Pulse controlled noise suppressed quantum computation

Quantum computation has become a very active field ever since the discovery that quantum computers can be much more powerful than their classical counterparts. Decoherence of the qubits caused by the inevitable interaction with the noisy environment is the major obstacle to realization of quantum computation. A recent innovative discovery is that reliable quantum computation is possible provided that the error per operation caused by decoherence is below a threshold value. The estimated threshold error rate is about 10/sup -6/. With the present technology, the real noise seems necessarily beyond this threshold. Therefore, it is essentially important to further suppress noise before taking the procedure of fault-tolerant quantum error correction. We propose a noise suppression scheme which operates by applying a sequence of bit-flipping and phase-flipping pulses on the system, with the pulse period less than the noise correlation time.