Instantaneous Quantum Channel Estimation during Quantum Information Processing

Understand

We present a nonintrusive method for reliably estimating the noise level during quantum computation and quantum communication protected by quantum error-correcting codes.

• As preprocessing of quantum error correction, our scheme estimates the current noise level through a negligible amount of classical computation using error syndromes and updates the decoder's knowledge on the spot before inferring the locations of errors.
• This preprocessing requires no additional quantum interaction or modification in the system.
• The estimate can be of higher quality than the maximum likelihood estimate based on perfect knowledge of channel parameters, thereby eliminating the need of the unrealistic assumption that the decoder accurately knows channel parameters a priori.