****NON-TECHNICAL ABSTRACT**** Electrons are characterized by their spin as well as charge properties. An electron can generate and interact with a magnetic field through its spin. By taking advantage of spin properties of electrons, one can develop quantum computers that can solve certain problems much faster than any of current classical computers. This individual investigator project studies how electron spins interact with the surrounding nuclear spins in a semiconductor. Experimental studies will be based on the use of laser pulses with durations of order picoseconds. Since interactions between electron and nuclear spins can prevent the proper function of electron spins in a quantum computer, a primary objective of this project is to decouple or isolate electron spins from the surrounding nuclear spins with the use of ultrafast laser pulses. Research conducted in this program will provide excellent training for graduate and undergraduate students in semiconductor physics, nanotechnology, and information science and technology, preparing them for careers in academe, industry, or government. The project receives support from the Divisions of Materials Research and Physics.
This individual investigator project seeks to advance our ability to control fundamental decoherence processes of electron spins in semiconductors. The project will study optical spin echoes and coherent nonlinear optical processes of localized electrons and two-dimensional electron gas in semiconductors. Donor bound electrons in high purity n-type GaAs and electron gas in modulation doped CdTe quantum wells will be used as model systems of localized electrons and two-dimensional electron gas, respectively. Spin decoherence arising from the coupling of an electron spin to the surrounding nuclear spin bath will be investigated with optical spin echoes and with a particular emphasis on the understanding of non-Markovian spin decoherence processes. Restoration of spin coherence lost due to the coupling to the nuclear spin bath will be explored with dynamical decoupling techniques. The issue of how many-body Coulomb interactions fundamentally modify coherent optical processes in a two-dimensional electron gas will be addressed with both two-pulse and three-pulse differential absorption techniques. Research conducted in this program provides training for graduate and undergraduate students in semiconductor physics, nanotechnology, and quantum information. The project receives support from the Divisions of Materials Research and Physics.
Electrons are characterized by their spin as well as charge properties. An electron spin can interact with and precess about an external magnetic field. Electron spins can be exploited for devices that perform functions similar to electronic devices but consume less energy. By taking advantage of spin properties of electrons, one can also develop quantum computers that can solve certain problems much faster than any of current classical computers. This individual investigator project developed experimental techniques that use optical pulses with duration of a few picoseconds to manipulate the orientation of electron spins in semiconductors. These optical pulses act as effective DC or AC magnetic fields. The electrons investigated include those of a two dimensional electron gas and also those of impurities in semiconductors. Precise control of the spin orientation was achieved with a pair of optical pulses that feature a well-defined relative phase and a frequency separation that matches the frequency of the spin precession. The ultrafast optical pulses can flip the electron spins while preserving the periodic electron spin precession and can also map the relative phase of the optical pulse pair onto the phase of the electron spin precession. The optical control of electron spins developed in this project is of importance for the development spin-based devises and for the experimental exploration of spin-based computers. The research program also provided excellent training for graduate students in areas, including optics and photonics, semiconductor physics, nanotechnology, and quantum information, which are of both scientific and technological importance. Three students supported by this program have graduated with PhD in physics. They are currently pursuing postdoctoral research at universities and national labs.
