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Readable Nuclear Spins Advance Quantum Computing
eldavojohn writes, "A University of Utah researcher and his team of German colleagues have shown that it is possible, using electronics, to read data stored as nuclear 'spins'. The lead researcher in the experiment was Dr. Christoph Boehme and his team's letter is available via Nature Physics (at a cost of $18 unless you are a subscriber). This is looking to be a large advance in quantum computing because prior to this, measuring the number of spins of a single phosphorus nucleus was very difficult." From the article: "The researchers used a piece of silicon crystal about 300 microns thick — about three times the width of a human hair — less than 3 inches long and about one-tenth of an inch wide. The silicon crystal was doped with phosphorus atoms. Phosphorus atoms were embedded in silicon because too many phosphorus atoms too close together would interact with each other so much that they couldn't store information. The concept is that the nuclear spin from one atom of phosphorus would store one qubit of information. The scientists used lithography to print two gold electrical contacts onto the doped silicon. Then they placed an extremely thin layer of silicon dioxide — about two billionths of a meter thick — onto the silicon between the gold contacts. As a result, the device's surface had tiny spots where the spins of phosphorus atoms could be detected."
What's the net potential energy difference between the difference between the different spin states, if any? And what does the curve look like - is there a big hump between them, or a small hump relative to any energy difference? If it's a hump, is it a trough to flip the states back?
I had to pull out my quantum mechanics book for this one. As a rough estimate for the energy difference between "up" and "down" spins, you can use the energy of the Zeeman effect (energy level splitting in an atom when in a magnetic field). The magnitude of that effect is (B/2.4e9 gauss) * 13.6 eV, where B is the size of the applied magnetic field. A supermagnet would produce fields on the order of 1e5 gauss, so we're not talking very much energy here. As another very crude estimate, consider that random thermal effects have enough energy to flip spins randomly, which is one of the big problems facing spintronics.
As to the humping issue, this is quantum mechanics; there is no curve. Only discrete states are allowed, with nothing in between.