We propose the use of interaction-free quantum measurements with electrons to eliminate sample damage in electron microscopy. This might allow noninvasive molecular-resolution imaging. We show the possibility of such measurements in the presence of experimentally measured quantum decoherence rates and using a scheme based on existing charged particle trapping techniques.

We propose a usage of microwave radiation in a magnetic trap for improving the cooling and trapping of cold antihydrogen atoms which are initially produced in high magnetic moment states. Inducing transitions toward lower magnetic moments near the turning points of the atom in the trap, followed by spontaneous emission, should enhance the number of trappable atoms. We present results of simulations based on a typical experimental condition of the antihydrogen experiments at CERN. This technique should also be applicable to other trapped high magnetic moment Rydberg atoms.

In this paper, we investigate multipartite unlockable stabilized bound entanglement. First, the mathematical structure of these stabilized bound entangled states is studied. Second, since stabilizer states are the local equivalent to the graph states, we study such stabilized mixed states in the graph-state formalism. As a result, the unlockable stabilized bound entangled states can be graphically depicted and decomposed in the product form. Some examples are discussed.

Implementation of quantum controlled-NOT (CNOT) gates in realistic molecular systems is studied using stimulated Raman adiabatic passage (STIRAP) techniques optimized in the time domain by genetic algorithms or coupled with optimal control theory. In the first case, with an adiabatic solution (a series of STIRAP processes) as starting point, we optimize in the time domain different parameters of the pulses to obtain a high fidelity in two realistic cases under consideration. A two-qubit CNOT gate constructed from different assignments in rovibrational states is considered in diatomic (NaCs) or polyatomic $\left({\text{SCCl}}_2\right)$ molecules. The difficulty of encoding logical states in pure rotational states with STIRAP processes is illustrated. In such circumstances, the gate can be implemented by optimal control theory and the STIRAP sequence can then be used as an interesting trial field. We discuss the relative merits of the two methods for rovibrational computing (structure of the control field, duration of the control, and efficiency of the optimization).

We describe how the effect of charge noise on a pair of spins coupled via the exchange interaction can be calculated by modeling charge fluctuations as a random telegraph noise process using probability density functions. We develop analytic expressions for the time-dependent superoperator of a pair of spins as a function of fluctuation amplitude and rate. We show that the theory can be extended to include multiple fluctuators, in particular, spectral distributions of fluctuators. These superoperators can be included in time-dependent analyses of the state of spin systems designed for spintronics or quantum information processing to determine the decohering effects of exchange fluctuations.

An approach for obtaining the ground state of Coulombic many-body systems is presented. This approach is based on the path-integral renormalization-group method with nonorthogonal Slater determinants, is free of the negative sign problem, and can handle higher dimensional systems with consideration of the correlation effect. Furthermore, it can be easily extended to the multicomponent quantum systems that contain more than two kinds of quantum particles. According to our results obtained with the present approach, it achieves the same accuracy as the variational Monte Carlo method with a few Slater determinants and enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation.

We present a theoretical method to study atomic photoabsorption processes in a temporally periodic external field. The time development of the atomic dipole moment is propagated by numerical time propagation, and the photoabsorption cross sections is obtained directly from the Fourier transform of the autocorrelation function without summing up over the Floquet-Fourier components. As an example, we study the photoabsorption spectra of hydrogen atoms exposed in a mixture of static and periodically oscillating magnetic fields for the transition from $1s\to 2p$. The atomic energy structure and photoabsorption spectra show interesting dependence on the strength of the oscillating magnetic field. Tuning the combination of the magnetic field strengths, we can control the photoabsorption process. The proposed method is general and can be applied to processes in which the number of relevant high harmonic components of the Fourier expansion is so large that the conventional Floquet method is intractable.

We present the theory of coherent optical spectroscopy for single quantum dot under the pump-probe driving. We generally study the line shapes, Mandel’s $Q$ parameters, and few photon emission probabilities of single quantum dot system. The probe signals demonstrate the Autler-Townes splitting effect, and the first moment of our results confirms recent experimental results [Xu et al., Science 317, 929 (2007)]. We show that the pump and probe fields modify the emission photon statistical properties and control emission photon properties.

We demonstrate experimentally and theoretically random-phase surface solitons in effectively instantaneous nonlinear media. The key mechanism for self-trapping is played by a nonlocal nature of the nonlinearity, in contrast to other incoherent solitons involving time averaging. These incoherent surface solitons display features different from their bulk counterparts and from other surface waves.

We develop the most probable wave functions for a single free quantum particle given its momentum and energy by imposing its quantum probability density to maximize Shannon information entropy. We show that there is a class of solutions in which the quantum probability density is self-trapped with finite-size spatial support, uniformly moving, hence keeping its form unchanged.

We analyze the time dependence of entanglement and total correlations between a system and fractions of its environment in the course of decoherence. For the quantum Brownian motion model, we show that the entanglement and total correlations have rather different dependence on the size of the environmental fraction. Redundancy manifests differently in both types of correlations and can be related with induced classicality. To study this, we present a measure of redundancy and compare it to the existing one.

We propose two types of quantum dense coding communication networks with optical continuous variables, in which a quadripartite entangled state of the optical field with totally three-party correlations of quadrature amplitudes is utilized. In the networks, the exchange of information between any two participants can be manipulated by one or two of the remaining participants. The channel capacities for a variety of communication protocols are numerically calculated. Due to the fact that the quadripartite entangled states applied in the communication systems have been successfully prepared already in the laboratory, the proposed schemes are experimentally accessible at present.

