Trip to Zurich for 8th Symposium on Topological Quantum Computing, Zurich 29th-31st August 2009.

**Thursday 8/27** - 7:30am SEA to 3:30pm IAD, 6:00pm IAD to 8:00am ZRH. Attempt to upgrade first leg failed which is too bad as it was the international version of the 767-300 which has a pretty nice (by American carrier standards) business class. Both flights are completely full. Am I the only one who often goes to the self check kiosks by the gates and attempts to move my seat to one beside an empty seat? Sleep approximately 2 hours. Why does the lady behind me think that it is okay to start a conversation at 5 a.m. in the morning? Blessed be noise canceling headphones, for in their shadow I am not aware that I could be annoyed.

**Friday 8/28** - Take train from ZRH to Zurich Hauptbahnhof (realize only later that there is an "English" button on the ticket kiosk which would have made getting a ticket more comprehensible and less subject to random error.) Zurich Hauptbahnhof to Hotel Sunneshus: decide that I can just walk as its not the far, then realize that Zurich is a town of hills! Get nice workout hiking to hotel to drop off bag. Now the important jet lag trick: time to go for a long walk. Head back down the hill and decide to go check out Bahnhofstrasse a long mile of shopping. It's a Friday morning, so lots of woman (only a few men) out pushing baby carriages. Swiss appear to prefer the very traditional carriage model with babies on their backs. Can't decide if the rule here is to cover up your baby completely or not.

Use iPhone to take some photos, and then go wandering around using WifiTrack to see if I can find a free wifi connection. Score: there is an Apple Store with benches outside and an open network. Spend some time checking emails and of course all hell has broken at work during the time I've been in transit (okay not all hell, but some hell, which maybe I should call "all purgatory?") Swiss have arranged for a very Swiss sky:

Head up the Limmat river:

and relax in the park behind the Schweiz Landesmuseum to try to get some work done. Meet up with colleagues, have dinner, and proudly crash at hotel at around 7pm.

Saturday 8/29 - First day of the symposium. Lots of good talks, but the highlight for me was the chalkboard talk given by Matthias Gaberdiel on the basics of 2-dimensional conformal field theories with an emphasis on WZW models. The coherence of the talk was awesome. Eddy Ardonne talked about the physics of interacting anyonic chains: imagine if you had these crazy anyons and then let them interact? Joost Slingerland talked about a new set of states for fractional quantum hall effect systems. One of the take home lessons from the study of the FQHE that it has taken me a long time to appreciate is that for a lot of the states that fall outside of Laughlin 1/k filling fraction (or the p/(2p+1) filling fraction states from the composite fermion picture) it is not at all clear what state is the correct state for the real physical systems. Jiannis Pachos talked about some nice work with moving vortices in the honeycomb model, as well as given the motivating reasons for how they could be used for quantum computing. It was particularly nice to hear him talk about the fact that the toric code states have lifetimes not proportional to their size, but to a Boltzman factor. An interesting thing I learned in discussions at the symposium was that the for FQHE systems the temperature is not the temperature of the GaAs-AlGaAs lattice which can be cooled down to mK temperatures, but the temperature of the electron gas, which is apparently decoupled at low temperatures and at least one order of magnitude higher. Finally Ady Stern talked about fractional topological insulators a subject I'm just beginning to even have an idea how to think about. Note to organizers of conferences: this sympossium had absolutely one of the best paces and spaces between the talks, ample time for lunch, etc that I've encountered. Usually at the end of a day I'm mentally exhausted, not to mention when flying from Seattle jetlagged all to purgatory, but I have to say this conference had just the right amount for my pea sized brain.

Dinner: a beer (or was it wine?) garden somewhere north of the main train station. There I encountered a salad with an outrageous amount of Bacon:

Jet lag note: I've been running regularly at home waking at 5:45am. I think the fact that I went out and ran while in Zurich helped reset my clock: this was the least jet lag I've experienced for a trip like this in a long time.

