We propose a scheme for electron spin quantum computing based on
electron spin in semiconductors. This scheme shares many similarities
with the existing Kane nuclear spin proposal. We show how quantum
computation may be carried out in this proposal, including single
qubit rotations and CNOT gate. We show how this control can
potentially lead to gate speeds 100-1000 times faster than the
existing nuclear spin proposal, and up to 106 times faster than a typical electron spin dephasing time, T2(e).
Single-spin measurement is an extremely important challenge, and
necessary for the future successful development of several recent spin-based proposals for quantum information processing. Magnetic resonance force microscopy (MRFM) has been suggested as a promising technique for single-spin detection. We discuss how to read out the quantum state of a single spin using the MRFM technique based on
cyclic adiabatic inversion (CAI). We include, in our analysis, a measurement device (an optical interferometer) to monitor the position of the cantilever, which then provides us with
information of the spin state. We consider various relevant sources
of noise and taken into account the effect of spin relaxation on the
single-spin detection scheme. We also present a realistic
continuous measurement model, and discuss the approximations and
conditions to achieve a quantum non-demolition measurement of a single
spin by MRFM. Finally we will present some simulation results for the
single-spin measurement process.
We give a quantum description of a Quantum Electro-Mechanical
System (QEMS) comprising a single quantum dot harmonically bound
between two electrodes and facilitating a tunnelling current
between them. An example of such a system is a fullerene molecule
between two metal electrodes. The description is based on a
quantum master equation for the density operator of the electronic
and vibrational degrees of freedom and thus incorporates the
dynamics of both diagonal (population) and off diagonal
(coherence) terms. We derive coupled equations of motion for the
electron occupation number of the dot and the vibrational degrees
of freedom, including damping of the vibration and thermo-mechanical noise, and give a semiclassical description of the dynamics under a variety of bias conditions. This dynamical description is related to observable features of the system including the stationary conductance as a function of bias voltage.
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