Chemical transformations are viewed here as quantum processes modulated by external fields, that is, as shifts in reactant to product amplitudes within a quantum state represented by a linear (coherent) superposition of electronuclear basis functions; their electronic quantum numbers identify the “chemical species.” This basis set can be mapped from attractors built from a unique electronic configurational space that is invariant with respect to the nuclear geometry. In turn, the quantum numbers that label these basis functions and the semiclassical potentials for the electronic attractors may be used to derive reaction coordinates to monitor progress as a function of the applied field. A generalization of Feynman's three-state model for the ammonia inversion process illustrates the scheme; to enforce symmetry for the entire inversion process model and ensure invariance with respect to nuclear configurations, the three attractors and their basis functions are computed with a grid of fixed floating Gaussian functions. The external-field modulation of the effective inversion barrier is discussed within this conceptual approach. This analysis brings the descriptions of chemical processes near modern technologies that employ molecules to encode information by means of confinement and external fields.

The variance of an arbitrary pointer observable is considered for the general case that a complex weak value is measured using a complex valued pointer state. For the typical cases where the pointer observable is either its position or momentum, the associated expressions for the pointer's variance after the measurement contain a term proportional to the product of the weak value's imaginary part with the rate of change of the third central moment of position relative to the initial pointer state just prior to the time of the measurement interaction when position is the observable—or with the initial pointer state's third central moment of momentum when momentum is the observable. These terms provide a means for controlling pointer position and momentum variance and identify control conditions which, when satisfied, can yield variances that are smaller after the measurement than they were before the measurement. Measurement sensitivities which are useful for estimating weak-value measurement accuracies are also briefly discussed.

We propose a scheme for implementing cross-Kerr nonlinearity between two superconducting transmission line resonators (TLRs) via their interactions with a coupler constructed by two superconducting transmon qubits connected to each other through a superconducting quantum interference device. When suitably driven, the coupler can induce very strong cross phase modulation (XPM) between the two TLRs due to its $N$-type level structure and the consequent electromagnetically induced transparency in its lowest states. The flexibility of our design can lead to various inter-TLR coupling configurations. The obtained cross-Kerr coefficient is large enough to allow many important quantum operations in which only few photons are involved. We further show that this scheme is very robust against fluctuations in solid-state quantum circuits. Our numerical calculations imply that the absorption and the dispersion of the TLRs resulting from the decoherence of the coupler are very small compared with the proposed XPM strength.

The influence of the isotope effect (mass dependence) on the charge-exchange process in low-energy collisions of light ions with hydrogen isotopes (H, D, and T) is studied using the adiabatic theory of transitions in slow collisions developed by E. Solov’ev [Sov. Phys. Usp. 32, 228 (1989)]. Results of the numerical calculations are presented for the charge-exchange probabilities and cross sections of Li, Be, and C ions colliding with hydrogen isotopes and for the inverse reactions.

In this paper we give a first principles microphysics derivation of the nonequilibrium forces between an atom, treated as a three-dimensional harmonic oscillator, and a bulk dielectric medium modeled as a continuous lattice of oscillators coupled to a reservoir. We assume no direct interaction between the atom and the medium but there exist mutual influences transmitted via a common electromagnetic field. By employing concepts and techniques of open quantum systems we introduce coarse-graining to the physical variables—the medium, the quantum field, and the atom’s internal degrees of freedom, in that order—to extract their averaged effects from the lowest tier progressively to the top tier. The first tier of coarse-graining provides the averaged effect of the medium upon the field, quantified by a complex permittivity (in the frequency domain) describing the response of the dielectric to the field in addition to its back action on the field through a stochastic forcing term. The last tier of coarse-graining over the atom’s internal degrees of freedom results in an equation of motion for the atom’s center of mass from which we can derive the force on the atom. Our nonequilibrium formulation provides a fully dynamical description of the atom’s motion including back-action effects from all other relevant variables concerned. In the long-time limit we recover the known results for the atom-dielectric force when the combined system is in equilibrium or in a nonequilibrium stationary state.

The unique time signature of the survival probability exactly at the exceptional point parameters is studied here for the hydrogen atom in strong static magnetic and electric fields. We show that indeed the survival probability $S\left(t\right)={\left|\langle \psi \left(0\right)|\psi \left(t\right)\rangle \right|}^2$ decays exactly as ${|1-at|}^2{e}^{-{\Gamma }_{\mathrm{EP}}t/\hslash }$, where ${\Gamma }_{\mathrm{EP}}$ is associated with the decay rate at the exceptional point and $a$ is a complex constant depending solely on the initial wave packet that populates exclusively the two almost degenerate states of the non-Hermitian Hamiltonian. This may open the possibility for a first experimental detection of exceptional points in a quantum system.

