Daniel Craft
REU Prospectus 2012
Measuring Electron Spin Lifetimes in Quantum Dots
My main goal for the duration of the REU is to gather and interpret data about how
varying temperatures and magnetic fields affect the T1 spin lifetime of electrons in gallium
arsenide quantum dots. It is important to understand electron spin lifetimes because they are
integral to future spintronic and quantum computing technologies. These technologies use
quantum states of atoms to do calculations and other operations instead of 1’s and 0’s as is done
in classical computing. Before this can be done, however, we must understand and be able to
control these quantum states, for example, electron spin.
Previously, to do these experiments we would “pump” the electrons of our sample with a
magnetic field and circularly polarized laser so that they are aligned mostly into a single spin
direction, then “probe” the sample with a second, linearly polarized laser. By changing the delay
between the two beams and examining the Kerr rotation(the degree of change in polarization
angle) of the reflected probe beam we could determine how long the electron spins remained
coherent. That is the T1 lifetime. With my project this summer there are three key changes.
First, instead of looking at the reflected beam, we will be measuring the transmitted beam. This
will help us in aligning our optics, as well as other ways. Second, instead of using a second laser
to pump our sample we will use an ND filter to split our probe laser into two beams, then
separately control those two beams as the pump and the probe. This gives us the advantage of
having the exact same wavelength for the two beams, which allows us to both excite and
measure the same quantum dots. Thirdly, instead of using a normal GaAs sample, we will be
using a quantum dot sample.
I personally am going to be doing several things to help this project. Because of the
change from two lasers to one, and transmitted instead of reflected, our optics table requires
serious reorganization, which I am primarily responsible for. I also will be working on writing
programs in LabVIEW to control our superconducting magnet. I will be correcting previous
mistakes, consolidating overcomplicated subroutines, and adding new features entirely. In
addition to these responsibilities I will be directly involved in setting up our sample for scans,
taking scans, and interpreting our results.