on the state of a system that was disturbed by a weak measurement. It can approximately recover the original state from the disturbed state especially with an additional information gain using the Hermitian conjugate of the measurement operator. We illustrate the general scheme by considering a quantum measurement consisting of spin systems with an experimentally feasible interaction and show that the reversing operation simultaneously increases both the fidelity to the original state and the information gain with such a high probability of success that their average values increase simultaneously.

A nonlinear evolution equation for sub- and a few-cycle pulse is derived in a cubic medium including the delayed nonlinear response. The equation is derived for the real electric field directly without separating the pulse into an envelope and the carrier wave. Using this equation, we numerically study the properties of eight-cycle pulse, at $0.39-\mu$m wavelength, propagating in a hollow-core fiber filled with $D_2$ gas.

It is pointed out that the bona fide Wigner distribution recently introduced [Phys. Rev. A 78, 060101(R) (2008)] is in fact the rotational Wigner function earlier derived and thoroughly studied [Phys. Rev. A 49, 3255 (1994); 71, 069901(E) (2005)], so the latter remains indeed the natural phase-space representation for the rotation-angle and angular-momentum pair.

For composite systems made of $N$ different particles living in a space characterized by the same deformed Heisenberg algebra, but with different deformation parameters, we define the total momentum and the center-of-mass position to first order in the deformation parameters. Such operators satisfy the deformed algebra with effective deformation parameters. As a consequence, a two-particle system can be reduced to a one-particle problem for the internal motion. As an example, the correction to the hydrogen atom $\mathit{nS}$ energy levels is re-evaluated. Comparison with high-precision experimental data leads to an upper bound of the minimal length for the electron equal to $3.3\times {10}^{-18}\hspace{0.5em}\mathrm{m}$. The effective Hamiltonian describing the center-of-mass motion of a macroscopic body in an external potential is also found. For such a motion, the effective deformation parameter is substantially reduced due to a factor $1/N^2$. This explains the strangely small result previously obtained for the minimal length from a comparison with the observed precession of the perihelion of Mercury. From our study, an upper bound of the minimal length for quarks equal to $2.4\times {10}^{-17}\hspace{0.5em}\mathrm{m}$ is deduced, which appears close to that obtained for electrons.

A parity measurement on two qubits, each consisting of a single atom in a cavity, can be realized by measuring the phase shift of a probe beam which interacts sequentially with the two qubits, but imperfections lead to decoherence within the subspaces of a given parity. We demonstrate that a different setup, where the probe light interacts repeatedly with the qubits, can reduce the rate of decoherence within the odd- or the even-parity subspace significantly. We consider both the case of a resonant and the case of a nonresonant light-atom interaction and find that the performance is comparable if the parameters are chosen appropriately.

For quantum states of two subsystems, highly entangled states have a higher capacity of transmitting classical as well as quantum information, and vice versa. We show that this is no more the case in general: Quantum capacities of multiaccess channels, motivated by communication in quantum networks, do not have any relation with genuine multiparty entanglement measures. Importantly, the statement is demonstrated for arbitrary multipartite entanglement measures. Along with revealing the structural richness of multiaccess channels, this gives us a tool to classify multiparty quantum states from the perspective of its usefulness in quantum networks, which cannot be visualized by any genuine multiparty entanglement measure.

The angular distribution of photoelectrons and linear magnetic dichroism in the angular distribution for the $4p$ photoemission from Rb atoms in the ground state, oriented by laser pumping, were measured in the photon energy range from $50$ to $100$ eV. The experimental results are compared with the multiconfiguration Dirac-Fock (MCDF) calculations. We show that the zero-crossing of the dichroism as a function of energy is connected with the Cooper minimum in the cross section. This fact can be used for an accurate determination of the position of the Cooper minimum.

Bloch band and stabilities of Bloch waves of superfluid Fermi gases in one-dimensional (1D) periodic optical lattices are discussed. Within the hydrodynamical theory and the two-mode approximation, the Bloch band structure, the energetic and dynamical instabilities of Bloch waves at the first Brilliouin zone are presented. The results show that, when the atom density is beyond a critical value, a loop structure in the Bloch band at the zone edge is developed along the BEC-BCS crossover. The Bloch band structure and the stabilities of Bloch waves are modified dramatically when the system crosses from the BEC side to the BCS side, and they can be adjusted to the required characteristics by changing the atom’s interaction (with the Feshbach resonance technique), the atom density, and the lattice parameters. The analytical expressions of the critical atom density for exciting the loop structure and maintaining the stabilities of Bloch waves are obtained.

