7 research outputs found
Qubit-Initialisation and Readout with Finite Coherent Amplitudes in Cavity QED
We consider a unitary transfer of an arbitrary state of a two-level atomic
qubit in a cavity to the finite amplitude coherent state cavity field. Such
transfer can be used to either provide an effective readout measurement on the
atom by a subsequent measurement on the light field or as a method for
initializing a fixed atomic state - a so-called "attractor state", studied
previously for the case of an infinitely strong cavity field. We show that with
a suitable adjustment of the coherent amplitude and evolution time the qubit
transfers all its information to the field, attaining a selected state of high
purity irrespectively of the initial state.Comment: 6 pages, 4 figure
Super Weyl invariance: BPS equations from heterotic worldsheets
It is well-known that the beta functions on a string worldsheet correspond to
the target space equations of motion, e.g. the Einstein equations. We show that
the BPS equations, i.e. the conditions of vanishing supersymmetry variations of
the space-time fermions, can be directly derived from the worldsheet. To this
end we consider the RNS-formulation of the heterotic string with (2,0)
supersymmetry, which describes a complex torsion target space that supports a
holomorphic vector bundle. After a detailed account of its quantization and
renormalization, we establish that the cancellation of the Weyl anomaly
combined with (2,0) finiteness implies the heterotic BPS conditions: At the one
loop level the geometry is required to be conformally balanced and the gauge
background has to satisfy the Hermitean Yang-Mills equations.Comment: 1+31 pages LaTeX, 5 figures; final version, discussion relation Weyl
invariance and (2,0) finiteness extended, typos correcte