Cottrell Scholar Awards - 2017
Combined Coherent Manipulation and Single-Shot Measurement of an Electron Spin
The promise of quantum computing is that it will perform certain calculations orders of magnitude faster than even the most powerful supercomputer that exists today. But getting to that point requires researchers to overcome many challenges, including a major one: determining the proper medium for embodying a quantum bit – a qubit – the basic unit of information for a quantum computer.
“One candidate qubit is the spin degree of freedom of a single electron trapped in a quantum dot,” says Edward B. Flagg, of the Department of Physics and Astronomy at West Virginia University. A quantum dot is a very tiny bit of semiconductor crystal; electron spin refers to the angular momentum, which can be either up or down, of an electron, a subatomic particle found in all atoms.
The electron spin must be initialized, manipulated, and then measured to obtain useful bits of information, but these three operations have proven difficult to combine.
“The operations require both magnetic fields and light. The problem is that manipulation requires a magnetic field pointing one way, and measurement requires a magnetic field pointing a perpendicular way. You can’t have both at the same time,” Flagg notes. “The key thing is that it’s hard, or impossible in some cases, to do all three operations to the same spin. That is the difficulty this research is trying to address.”
Flagg has received a Cottrell Scholar Award from Research Corporation for Science Advancement to explore the possibility of reading electron spin states using the AC Stark effect, a phenomenon associated with laser light. The Stark effect, named for physicist Johannes Stark, who discovered it in 1913, is the shifting and splitting of spectral lines of atoms and molecules due to the presence of an external electric field. Flagg is proposing to read quantum information optically, a process he hopes to accomplish by preparing the spin for measurement by hitting it with a laser beam to reveal the up or down nature of electron spin, without altering that spin. This would allow the three operations of initialization, manipulation, and measurement of an electron to be combined.
There is also an educational component to the Cottrell Scholar Award. Flagg intends to develop, evaluate, disseminate and support three full-course packages for upper-division physics that integrate active learning techniques developed in recent physics education research.
“A complete and readily available course package would allow instructors – especially new faculty and those teaching a course for the first time – to easily incorporate such techniques when they teach,” he said.