**Sunday 8/30** - The morning included a talk by Jurg Frohlich on the theory of quantum hall fluids. The nice part of this talk was the simple examples that Jurg used to explain some of the key ideas. The bad part was that he is clearly very skeptical of quantum computing :) This was followed by a talk by Rudolf Morf who discussed the mounting evidence, both from theory and some experiment, that the filling fraction 5/2 fractional quantum hall state will support non-Abelian (in this case Ising) anyons. The settling of this seems to me to be a topic where experiments will probably be making great progress in the coming few years. Simon Trebst, from Microsoft station Q, talked about interacting anyon models (here, as opposed to in Eddy Androne's talk, the models where in two-dimensions.) In particular he discussed how interacting anyon models can give rise to a gaped quantum liquid inside the parent quantum liquid. Quantum liquids within quantum liquids, oh my that makes my head hurt. Ville Lahtinen gave a talk describing his work on Kitaev's honeycomb lattice and in particular gave a brief history of his coming of age in the model (childhood, adolescence, adulthood.) Interesting phases when you consider the model with various vortices in the system.

Then it was off to dinner at Uto Kulm, a restaurant on a nearby hill with a spectacular view of Zurich and the surrounding mountains. We hiked up the hill to the dinner, which was very pleasant. Watching physicists hike and chat is always great fun. If you've ever seen the movie "IQ" (Tim Robbins, Meg Ryan, Walter Matthau) there is a great scene where Podolsky, Godel, and Liebknecht are out wandering around a park. That scene does a great time capturing what it's like to go for a walk with a bunch of physicists and mathematicians: it usually involves a smattering a science, small talk, and humor. That and a certain lack of focus on where exactly they are going. A view of the tower up top from another tower up top:

**Monday 8/31** - The first talk of the day was by a crazy guy from the University of Washington. He completely misjudge how much he could cover in 45 minutes. Graham Kells talked about his work in arXiv:0903.5221 where he and coauthors introduced a fermionization procedure for exactly solving Kitaev's honeycomb model. This procedure has an advantage over the way in which Kitaev proceeded, which was to introduce extra degrees of freedom and then project back to the solution space. Oliver Buerschaper talked about quantum double models and tensor networks. In particular he showed a very nice tensor network representation of the ground states of these models. He then began to talk about generalizations to non-trivial Hopf algebras but, unfortunately, ran out of time to go into the details of these constructions. Gavin Brennen gave a talk about quantum walks with anyons, something of great interest to me as I've been working on some ideas using these walks. Finally there was an extra session by Stefano Chesi dedicated to a paper that had appeared on the arXiv just hours earlier: arXiv:0908.4262! This paper gives a construction of a self-correcting quantum system in two-dimensions if one allows >2 body interactions which are long distance interactions. The basic idea is to take the toric code Hamiltonian and give it constant, 1/r or 1/r^{2} long-range interactions. There was interesting discussions about whether this model is realistic or not. My own worry was that it is not clear how realistic greater than two-qubit long range interactions are. For example is it possible to obtain an effective many-qubit long range interaction out of two-qubit interaction without going to a higher spatial dimension?

**Tuesday 9/1** - ZRH 11:55 AM to IAD 3:18 PM, IAD 5:50 PM to SEA 7:43 PM, arriving an hour early. Trying to stay awake on the final hour of the trip succeeded due to an extra babbling four year old.

Zurich definitely lived up to its reputation as a very livable city, with excellent public transportation, and a beautiful setting. I reminded me a lot of Seattle, what with the lake and nearby mountains. But, holy moly expensive! I hope the ETH pays their students well! Some photos:

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Anyons? Seriously?

Most anyons I know have not been serious. They just can't get too charged up to really get mad.

ETH does pay their students pretty well: as full time PhD student, you might earn more money than a professor in Canada...

That's good to know Swiss Chris. I was also told the salaries in the city are also significantly higher. Now I just need to decide what to do with the 80 swiss francs I ended up not spending on chocolate to take home :)

So Dave, will you be heading back to Switzerland in January for QIP?