We present the results of optimal-control experiments and calculations on the production of highly charged ions in intense laser field irradiation of large xenon clusters. Experimentally, a spectacular enhancement in the yield of highly charged ions is observed when clusters are subjected to an optimized laser field consisting of a sequence of two pulses, with a time delay that depends on the intensity of the laser and the size of the clusters. Similar results are obtained in optimal-control calculations, which demonstrate that the optimized pulse shape maximizes the efficiency of resonant heating.

The purity of a reduced state for spins that is pure in the rest frame will most likely appear to degrade because spin and momentum become mixed when viewed by a moving observer. We show that such a boost-induced decrease in spin purity observed in a moving reference frame is intrinsically related to the spatial localization properties of the wave package observed in the rest frame. Furthermore, we prove that, for any localized pure state with separable spin and momentum in the rest frame, its reduced density matrix for spins inevitably appears to be mixed whenever viewed from a moving reference frame.

We investigate entanglement between electronic and nuclear degrees of freedom for a model nonadiabatic system. We find that entanglement (measured by the von Neumann entropy of the subsystem for the eigenstates) becomes nearly maximum when the system shows “nonadiabatic chaos” behavior which was found in our previous work [Phys. Rev. E 63, 066221 (2001)], but the reverse is not necessarily the case.

Optimal labeling schemes lead to efficient experimental protocols for quantum-information processing by nuclear magnetic resonance (NMR). A systematic approach to finding optimal labeling schemes for a given computation is described here. The scheme is described for both quadrupolar systems and spin-$\frac{1}{2}$ systems. Using the technique of transition selective pulses, one of the optimal labeling schemes has been applied to experimentally implement a quantum full adder in a four-qubit system by NMR.

We associate with every quantum channel $T$ acting on a Hilbert space $\mathcal{H}$ a pair of Hermitian operators, referred to as “Hamiltonians,” over the symmetric subspace of ${\mathcal{H}}^{\otimes 2}$. The expectation values of these Hamiltonians over symmetric product states give either the purity or the pure-state fidelity of $T$. This allows us to analytically compute these measures for a wide class of channels, and to identify states that are optimal with respect to these measures.

A possible experimental scheme of the Garisto-Hardy disentanglement eraser based on a cavity QED system is presented. This scheme can be used for a delayed choice quantum eraser. It also allows us to acquire single-qubit control over teleportation of an arbitrary binary state.

The problem of finding the optimal strategy for estimating a generalized amplitude damping channel ${\Gamma }_{\eta }^{\left(p\right)}$ by means of the extension $\mathrm{id}\otimes {\Gamma }_{\eta }^{\left(p\right)}$ is addressed. We first evaluate the quantum Fisher information of output states based on the symmetric logarithmic derivative and specify all pure-state inputs that maximize the quantum Fisher information. We next investigate the ${\nabla }^e$ autoparallelity of output state manifolds and characterize the condition for the existence of an efficient estimator. A comparison of these results concludes that, while there is no uniformly optimal input for all $p$ and $\eta$, a maximally entangled input is an admissible one under a nonasymptotic setting.

In this paper, we study the quantum computation realized by an interaction-free measurement (IFM). Using the interferometer of Kwiat et al., we construct a two-qubit quantum gate that changes one particle’s trajectory according to whether or not the other particle exists in the interferometer. We propose a method for distinguishing Bell-basis vectors, each of which consists of a pair of an electron and a positron, by this gate. (This is called the Bell-basis measurement.) This method succeeds with probability $1$ in the limit of $N\to \infty$, where $N$ is the number of beam splitters in the interferometer. Moreover, we can carry out a controlled-NOT gate operation by the above Bell-basis measurement and the method proposed by Gottesman and Chuang. Therefore, we can prepare a universal set of quantum gates by the IFM. This means that we can execute any quantum algorithm by the IFM.

