The driven-damped Jaynes-Cummings model in the regime of strong coupling is found to exhibit a coexistence between the quantum photon blockaded state and a quasicoherent bright state. We characterize the slow time scales and the basin of attraction of these metastable states using full quantum simulations. This form of bistability can be useful for implementing a qubit readout scheme that does not require additional circuit elements. We propose a coherent control sequence that makes use of a simple linear chirp of drive amplitude and frequency as well as qubit frequency. By optimizing the parameters of the system and the control pulse, we demonstrate theoretically very high readout fidelities ($>$$98\%$) and high contrast with experimentally realistic parameters for qubits implemented in the circuit QED architecture.

Quantum dot arrays are a promising medium for transferring quantum information between two distant points without resorting to mobile qubits. Here we study the two most common disorders, namely hyperfine interaction and exchange coupling fluctuations, in quantum dot arrays and their effects on quantum communication through these chains. Our results show that the hyperfine interaction is more destructive than the exchange coupling fluctuations. The average optimal time for communication is not affected by any disorder in the system and our simulations show that antiferromagnetic chains are much more resistive than the ferromagnetic ones against both kind of disorders. Even when time modulation of a coupling and optimal control is employed to improve the transmission, the antiferromagnetic chain performs much better. We have assumed the quasistatic approximation for hyperfine interaction and time-dependent fluctuations in the exchange couplings. Particularly for studying exchange coupling fluctuations we have considered the static disorder, white noise, and $1/f$ noise.

We apply the relativistic configuration-interaction method coupled with the many-body perturbation theory (CI+MBPT) to describe low-energy dielectronic recombination. We combine the CI+MBPT approach with the complex rotation method (CRM) and compute the dielectronic recombination spectrum for Li-like carbon, which recombines into Be-like carbon. We demonstrate the utility and evaluate the accuracy of this newly developed CI+MBPT+CRM approach by comparing our results with the results of the previous high-precision study of the Ciii system [Mannervik et al., Phys. Rev. Lett. 81, 313 (1998)].

The experimental finding of significant enhancement or suppression of particular harmonics generated by the ionic component of laser-produced plasmas of transition-metal atoms is explained theoretically in terms of the standard three-step scenario for strong-field harmonic generation, taking into account the potential barrier effects that lead to a strong $3p\to 3d$ electric dipole transition that dominates the photoionization cross sections of the outer subshells of those ions.

We investigate how the vortex-vortex separation changes Majorana zero modes in the vicinity of the BCS-BEC (Bose-Einstein condensation) topological phase transition of $p$-wave resonant Fermi gases. By analytically and numerically solving the Bogoliubov–de Gennes equation for spinless $p$-wave superfluids with plural vortices, it is demonstrated that the quasiparticle tunneling between neighboring vortices gives rise to the quantum oscillation of the low-lying spectra on the scale of the Fermi wavelength in addition to the exponential splitting. This rapid oscillation, which appears in the weak-coupling regime as a consequence of quantum oscillations of quasiparticle wave functions, disappears in the vicinity of the BCS-BEC topological phase transition. This is understandable from that the wave function of the Majorana zero modes is described by the modified Bessel function in the strong-coupling regime, and thus it becomes spread over the vortex core region. Due to the exponential divergence of the modified Bessel function, the concrete realization of the Majorana zero modes near the topological phase transition requires the neighboring vortices to be separated beyond the length scale defined by the coherence length and the dimensionless coupling constant. All these behaviors are also confirmed by carrying out the full numerical diagonalization of the nonlocal Bogoliubov–de Gennes equation in a two-dimensional geometry. Furthermore, this argument is expanded into the case of three-vortex systems, where a pair of core-bound and edge-bound Majorana states survive at zero-energy state regardless of the vortex separation.

We present a comprehensive numerical simulation of an echo-type atom interferometer. The simulation confirms an interesting theoretical description of this interferometer that includes effects due to spontaneous emission and magnetic sublevels. Both the simulation and the theoretical model agree with the results of experiments. These developments provide an improved understanding of several observable effects. The evolution of state populations due to stimulated emission and absorption during the standing-wave interaction imparts a time-dependent phase on each atomic momentum state. This manifests itself as an asymmetry in the signal shape that depends on the strength of the interaction as well as spontaneous emission due to a nonzero population in the excited states. The degree of asymmetry is a measure of a nonzero relative phase between interfering momentum states.

