Multiqubit computing and error-avoiding codes in subspace using quantum dots
Bi Qiao, Harry E. Ruda, Jian Wang · Journal of Applied Physics · 2002
An approach is presented for directly constructing cn-Not multi-qubit logic gates using quantum dots. In addition, error-avoiding codes in the projected subspace are discussed, offering a potentially robust scheme for protecting against decoherence. The following general conditions were found: (1) a projected subspace can always be constructed, in which decoherence effects can be cancelled by adjusting the interaction coupling time, enabling error-correction to be performed. This subspace is closed for the projected states. (2) The necessary and sufficient conditions for a decoherence-free subspace are that the second term in the subdynamic equation, be equal to zero. Commonly formulated conditions for a decoherence-free subspace are shown to be particular approximations of this condition, including the so-called Born–Markovian approximation.