In the presence of a magnetic field atomic ions are shown to generate monochromatic radiation with the frequency $\omega =QB/M$, depending on the field strength B and the ion mass M and charge Q. The origin of the effect is the interaction of the bound electrons with the oscillating field of the Stark term coupling the center of mass and electronic motions of an ion due to the nonseparability of the collective and internal degrees of freedom in the system. The intensity of the radiation is defined by the velocities of the ions and the magnetic field strength.

We have observed Larmor spin precession in the ground state of laser-cooled ${}^{85}\mathrm{Rb}$ atoms through paramagnetic Faraday rotation. We have been able to obtain a precision of $18\mathrm{pT}$ in the determination of the applied magnetic field, which proves the usefulness of laser-cooled atoms as an atomic magnetometer.

Strongly field-phase-dependent ionization is demonstrated by using a convenient experimental setup appropriate for excitation schemes involving an even number of photons. In this paper, ionization in Xe occurs via two phase-correlated electromagnetic fields, namely, the fundamental and the second harmonic of the laser. Since the fields are in the visible and ultraviolet regime, they have readily controllable amplitudes. Thus excitation interference conditions and, consequently, phase-sensitive ionization can be easily and efficiently established.

We present tunneling ionization rates from a double-well potential in the presence of an external dc electric field in order to better understand the behavior of molecules in strong laser fields. Our calculations confirm the well-established peak in the ionization rate as a function of internuclear separation at a critical separation $R_{\max }.$ However, we also find that $R_{\max }$ is a function of the external field strength F such that $R_{\max }\mathrm{}\left(F\right)F$ is approximately constant. Because these numerical calculations make no assumptions beyond the shape of the potential well, we can test commonly used approximations to the shift in the energy levels as a function of internuclear separation and field strength. Finally, we find that the tunneling ionization rate is not a monotonic function of the field strength showing a pronounced minimum and thus is qualitatively different from tunneling ionization rates in atoms. To our knowledge, this behavior has not been predicted previously for molecules in strong fields.

Romero and Aucar [Phys. Rev. A 57, 2212 (1998)] have found a vanishing result for the relativistic correction to the dipole sum rule $\Delta S_1$ for a one-electron system. They have given a result for the dipole sum rule $\Delta S_2$ as well. We argue that these results are both incorrect and show explicitly that their approach yields a nonvanishing result for $\Delta S_1.$ The corrected result is in agreement with that which we have obtained in a recent paper, in which we present explicit expressions for $\Delta S_1,$ $\Delta S_2,$ and several other more general sum rules.

We have recently calculated corrections to the $S_1$ and $S_2$ generalized oscillator strength sum rules [Phys. Rev. A 57, 2212 (1998)]. In a recent Comment, Cohen and Leung have pointed out the need of taking into account the normalization of the large component of Dirac wave functions. We agree on that and, although this will change the final results presented in the original paper, it is shown that, by including the normalization for the large components in a general way, the method of analysis remains valid and general.

Spin-polarized electron pairs are generated following the ionization of the valence electron of polarized Li atoms by polarized low-energy electron impact. It is shown that the shapes of energy-sharing spectra of the pairs are influenced by an interplay of structures resulting from binary-encounter and exchange effects of the two electrons. The spin asymmetry is measured at an excess energy as low as 20 eV and compared with dynamical calculations of different models. The shape of the asymmetry is explained on the grounds of symmetry and dynamics.

We use quantum scattering methods to calculate the light-induced collisional loss of laser-cooled and trapped magnesium atoms for detunings up to 30 atomic linewidths to the red of the ${}^1{S}_0{-}^1{P}_1$ cooling transition. Magnesium has no hyperfine structure to complicate the theoretical studies. We evaluate both the radiative and nonradiative mechanisms of trap loss. The radiative escape mechanism via allowed ${}^1{\Sigma }_u$ excitation is dominant for more than about one atomic linewidth detuning. Molecular vibrational structure due to photoassociative transitions to bound states begins to appear beyond about ten linewidths detuning.

