Personally, I think that the most promising approach is `topological quantum computation', where unitary operations are performed by braiding quasiparticles in supercooled laminae. Every operation is exact (there's no potential for small inaccuracies due to imperfect implementation of quantum gates, since the entire state only depends on the homotopy class of the operations performed). It's also very fault-tolerant (faults can only occur if virtual pairs interact with at least two permanent quasiparticles, and this can be avoided by ensuring a large separation at all times). It's still unknown whether this is theoretically possible, since it relies on the quasiparticles obeying non-Abelian braiding statistics. Basically, we need more experimental evidence to determine whether the nu = 12/5 and/or nu = 5/2 fractional quantum Hall states exhibit this desired behaviour. There's an excellent review here: http://arxiv.org/abs/0707.1889 Sincerely, Adam P. Goucher
Sent: Monday, October 13, 2014 at 5:58 PM From: "Warren D Smith" <warren.wds@gmail.com> To: math-fun <math-fun@mailman.xmission.com> Subject: [math-fun] Good qubits made in silicon
http://arxiv.org/abs/1407.1950 http://arxiv.org/abs/1402.7140
These sounded promising at least before I noticed that all their experiments were done at about 0.05 kelvin temperature and apparenly they've never managed to build a q-gate, only single qubits.
You get a crystal of ultrapure silicon-28 (spin-0 isotope of Si). You put in a phosphorus-31 dopant atom. Different spin states of the dopant atom nucleus & electron store two qubits. Atomic state-transition spectral frequencies can be used to stimulate transitions, thus controlling the state of the qubit. Now you can create an electric field near that dopant atom by charging some metal gate. This "Stark shifts" its spectral frequencies. That way, by charging only the gate you want, you can control only the qubit you want and leave the others alone. Instead of using a phosphorus dopant atom, you can use an "artificial atom" (system with state-transitions) made from a "quantum dot."
Can systems with many interacting qubits (via q-gates) thus be built?
-- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
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