We address the problem of unambiguous discrimination among a given set of quantum operations. The necessary and sufficient condition for them to be unambiguously distinguishable is derived in the cases of single use and multiple uses, respectively. For the latter case we explicitly construct the input states and corresponding measurements that accomplish the task. It is also found that the introduction of entanglement can improve the discrimination.

We examined the relative ionization and fragmentation probabilities of ${\mathrm{C}}_{60}$ after excitation by monochromatized synchrotron radiation in the energy range of $18–280\mathrm{eV}$. The energy dependence of the relative cross sections of $\mathrm{C}_{60}{}^{q+}$ $(q=1–4)$ and the associated fragments $\mathrm{C}_{60–2n}{}^{q+}$ ($n=1–6$ for $q=2,3$ and $n=1,2$ for $q=4$) are analyzed. We present the ionization and appearance energies for those ions and fragments as well as the partial cross sections for the ${\mathrm{C}}_{60}$ ions.

We derive and analyze shock-wave solutions of hydrodynamic equations describing repulsively interacting one-dimensional Bose gas. We also use the number-conserving Bogolubov approach to verify accuracy of the Gross-Pitaevskii equation in shock wave problems. We show that quantum corrections to dynamics of shocks (dark-shock-originated solitons) in a Bose-Einstein condensate are negligible (important) for a realistic set of system parameters. We point out possible signatures of a Bose-Einstein condensate—Tonks crossover in shock dynamics. Our findings can be directly verified in different experimental setups.

We manipulate a Bose–Einstein condensate using the optical trap created by the diffraction of a laser beam on a fast ferroelectric liquid crystal spatial light modulator. The modulator acts as a phase grating which can generate arbitrary diffraction patterns and be rapidly reconfigured at rates up to $1\mathrm{kHz}$ to create smooth, time-varying optical potentials. The flexibility of the device is demonstrated with our experimental results for splitting a Bose–Einstein condensate and independently transporting the separate parts of the atomic cloud.

We analyze the dynamics of atom-laser interactions for atoms having multiple, closely spaced, excited-state hyperfine manifolds. The system is treated fully quantum mechanically, including the atom’s center-of-mass degree of freedom, and motion is described in a polarization gradient field created by a three-dimensional laser configuration. We develop the master equation describing this system, and then specialize it to the low-intensity limit by adiabatically eliminating the excited states. We show how this master equation can be simulated using the Monte Carlo wave function technique, and we provide details on the implementation of this procedure. Monte Carlo calculations of steady state atomic momentum distributions for two fermionic alkaline earth isotopes, ${}^{25}\mathrm{Mg}$ and ${}^{87}\mathrm{Sr}$, interacting with a three-dimensional lin-⊥-lin laser configuration are presented, providing estimates of experimentally achievable laser-cooling temperatures.

An rms nuclear charge radius $r_{\mathrm{c}}=1.9642\left(11\right)\mathrm{fm}$ for ${}^3\mathrm{He}$ is derived from measurements of the $2{}^{3}S_1\text{−}2{}^{3}P_0$ isotope shift combined with the best available data on the fine structure of ${}^4\mathrm{He}$, the hyperfine structure of ${}^3\mathrm{He}$, and an assumed $r_{\mathrm{c}}=1.673\left(1\right)\mathrm{fm}$ for ${}^4\mathrm{He}$. The result removes a small discrepancy between some older spectroscopic determinations of $r_{\mathrm{c}}$ for ${}^3\mathrm{He}$ from this transition and a more recent measurement.

We investigated the tunnelling dynamics of a zero-temperature Bose-Einstein condensate in configuration of four potential wells arranged in a loop. We found three interesting dynamic regimes: (a) flows of matter with small amplitude, (b) steady flow, and (c) forced flow of matter for large amplitudes. The regime of quantum self-confinement has been studied and a new variant of it has been found for this system.

We propose a potential scheme for carrying out two-qubit unconventional geometric logic gates on two identical three-level atoms in a cavity, strongly driven by a resonant classical field. Compared to a previous scheme [S. B. Zheng, Phys. Rev. A 70, 052320 (2004)] based on the large-detuning interaction of the two identical three-level atoms with the cavity mode, our scheme can, in principle, achieve a faster gating because of the resonant coupling of the atoms to the classical field. We present the two-qubit unconventional geometric phase gates in both an ideal cavity and a real cavity with decay. Discussions about the fidelity and the success probability of the proposed scheme as well as the experimental feasibility are made in detail.

We present a complete analysis of the multipartite entanglement of three-mode Gaussian states of continuous-variable systems. We derive standard forms which characterize the covariance matrix of pure and mixed three-mode Gaussian states up to local unitary operations, showing that the local entropies of pure Gaussian states are bound to fulfill a relationship which is stricter than the general Araki-Lieb inequality. Quantum correlations can be quantified by a proper convex roof extension of the squared logarithmic negativity, the continuous-variable tangle, or contangle. We review and elucidate in detail the proof that in multimode Gaussian states the contangle satisfies a monogamy inequality constraint [G. Adesso and F. Illuminati, New J. Phys8, 15 (2006)]. The residual contangle, emerging from the monogamy inequality, is an entanglement monotone under Gaussian local operations and classical communications and defines a measure of genuine tripartite entanglements. We determine the analytical expression of the residual contangle for arbitrary pure three-mode Gaussian states and study in detail the distribution of quantum correlations in such states. This analysis yields that pure, symmetric states allow for a promiscuous entanglement sharing, having both maximum tripartite entanglement and maximum couplewise entanglement between any pair of modes. We thus name these states $\mathrm{GHZ}∕W$ states of continuous-variable systems because they are simultaneous continuous-variable counterparts of both the GHZ and the $W$ states of three qubits. We finally consider the effect of decoherence on three-mode Gaussian states, studying the decay of the residual contangle. The $\mathrm{GHZ}∕W$ states are shown to be maximally robust against losses and thermal noise.

