Quantum computing via local control
Einat
Frishman and David Tannor,
The Weizmann
The central goal of quantum computing is the creation of a desired unitary
transformation, which is identified with the computation. As was recently shown
[Sklarz and Tannor '04,
'06], local control theory can be used to calculate fields that will produce
these transformations. In contrast to strategies using optimal control theory,
the present approach maintains the system at the computational sub-space at
intermediate times, thus avoiding unwanted decay processes and sensitivity to
the initial state of the mediating sub-space.
We consider a system with direct-product structure with respect to the
computational register and mediating states, where dynamics takes place in
Liouville space. This implementation leads to "virtual entanglement"
- in which second order transitions take
place through entangled states, yet leave the sub-systems nearly separable.
In this work we show how to produce arbitrary entangling two-qubit gates directly using this approach. The advantage of
this method is that it avoids the need to produce unitary gates as a sequence of
(perhaps a large number of) basis gate operations, thus increasing
the robustness and fidelity of the computation.