arXiv subjects

Kerson Huang

Publications and source records attributed to Kerson Huang.

25 records · Page 2Linked to original sources

arXiv2000

How to mode-lock an atom laser

We consider a possible technique for mode-locking an atom laser, based on the generation of a dark soliton in a ring-shaped Bose-Einstein condensate, with repulsive atomic interactions. The soliton is a kink, with angular momentum per particle equal to \hbar/2. It emerges naturally, when the condensate is stirred at the soliton velocity, and subsequently outcoupled with a periodic Raman pulse-train. The result is a replicating coherent field inside the atom laser. We give a numerical demonstration of the generation and stabilization of the soliton.

cond-mat↗

arXiv1999

Instability of a Bose-Einstein Condensate with Attractive Interaction

We study the stability of a Bose-Einstein condensate of harmonically trapped atoms with negative scattering length, specifically lithium 7. Our method is to solve the time-dependent nonlinear Schrodinger equation numerically. For an isolated condensate, with no gain or loss, we find that the system is stable (apart from quantum tunneling) if the particle number N is less than a critical number N_c. For N > N_c, the system collapses to high-density clumps in a region near the center of the trap. The time for the onset of collapse is on the order of 1 trap period. Within numerical uncertainty, the results are consistent with the formation of a "black hole" of infinite density fluctuations, as predicted by Ueda and Huang. We obtain numerically N_c approximately 1251. We then include gain-loss mechanisms, i.e., the gain of atoms from a surrounding "thermal cloud", and the loss due to two- and three-body collisions. The number N now oscillates in a steady state, with a period of about 145 trap periods. We obtain N_c approximately 1260 as the maximum value in the oscillations.

cond-mat↗

arXiv1998

Fate of a Bose-Einstein condensate with attractive interaction

We calculate the decay amplitude of a harmonically trapped Bose-Einstein condensate with attractive interaction via the Feynman path integral. We find that when the number of particles is less than a critical number, the condensate decays relatively slowly through quantum tunneling. When the number exceeds the critical one, a "black hole" opens up at the center of the trap, in which density fluctuations become large due to a negative pressure, and collisional loss will drain the particles from the trap. As the black hole is fed by tunneling particles, we have a novel system in which quantum tunneling serves as a hydrodynamic source.

cond-mat↗

arXiv1996

Methods for a Nonuniform Bose Gas

We review mathematical methods for the treatment of a system of Bose particles with nonuniform density. Common pitfalls are pointed out.

cond-mat↗

arXiv1995

Non-Trivial Directions for Scalar Fields

We study the eigenvectors of the renormalization-group matrix for scalar fields at the Gaussian fixed point, and find that that there exist ``relevant'' directions in parameter space. They correspond to theories with exponential potentials that are nontrivial and asymptotically free. All other potentials, including polynomial potentials, are ``irrelevant,'' and lead to trivial theories. Away from the Gaussian fixed point, renormalization does not induce derivative couplings, but it generates non-local interactions.

hep-th↗

arXiv1994

Fixed-Point Structure of Scalar Fields

We search for alternatives to the trivial $ϕ^4$ field theory by including arbitrary powers of the self-coupling. Such theories are renormalizable when the natural cutoff dependencies of the coupling constants are taken into account. We find a continuum of fixed points, which includes the well-known Gaussian fixed point. The fixed point density has a maximum at a location corresponding to a theory with a Higgs mass of approximately 2700 GeV. The Gaussian fixed point is UV stable in some directions in the extended parameter space. Along such directions we obtain non-trivial asymptotically free theories.

hep-th↗

arXiv1993

An Asymptotically Free Phi4 Theory

The Phi4 theory in 4-epsilon dimensions has two fixed points, which coincide in the limit epsilon->0. One is a Gaussian UV fixed point, and the other a non-trivial IR fixed point. They lead to two different continuum field theories. The commonly adopted IR theory is ``trivial,'' behaves like perturbation theory, and suggests an upper bound on the Higgs boson mass. The UV theory is asymptotically free, and does not impose a bound on the Higgs mass. The UV continuum limit can also be reached in 4 dimensions with momentum or lattice cutoff.

hep-ph↗