82,469 research outputs found
Monte Carlo Studies of the Fundamental Limits of the Intrinsic Hyperpolarizability
The off-resonant hyperpolarizability is calculated using the dipole-free
sum-over-stats expression from a randomly chosen set of energies and transition
dipole moments that are forced to be consistent with the sum rules. The process
is repeated so that the distribution of hyperpolarizabilities can be
determined. We find this distribution to be a cycloid-like function. In
contrast to variational techniques that when applied to the potential energy
function yield an intrinsic hyperpolarizability less than 0.71, our Monte Carlo
method yields values that approach unity. While many transition dipole moments
are large when the calculated hyperpolarizability is near the fundamental
limit, only two excited states dominate the hyperpolarizability - consistent
with the three-level ansatz.Comment: 7 pages, 5 figure
Color superconductivity and the strange quark
At ultra-high density, matter is expected to form a degenerate Fermi gas of
quarks in which there is a condensate of Cooper pairs of quarks near the Fermi
surface: color superconductivity. In these proceedings I review some of the
underlying physics, and discuss outstanding questions about the phase structure
of ultra-dense quark matter.Comment: 11 pages, proceedings of QCD@Work 2005 and Johns Hopkins Workshop
200
Compact Sum-Over-States Expression without Dipolar Terms for Calculating Nonlinear Susceptibilities
Using sum rules, the dipolar terms can be eliminated from the commonly-used
sum-over-states (SOS) expression for nonlinear susceptibilities. This new
dipole-free expression is more compact, converges to the same results as the
common SOS equation, and is more appropriate for analyzing certain systems such
as octupolar molecules. The dipole-free theory can be used as a tool for
analyzing the uncertainties in quantum calculations of susceptibilities, can be
applied to a broader set of quantum systems in the three-level model where the
standard SOS expression fails, and more naturally leads to fundamental limits
of the nonlinear susceptibilities.Comment: 6 pages and 4 figures Paper now in prin
- …