13,249 research outputs found
Control of quantum fluctuations for a Yukawa interaction in the Kaluza Klein picture
We study a system of fermions interacting with a scalar field, in 4+1
dimensions where the 5th dimension is compactified, using an exact functional
method, where quantum fluctuations are controlled by the amplitude of the bare
fermion mass. The integration of our equationsleads to the properties of the
dressed Yukawa coupling, that we study at one-loop so as to show the
consistency of the approach. Beyond one loop, the non-perturbative aspect of
the method gives us the possibility to derive the dynamical fermion mass. The
result obtained is cut off independent and this derivation proposes an
alternative to the Schwinger-Dyson approach.Comment: extended discussion on the scalar effective potentia
QED with Dynamical Fermions in an External Magnetic Field
In this paper, we present results of numerical lattice simulations of
two-flavor QED in three space-time dimensions. First, we provide evidence that
chiral symmetry is spontaneously broken in the chiral and continuum limit. Next
we discuss the role of an external magnetic field on the dynamically
generated fermion mass. We investigate the -dependence of the condensate
through calculations with dynamical fermions using the non-compact formulation
of the gauge field, and compare the results with those of a comparable study
using the quenched approximation.Comment: 21 pages, 12 figure
The Boltzmann equation without angular cutoff in the whole space: II, Global existence for hard potential
As a continuation of our series works on the Boltzmann equation without
angular cutoff assumption, in this part, the global existence of solution to
the Cauchy problem in the whole space is proved in some suitable weighted
Sobolev spaces for hard potential when the solution is a small perturbation of
a global equilibrium
A control on quantum fluctuations in 2+1 dimensions
A functional method is discussed, where the quantum fluctuations of a theory
are controlled by a mass parameter and the evolution of the theory with this
parameter is connected to its renormalization. It is found, in the framework of
the gradient expansion, that the coupling constant of a N=1 Wess-Zumino theory
in 2+1 dimensions does not get quantum corrections.Comment: Comments adde
Improved Superconducting Qubit Readout by Qubit-Induced Nonlinearities
In dispersive readout schemes, qubit-induced nonlinearity typically limits
the measurement fidelity by reducing the signal-to-noise ratio (SNR) when the
measurement power is increased. Contrary to seeing the nonlinearity as a
problem, here we propose to use it to our advantage in a regime where it can
increase the SNR. We show analytically that such a regime exists if the qubit
has a many-level structure. We also show how this physics can account for the
high-fidelity avalanchelike measurement recently reported by Reed {\it et al.}
[arXiv:1004.4323v1].Comment: 4 pages, 5 figure
Tunable joint measurements in the dispersive regime of cavity QED
Joint measurements of multiple qubits have been shown to open new
possibilities for quantum information processing. Here, we present an approach
based on homodyne detection to realize such measurements in the dispersive
regime of cavity/circuit QED. By changing details of the measurement, the
readout can be tuned from extracting only single-qubit to only multi-qubit
properties. We obtain a reduced stochastic master equation describing this
measurement and its effect on the qubits. As an example, we present results
showing parity measurements of two qubits. In this situation, measurement of an
initially unentangled state can yield with near unit probability a state of
significant concurrence.Comment: 4 pages, 4 figure
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