We derive an effective action for the vortex-position degree of freedom in a superfluid by integrating out condensate phase- and density-fluctuation environmental modes. When the quantum dynamics of environmental fluctuations is neglected, we confirm the occurrence of the vortex Magnus force and obtain an expression for the vortex mass. We find that this adiabatic approximation is valid only when the superfluid droplet radius $R$, or the typical distance between vortices, is very much larger than the coherence length $\xi$. We go beyond the adiabatic approximation numerically, accounting for the quantum dynamics of environmental modes and capturing their dissipative coupling to condensate dynamics. For the case of an optical-lattice superfluid, we demonstrate that vortex motion damping can be adjusted by tuning the ratio between the tunneling energy $J$ and the on-site interaction energy $U$. We comment on the possibility of realizing vortex-Landau-level physics.

The hyperfine structure (HFS) of a bound electron is modified by the self-interaction of the electron with its own radiation field. This effect is known as the self-energy correction. In this work, we discuss the evaluation of higher order self-energy corrections to the HFS of bound $P$ states. These are expressed in a semianalytic expansion involving powers of $Z\alpha$ and $\ln (Z\alpha )$, where $Z$ is the nuclear charge number and $\alpha$ is the fine-structure constant. We find that the correction of relative order $\alpha \hspace{0.5em}(Z\alpha ){}^2$ involves only a single logarithm $\ln (Z\alpha )$ for $P_{1/2}$ states [but no term of order $\alpha \hspace{0.5em}(Z\alpha ){}^2\ln {}^2(Z\alpha )$], whereas for $P_{3/2}$ states, even the single logarithm vanishes. By a Foldy-Wouthuysen transformation, we identify a nuclear-spin-dependent correction to the electron’s transition current, which contributes to the HFS of $P$ states. A comparison of the obtained analytic results to a numerical approach is made.

We report on analysis of the mode structure of a Bose-Einstein condensate loaded in a complex parabolic potential and subjected to a constant pump. Stationary solutions for the positive and negative scattering lengths are addressed. In the case of a positive scattering length and large number of atoms the ground state is described by the Thomas-Fermi distribution, whose properties in the presence of the dissipation are very different from its conservative counterpart. It is shown that for a positive scattering length only the ground state appears to be stable.

A Bose-Einstein condensate exhibiting a nontrivial phase induces an artificial magnetic field in immersed impurity atoms trapped in a stationary, ring-shaped optical lattice. We present an effective Hamiltonian for the impurities for two condensate setups: the condensate in a rotating ring and in an excited rotational state in a stationary ring. We use Bogoliubov theory to derive analytical formulas for the induced artificial magnetic field and the hopping amplitude in the limit of low condensate temperature where the impurity dynamics is coherent. As methods for observing the artificial magnetic field we discuss time-of-flight imaging and mass current measurements. Moreover, we compare the analytical results of the effective model to numerical results of a corresponding two-species Bose-Hubbard model. We also study numerically the clustering properties of the impurities and the quantum chaotic behavior of the two-species Bose-Hubbard model.

The process of high-order harmonic generation in gases is numerically investigated in the presence of a few-cycle pulsed-Bessel-beam pump, featuring a periodic modulation in the peak intensity due to large carrier-envelope-phase mismatch. A two-decade enhancement in the conversion efficiency is observed and interpreted as the consequence of a mechanism known as a nonlinearly induced modulation in the phase mismatch.

Superconducting quantum circuits, such as the superconducting phase qubit, have multiple quantum states that can interfere with ideal qubit operation. The use of multiple frequency control pulses, resonant with the energy differences of the multistate system, is theoretically explored. An analytical method to design such control pulses is developed, using a generalization of the Floquet method to multiple frequency controls. This method is applicable to optimizing the control of both superconducting qubits and qudits and is found to be in excellent agreement with time-dependent numerical simulations.