1202.5032 (Xin Wang et al.)

Composite pulses for robust universal control of singlet-triplet qubits    [PDF]

Xin Wang, Lev S. Bishop, J. P. Kestner, Edwin Barnes, Kai Sun, S. Das Sarma

Qubit manipulation is fundamental to quantum computing. However, the stray
coupling between the qubit and the environment usually present in real
experimental systems hinders the high-precision control necessary for a quantum
computer with error rates below the quantum error correction threshold. We
consider this problem in the context of the singlet-triplet spin qubit in a
semiconductor double quantum dot system, where the experimenter has precise
control over the exchange interaction only, while statistical fluctuations in
the magnetic field gradient produce drift error about the x-axis of the Bloch
sphere. The exchange interaction is restricted to be positive and finite.
Taking these constraints into account, we design experimentally viable
electrical pulse sequences that, for small magnetic field gradients, carry out
rotations around z while canceling gate errors up to the sixth order in the
gradient fluctuations, and for large gradients, perform arbitrary rotations
while canceling the leading order error.

View original: http://arxiv.org/abs/1202.5032