1,510 research outputs found
Frustration and glassiness in spin models with cavity-mediated interactions
We show that the effective spin-spin interaction between three-level atoms
confined in a multimode optical cavity is long-ranged and sign-changing, like
the RKKY interaction; therefore, ensembles of such atoms subject to frozen-in
positional randomness can realize spin systems having disordered and frustrated
interactions. We argue that, whenever the atoms couple to sufficiently many
cavity modes, the cavity-mediated interactions give rise to a spin glass. In
addition, we show that the quantum dynamics of cavity-confined spin systems is
that of a Bose-Hubbard model with strongly disordered hopping but no on-site
disorder; this model exhibits a random-singlet glass phase, absent in
conventional optical-lattice realizations. We briefly discuss experimental
signatures of the realizable phases.Comment: 5 pages, 2 figure
Phase boundary and finite temperature crossovers of the quantum Ising model in two dimensions
We revisit the two-dimensional quantum Ising model by computing
renormalization group flows close to its quantum critical point. The low but
finite temperature regime in the vicinity of the quantum critical point is
squashed between two distinct non-Gaussian fixed points: the classical fixed
point dominated by thermal fluctuations and the quantum critical fixed point
dominated by zero-point quantum fluctuations. Truncating an exact flow equation
for the effective action we derive a set of renormalization group equations and
analyze how the interplay of quantum and thermal fluctuations, both
non-Gaussian in nature, influences the shape of the phase boundary and the
region in the phase diagram where critical fluctuations occur. The solution of
the flow equations makes this interplay transparent: we detect finite
temperature crossovers by computing critical exponents and we confirm that the
power law describing the finite temperature phase boundary as a function of
control parameter is given by the correlation length exponent at zero
temperature as predicted in an epsilon-expansion with epsilon=1 by Sachdev,
Phys. Rev. B 55, 142 (1997).Comment: submitted to Phys. Rev. B Rapid Communication
Continuous time contests with private information
This paper introduces a class of contest models in which each player decides when to stop a privately observed Brownian motion with drift and incurs costs depending on his stopping time. The player who stops his process at the highest value wins a prize. We prove existence and uniqueness of a Nash equilibrium outcome and derive the equilibrium distribution in closed form. As the variance tends to zero, the equilibrium outcome converges to the symmetric equilibrium of an all-pay auction. For two players and constant costs, each player’s equilibrium profit decreases if the drift increases, the variance decreases, or the costs decrease
Soft quantum vibrations of a PT-symmetric nonlinear ion chain
Theoretical Physic
Effects of Next-Nearest-Neighbor Hopping on the Hole Motion in an Antiferromagnetic Background
In this paper we study the effect of next-nearest-neighbor hopping on the
dynamics of a single hole in an antiferromagnetic (N\'{e}el) background. In the
framework of large dimensions the Green function of a hole can be obtained
exactly. The exact density of states of a hole is thus calculated in large
dimensions and on a Bethe lattice with large coordination number. We suggest a
physically motivated generalization to finite dimensions (e.g., 2 and 3). In
we present also the momentum dependent spectral function. With varying
degree, depending on the underlying lattice involved, the discrete spectrum for
holes is replaced by a continuum background and a few resonances at the low
energy end. The latter are the remanents of the bound states of the
model. Their behavior is still largely governed by the parameters and .
The continuum excitations are more sensitive to the energy scales and
.Comment: To appear in Phys. Rev. B, Revtex, 23 pages, 10 figures available on
request from [email protected]
Off-diagonal Interactions, Hund's Rules and Pair-binding in Hubbard Molecules
We have studied the effect of including nearest-neighbor, electron-electron
interactions, in particular the off-diagonal (non density-density) terms, on
the spectra of truncated tetrahedral and icosahedral ``Hubbard molecules,''
focusing on the relevance of these systems to the physics of doped C.
Our perturbation theoretic and exact diagonalization results agree with
previous work in that the density-density term suppresses pair-binding.
However, we find that for the parameter values of interest for the
off-diagonal terms {\em enhance} pair-binding, though not enough to offset the
suppression due to the density-density term. We also find that the critical
interaction strengths for the Hund's rules violating level crossings in
C, C and C are quite insensitive to the
inclusion of these additional interactions.Comment: 20p + 5figs, Revtex 3.0, UIUC preprint P-94-10-08
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