  Postselected quantum computation is distinguished from regular quantum
computation by accepting the output only if measurement outcomes satisfy
predetermined conditions. The output must be accepted with nonzero probability.
Methods for implementing postselected quantum computation with noisy gates are
proposed. These methods are based on error-detecting codes. Conditionally on
detecting no errors, it is expected that the encoded computation can be made to
be arbitrarily accurate. Although the probability of success of the encoded
computation decreases dramatically with accuracy, it is possible to apply the
proposed methods to the problem of preparing arbitrary stabilizer states in
large error-correcting codes with local residual errors. Together with
teleported error-correction, this may improve the error tolerance of
non-postselected quantum computation.
