Quantum Bit Regeneration
Isaac L. Chuang, Y. Yamamoto · Physical Review Letters · 1996
Decoherence and loss will limit the practicality of quantum cryptography and computing unless successful error correction techniques are developed. To this end, we have discovered a new scheme for perfectly detecting and rejecting the error caused by loss (amplitude damping to a reservoir at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$), based on using a dual-rail representation of a quantum bit. This is possible because (1) balanced loss does not perform a ``which-path'' measurement in an interferometer, and (2) balanced quantum nondemolition measurement of the ``total'' photon number can be used to detect loss-induced quantum jumps without disturbing the quantum bit's coherence.