Quantum Computing with Quantum Dots

Image courtesy Prof. Petrof, UCSB

Why Quantum Dots (QDs)?

To do Quantum Computing (QC), we need well-defined, controllable energy levels. QDs provide that.

What energy levels?

We're using the charge (or space) levels of electrons in quantum dots. Other groups are trying to manipulate the spin levels. Spin manipulation usually requires big magnetic fields. We think that charge manipulation of the electronic levels via electric fields might be easier in the short-term.

Why Self-Assembled QDs (SAQDs)?

SAQDs don't have to be processed -- that is, they don 't have to be carved out of a quantum well or wire by etching techninques -- so we can access a lot of them relatively easily.

Why do you need a lot of them?

Ideally, we don't. But to look at the effects of our manipulations, it's much easier to observer many dots at once, manipulating them en masse.

Why double QDs?

Our first inclination is to use an array of single dots. However, we must keep our energy spacing between levels lower than the GaAs optical phonon energy so that vibrations (which couple strongly to charge levels, but not so to spin) don't interfere with our levels. Unfortunately, the large dots that are necessary to get such a small spacing between levels aren't available in large, homogeneous quantities that we need to do our collective experiments.

Instead, we have two dot layers grown, one on top of the other, so that the individual dots couple to each other. The (single-elecron) ground state splits by an energy that falls in THz range. The transitions we observe are between bonding and anti-bonding states of these coupled quantum dots.

Since dot formation is strain-induced (see the above link to SAQDs), the second layer of dots forms directly above the dots in the first layer. What we end up with are self-organized pairs of QDs.

Why InAs/GaAs?

Our growers are experienced in growing InAs quantum dots in GaAs matrices. So we take advantage of that.

What do you with your quantum dots?

We do photoluminesence (PL), capacitance-voltage (CV), and fourier-transform infrared (FTIR) spectroscopies.

This research is supported by DARPA.

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