87,908 research outputs found
Superradiant Phase Transitions and the Standard Description of Circuit QED
We investigate the equilibrium behaviour of a superconducting circuit QED
system containing a large number of artificial atoms. It is shown that the
currently accepted standard description of circuit QED via an effective model
fails in an important aspect: it predicts the possibility of a superradiant
quantum phase transition, even though a full microscopic treatment reveals that
a no-go theorem for such phase transitions known from cavity QED applies to
circuit QED systems as well. We generalize the no-go theorem to the case of
(artificial) atoms with many energy levels and thus make it more applicable for
realistic cavity or circuit QED systems.Comment: 4+6 pages, 3+1 figure
Symbolic QED Pre-silicon Verification for Automotive Microcontroller Cores: Industrial Case Study
We present an industrial case study that demonstrates the practicality and
effectiveness of Symbolic Quick Error Detection (Symbolic QED) in detecting
logic design flaws (logic bugs) during pre-silicon verification. Our study
focuses on several microcontroller core designs (~1,800 flip-flops, ~70,000
logic gates) that have been extensively verified using an industrial
verification flow and used for various commercial automotive products. The
results of our study are as follows: 1. Symbolic QED detected all logic bugs in
the designs that were detected by the industrial verification flow (which
includes various flavors of simulation-based verification and formal
verification). 2. Symbolic QED detected additional logic bugs that were not
recorded as detected by the industrial verification flow. (These additional
bugs were also perhaps detected by the industrial verification flow.) 3.
Symbolic QED enables significant design productivity improvements: (a) 8X
improved (i.e., reduced) verification effort for a new design (8 person-weeks
for Symbolic QED vs. 17 person-months using the industrial verification flow).
(b) 60X improved verification effort for subsequent designs (2 person-days for
Symbolic QED vs. 4-7 person-months using the industrial verification flow). (c)
Quick bug detection (runtime of 20 seconds or less), together with short
counterexamples (10 or fewer instructions) for quick debug, using Symbolic QED
Precision Study of Positronium: Testing Bound State QED Theory
As an unstable light pure leptonic system, positronium is a very specific
probe atom to test bound state QED. In contrast to ordinary QED for free
leptons, the bound state QED theory is not so well understood and bound state
approaches deserve highly accurate tests. We present a brief overview of
precision studies of positronium paying special attention to uncertainties of
theory as well as comparison of theory and experiment. We also consider in
detail advantages and disadvantages of positronium tests compared to other QED
experiments.Comment: A talk presented at Workshop on Positronium Physics (ETH Zurich, May
30-31, 2003
Quantum electrodynamics corrections to energies, transition amplitudes and parity nonconservation in Rb, Cs, Ba, Tl, Fr and Ra
We use previously developed radiative potential method to calculate quantum
electrodynamic (QED) corrections to energy levels and electric dipole
transition amplitudes for atoms which are used for the study of the parity
non-conservation (PNC) in atoms. The QED shift in energies and dipole
amplitudes leads to noticeable change in the PNC amplitudes. This study
compliments the previously considered QED corrections to the weak matrix
elements. We demonstrate that the QED corrections due to the change in energies
and dipole matrix elements are comparable in value to those due to change in
weak matrix elements.Comment: 5 pages, 1 figur
Higher order QED in high mass e+ e- pairs production at RHIC
Lowest order and higher order QED calculations have been carried out for the
RHIC high mass e+ e- pairs observed by PHENIX with single ZDC triggers. The
lowest order QED results for the experimental acceptance are about two standard
deviations larger than the PHENIX data. Corresponding higher order QED
calculations are within one standard deviation of the data.Comment: 2 page
Limits on Non-Linear Electrodynamics
In this paper we set a framework in which experiments whose goal is to test
QED predictions can be used in a more general way to test non-linear
electrodynamics (NLED) which contains low-energy QED as a special case. We
review some of these experiments and we establish limits on the different free
parameters by generalizing QED predictions in the framework of NLED. We finally
discuss the implications of these limits on bound systems and isolated charged
particles for which QED has been widely and successfully tested
Vanishing magnetic mass in QED with a Chern-Simons term
We show that, at one loop, the magnetic mass vanishes at finite temperature
in QED in any dimension. In QED, even the zero temperature part can be
regularized to zero. We calculate the two loop contributions to the magnetic
mass in QED with a Chern-Simons term and show that it vanishes. We give a
simple proof which shows that the magnetic mass vanishes to all orders at
finite temperature in this theory. This proof also holds for QED in any
dimension.Comment: revtex, 7 pages, 5 figure
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