We study entropy generation in a one-dimensional (1D) model of bosons in an optical lattice experiencing two-particle losses. Such heating is a major impediment to observing exotic low temperature states, and “simulating” condensed matter systems. Developing intuition through numerical simulations, we present a simple empirical model for the entropy produced in this 1D setting. We also explore the time evolution of one- and two-particle correlation functions, showing that they are robust against two-particle loss. Because of this robustness, induced two-body losses can be used as a probe of short-range magnetic correlations.

We theoretically characterize the collective radiative behavior of $N$ classical emitters near an interface between different dielectrics that supports the transfer of surface plasmon modes into the far-field of electromagnetic radiation. The phenomena of superradiance and surface plasmons can be combined to amplify the emitted radiation intensity $S$ as $S=A{N}^2{S}_0$ compared to a single emitter’s intensity $S_0$ in free space. For a practical case study within the article $A=240$, compared to $A=1$ in free space. We furthermore demonstrate that there are collective modes for which the intensity of the emitted radiation is suppressed by 2 orders of magnitude despite their supperadiant emission characteristics. A method to control the emission characteristics of the system and to switch from super- to subradiant behavior with a suitably detuned external driving field is devised.

An imaging approach, based on ghost imaging, is reported to recover a pure-phase object or a complex-valued object. Our analytical results, which are backed up by numerical simulations, demonstrate that both the complex-valued object and its amplitude-dependent part can be separately and nonlocally reconstructed using this approach. Both effects influencing the quality of reconstructed images and methods to further improve the imaging quality are also discussed.

The internal conversion coefficient for bound-free electron transition of originally energetically forbidden internal conversion processes induced by intense, few-cycle UV laser pulse of Gaussian shape in the case of isomers ${}^{107}\mathrm{Ag}$${}^m$ ($K$ shell, $E3$, $25.47$ keV), ${}^{90}\mathrm{Nb}$${}^m$ ($L_2$ shell, $M2+E3$, $2.3$ keV), ${}^{183}{W}^{m1}$($M_5$ shell, $E2$, $1.79$ keV), ${}^{183}{W}^{m2}$ ($N_1$ shell, $E1$, $548$ eV), and ${}^{188}\mathrm{Re}$${}^m$ ($M_2$ shell, $M3+E4$, $2.63$ keV), and ${}^{235}\mathrm{U}$${}^m$ ($O_4$ and $O_5$ shells, $E3$, $73.5$ eV) is determined numerically. Experimental conditions and possibilities of the laser-induced internal conversion process of ${}^{183}{W}^{m2}$ from the $N_1$ shell are discussed in more detail.

The time-reversal process provides the possibility to counteract the time evolution of a physical system. Recent research has shown that such a process can occur in the first-order field correlation of chaotic light and result in the spatial interference and phase-reversal diffraction in an unbalanced interferometer. Here we report experimental investigations on the invisibility cloak and illusion phenomena in chaotic light. In an unbalanced interferometer illuminated by thermal light, we have observed the cloak effect and the optical transformation of one object into another object. The experimental results can be understood by the phase-reversal diffraction, and they demonstrate the theoretical proposal of similar effects in complementary media.

Parabolic amplifier similaritons are observed inside a normal-dispersion laser. The self-similar pulse is a local nonlinear attractor in the gain segment of the oscillator. The evolution in the laser exhibits large (20 times) spectral breathing, and the pulse chirp is less than the group-velocity dispersion of the cavity. All of these features are consistent with numerical simulations. The amplifier similariton evolution also yields practical features such as parabolic output pulses with high energies, and the shortest pulses to date from a normal-dispersion laser.

The measurement result of the moved distance for a free mass $m$ during the time $\tau$ between two position measurements cannot be predicted with uncertainty smaller than $\sqrt{\hslash \tau /m}$. This is formulated as a standard quantum limit and it has been proven to always hold for the following position measurement: a probe is set in a prescribed position before the measurement. Just after the interaction of the mass with the probe, the probe position is measured, and using this value, the measurement results of the premeasurement and postmeasurement positions are estimated.

We use a non-Markovian approach to study the decoherence dynamics of a qubit in either a low- or high-frequency bath modeling the qubit environment. This is done for two separate cases: either with measurements or without them. This approach is based on a unitary transformation and does not require the rotating-wave approximation. In the case without measurement, we show that, for low-frequency noise, the bath shifts the qubit energy toward higher energies (blue shift), while the ordinary high-frequency cutoff Ohmic bath shifts the qubit energy toward lower energies (red shift). In order to preserve the coherence of the qubit, we also investigate the dynamics of the qubit subject to measurements (quantum Zeno regime) in two cases: low- and high-frequency baths. For very frequent projective measurements, the low-frequency bath gives rise to the quantum anti-Zeno effect on the qubit. The quantum Zeno effect only occurs in the high-frequency-cutoff Ohmic bath, after counterrotating terms are considered. In the condition that the decay rate due to the two kinds of baths are equal under the Wigner-Weisskopf approximation, we find that without the approximation, for a high-frequency environment, the decay rate should be faster (without measurements) or slower (with frequent measurements, in the Zeno regime), compared to the low-frequency bath case. The experimental implementation of our results here could distinguish the type of bath (either a low- or high-frequency one) and protect the coherence of the qubit by modulating the dominant frequency of its environment.