We discuss the ground state entanglement of a bi-partite system, composed by a qubit strongly interacting with an oscillator mode, as a function of the coupling strength, the transition frequency and the level asymmetry of the qubit. This is done in the adiabatic regime in which the time evolution of the qubit is much faster than the oscillator one. Within the adiabatic approximation, we obtain a complete characterization of the ground state properties of the system and of its entanglement content.

We have observed microwave resonance transitions between the autoionizing Ba $5d_{3∕2}ng$ $J=2$ and $5d_{3∕2}(n+1)h$ $J=3$ states for $45⩽n⩽49$. These measurements, made between 50 and $75\mathrm{GHz}$, lead to quantum defects of $+0.019\left(2\right)$ and $+0.003\left(2\right)$ for this pair of $ng$ and $nh$ states. These measurements demonstrate that the core polarization model, widely used to characterize nonpenetrating Rydberg states, fails to describe Rydberg states converging to anisotropic or non $s$ cores. In particular, the second order quadrupole interaction cannot, in general, be represented in this manner.

We show that a single, trapped, laser-driven atom in a high-finesse optical cavity allows for the quantum-coherent generation of entangled light pulses on demand. We report the detailed description of schemes for generating simultaneous and temporally separated pulse pairs, presented in [G. Morigi et al., Phys. Rev. Lett., 96, 023601 (2006)]. The mechanical effect of the laser excitation on the quantum motion of the cold trapped atom mediates the entangling interaction between two cavity modes and between the two subsequent pulses, respectively. The entanglement is of EPR-type, and its degree can be controlled through external parameters. At the end of the generation process the atom is decorrelated from the light field. Possible experimental implementations of the proposals are discussed.

We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ is analyzed as a suitable source of photon pairs having high efficiency.

We present the final results of an experimental study of $\mu d$ and $\mu t$ atom scattering in solid hydrogen cooled to $3\mathrm{K}$. Strong effects resulting from the Ramsauer-Townsend effect have been observed in the TRIUMF experiment E742 where muons were stopped in thin frozen layers of hydrogen. The measured Ramsauer-Townsend minimum energy for both $\mu d$ and $\mu t$ atoms and the minimum cross section are in agreement with theory.

We present a feedback control scheme that designs time-dependent laser-detuning frequency to suppress possible dynamical instability in coupled free-quasibound-bound atom-molecule condensate systems. The proposed adaptive frequency chirp with feedback is shown to be highly robust and very efficient in the passage from an atomic to a stable molecular Bose-Einstein condensate.

We demonstrate the continuous injection and propagation of a cold atomic beam in a high-gradient (up to $2.7\mathrm{kG}∕\mathrm{cm}$) magnetic guide of $1.7\mathrm{m}$ length. Continuous injection is accomplished using a side-loading scheme that involves a sequence of two modified magneto-optic traps. Methods are developed to measure the atomic-flow temperatures and the flux under steady-state conditions. In the high-gradient portion of the guide, the guided atomic beam has a transverse temperature of $420\mu \mathrm{K}\pm 40\mu \mathrm{K}$, a longitudinal temperature of $1\mathrm{mK}$, and an average velocity of order $1\mathrm{m}∕\mathrm{s}$. Using a radio-frequency current of a fixed frequency $\nu$ coupled directly into the guide wires, atoms exceeding a transverse energy of $h\nu$ can be continuously and selectively removed from the atomic beam.

We analyze the Heisenberg limit on phase estimation for Gaussian states. In the analysis, no reference to a phase operator is made. We prove that the squeezed vacuum state is the most sensitive for a given average photon number. We provide two adaptive local measurement schemes that attain the Heisenberg limit asymptotically. One of them is described by a positive operator-valued measure and its efficiency is exhaustively explored. We also study Gaussian measurement schemes based on phase quadrature measurements. We show that homodyne tomography of the appropriate quadrature attains the Heisenberg limit for large samples. This proves that this limit can be attained with local projective von Neuman measurements.

We investigate the short-time dynamics of a delta-function potential barrier on an initially confined wave packet. There are mainly two conclusions: (A) At short times the probability density of the first particles that passed through the barrier is unaffected by it. (B) When the barrier is absorptive (i.e., its potential is imaginary) it affects the transmitted wave function at shorter times than a real potential barrier. Therefore, it is possible to distinguish between an imaginary and a real potential barrier by measuring its effect at short times only on the transmitting wave function.

We present a general theoretical formalism to compute the fidelity of transformations of unknown quantum states, and we apply our theory to Gaussian transformations of continuous variable quantum systems. For the case of a Gaussian distribution of displaced coherent states, the theory is readily tractable by a covariance matrix formalism, and a wider class of states, exemplified by Fock states, can be treated efficiently by the Wigner function formalism. Given the distribution of input states, the optimum feedback gain is identified, and analytical results for the fidelities are presented for recently implemented teleportation and memory storage protocols for continuous variables.

Dark-state polaritons in a five-level $M$-type atomic ensemble are proposed in the electromagnetically induced transparency. Under conditions of the low excitation limit and adiabatic following, the quantum field can be mapped onto the atomic polarization states, forming the shape preserving quantum states of polaritons. Two channels for robust quantum memory are provided, which enables the potential applications in quantum-information processing.