Electron Spin Resonance on Si/SiGe Quantum Dots
Speaker: Jianhua He
Series: Final Public Orals
Location: Engineering Quadrangle J401
Date/Time: Wednesday, July 11, 2012, 9:00 a.m. - 10:30 a.m.
A quantum computer stores and processes information in quantum bits (qubits) using the quantum properties of a system. Despite not having been proved to be always superior to a classical computer, research has shown that a quantum computer is more powerful for certain important tasks. Implementations based on qubits embedded in a solid material are currently among the leading efforts to build a large scale quantum computer. One of the major challenges is the short lifetime of a quantum state (coherence time) due to environmental noise in the host material.
This thesis follows the implementation scheme of using electron spins (an electrons intrinsic property, like its charge) in silicon nanostructures, namely quantum dots, as the qubits. We aim to experimentally characterize the coherence time of an electron spin in a silicon quantum dot by electron spin resonance, a technique that is analogous to that used in magnetic resonance imaging (MRI). A spin coherence time of 0.25 ms was measured at a temperature of 0.35 K. This is the first demonstration of the expected long electron spin coherence time of a quantum dot in silicon. With a quantum operation time of a few tens of nanoseconds, the spin qubit can remain coherent for much more than 104 operations, a threshold that is required for large scale quantum computing.