1,883 research outputs found
Demonstration of subchondral bone density patterns by three-dimensional CT-osteoabsorptiometry (CT-OAM) as a non-invasive method for in vivo assessment of individual long-term stresses in joints
Seiberg-Witten map for noncommutative super Yang-Mills theory
In this letter we derive the Seiberg-Witten map for noncommutative super
Yang-Mills theory in Wess-Zumino gauge. Following (and using results of)
hep-th/0108045 we split the observer Lorentz transformations into a covariant
particle Lorentz transformation and a remainder which gives directly the
Seiberg-Witten differential equations. These differential equations lead to a
theta-expansion of the noncommutative super Yang-Mills action which is
invariant under commutative gauge transformations and commutative observer
Lorentz transformation, but not invariant under commutative supersymmetry
transformations: The theta-expansion of noncommutative supersymmetry leads to a
theta-dependent symmetry transformation. For this reason the Seiberg-Witten map
of super Yang-Mills theory cannot be expressed in terms of superfields.Comment: 9 page
Space/time noncommutative field theories and causality
As argued previously, amplitudes of quantum field theories on noncommutative
space and time cannot be computed using naive path integral Feynman rules. One
of the proposals is to use the Gell-Mann--Low formula with time-ordering
applied before performing the integrations. We point out that the previously
given prescription should rather be regarded as an interaction point
time-ordering. Causality is explicitly violated inside the region of
interaction. It is nevertheless a consistent procedure, which seems to be
related to the interaction picture of quantum mechanics. In this framework we
compute the one-loop self-energy for a space/time noncommutative \phi^4 theory.
Although in all intermediate steps only three-momenta play a role, the final
result is manifestly Lorentz covariant and agrees with the naive calculation.
Deriving the Feynman rules for general graphs, we show, however, that such a
picture holds for tadpole lines only.Comment: 16 pages, LaTeX, uses feynmf macros, one reference added; ooops,
version 2 was an older one
Flopping-mode electric dipole spin resonance
Traditional approaches to controlling single spins in quantum dots require
the generation of large electromagnetic fields to drive many Rabi oscillations
within the spin coherence time. We demonstrate "flopping-mode" electric dipole
spin resonance, where an electron is electrically driven in a Si/SiGe double
quantum dot in the presence of a large magnetic field gradient. At zero
detuning, charge delocalization across the double quantum dot enhances coupling
to the drive field and enables low power electric dipole spin resonance.
Through dispersive measurements of the single electron spin state, we
demonstrate a nearly three order of magnitude improvement in driving efficiency
using flopping-mode resonance, which should facilitate low power spin control
in quantum dot arrays
IR-Singularities in Noncommutative Perturbative Dynamics?
We analyse the IR-singularities that appear in a noncommutative scalar
quantum field theory on . We demonstrate with the help of the
quadratic one-loop effective action and an appropriate field redefinition that
no IR-singularities exist. No new degrees of freedom are needed to describe the
UV/IR-mixing.Comment: 6 pages, amsLaTe
A Coherent Spin-Photon Interface in Silicon
Electron spins in silicon quantum dots are attractive systems for quantum
computing due to their long coherence times and the promise of rapid scaling
using semiconductor fabrication techniques. While nearest neighbor exchange
coupling of two spins has been demonstrated, the interaction of spins via
microwave frequency photons could enable long distance spin-spin coupling and
"all-to-all" qubit connectivity. Here we demonstrate strong-coupling between a
single spin in silicon and a microwave frequency photon with spin-photon
coupling rates g_s/(2\pi) > 10 MHz. The mechanism enabling coherent spin-photon
interactions is based on spin-charge hybridization in the presence of a
magnetic field gradient. In addition to spin-photon coupling, we demonstrate
coherent control of a single spin in the device and quantum non-demolition spin
state readout using cavity photons. These results open a direct path toward
entangling single spins using microwave frequency photons
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