Geometric Aspects of Composite Pulses

Unitary operations acting on a quantum system must be robust against systematic errors in control parameters for reliable quantum computing. Composite pulse technique in NMR realises such a robust operation by employing a sequence of possibly poor quality pulses. In this talk, we demonstrate that two kinds of composite pulses, one compensates for a pulse length error in a one-qubit system and the other compensates for a J-coupling error in a two-qubit system, have vanishing dynamical phase and thereby can be seen as geometric quantum gates, which implement unitary gates.