We present an explicit transformation of optimal asymmetric $1\to 2$ real state cloning in two dimensions. Interestingly, the distribution of the two fidelities of the cloning is the same as its counterpart in optimal asymmetric phase-covariant cloning. We also generalize the cloner to the $d$-dimensional case and derive the explicit transformation of the optimal symmetric $1\to 2$ real state cloning in the $d$-dimensional system. The maximal fidelity of two clones obtained coincides with the theoretical value [P. Vavez and N. J. Cerf, Phys. Rev. A 68, 032313 (2003)].

We experimentally implement direct characterization of quantum dynamics (DCQD) algorithm of a single qubit proposed in M. Mohseni and D. A. Lidar [Phys. Rev. Lett. 97, 170501 (2006)], which does not require quantum state tomography. The number of experimental configurations is reduced by a factor of 2 compared with that of standard quantum process tomography, which can be increased four times with an ideal Bell state analyzer. We combine the DCQD algorithm with maximum-likelihood estimation to give the physical characterization of quantum dynamics. It can also be applied to obtaining partial information about quantum dynamics.

We have measured the electric tensor polarizabilities of the hyperfine levels of Cs atoms embedded in a body-centered cubic ${}^4\mathrm{He}$ crystal. The polarizabilities are inferred from the shift of optically detected magnetic resonance lines in each hyperfine level induced by static electric fields up to $50\mathrm{kV}∕\mathrm{cm}$. We recorded the magnetic resonances both by scanning the rf frequency and in a configuration in which the system is operated as a phase-stabilized magnetometer. The results from both measurements agree well with model calculations taking the effect of the solid helium matrix and our recent extension of the theory of forbidden tensor polarizabilities into account. We have also performed the first measurement of the differential tensor Stark splittings of the $F=3$ and $F=4$ hyperfine levels of the ground state, thus confirming the recently revised sign of this shift which affects the blackbody correction of primary frequency standards.

The existence and structure of positronic atoms with a total angular momentum of $L=1$ is studied with the configuration interaction method. Evidence is presented that there is a ${}^{2}P^o$ state of $e^{+}\mathrm{Ca}$ and ${}^{2,4}P^o$ states of $e^{+}\mathrm{Be}\left({}^{3}P^o\right)$ that are electronically stable with binding energies of $45\mathrm{meV}$ and $2.6\mathrm{meV}$, respectively. These predictions rely on the use of an asymptotic series analysis to estimate the angular $L\to \infty$ limit of the energy. Incorporating corrections that compensate for the finite range of the radial basis increased the binding energies of $e^{+}\mathrm{Ca}$ and $e^{+}\mathrm{Be}$ to $71\mathrm{meV}$ and $42\mathrm{meV}$, respectively.

We advance a scaling procedure for molecular dynamics (MD) simulations which allows for the computation of extreme ionization levels, multielectron dynamics, and Coulomb explosion (CE) energetics of very large elemental and molecular clusters driven by ultraintense (peak intensities $I_M={10}^{15}–{10}^{21}\mathrm{W}{\mathrm{cm}}^{-2}$) laser fields. The procedure of scaled particle dynamics uses a standard MD code for a scaled cluster with a reduced number of composite ions (nuclei) (heavy pseudoparticles) and of composite electrons (light pseudoparticles). A single scaling parameter $s$ was used for the composition, charge, and mass of all the pseudoparticles, while the initial distances between pseudoparticles and the short-range potential parameters were scaled by $s^{1∕3}$. The scaling procedure was applied for the computation of the ion energies from CE of ${\left({\mathrm{D}}_2\right)}_{n∕2}$ and ${\left(\mathrm{C}{\mathrm{H}}_4\right)}_n$ clusters over the size domain of $n={10}^3–{10}^7$, bridging between clusters and nanodroplets. Deuterons with a maximal energy of $110\mathrm{keV}$ can be effectively produced and utilized for nuclear fusion driven by CE of ${\left(\mathrm{D}\right)}_n$ clusters with $n=1.7\times {10}^6$. The intensity dependence of the ionization levels of ${\left(\mathrm{C}{\mathrm{H}}_4\right)}_n$ clusters $(n=8\times {10}^4–{10}^6)$ manifests ignition and nanoplasma screening effects, establishing the conditions for the production of bare ${\mathrm{C}}^{6+}+{\mathrm{H}}^{+}$ nuclear matter for nucleosynthesis. The scaling procedure will be applicable for large finite systems where the particle motion is mainly governed by long-range (e.g., Coulomb) interactions.