The accuracy of the Pluvinage wave function for the ground state of helium is investigated by considering a number of different physical processes including double ionization by photoabsorption, Compton scattering, and electron impact. In the high-energy limit of these processes, the accuracy of the initial ground state can be ascertained without reference to the final double-continuum state. In this limit, we find that a Hylleraas description is superior to the Pluvinage one. For intermediate energies, final-state correlation becomes important, so we employ a 3C description of the final state (the 3C wave function is the double-continuum analog of the Pluvinage wave function). In this case, however, better agreement with experiment is obtained with the Pluvinage initial state. A possible explanation for this seemingly paradoxical result is suggested.

We study the motion of two atoms trapped at distant positions in the field of a driven standing-wave high-$Q$ optical resonator. Even without any direct atom-atom interaction the atoms are coupled through their position dependent influence on the intracavity field. For sufficiently good trapping and low cavity losses the atomic motion becomes significantly correlated and the two particles oscillate in their wells preferentially with a $90°$ relative phase shift. The onset of correlations seriously limits cavity cooling efficiency, raising the achievable temperature to the Doppler limit. The physical origin of the correlation can be traced back to a cavity mediated crossfriction, i.e., a friction force on one particle depending on the velocity of the second particle. Choosing appropriate operating conditions allows for engineering these long range correlations. In addition this cross-friction effect can provide a basis for sympathetic cooling of distant trapped clouds.

We examine the topology of eigenenergy surfaces associated to a three-state system driven by two quasi-resonant fields. We deduce mechanisms that allow us to generate various coherent superposition of two states using an additional field, far off resonances. We report the numerical validations in mercury atoms as a model system, creating the coherent superpositions of two excited states and of two states coupled by a Raman process.

We report the efficient production of a large Bose-Einstein condensate in ${}^{87}\mathrm{Rb}$ atoms. This is achieved by quickly reducing the radio frequency of the magnetic field at a rate of $-96.8\mathrm{kHz}∕\mathrm{s}$ during the final stage of evaporative cooling, and we have produced a condensate with $(2.2\pm 0.1)\times {10}^6$ atoms against a serious three-body recombination loss. We observed the dependence of the cooling efficiency on the rate at which the truncated energy changes by measuring the condensate growth for three kinds of radio-frequency sweep. The experimental results quantitatively agree with calculations based on the quantum kinetic theory of a Bose gas.

Using numerical solutions of the time-dependent Schrödinger equation for a hydrogen and a helium atom in a linearly polarized laser field, we calculate the photoelectron signal $P_{+}$, $P_{-}$ measured by two opposing detectors placed along the laser polarization vector, with laser focus in the center. Our calculations show a significant sensitivity of the normalized asymmetry coefficient $a=(P_{+}-P_{-})∕(P_{+}+P_{-})$ to the carrier-envelope (CE) phase for few-cycle laser pulses. We find a very simple dependence of this coefficient on the CE phase $\varphi$ and on pulse duration for laser intensities slightly below the tunneling regime, i.e., for the intensities range between the perturbative-multiphoton and tunneling regime, for laser pulses shorter than two laser cycles. In particular, we find that in this intensity regime, the asymmetry is zero for a fixed, particular value of $\varphi ={\varphi }_0\simeq -0.3\pi$ and is maximum for $\varphi ={\varphi }_M={\varphi }_0+\pi ∕2$. These regularities would allow one to measure the CE phase. In particular, the condition of zero asymmetry for few-cycle pulses can be useful for stabilizing the CE phase.

We study the dynamical response of cold interacting atoms in the Mott insulator phase to a static force. As shown in the experiment by [M. Greiner et al., Nature 415, 39 (2002)], this response has resonant character, with the main resonance defined by coincidence of Stark energy and on-site interaction energy. We analyze the dynamics of the atomic momentum distribution, which is the quantity measured in the experiment, for near resonant forcing. The momentum distribution is shown to develop a recurring interference pattern, with a recurrence time which we define in the paper.