Picosecond laser pulses have been used to produce Rydberg wave packets in calcium atoms in the presence of a strong static electric field. The dynamics of the Stark wave packets have been observed by measuring the momentum-space probability distribution as a function of time. The full precession of the electronic orbital angular momentum, the appearance of a large-amplitude, linear oscillation of the electronic dipole moment, and a pronounced, periodic up-down asymmetry in the momentum distribution are all observed directly.

We analyze the quantum dynamics of the one-dimensional periodically kicked Rydberg atom. The time-dependent Schrödinger equation is solved by employing a nonunitary representation of the period-one evolution operator in a finite basis set that accounts for the outbound probability flux. We find a direct correspondence between stable classical islands in phase space and the quantum Husimi distributions of stable Floquet states. These results explain the pronounced peak recently found experimentally in the frequency-dependent survival probability of Rydberg states subject to a sequence of half-cycle pulses.

We propose a method to study the degeneracy of a trapped atomic gas of fermions through the relaxation of the motion of a test particle. In the degenerate regime, and for an energy of the test particle well below the Fermi energy, we show that the Fermi-Dirac statistics is responsible for a strong decrease in the relaxation rate. This method can be used to directly measure the temperature of the fermionic gas.

Population dynamics of atomic inner-shell vacancy states are analyzed for the possibility of inversion in relation to keV x-ray laser schemes. Transitions between pairs of inner-shell vacancy states are considered in which the states are pumped via electron-impact inner-shell ionization by a femtosecond high-energy electron pulse. For appropriate atomic systems, transient inversion is predicted due to rapid lower state depopulation via Coster-Kronig decay.

The behavior of a particle possessing a permanent or induced electric dipole moment and interacting with external electromagnetic fields is described. For a special configuration of the fields, a quantum effect is obtained for a moving dipole. The experimental observation of this effect is within reach of atom or molecular interferometry.

In a gedanken experiment N particles in a generalized Greenberger-Horne-Zeilinger-(GHZ)-type beam-entangled state (each particle can be in one of M beams) are fed into N symmetric $2M$-port beam splitters (spatially separated). Correlation functions for such a process (using the Bell numbers value assignment approach) reveal a remarkable symmetry. For $N=M+1\mathrm{}>~4$ a series of GHZ paradoxes are shown.

We propose a quantum optical version of Schrödinger’s famous gedanken experiment in which the state of a microscopic system (a cavity field) becomes entangled with and disentangled from the state of a massive object (a movable mirror). Despite the fact that a mixture of Schrödinger cat states is produced during the evolution (due to the fact that the macroscopic mirror starts off in a thermal state), this setup allows us to systematically probe the rules by which a superposition of spatially separated states of a macroscopic object decoheres. The parameter regime required to test environment-induced decoherence models is found to be close to those currently realizable, while that required to detect gravitationally induced collapse is well beyond current technology.

Using the Frieden and Soffer principle of extreme physical information we present a method for the construction of WKB wave functions that avoids the matching problem between the classically allowed and forbidden regions. When this formalism is applied in conjunction with the semiclassical methods for N-fermion systems, it provides one with Thomas-Fermi and Wigner-Kirkwood densities, valid beyond the turning points that also include shell effects. The method is illustrated with reference to both the sextic bistable and the Morse potential.

We consider the definition that might be given, in quantum theory, to the time at which a particle arrives at a given place. We discuss an ambiguity that arises in three, but not in one, spatial dimensions. We first express this ambiguity within the ontology of Bohmian quantum theory, but we also show that it can be expressed independently of that ontology.

A first quantized theory of the photon is developed that incorporates all of the usual rules of quantum mechanics. The state vector is argued to be proportional to the four-vector potential. Scalar products and the probability amplitude are invariant under gauge transformations that satisfy the Lorentz gauge condition. The eigenvectors of a recently constructed Hermitian position operator with commuting components provide a basis for the position representation.