Two-level atom at finite temperature

Properties of a two-level atom coupled to the quantized electromagnetic field at finite temperature are determined. The analysis is based on a new method (inspired by QED) of describing qubits, developed previously at zero temperature (Phys. Rev. A 76, 062106 (2007)). In this paper, we make a generalization to finite temperature by introducing the Matsubara formalism and the temperature propagators. We analyze the spectral properties of different types of propagators and we derive a direct connection between the temperature propagators and the real time propagators. To show the effectiveness of this method, we calculate the temperature dependence of the polarizability of a two-level atom in the lowest order of perturbation theory and we predict an unexpected sharpening of the resonance. The whole discussion is carried out without the rotating wave approximation.Comment: 12 page

Information-Entropic Stability Bound for Compact Objects: Application to Q-Balls and the Chandrasekhar Limit of Polytropes

Spatially-bound objects across diverse length and energy scales are characterized by a binding energy. We propose that their spatial structure is mathematically encoded as information in their momentum modes and described by a measure known as configurational entropy (CE). Investigating solitonic Q-balls and stars with a polytropic equation of state $P = K{\rho}^{\gamma}$, we show that objects with large binding energy have low CE, whereas those at the brink of instability (zero binding energy) have near maximal CE. In particular, we use the CE to find the critical charge allowing for classically stable Q-balls and the Chandrasekhar limit for white dwarfs $({\gamma} = 4/3)$ with an accuracy of a few percent.Comment: 4 figure

Information-Entropic Signature of the Critical Point

We investigate the critical behavior of continuous phase transitions in the context of Ginzburg Landau models with a double well effective potential. In particular, we show that the recently proposed configurational entropy, a measure of spatial complexity of the order parameter based on its Fourier mode decomposition, can be used to identify the critical point. We compute the CE for different temperatures and show that large spatial fluctuations near the critical point lead to a sharp decrease in the CE. We further show that the CE density has a marked scaling behavior near criticality, with the same power law as Kolmogorov turbulence. We reproduce the behavior of the CE at criticality with a percolating many bubble model

Exploring the Spin Structure of the Proton with Two-Body Partonic Scattering at RHIC

The STAR collaboration at the Relativistic Heavy Ion Collider is using polarized proton beams at sqrt{s} = 200 GeV to study the spin structure of the proton. The first results for the double spin helicity dependence of inclusive jet production are presented along with projections for additional data taken in 2005 and 2006. When fully analyzed these data sets should place strong constraints on the possible contribution of gluonic spin to the proton spin as expressed by Delta G. Future studies using 2-jet or photon-jet coincidences to map out the gluon spin distribution vs. the gluon's momentum fraction of the proton are discussed.Comment: 4 pages, 2 figures, presented at the 18th Int. IUPAP Conf. on Few-Body Problems in Physics, Santos, Sao Paulo, Brazil, August 21-26,200