SEMINARIO DE FISICA TEORICA I Y II

Titulo:         Long-lived states in silicon-based quantum computing architectures: decoherence and relaxation for spin and valley states
Conferenciante: Marta Prada (University of Wisconsin-Madison, USA)
Dia y hora:     3, 14:15 (Sala de grados)

Resumen:

The pursuit of spin and quantum entanglement-based devices in solid state
systems has become a global endeavor.
Semiconductor architectures hold promise for quantum information processing
(QIP) applications due to their large industrial base and perceived scalability
potential.
Electron spins in silicon in particular may be an excellent architecture
for QIP, and also for spin electronics (spintronics) applications. While the
charge of an electron is easily manipulated by charged gates, the spin degree
of freedom is well isolated from charge fluctuations. This leads to very good
spin quantum bit (qubit) stability or quantum coherence properties, based in a
material with a mature existing technology.
Inherently small spin-orbit coupling and the existence of a spin-zero Si
isotope also facilitate long single spin coherence times.
The many-valley nature of silicon is in principle a drawback for QIP,
however, in the presence of bi-axially strain only the two lowest valleys are
present, which further split in the presence of confinement.

Here we present a theoretical study of the relaxation processes in Si
quantum dot based architectures.
We find T_1, the spin-flip time, to be extremely large, dominated
by a two-phonon (Orbach) processes at B=0.
For the singlet-triplet relaxation, T_{ST}, we find that
relaxation occurs mainly due to higher energy virtual states with
phonon emission.
Our calculations show that relaxation processes are at least three orders of
magnitude larger than for similar GaAs proposed architectures, presenting
important practical milestones on the way to design and construct a
silicon-based quantum computer.