Universal Refocusing of Systematic Quantum Noise

Understand

Refocusing of a quantum system in NMR and quantum information processing can be achieved by application of short pulses according to the methods of spin echo and dynamical decoupling.

• However, these methods are strongly limited by the requirement that the evolution of the system between pulses be suitably small.
• Here we show how refocusing may be achieved for arbitrary (but time-independent) evolution of the system between pulses.
• We first illustrate the procedure with one-qubit systems, and then generalize to $d$-dimensional quantum systems.