This is an Information Technology Research (ITR) medium award. Quantum information processing and computing offer the prospect of new technologies that rely fundamentally on quantum coherent phenomena for their operation. For such technologies to be successful, means of storing and reading out quantum information must both be developed. This project will focus on using the electronic spin to store quantum information. Spin, unlike charge, interacts weakly with its surroundings and better maintains quantum coherence. The same weakness of interaction, however, makes readout of individual electronic spins difficult. This proposal focuses on development of two different schemes for detection of individual spins in semiconductor quantum dots. Both rely on readout by means of spin-charge transduction, in which spin information is converted to charge information. In one case, spin blockade, in which the Pauli exclusion principle causes spin-dependent tunneling between dots, will be detected using a radio-frequency single-electron transistor. In the other, transduction will be accomplished by spin-dependent microwave excitation of an asymmetric quantum dot. Both schemes will initially be demonstrated in GaAs quantum dots, and later transferred to SiGe dots, which will be more compatible with existing microelectronics. A coordinated theoretical component will focus on calculations of decoherence times and on modeling of the devices themselves. This research could help in development of new information technologies based on detection and manipulation of individual spins. Science education and outreach are integrated into the project both in terms of training and in the development of curricular materials flowing directly out of the research. %%% This is an Information Technology Research (ITR) medium award. Quantum information processing and computing offer the prospect of new technologies that rely on fundamentally quantum mechanical phenomena for their operation. For such technologies to be successful, means of storing and reading out quantum information must both be developed. This project will focus on using the intrinsic magnetism, or spin, of an electron to store quantum information. The spin of an electron, unlike its electrical charge, interacts weakly with its surroundings, so that the quantum information is less easily lost. The same weakness of interaction, however, makes readout of the spin difficult. This proposal focuses on development of two different schemes for detection of individual spins in semiconductor quantum dots; both use conversion of spin information to charge information for readout. In one case spin-dependent electron transfer between a pair of quantum dots will be detected using a fast and sensitive electrometer called a single-electron transistor. In the other, conversion will be accomplished by spin-dependent microwave excitation of an asymmetric quantum dot. Both schemes will initially be demonstrated in gallium arsenide dots, and later transferred to silicon-based ones that will be more compatible with existing microelectronics. Coordinated theoretical research will model the devices and calculate the time scales on which quantum information is lost. This research could help develop new information technologies based on detection and manipulation of individual spins. Science education and outreach are integrated into the project both in terms of training and in the development of curricular materials flowing directly out of the research.
