Fullerene graphs have exponentially many perfect matchings

A fullerene graph is a planar cubic 3-connected graph with only pentagonal and hexagonal faces. We show that fullerene graphs have exponentially many perfect matchings.Comment: 7 pages, 3 figure

Symposium in Celebration of the Fixed Target Program with the Tevatron

This document is an abridgement of the commemorative book prepared on the occasion of the symposium "In Celebration of the Fixed Target Program with the Tevatron" held at Fermilab on June 2, 2000. The full text with graphics contains, in addition to the material here, a section for each experiment including a "plain text" description, lists of all physics publications, lists of all degree recipients and a photo from the archives. The full text is available on the web at: http://conferences.fnal.gov/tevft/book

Time-dependent natural orbitals and occupation numbers

We report equations of motion for the occupation numbers of natural spin orbitals and show that adiabatic extensions of common functionals employed in ground-state reduced-density-matrix-functional theory have the shortcoming of leading always to occupation numbers which are independent of time. We illustrate the exact time-dependence of the natural spin orbitals and occupation numbers for the case of electron-ion scattering and for atoms in strong laser fields. In the latter case, we observe strong variations of the occupation numbers in time.Comment: 5 pages, 5 figure

Stochastic Cutoff Method for Long-Range Interacting Systems

A new Monte-Carlo method for long-range interacting systems is presented. This method consists of eliminating interactions stochastically with the detailed balance condition satisfied. When a pairwise interaction $V_{ij}$ of a $N$-particle system decreases with the distance as $r_{ij}^{-\alpha}$, computational time per one Monte Carlo step is ${\cal O}(N)$ for $\alpha \ge d$ and ${\cal O}(N^{2-\alpha/d})$ for $\alpha < d$, where $d$ is the spatial dimension. We apply the method to a two-dimensional magnetic dipolar system. The method enables us to treat a huge system of $256^2$ spins with reasonable computational time, and reproduces a circular order originated from long-range dipolar interactions.Comment: 18 pages, 9 figures, 1 figure and 1 reference are adde

Non-Destructive Probing of Rabi Oscillations on the Cesium Clock Transition near the Standard Quantum Limit

We report on non-destructive observation of Rabi oscillations on the Cs clock transition. The internal atomic state evolution of a dipole-trapped ensemble of cold atoms is inferred from the phase shift of a probe laser beam as measured using a Mach-Zehnder interferometer. We describe a single color as well as a two-color probing scheme. Using the latter, measurements of the collective pseudo-spin projection of atoms in a superposition of the clock states are performed and the observed spin fluctuations are shown to be close to the standard quantum limit.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

Giant enhancement of anisotropy by electron-phonon interaction

Anisotropic electron-phonon interaction is shown to lead to the anisotropic polaron effect. The resulting anisotropy of the polaron band is an exponential function of the electron-phonon coupling and might be as big as $10^3$. This also makes anisotropy very sensitive to small changes of coupling and implies wide variations of anisotropy among compounds of similar structure. The isotope effect on mass anisotropy is predicted. Polaron masses are obtained by an exact Quantum Monte Carlo method. Implications for high-temperature superconductors are briefly discussed.Comment: 5 pages, 4 figure

Excitonic - vibronic coupled dimers: A dynamic approach

The dynamical properties of exciton transfer coupled to polarization vibrations in a two site system are investigated in detail. A fixed point analysis of the full system of Bloch - oscillator equations representing the coupled excitonic - vibronic flow is performed. For overcritical polarization a bifurcation converting the stable bonding ground state to a hyperbolic unstable state which is basic to the dynamical properties of the model is obtained. The phase space of the system is generally of a mixed type: Above bifurcation chaos develops starting from the region of the hyperbolic state and spreading with increasing energy over the Bloch sphere leaving only islands of regular dynamics. The behaviour of the polarization oscillator accordingly changes from regular to chaotic.Comment: uuencoded compressed Postscript file containing text and figures. In case of questions, please, write to [email protected]

Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression

Resistance, magnetoresistance and their temperature dependencies have been investigated in the 2D hole gas at a [001] p-GaAs/Al$_{0.5}$Ga$_{0.5}$As heterointerface under [110] uniaxial compression. Analysis performed in the frame of hole-hole scattering between carriers in the two spin splitted subbands of the ground heavy hole state indicates, that h-h scattering is strongly suppressed by uniaxial compression. The decay time $\tau_{01}$ of the relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3 kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.

An Improved upper limit on the decay K^+ -> pi^+ mu^+ e^-

Based on results of a search for the lepton-family-number-violating decay $K^+ \to \pi^+\mu^+ e^-$ with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at $2.1 \times 10^{-11}$ (90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of $1.3 \times 10^{-11}$ (90% C.L.) is obtained.Comment: v2: 13 pages, submitted to the Phys. Rev. D v3: 13 pages, resubmitted to Phys. Rev. D (corrections include: a more detailed overview of the combined analysis of the available experimntal data