We developed a method to calculate positions and widths of three-body resonances. The method combines the hyperspherical adiabatic approach, slow variable discretization method [O. I. Tolstikhin et al., J. Phys. B 29, L389 (1996)], and a complex absorbing potential. The method can be used to obtain resonances having short-range or long-range wave functions. In particular, we have applied the method to obtain very shallow three-body Efimov resonances for a model system [E. Nielsen et al., Phys. Rev. A 66, 012705 (2002)].

The dispersion coefficients of a number of the low-lying states of Li are determined for the homonuclear case. The Li wave functions and energies were computed in a frozen core Hamiltonian with a semiempirical polarization potential. Besides computing the dispersion coefficients, the scalar and tensor polarizabilities and oscillator strengths are computed and generally seen to be in good agreement with other accurate calculations.

We present a density-functional scheme for calculating the pair density (PD) by means of the correlated wave function. The Jastrow wave function is adopted as the correlated wave function. By using the lowest-order approximation to the Jastrow wave function PDs, the search region for the ground-state PD is substantially extended as compared with our previous theory [Physica B 387, 117 (2007)]. The variational principle results in simultaneous equations that are practicable to calculate the ground-state PD.

We simulate numerically the free expansion of a repulsive Bose-Einstein condensate with an initially Gaussian density profile. We find a self-similar expansion only for weak interatomic repulsion. In contrast, for strong repulsion we observe the spontaneous formation of a shock wave at the surface followed by a significant depletion inside the cloud. In the expansion, contrary to the case of a classical viscous gas, the quantum fluid can generate radial rarefaction density waves with several minima and maxima. These intriguing nonlinear effects, never observed in free-expansion experiments with ultracold alkali-metal atoms, can be detected with the available setups.

We use the hydrodynamic representation of the Gross-Pitaevskii and nonlinear Schrödinger equations in order to analyze the dynamics of macroscopic tunneling processes. We observe a tendency to wave breaking and shock formation during the early stages of the tunneling process. A blip in the density distribution appears on the outskirts of the barrier and under proper conditions it may transform into a bright soliton. Our approach, based on the theory of shock formation in solutions of the Burgers equation, allows us to find the parameters of the ejected blip (or soliton if formed), including the velocity of its propagation. The blip in the density is formed regardless of the value and sign of the nonlinearity parameter. However, a soliton may be formed only if this parameter is negative (attraction) and large enough. A criterion is proposed. An ejection of a soliton is also observed numerically. We demonstrate, theoretically and numerically, controlled formation of a soliton through tunneling. The mass of the ejected soliton is controlled by the initial state.

A scheme is proposed to realize a two-qubit quantum phase gate for the intracavity modes. In the scheme, two qubits are encoded in zero- and one-photon Fock states of two intracavity modes, and the three-level $\Lambda$-type atom trapped in a high-$Q$ cavity mediates the conditional phase gate within a given interaction time. The influence of cavity decay and atomic spontaneous emission on the gate fidelity is also discussed.

We propose a refined iterative likelihood-maximization algorithm for reconstructing a quantum state from a set of tomographic measurements. The algorithm is characterized by a very high convergence rate and features a simple adaptive procedure that ensures likelihood increase in every iteration and convergence to the maximum-likelihood state. We apply the algorithm to homodyne tomography of optical states and quantum tomography of entangled spin states of trapped ions and investigate its convergence properties.

A general formalism of the problem of perfect state transfer is presented. We show that there are infinitely many Hamiltonians that may provide a solution to this problem. In a first attempt to give a classification of them we investigate their possible forms and the related dynamics during the transfer. Finally, we show how the present formalism can be used for the engineering of perfect quantum wires of various topologies and coupling configurations.

Liquid-phase NMR is a general-purpose testbed for developing methods of coherent control relevant to quantum information processing. Here we extend these studies to the coherent control of logical qubits and in particular to the unitary gates necessary to create entanglement between logical qubits. We report an experimental implementation of a conditional logical gate between two logical qubits that are each in decoherence-free subspaces that protect the quantum information from fully correlated dephasing.

