TUESDAY, October 20

IQI Seminar, 3:00 PM - 4:00 pm, 105 Annenberg (Bldg 16)
"Measurement-Based Quantum Computation in Realistic Spin-1 Chains," Joe Renes, Technical University of Darmstadt.

Abstract:

The excitement surrounding meausrement-based quantum computation comes not just from the intriguing theoretical result that the power of a quantum computer can be attributed to the nature of the initial state, but also the more practical feature that it might be possible to find or engineer physical systems which would naturally provide such initial states as ground states. Since no system can be controlled or engineered perfectly, it is therefore vital to develop methods which characterize how suitable a given physical system is for this purpose.
Moreover, this must be done in a way which circumvents the apparent need to evaluate the result for arbitrary computational measurement sequences, as these grow exponentially in number. We study this problem at the single-qubit level for the hybrid scheme recently introduced by Brennen and Miyake [1] using gapped one-dimensional spin-1 AKLT chains. Here individual qubit gates are performed by measurement while two-qubit gates are performed by coupling different chains. Brennen and Miyake describe a implementations using either atoms or polar molecules in optical lattices, where the gap is expected to help suppress decoherence. We show that the approach taken by Doherty and Bartlett to characterize the computational power of nearly-cluster state quantum computers [2] can be profitably adapted to this case, avoiding the exponential counting trap mentioned above. By numerical analysis we find that arbitrary single-qubit operations can be faithfully executed over a reasonbly wide parameter range of bilinear-biquadratic Hamiltonians near the AKLT point. Furthermore, we find a simple decimation transformation making nearby groundstates more AKLT-like, resulting in improved operation fidelity.

This is joint work with Stephen Bartlett, Gavin Brennen, and Akimasa Miyake.

[1] Brennen and Miyake, Phys. Rev. Lett. 101, 010502 (2008).
[2] Doherty and Bartlett, Phys. Rev. Lett. 103, 020506 (2009).