Your Week in Seminars: Short Thanksgiving edition

Good Monday evening all, and welcome to another edition of Your Week in Seminars. Last week was a half week here in Cornell, but we still managed two talks, the general colloquium and the Wednseday-talk-on-Tuesday.



Monday we had Charles Marcus of Harvard talk about Building Schrödinger's Chip.

This was a quantum computing talk. We don't actually have a quantum computing group in Cornell, but I've taken a couple of courses on it back home, and it's an interesting subject, although I've been a bit disillusion by the notable lack of problems solvable by quantum computers.

Marcus started by talking about the wonders and insanities of quantum mechanics - the usual spiel about the two slit experiment, electrons passing through walls, and Schrödinger's cat. He said he dubbed the talk Schrödinger's chip because unlike cats, that appear to break when we put them in the kind of low-temperature vacuum conditions we like to do quantum experiments in, chips keep working pretty well.

Next he introduced the concept of entanglement, which is at the basis of the whole concept of quantum computing. Entangled particles are two or more particles that do not have a definite quantum state, but are definitely in the same quantum state. If I take them apart and measure their state - say, spin up or down - then I do not know the answer, but as soon one turns up, the other is up as well, and if one is down the other is immediately down as well.

The experimental side of quantum computing is all about making little quantum boxes that contain a small number of states (like up or down) and then making it possible to entangle two of those boxes together. Add up enough boxes, under some criteria that were posited a decade ago but still not achieved, and you have a quantum computer.

The majority of the talk was a survey of the various state of the art boxes and the methods used to make them. For those keeping track, 15 is still the largest number factored by a quantum computer.


On Tuesday, I came in just in time for the second half of John Terning's talk on Monopoles, Anomalies, and Electroweak Symmetry Breaking.

It's not really ideal to go into the second half of a talk in Newman 311, and this one actually sounded like I missed some interesting stuff. The part that I heard was about adding magnetic monopoles to the standard model., Those lovely magnetic equivalents of the electric point charge that we all heard about in our undergraduate E&M course turn out to be surprisingly hard to integrate into basic particle theories, which is perhaps for the best as we have not detected them so far.

The gist of what I got from the second half of the talk was that it is not enough to add a magnetic counterpart to the electric part of the standard model, but in fact one needs a magnetic QCD and Weak force as well. Under some conditions, this kind of configuration can work, and predict magnetic monopoles with TeV-scale masses - the kind we might see in the LHC.

Terning also talked about how these could be detected in the LHC. It turns out this isn't simple, because at TeV we would be producing monopole-anti-monopole pairs just barely, and so without a lot of kinetic energy they would tend to collapse back on themselves and annihilate, creating what is essentially an omnidirectional shower of photons. He mentioned that one of the big detectors at the LHC - the CMS - was equipped to detect these kind of photon bursts, and so this another prediction or possibility that we can look forward to seeing or not seeing soon.


That's it for last week, kind of on the short side due to the holiday and so on. This week is our last normal one, as the semester ends, but I'll have a couple more particle talks the week after that, as well.