A critical step in experimental quantum information processing (QIP) is to implement control of quantum systems protected against decoherence via informational encodings, such as quantum error-correcting codes, noiseless subsystems, and decoherence-free subspaces. These encodings lead to the promise of fault-tolerant QIP, but they come at the expense of resource overheads. Part of the challenge in studying control over multiple logical qubits is that QIP testbeds have not had sufficient resources to analyze encodings beyond the simplest ones. The most relevant resources are the number of available qubits and the cost to initialize and control them. Here we demonstrate an encoding of logical information that permits control over multiple logical qubits without full initialization, an issue that is particularly challenging in liquid-state NMR. The method of subsystem pseudopure states will allow the study of decoherence control schemes on up to six logical qubits using liquid-state NMR implementations.

We discuss an interferometric approach to the estimation of quantum mechanical damping. We study specific classes of entangled and separable probe states consisting of superpositions of coherent states. Based on the assumption of limited quantum resources we show that entanglement improves the estimation of an unknown damping constant.

Absolute differential cross sections have been measured for elastic electron scattering from tetrahydrofuran in the electron impact energy from $6\text{to}20\mathrm{eV}$ and in a wide scattering angle range from 20° to 180°. In the measurements the magnetic-angle-changing technique has been employed to detect the backward scattering of electrons. The integral and momentum transfer cross sections for elastic scattering have been also determined through integration of the measured differential cross sections. A detailed comparison of the obtained differential cross sections has been made with the results of very recent theoretical calculations. In the measurements attention has been paid to observe negative-ion resonances predicted in these theoretical calculations.

Time-of-flight-based mass analysis of charged water fragments have been used to measure the dissociative and the nondissociative reaction pathways of water formed during collisions with $15\text{to}100\mathrm{keV}$ and $500\text{to}3500\mathrm{keV}$ ${\mathrm{H}}^{+}$ projectiles and with $8\text{to}100\mathrm{keV}$ ${\mathrm{H}}^0$ projectiles. The fragmentation pathways resulting from the ionization and the electron capture collisions with the incident ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ projectiles, as well as collisions involving projectile electron loss by the incident ${\mathrm{H}}^0$ projectiles, were separately recorded by detecting the target product ions in coincidence with either the ejected target electrons or the charge-analyzed projectiles. The fragmentation profile shows that at high collision energies the ionization of water arises mainly through outer shell processes. At lower energies valence electron capture and ionization dominate and transfer ionization leads to substantially different fragmentation patterns. ${\mathrm{H}}^0$ and ${\mathrm{H}}^{+}$ projectiles are found to be equally efficient at ionizing the water molecule. These results are of particular interest to workers in astrophysics and those involved in cancer therapy with heavy particle ion beams.

We study the two-particle wave function of paired atoms in a Fermi gas with tunable interaction strengths controlled by Feshbach resonance. The Cooper pair wave function is examined for its bosonic characters, which is quantified by the correction of the Bose enhancement factor associated with the creation and annihilation composite particle operators. An example is given for a three-dimensional uniform gas. Two definitions of Cooper pair wave function are examined. One of which is chosen to reflect the off-diagonal long range order (ODLRO). Another one corresponds to a pair projection of a BCS state. On the side with negative scattering length, we found that paired atoms described by ODLRO are more bosonic than the pair projected definition. It is also found that at ${\left(k_{F}a\right)}^{-1}⩾1$, both definitions give similar results, where more than 90% of the atoms occupy the corresponding molecular condensates.

We analyze strongly interacting Fermi gases in the unitary regime by considering the generalization to an arbitrary number $N$ of spin-$1∕2$ fermion flavors with $\mathrm{Sp}\left(2N\right)$ symmetry. For $N\to \infty$ this problem is exactly solved by the Bardeen-Cooper-Schrieffer–Bose-Einstein condensate mean-field theory, with corrections small in the parameter $1∕N$. The large-$N$ expansion provides a systematic way to determine corrections to mean-field predictions, allowing the calculation of a variety of thermodynamic quantities at (and in proximity to) unitarity, including the energy, the pairing gap, and the upper-critical polarization (in the case of a polarized gas) for the normal to superfluid instability. For the physical case of $N=1$, among other quantities, we predict in the unitarity regime, the energy of the gas to be $\xi =0.28$ times that for the noninteracting gas and the pairing gap to be 0.52 times the Fermi energy.