Speaker: Stephen Lyon, Princeton University
Date & Time: March 27, 2008 - 1:30pm
Location: Serin E385
Preserving the coherence of spin qubits in silicon
Physics and Astronomy
Stephen Lyon, Princeton University
1:30 PM, Serin E385
Since they have long coherence times, electron spins in Si have been suggested as quantum bits (qubits) for quantum information processing. Electrons bound to donors have shown coherence times approaching a tenth of a second. However, they are susceptible to a variety of noise processes - minute magnetic field variations, fluctuations in the local electric fields which couple to the spin through spin-orbit and hyperfine interactions, etc. These forms of noise are typically not Gaussian, but often 1/f. Dynamical decoupling (repeatedly flipping the spins) has been proposed as a means to preserve the qubit coherence in spite of this type of noise.
We find that classical sequences from NMR (Carr-Purcell, CP, and Carr-Purcell-Meiboom-Gill, CPMG) are too susceptible to pulse errors, but more recently proposed pulse sequences are more effective at preserving quantum states in spite of errors. Recently, we have used microwave and RF pulses to reversibly transfer a quantum state from the electrons bound to phosphorus donors to the donor nuclei, and combined that with dynamical decoupling of the nuclear spins to preserve the states for over one second in isotopically enriched Si.