We present a numerical study of the properties of optical forces on moving atoms derived from purely stimulated processes produced by multiple adiabatic rapid-passage sequences. The optical Bloch equations are solved for a carefully timed sequence of frequency-swept pulses that can produce a force much larger than the ordinary radiative force. We describe the effects of the sweep range, peak intensity, sweep direction, number of pulses, atomic velocity, and spontaneous emission. Since the momentum of thermal atoms is much larger than that transferred by a single absorption-stimulated emission cycle, multiple repetitions are needed to make a significant velocity change.

We investigate tunneling properties of collective modes in the polar phase of a spin-1 spinor Bose-Einstein condensate (BEC). This spinor BEC state has two kinds of gapless modes (i.e., Bogoliubov and spin-wave). Within the framework of mean-field theory at $T=0$, we show that these Goldstone modes exhibit perfect transmission in the low-energy limit. Their anomalous tunneling behavior still holds in the presence of superflow, except in the critical current state. In the critical current state, while the tunneling of Bogoliubov mode is accompanied by finite reflection, the spin wave still exhibits perfect transmission, unless the strengths of spin-dependent and spin-independent interactions take the same value. We discuss the relation between perfect transmission of a spin wave and underlying superfluidity through a comparison of wave functions of the spin wave and the condensate.

The static fluctuation approximation (SFA) is used to study the condensate fraction and the specific heat capacity of finite two-dimensional spin-polarized atomic hydrogen. It is found that Bose-Einstein condensation occurs in this system. The transition temperature at different densities decreases as the number of particles of the system increases. At low density, a sharp peak in the specific heat capacity is observed at the transition temperature. On the other hand, as the density of the system increases, the transition temperature becomes no longer well-defined, and a hump is observed in the specific heat capacity around the transition temperature. A qualitative comparison of our results to published results for finite Bose systems shows good agreement.

A two-dimensional (2D), cylindrical, periodic surface lattice (PSL) forming a surface field cavity is considered. The lattice is created by introducing 2D periodic perturbations on the inner surface of a cylindrical waveguide. The PSL facilitates a resonant coupling of the surface and near cutoff volume fields, leading to the formation of a high-$Q$ cavity eigenmode. The cavity eigenmode is described and investigated using a modal approach, considering the model of a cylindrical waveguide partially loaded with a metadielectric. By using a PSL-based cavity, the concept of a high-power, 0.2-THz Cherenkov source is developed. It is shown that if the PSL satisfies certain defined conditions, single-mode operation is observed.

We investigate light storage by electromagnetically induced transparency in a Pr${}^{3+}$:Y${}_2$SiO${}_5$ crystal. The retrieval efficiency versus storage time shows pronounced oscillations, which are due to beating of dark-state polaritons in multiple Zeeman-shifted $\Lambda$ systems. As a significant obstacle for applications, the beating leads to periodic collapses of the retrieved signal. We demonstrate how to systematically control the perturbing oscillations in the retrieval efficiency by external magnetic fields. This enables suppression of collapses and retrieval of stored data at any storage time, approaching the limit set by the coherence time in the medium.

An analytic solution for a uniaxial spherical resonator is presented using the method of Debye potentials. This serves as a starting point for the calculation of whispering gallery modes (WGMs) in such a resonator. Suitable approximations for the radial functions are discussed in order to best characterize WGMs. The characteristic equation and its asymptotic expansion for the anisotropic case is also discussed, and an analytic formula with a precision of the order $O[{\nu }^{-1}]$ is also given. Our careful treatment of both boundary conditions and asymptotic expansions makes the present work a particularly suitable platform for a quantum theory of whispering gallery resonators.

We demonstrate a general procedure to construct entanglement witnesses for any entangled state. This procedure is based on the trace inequality and a general form of entanglement witnesses, which is in the form $W=\rho -c_{\rho }I$, where $\rho$ is a density matrix, $c_{\rho }$ is a non-negative number related to $\rho$, and $I$ is the identity matrix. The general form of entanglement witnesses is deduced from Choi-Jamiołkowski isomorphism, that can be reinterpreted as that all quantum states can be obtained by a maximally quantum entangled state pass through certain completely positive maps. Furthermore, we provide the necessary and sufficient condition of the entanglement witness $W=\rho -c_{\rho }I$ in operation, as well as in theory.

Neutral fractions of scattered ground-state hydrogen atoms after grazing incidence collisions of both H(1$s$) and H${}^{+}$ projectiles with an Al(111) surface have been computed within the impact velocity range $0.1⩽v⩽2.0$ a.u. by means of the etisc1d code. Comparison between the results related to the H(1$s$) beam with those obtained for H${}^{+}$ projectiles—which we found in earlier work to be in good agreement with experimental data—shows that in the velocity range $0.3⩽v⩽1.3$ a.u. neutral fractions keep the memory of the initial state, whereas in the extreme ranges of low velocities ($v\lesssim 0.3$ a.u.) and high velocities ($v\gtrsim 1.3$ a.u.), the outgoing charge fractions do not depend on the charge state of the initial beam. In order to analyze qualitatively these findings, rate-equations calculations as well as a simplified analytical model have been also implemented. Due to the lack of experimental data for impinging H(1$s$), the present results represent important theoretical predictions which might stimulate further experimental works.

