NASA - National Aeronautics and Space Administration

The interstitial lithium donor in silicon is unique amongst shallow donors because it has an inverted level structure and a degeneracy within the 1s ground state manifold. The latter gives rise to a strong long-range elastic-dipole coupling of the neutral Li donor orbital states, similar to that obtained earlier for acceptors in Si by Golding and Dykman but absent in the case of other donors.

This coupling can be used for a quantum computing architecture based on the stress-defined orbital qubits in lithium donors in silicon. The above interaction can be used to enable 2-qubit gates while individual qubit control can be done by a resonant excitation of acoustic waves. At the same time the near degeneracy of 1s manifold in lithium donor in silicon also gives rise to a nontrivial coupling between the spin and orbital degrees of freedom first investigated by Watkins and Ham. One can expect that the inverted level structure and near degeneracy in 1s manifold will lead to a very short electron spin relaxation times which can also strongly affect orbital relaxation and be detrimental for QIP. Somewhat surprisingly, in view of extensive studies of spin relaxation of other shallow donors in silicon since the early sixties, both experimental and theoretical, the question about Li spin relaxation has not been addressed.

We investigate the lithium spin relaxation in ESR and FTIR experiments as well as control of individual qubits and 2-gate operations.

Substitutional donors in Si

Effective mass theory (EMT), Kohn & Luttinger, 1955

Non-EMT corrections: valley-orbit splitting

Interstitial donor Li in Si

Si:Li spectrum under uniaxial stress

FTIR to probe stress excited Li in Si

experiments at ALS, collaborators. M. Martin and Z. Hao

optics box for coupling of He-3 cryostat to FTIR spectrometer

Design of FIR accessible sampel holder with stress and static magnetic field (homogeneous, 0.6 T) for He-3 system

have design of a homogeneous hybrid magnet with 0.6 T strength and low temperature compadibility, need to modify LHe shield in the He-3 cryostat, fabricate and test the holder with magnetic field and stress

Co. N. Andresen, D. Humphries, and J. H. Vainionpaa, LBNL

First-principles charge density on Si:Lidonor

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