In this paper, we report a realization of synchronization-free quantum teleportation and narrowband three-photon entanglement through interfering narrowband photon sources. Since both the single-photon and the entangled photon pair utilized are completely autonomous, it removes the requirement of high-demanding synchronization techniques in long-distance quantum communication with pulsed spontaneous parametric down-conversion sources. The frequency linewidth of the three-photon entanglement realized is on the order of several MHz, which matches the requirement of atomic ensemble based quantum memories. Such a narrowband multiphoton source will have applications in some advanced quantum communication protocols and linear optical quantum computation.

We show that the quantum disentanglement eraser implemented on a two-photon system from parametric downconversion is a general method to create hybrid photonic entanglement, namely the entanglement between different degrees of freedom of the photon pair. To demonstrate this, we generate and characterize a source with tunable degree of hybrid entanglement between two qubits, one encoded in the transverse momentum and position of a photon, and the other in the polarization of its partner. In addition, we show that a simple extension of our setup enables the generation of two-photon qubit-qudit hybrid entangled states. Finally, we discuss the advantages that this type of entanglement can bring for an optical quantum network.

We analyze a protocol of quantum energy teleportation that transports energy from the left edge of a linear ion crystal to the right edge by local operations and classical communication at a speed considerably greater than the speed of a phonon in the crystal. A probe qubit is strongly coupled with phonon fluctuation in the ground state for a short time and it is projectively measured in order to obtain information about this phonon fluctuation. During the measurement process, phonons are excited by the time-dependent measurement interaction and the energy of the excited phonons must be infused from outside the system. The obtained information is transferred to the right edge of the crystal through a classical channel. Even though the phonons excited at the left edge do not arrive at the right edge at the same time as when the information arrives at the right edge, we are able to soon extract energy from the ions at the right edge by using the transferred information. Because the intermediate ions of the crystal are not excited during the execution of the protocol, energy is transmitted in the energy-transfer channel without heat generation.

The line-profile approach is applied to the evaluation of the electron recombination on the highly charged ions within the framework of QED. Both dielectronic recombination and radiative recombination processes are considered. The interelectron interaction is taken into account partly to all orders of the QED perturbation theory. The radiative corrections to the lowest order (the electron self-energy and the vacuum polarization) are also included. With this approach the most accurate contemporary results for the electron-recombination cross section on the one-electron uranium ion are obtained; these results are compared with the earlier calculations and with existing experimental data.

The energies, widths, and angular behavior of negative-ion resonances in zinc atoms are determined using the complementary experimental techniques of electron transmission and angular differential elastic scattering. The observed resonances include states formed by the excitation of an inner $3d$ electron and assigned to a $3d^{9}4s^{2}n{\ell }^2$ electron configuration, $\ell =1$ for $n=4$ and $\ell =0,1$ for $n=5$. The differential elastic scattering indicates that all negative ions in the $3d^{9}4s^{2}4p^2$ manifold are formed from, and decay by, emission of a $d$-wave electron.

Polarizable atoms and molecules experience the Casimir-Polder force near magnetoelectric bodies, a force that is induced by quantum fluctuations of the electromagnetic field and the matter. Atoms and molecules in relative motion to a magnetoelectric surface experience an additional velocity-dependent force. We present a full quantum-mechanical treatment of this force and identify a generalized Doppler effect, the time delay between photon emission and reabsorption, and the Röntgen interaction as its three sources. For ground-state atoms, the force is very small and always decelerating, hence commonly known as quantum friction. For atoms and molecules in electronically excited states, on the contrary, both decelerating and accelerating forces can occur depending on the magnitude of the atomic transition frequency relative to the surface-plasmon frequency.

The angular distribution of photofragments resulting from two-frequency multiphoton dissociation of ${\text{HD}}^{+}$ and their branching ratios to different photon absorption channels have been calculated by the time-independent close-coupling method within the framework of two lowest electronic state model. It is shown that when one of the frequencies, ${\omega }_1$, is close to an allowed rovibrational transition caused by the permanent dipole moment, the total dissociation linewidth, detailed pattern of angular distribution, and branching ratios to different photon absorption channels vary with the second frequency ${\omega }_2$. We have varied ${\omega }_1$ over a narrow range around $11000{\text{cm}}^{-1}$, which is close to the energy of the $v=0\to 7$ transition, while ${\omega }_2$ was varied by about $2500{\text{cm}}^{-1}$ up to the dissociation threshold. The branching ratios can be explained in terms of the shape resonances on two different adiabatic potentials caused by the permanent dipole moment and the nonadiabatic couplings with other potentials. Prominent rings in the angular distribution are obtained when the resonance condition is satisfied. They are shown to arise from the mixing of various rotational states due to multiphoton interactions.

We numerically demonstrate the existence of a discrete family of robust dissipative soliton bound state solutions (soliton molecules) in a mode-locked fiber laser with an instantaneous saturable absorber in the normal dispersion domain. For a certain domain of the small-signal gain, we obtain a robust first-level bound state with almost constant separation where the phase of the two pulses evolves independently. Moreover, their phase difference can evolve either periodically or chaotically depending on the small-signal gain. Interestingly, higher level bound states exhibit a fundamentally different dynamics. They represent oscillating solutions with a phase difference alternating between zero and $\pi$. We identify the crucial role of the linear gain saturation for the existence of these robust molecules independently of their level.