We describe an experiment confirming the evidence of the antibunching effect on a beam of noninteracting thermal neutrons. The comparison between the results recorded with a high-energy-resolution source of neutrons and those recorded with a broad-energy-resolution source enables us to clarify the role played by the beam coherence in the occurrence of the antibunching effect.

We have produced a quantum degenerate mixture of fermionic alkali-metal ${}^6$Li and bosonic spin-singlet ${}^{174}$Yb gases. This was achieved using sympathetic cooling of lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant optical dipole trap. We observe the coexistence of Bose-condensed ($T/T_{\mathrm{c}}\simeq 0.8$) ${}^{174}$Yb with $2.3\times {10}^4$ atoms and Fermi degenerate ($T/T_{\mathrm{F}}\simeq 0.3$) ${}^6$Li with $1.2\times {10}^4$ atoms. Quasipure Bose-Einstein condensates of up to $3\times {10}^4$ ${}^{174}$Yb atoms can be produced in single-species experiments. Our results mark a significant step toward studies of few- and many-body physics with mixtures of alkali-metal and alkaline-earth-metal-like atoms, and for the production of paramagnetic polar molecules in the quantum regime. Our methods also establish a convenient scheme for producing quantum degenerate ytterbium atoms in a 1064 nm optical dipole trap.

While exponential decay is ubiquitous in nature, deviations at both short and long times are dictated by quantum mechanics. Nonexponential decay is known to arise due to the possibility of reconstructing the initial state from the decaying products. We discuss the quantum decay dynamics by tunneling of a many-particle system, characterizing the long-time nonexponential behavior of the nonescape and survival probabilities. The effects of contact interactions and quantum statistics are described. It is found that, whereas for noninteracting bosons the long-time decay follows a power law with an exponent linear in the number of particles $N$, the exponent becomes quadratic in $N$ in the fermionic case. The same results apply to strongly interacting many-body systems related by the generalized Bose-Fermi duality. The faster fermionic decay can be traced back to the effective hard-core interactions between particles, which are as well the decaying products, and exhibit spatial antibunching which hinders the reconstruction of the initial unstable state. The results are illustrated with a paradigmatic model of quantum decay from a trap allowing leaks by tunneling, whose dynamics is described exactly by means of an expansion in resonant states.

We investigate the dynamics of a quantum oscillator, whose evolution is monitored by a Bose-Einstein condensate (BEC) trapped in a symmetric double-well potential. It is demonstrated that the oscillator may experience various degrees of decoherence depending on the variable being measured and the state in which the BEC is prepared. These range from a “coherent” regime in which only the variances of the oscillator position and momentum are affected by measurement, to a slow (power-law) or rapid (Gaussian) decoherence of the mean values themselves.

We present a simple and practical quantum protocol involving two mistrustful agencies in Minkowski space, which allows Alice to transfer data to Bob at a space-time location that neither can predict in advance. The location depends on both Alice’s and Bob’s actions. The protocol guarantees unconditionally to Alice that Bob learns the data at a randomly determined location; it guarantees to Bob that Alice will not learn the transfer location even after the protocol is complete. The task implemented, transferring data at a space-time location that remains hidden from the transferrer, has no precise analog in nonrelativistic quantum cryptography. It illustrates further the scope for novel cryptographic applications of relativistic quantum theory.

We report an experimental determination of the diamagnetic correction to the ${}^9$Be${}^{+}$ ground state hyperfine constant $A$. We measured $A$ $=$ $-625008837.371\left(11\right)$ Hz at a magnetic field $B$ of 4.4609 T. Comparison with previous results, obtained at lower values of $B$ (0.68 T and 0.82 T), yields the diamagnetic shift coefficient $k$ $=$ $2.63\left(18\right)\times {10}^{-11}$ T${}^{-2}$, where $A\left(B\right)=A_0(1+k{B}^2)$. The zero-field hyperfine constant $A_0$ is determined to be $-625008837.044\left(12\right)$ Hz. The $g$-factor ratio ${g_I}^{\prime }/g_J$ is determined to be $2.1347798527\left(10\right)\times {10}^{-4}$, which is equal to the value measured at lower $B$ to within experimental error. Upper limits are placed on some other corrections to the Breit-Rabi formula. The measured value of $k$ agrees with theoretical estimates.