[QIP-Sem] QIP seminar, Mon 10/4, 4:00, 36-428, Bartlett,Stephen

[Peter Shor]

MIT Quantum Information Processing seminar
Monday 10/4 at 4:00 in 36-428
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 Bartlett,Stephen (University of Sydney)

Quantum computational phases of matter:  quantum computing in the Haldane phase of a spin-1 chain

Abstract:

A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-spin measurements on an appropriate quantum state.  One exciting prospect is that the ground or low-temperature thermal state of an interacting quantum many-body system can serve as such a resource state for quantum computation.  The system would simply need to be cooled sufficiently and then subjected to measurements.  It would be unfortunate, however, if the usefulness of a ground or low-temperature thermal state for quantum computation was critically dependent on the details of the system's Hamiltonian; if so, engineering such systems would be difficult or even impossible.  A much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation.  I'll discuss some recent results on the existence of such a quantum computational phase of matter.  I'll first ou
 tline some positive results on a phase of a toy model that allows for quantum computation.  Then, in a realistic model of a coupled spin-1 chain, I'll demonstrate the existence of a computational phase.  This result is obtained by using a measurement sequence to "renormalize" the state to a computationally-universal fixed point - the so-called AKLT state in the Haldane phase.  Together, these results reveal that the characterization of computational phases of matter has a rich, complex structure -- one which is still poorly understood.  Joint work with Gavin Brennen, Akimasa Miyake, and Joseph Renes.

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