Optical Pulse Control of Electron and Nuclear Spins in Quantum Dots
NAVAL RESEARCH LAB WASHINGTON DC ELECTRONICS SCIENCE AND TECHNOLOGY DIV
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Quantum information has the potential to revolutionize secure communications and computation, both important to the Department of Defense. The unique properties of quantum bits qubits, units of quantum information and the phenomenon of entanglement non-local, non-classical correlation prevent eavesdropping over quantum communication channels and enable the solving of problems that grow exponentially difficult with classical computation, including decryption of codes with long encryption keys. Electron spins in quantum dots QDs are being widely investigated as qubits for storage and processing of quantum information, with the two different directions of the spin, up or down, forming the two states of the qubit. NRL is a leader in developing semiconductor QDs for quantum information, both in materials development and in probing the quantum nature of these nanometer-scale structures. Controlling the spin in these QDs, including increasing the spin coherence time, is a key area of NRL research. The electron spin coherence time in a QD, or lifetime of the qubit, can be at least microseconds, but the coherence is easily masked by the many 10,000-100,000 randomly oriented nuclear spins that also exist in the QD. The net nuclear spin acts as a temporally fluctuating magnetic field that randomizes the phase of the electron spin qubit. We use a train of picosecond laser pulses at wavelengths near an electronic QD transition to manipulate the electron spin polarization and thereby control the nuclear spin polarization. This technique can be used to extend the electron spin coherence time in QDs, making this system more attractive for quantum information applications.
- Nuclear Physics and Elementary Particle Physics
- Quantum Theory and Relativity