We show that the hyperfine polarization in the vicinity $(\sim {10}^{-5}\mathrm{cm})$ of cell surfaces can be used as a way to quantify and map the regional surface property inside optical pumping cells. In silicone-coated cells our method allows us to image the regional quality of the coatings, revealing the existence of areas that have strikingly different qualities.

We use classical statistical mechanics and thermodynamics to describe the response of a trapped multi-species atomic sample to a local deformation in the confining potential. An adiabatic deformation may not only increase the peak phase-space density, but also lower the temperature and spin-polarize the atoms.

A relativistic many-body calculation is performed for the low-lying states of the alkaline earth ions ${}^{43}\mathrm{Ca}^{+}$ and ${}^{87}\mathrm{Sr}^{+}$. The zeroth-order hyperfine structure constants are evaluated with Dirac-Fock wave functions, and the finite basis sets of the Dirac-Fock equation are constructed by $B$ splines. With the finite basis sets, the core polarization and the correlation effect are calculated. The final results for ${}^{43}\mathrm{Ca}^{+}$ are $a\left(4S_{1∕2}\right)=-805.3\mathrm{MHz}$, $a\left(4P_{1∕2}\right)=-143.1\mathrm{MHz}$, $a\left(4P_{3∕2}\right)=-30.5\mathrm{MHz}$, $b\left(4P_{3∕2}\right)∕Q=151.8{\mathrm{MHz}\mathrm{b}}^{-1}$, $a\left(3D_{3∕2}\right)=-47.8\mathrm{MHz}$, $b\left(3D_{3∕2}\right)∕Q=68.1{\mathrm{MHz}\mathrm{b}}^{-1}$, $a\left(3D_{5∕2}\right)=-3.6\mathrm{MHz}$, and $b\left(3D_{5∕2}\right)∕Q=100.2{\mathrm{MHz}\mathrm{b}}^{-1}$. The results for ${}^{87}\mathrm{Sr}^{+}$ are $a\left(5S_{1∕2}\right)=-1003.2\mathrm{MHz}$, $a\left(5P_{1∕2}\right)=-178.4\mathrm{MHz}$, $a\left(5P_{3∕2}\right)=-35.1\mathrm{MHz}$, $b\left(5P_{3∕2}\right)∕Q=274.3{\mathrm{MHz}\mathrm{b}}^{-1}$, $a\left(4D_{3∕2}\right)=-47.4\mathrm{MHz}$, $b\left(4D_{3∕2}\right)∕Q=118.2{\mathrm{MHz}\mathrm{b}}^{-1}$, $a\left(4D_{5∕2}\right)=2.5\mathrm{MHz}$, and $b\left(4D_{5∕2}\right)∕Q=169.5{\mathrm{MHz}\mathrm{b}}^{-1}$.

Absolute $\left(e,3e\right)$ measurements on helium, at high incident energy, have been recently reproduced by a calculation in the first Born approximation [Phys. Rev. Lett. 91, 73201 (2003)]. The theoretical model is based on the product of three Coulomb waves for the final state and the use of Pluvinage wave function for the initial helium ground state. The authors suggest that the good agreement obtained is strongly related to the quality of the initial state, in particular to the fact that it is diagonal in all Coulomb interactions. In this paper, we show that this conclusion is not correct. We construct three other helium ground states to demonstrate that diagonalizing the Hamiltonian is not the deciding factor in obtaining agreement with the absolute experimental data.

High-order harmonic generation process in the few- and multiple-optical-cycle regime is theoretically investigated, using the saddle-point method generalized to account for nonadiabatic effects. The influence of the carrier-envelope phase of the driving pulses on the various electron quantum paths is analyzed. We demonstrate that the short and long quantum paths are influenced in different ways by the carrier-envelope phase. In particular, we show that clear phase effects are visible on the long quantum paths even in the multiple-optical-cycle regime, while the short quantum paths are significantly influenced by the carrier-envelope phase only in the few-optical-cycle regime.