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A single electron spin in an external magnetic field forms a two-level system that can be used to create a spin qubit.
 

Summary: A single electron spin in an external magnetic field forms a
two-level system that can be used to create a spin qubit.
However, achieving fast single spin rotations, as would be
required to control a spin qubit, is a major challenge. It is
difficult to drive spin rotations on timescales that are faster
than the spin dephasing time and to individually address a
single spin on the nanometer scale. We have developed a new
method for quantum control of single spins that does not
involve conventional electron spin resonance (ESR). In
analogy with an optical beam splitter, we use an anticrossing
in the energy level spectrum of our quantum dot "artificial
atom" as a beam splitter for an incoming quantum state. The
anti-crossing is used to prepare a superposition of singlet and
triplet spin states, which then evolve according to the time-
dependent Schrodinger equation. A return sweep through the
anti-crossing results in quantum interference of the spin
states. By changing the effective path length of one arm of
our interferometer, we are able to achieve coherent rotations
between a singlet state and a T+ triplet state. The rotations are
nearly a factor of 100 faster than spin rotations achieved using

  

Source: Akhmedov, Azer - Department of Mathematics, University of California at Santa Barbara

 

Collections: Mathematics