Classical Trajectory Perspective on Double Ionization Dynamics of Diatomic Molecules Irradiated by Ultrashort Intense Laser Pulses

In the present paper, we develop a semiclassical quasi-static model accounting for molecular double ionization in an intense laser pulse. With this model, we achieve insight into the dynamics of two highly-correlated valence electrons under the combined influence of a two-center Coulomb potential and an intense laser field, and reveal the significant influence of molecular alignment on the ratio of double over single ion yield. Analysis on the classical trajectories unveils sub-cycle dynamics of the molecular double ionization. Many interesting features, such as the accumulation of emitted electrons in the first and third quadrants of parallel momentum plane, the regular pattern of correlated momentum with respect to the time delay between closest collision and ionization moment, are revealed and successfully explained by back analyzing the classical trajectories. Quantitative agreement with experimental data over a wide range of laser intensities from tunneling to over-the-barrier regime is presented.Comment: 8 pages, 9 figure

Complex Dynamics of Correlated Electrons in Molecular Double Ionization by an Ultrashort Intense Laser Pulse

With a semiclassical quasi-static model we achieve an insight into the complex dynamics of two correlated electrons under the combined influence of a two-center Coulomb potential and an intense laser field. The model calculation is able to reproduce experimental data of nitrogen molecules for a wide range of laser intensities from tunnelling to over-the-barrier regime, and predicts a significant alignment effect on the ratio of double over single ion yield. The classical trajectory analysis allows to unveil sub-cycle molecular double ionization dynamics.Comment: 5 pages, 5 figures. to appear in Phys. Rev. Lett.(2007

90 degree polarization rotator using a bilayered chiral metamaterial with giant optical activity

A bilayered chiral metamaterial (CMM) is proposed to realize a 90 degree polarization rotator, whose giant optical activity is due to the transverse magnetic dipole coupling among the metallic wire pairs of enantiomeric patterns. By transmission through this thin bilayered structure of less than \lambda/30 thick, a linearly polarized wave is converted to its cross polarization with a resonant polarization conversion efficiency (PCE) of over 90%. Meanwhile, the axial ratio of the transmitted wave is better than 40 dB. It is demonstrated that the chirality in the propagation direction makes this efficient cross-polarization conversion possible. The transversely isotropic property of this polarization rotator is also experimentally verified. The optical activity of the present structure is about 2700 degree/\lambda, which is the largest optical activity that can be found in literature.Comment: 16 pages, 4 figure

Nature vs. Nurture: Predictability in Low-Temperature Ising Dynamics

Consider a dynamical many-body system with a random initial state subsequently evolving through stochastic dynamics. What is the relative importance of the initial state ("nature") vs. the realization of the stochastic dynamics ("nurture") in predicting the final state? We examined this question for the two-dimensional Ising ferromagnet following an initial deep quench from $T=\infty$ to $T=0$. We performed Monte Carlo studies on the overlap between "identical twins" raised in independent dynamical environments, up to size $L=500$. Our results suggest an overlap decaying with time as $t^{-\theta_h}$ with $\theta_h = 0.22 \pm 0.02$; the same exponent holds for a quench to low but nonzero temperature. This "heritability exponent" may equal the persistence exponent for the 2D Ising ferromagnet, but the two differ more generally.Comment: 5 pages, 3 figures; new version includes results for nonzero temperatur

Spin squeezing in optical lattice clocks via lattice-based QND measurements

Quantum projection noise will soon limit the best achievable precision of optical atomic clocks based on lattice-confined neutral atoms. Squeezing the collective atomic pseudo-spin via measurement of the clock state populations during Ramsey interrogation suppresses the projection noise. We show here that the lattice laser field can be used to perform ideal quantum non-demolition measurements without clock shifts or decoherence and explore the feasibility of such an approach in theory with the lattice field confined in a ring-resonator. Detection of the motional sideband due to the atomic vibration in the lattice wells can yield signal sizes a hundredfold above the projection noise limit.Comment: Substantially expanded versio

Topological Quantum Phase Transition in Synthetic Non-Abelian Gauge Potential

The method of synthetic gauge potentials opens up a new avenue for our understanding and discovering novel quantum states of matter. We investigate the topological quantum phase transition of Fermi gases trapped in a honeycomb lattice in the presence of a synthetic non- Abelian gauge potential. We develop a systematic fermionic effective field theory to describe a topological quantum phase transition tuned by the non-Abelian gauge potential and ex- plore its various important experimental consequences. Numerical calculations on lattice scales are performed to compare with the results achieved by the fermionic effective field theory. Several possible experimental detection methods of topological quantum phase tran- sition are proposed. In contrast to condensed matter experiments where only gauge invariant quantities can be measured, both gauge invariant and non-gauge invariant quantities can be measured by experimentally generating various non-Abelian gauges corresponding to the same set of Wilson loops

Extreme non-linear response of ultra-narrow optical transitions in cavity QED for laser stabilization

We explore the potential of direct spectroscopy of ultra-narrow optical transitions of atoms localized in an optical cavity. In contrast to stabilization against a reference cavity, which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from Brownian thermal noise. Spectroscopy of ultra-narrow optical transitions in a cavity operates in a very highly saturated regime in which non-linear effects such as bistability play an important role. From the universal behavior of the Jaynes-Cummings model with dissipation, we derive the fundamental limits for laser stabilization using direct spectroscopy of ultra-narrow atomic lines. We find that with current lattice clock experiments, laser linewidths of about 1 mHz can be achieved in principle, and the ultimate limitations of this technique are at the 1 $\mu$ Hz level.Comment: 5 pages, 4 figure

Modelling of quantum information processing with Ehrenfest guided tra jectories: a case study

We apply a numerical method based on multi-configurational Ehrenfest tra jectories, and demonstrate converged results for the Choi fidelity of an entangling quantum gate between two two-level systems interacting through a set of bosonic modes. We consider both spin-boson and rotating wave Hamiltonians, for various numbers of mediating modes (from 1 to 100), and extend our treatment to include finite temperatures. Our results apply to two-level impurities interacting with the same band of a photonic crystal, or to two distant ions interacting with the same set of motional degrees of freedom.Comment: 12 pages, figures aplent

Prospects for a mHz-linewidth laser

We propose a new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultra-narrow clock transition into the mode of a high Q-resonator. The resultant optical radiation has an extremely narrow linewidth in the mHz range, even smaller than that of the clock transition itself due to collective effects. A power level of order $10^{-12}W$ is possible, sufficient for phase-locking a slave optical local oscillator. Realizing this light source has the potential to improve the stability of the best clocks by two orders of magnitude.Comment: minor revisions + shortening; factor 2 algebra mistake correcte