Nuclear spins in silicon are very promising solid-state memory qubits due to their extremely long decoherence times. They have been proposed as qubit memories for quantum repeaters and quantum computers, and as a medium for solid-state atomic clocks and magnetometers. In order to realize many of these applications, single-donor spin measurement is required. In this project we are studying the use of hyperfine-state-selective optical pumping combined with a quantum Hall charge sensor device to perform single-donor nuclear spin measurement.
Two important characteristics of donors in silicon make this measurement scheme possible. First, the neutral-donor to donor-bound-exciton optical transitions in silicon has been shown to have linewidths significantly narrower than the hyperfine splitting. Second, the dominant decay mechanism from this state in silicon is Auger recombination, leading to ionization of the donor. These two effects allow the selective ionization of a donor with a particular nuclear spin state through optical pumping into the donor-bound-exciton state and subsequent ionization.
In the quantum Hall regime, the lowest energy forward- and backward-propagating edge channels are forced to overlap within a quantum point contact (QPC). The conductivity through this QPC is sensitive to the ionization state of a single donor located a few nanometers below the edge channels within the QPC and is insensitive to donors or defects outside of the QPC region. By measuring the conductivity through the QPC while optically pumping on the donor, the nuclear spin state of the donor can be determined.
Figure 1. Quantum Hall edge channels in the device. (a) Only one occupied edge channel (yellow) tunnels into the QPC. (b) The edge channels are transmitted in the D+ (ionized) case, while (c) the edge channels reflect from the donor in the D0 (neutral) case.
D Sleiter, N Y Kim, K Nozawa, T D Ladd, M L W Thewalt and Y Yamamoto, "Quantum Hall charge sensor for single-donor nuclear spin detection in silicon," New J. Phys. 12, 093028 (2010). [http://dx.doi.org/10.1088/1367-2630/12/9/093028]
Dr. Na Young Kim
Dr. Thaddeus Ladd
Prof. Yoshihisa Yamamoto
Dr. Katsuya Nozawa (Panasonic Corp., Japan)
Prof. Michael Thewalt (Simon Fraser University, Canada)