Determinisitic Optical Fock State Generation

We present a scheme for the deterministic generation of N-photon Fock states from N three-level atoms in a high-finesse optical cavity. The method applies an external laser pulsethat generates an $N$-photon output state while adiabatically keeping the atom-cavity system within a subspace of optically dark states. We present analytical estimates of the error due to amplitude leakage from these dark states for general N, and compare it with explicit results of numerical simulations for N \leq 5. The method is shown to provide a robust source of N-photon states under a variety of experimental conditions and is suitable for experimental implementation using a cloud of cold atoms magnetically trapped in a cavity. The resulting N-photon states have potential applications in fundamental studies of non-classical states and in quantum information processing.Comment: 25 pages, 9 figure

A PW91 density functional study of conformational choice in 2-phenylethanol, n-butylbenzene, and their cations: Problems for density functional theory?

Absolute energies, geometric structures, harmonic vibrational frequencies, and partial charge distributions (NPA) are obtained from ab initio (HF/MP2) and density functional theory (DFT) calculations of stable conformers of neutral and cationic 2-phenylethanol and n-butylbenzene, model aromatic molecules with flexible side chains. We focus on exploring the conformational preferences of the cations and find that cationic conformational preference is more pronounced in the system with the strongly interacting side chain. The DFT calculations presented use the Perdew−Wang exchange and correlation functional, PW91. For the neutral conformers, PW91 performs extremely well compared to MP2, indicating that this functional will be highly useful for future computational studies of neutral aromatic molecules with flexible side chains. For the cationic conformers, PW91 again performs well compared to MP2 for n-butylbenzene, a system in which the side chain interacts only weakly with the aromatic ring. However, considerable discrepancies occur between the MP2 and DFT calculations for 2-phenylethanol+. The results indicate that density functional theory does not provide a reliable description of the potential energy surface of 2-phenylethanol+, and that high levels of theory may be necessary to accurately treat similar cations. The present study represents the first systematic comparison of HF, MP2, and DFT calculations of cationic conformers of aromatic molecules with flexible side chains

Ionic fragmentation versus electron detachment in isolated transition metal complex dianions

Gas-phase multiply charged anions represent highly energetic species that are susceptible to decay by electron detachment or fragmentation into two ions. The relative activation barriers for decay via these channels have been investigated for using collisional excitation of ions isolated within a quadrupole trap. All of the dianions decayed via ionic fragmentation, demonstrating that the repulsive Coulomb barrier (RCB) for ionic fragmentation lies below the RCB for electron detachment. Our results indicate that ionic fragmentation will represent the preferred lowest energy decay pathway for these, and other, dianions that can dissociate to form stable anions

Characterizing the intrinsic stability of gas-phase clusters of transition metal complex dianions with alkali metal counterions: Counterion perturbation of multiply charged anions

The authors report the gas-phase generation and characterization of a series of cation-dianion clusters, e.g., M+·PtCl62-, M+·PtCl42-, M+·Pt(CN)62-, and M+·Pd(CN)42-, where M+=Na+,K+,Rb+, as model systems for investigating gas-phase contact ionpairs. Low-energy collisional excitation of these systems isolated within a quadrupole ion trap reveals that the fragmentation products are determined by the dianion and are independent of the counterion. This indicates that cation-dianion clusters represent gaseous ion-pair complexes, in line with recent findings for K+·Pt(CN)n2-, n=4,6 [Burke et al., J. Chem. Phys. 125, 021105 (2006)]. The relative fragmentation energies of several cation-dianion systems are obtained as a function of the counterion to explore the nature of ion-pair binding. For most of the systems studied, e.g., M+·PtCl62-, the fragmentation energy increases as the cation size decreases, in line with a simple electrostatic description of the cation-dianion binding. However, the M+·Pt(CN)42- clusters displayed the reverse trend with the fragmentation energy increasing as the cation size increases. Density functional theory calculations of the cation-dianion fragmentation potential energy surfaces reveal the existence of a novel double-minima surface, separated by a repulsive Coulomb barrierlike feature at short range. The experimentally observed trends in the fragmentation energies can be fully understood with reference to the computed surfaces, hence providing strong support for the existence of the double-minima surface