We present a scheme to generate any two-dimensional cluster state efficiently. The number of the basic gate (entangler) operations is on the order of the entanglement bonds of a cluster state. This deterministic scheme, which demands few ancilla resources and no quantum memory, is suitable for large-scale quantum computation.

This article is devoted to the development of analytical and numerical approaches to the problem of the end-to-end quantum state transfer along the spin-1/2 chain using two methods: (a) a homogeneous spin chain with week end bonds and equal Larmor frequencies and (b) a homogeneous spin chain with end Larmor frequencies different from inner ones. A tridiagonal matrix representation of the $\mathit{XY}$ Hamiltonian with nearest neighbor interactions relevant to the quantum state transfer is exactly diagonalized for a combination of the preceding two methods. In order to take into account interactions of the remote spins, we used numerical simulations of the quantum state transfer in 10-node chains. We compare the state transfer times obtained using the two preceding methods for chains governed by the both $\mathit{XY}$ and $\mathit{XXZ}$ Hamiltonians and using both nearest neighbor and all-node interactions.

We present an adiabatic quantum algorithm for the abstract problem of searching marked vertices in a graph, or spatial search. Given a random walk (or Markov chain) $P$ on a graph with a set of unknown marked vertices, one can define a related absorbing walk $P^{\text{'}}$ where outgoing transitions from marked vertices are replaced by self-loops. We build a Hamiltonian $H(s)$ from the interpolated Markov chain $P(s)=(1-s)P+{\mathit{sP}}^{\text{'}}$ and use it in an adiabatic quantum algorithm to drive an initial superposition over all vertices to a superposition over marked vertices. The adiabatic condition implies that, for any reversible Markov chain and any set of marked vertices, the running time of the adiabatic algorithm is given by the square root of the classical hitting time. This algorithm therefore demonstrates a novel connection between the adiabatic condition and the classical notion of hitting time of a random walk. It also significantly extends the scope of previous quantum algorithms for this problem, which could only obtain a full quadratic speedup for state-transitive reversible Markov chains with a unique marked vertex.

We propose and investigate a protocol for Gaussification of quantum states of traveling light beams in an atomic quantum memory that couples to light via quantum nondemolition (QND) interaction. The protocol relies on a periodic switching between two different QND couplings and the total coupling strength scales only logarithmically with number of Gaussified light modes. The present scheme can be used to prepare entangled states of two distant atomic ensembles and to purify and Gaussify noisy non-Gaussian entangled states of light while simultaneously storing the purified state in atomic memories.

In photoionization microscopy experiments, an atom in an electric field is ionized by a laser with sharply defined frequency, the electron is drawn toward a position-sensitive detector, and the current is measured as a function of position. Multiple classical paths lead from the atom to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If a magnetic field is added parallel to the electric field, trajectories become chaotic. There is an infinite set of different families of trajectories, leading to an extremely complicated interference patterns on the detector. We present calculations predicting the kind of structure that will be seen in experiments.

We search for the existence of weakly bound He-He-Rb molecules. The He-He-Rb molecule is treated as a three-body system. By using hyperspherical coordinates, the Schrödinger equation for the triatomic system is solved in the adiabatic approximation. A bound state is found for each of the ${}^3\mathrm{He}$-${}^3\mathrm{He}$-${}^{85}\mathrm{Rb}$, ${}^3\mathrm{He}$-${}^4\mathrm{He}$-${}^{85}\mathrm{Rb}$, and ${}^4\mathrm{He}$-${}^4\mathrm{He}$-${}^{85}\mathrm{Rb}$ trimers, respectively. The bound state for the ${}^3\mathrm{He}$-${}^3\mathrm{He}$-${}^{85}\mathrm{Rb}$ molecule is a Borromean state found in a realistic molecular systems because there are no bound states in both the ${}^3\mathrm{He}$-${}^3\mathrm{He}$ and ${}^3\mathrm{He}$-${}^{85}\mathrm{Rb}$ dimers.