What Are Error Correction/Mitigation Protocols?

Quantum Error Correction

Error correction protocols are used to detect if and where an error has occurred. These errors can then be corrected.  Errors can be detected and corrected using either active error correction or passive error mitigation.  

Using a feed-forward approach, pulses can be applied to the errant qubits to correct an error. This approach actively looks for and corrects errors and is thus referred to as "active error correction".  Implementing active error correction is very resource intensive as it requires significant overheard in terms of ancilla qubits, quantum operations, and measurements. 

"Passive error mitigation" can reduce physical qubit error rates. To accomplish this, specific pulse sequences are used to either mitigate under-rotation or over-rotation of the Bloch vector potentially caused be miscalibration or to undo coherent dephasing errors.  The purpose of these pulses is to counteract typical errors. Thus, this technique is labeled as passive in that  preventative measures to counteract certain systematic noise are taken.  Note that it is not considered “active" as specific error are not identified and corrected.