Condensed Matter and Biological Physics Seminars

Spin coherence times in silicon at low temperature are extremely long, and have been known to be so for almost a half century. Such coherence offers many interesting opportunities for silicon in quantum computing. Nonetheless until recently, and not withstanding the stunning successes of the silicon microelectronics industry, certain features of this material have made exploration of silicon quantum electronics very challenging. Chief among these is the critical role of strain in silicon/silicon-germanium heterostructures – germanium is simply 4% larger than silicon, and this is a staggering difference in lattice constant for epitxay and heterostructure growth. I will discuss a number of critical advances that have allowed these obstacles to be overcome. Among those we have played a role in is the development of coherently strained membranes, structures that are flexible, centimeters wide but only 100 nm thick, and yet entirely single crystal. Further, I will present results on few-electron silicon quantum dots measured at milliKelvin temperatures that display manifestly quantum physics such as the Kondo and Fano effects. Finally, I will discuss recent progress understanding the most critical issue facing schemes for silicon quantum dot quantum computing: the role of valleys, a direct consequence of silicon’s indirect band gap, and, until recently, a major concern for the viability of silicon qubits.