January 21, 2006

Experimentalist bloggers and Joule heating

Posted by Arcane Gazebo at January 21, 2006 10:50 PM

Yesterday Chad Orzel speculated about the relative absence of experimental physicists in the blogging community. Unfortunately, I didn't have time to comment until now, because I was busy working in the lab. (Actually we were gearing up for, and then undergoing, a major safety inspection. The inspectors, who were reminiscent of the consultants from Office Space, stood around trying to invent scenarios under which a graduate student could suffer oxygen deprivation folowing sudden helium vaporization in our dilution fridge.)

Anyway, Chad's hypothesis was that theorists spend more time in front of computers on a daily basis, and thus blogging is just more convenient. This seems right to me: I'm one of the few condensed matter experimentalists who maintains a blog (and it probably helps that I'm a grad student rather than a postdoc or on the tenure track), and whether or not I have time to post mostly depends on how much time I'm spending on the computer, versus in front of an oscilloscope or soldering iron (or bolting power strips to desks two feet above the floor to satisfy safety inspectors).

For a period of about 10 months last year, we did not have an experiment running as we were fabricating a new sample. And due to the division of labor among the grad students on this project, I was not closely involved with the fabrication process, and instead spent my time reading papers, writing papers and reports to funding agencies, writing software, designing circuits, and doing simulations. These were all computer-intensive activities, and I was able to get a fair amount of blogging done. For the last two months, however, we've been doing measurements on the chip we made last year, and I've spent a lot of time taking data, looking at scope traces, and reconfiguring wiring. Hence, I think up a bunch of posts over the week and write them up on Saturday night, which is a bit lame.

Fortunately, I do frequently have the ability to post even under these conditions, due to the phenomenon of Joule heating: if a current I is applied to an electrical resistance at a voltage V heat will be dissipated at a rate equal to the product IV. Every time we make a measurement, we apply a current pulse to our device, which produces a voltage and a corresponding amount of heat. If this heat is allowed to accumulate on the chip, it will wipe out the quantum effects we're trying to study, so between each measurement we have to wait long enough for the chip to cool off. In practice, this means instead of taking a million measurements in a second we are reduced to about 2,000. Furthermore, to get good statistics and sweep over an interesting range of parameters we have to take a large number of measurements, so it turns out that to get interesting results we need to measure continuously for at least 12 hours. I've written an overly baroque computer program to automate all this, so once I know what I want to measure, I can push a button to start the experiment, do something else for a while (usually analyzing data from the previous run), and then collect all the data hours later (or the next day). (This is only when everything is working properly; otherwise it's back to the oscilloscope and wiring diagrams.) And in the gaps I can do a little blogging.

These days, the trend in the superconducting qubit community is towards nondissipative readout—i.e., measurements which leave the device in the superconducting state and thus produce no heat. This might threaten to take away my blogging windows, except that it would also enable measurements that require even better statistics and broader sweeps, and so there will still be reasons to do 12- and 24-hour runs. (Actually, our record is about 48 hours, but we don't currently have the battery life to repeat that.)

Tags: Lab, Life, Physics, Quantum Information, Science
Comments

Hmmm... you again show the ability to exposit very well, although I do believe there was a recent Physics Today article that may have moved onto your subject territory. Plus Physics Today has a bit of a rep for not being as amenable to proposed topics as they could be (that's how it was in my limited experience, and at least one person whose written an article they published seems to share it). That notwithstanding, I still think you should write up some of your stuff for that kind of article (well, part of it would be compiling some of the stuff you've written in blog entries) and give it a go. It's extremely rewarding (if occasionally time-consuming), and it is also a good way to get your research noticed by a wide cross section of the physics community. (The analness of Physics Today in my case has meant that I have instead been writing things for the mathematics equivalent, whose editors have been extremely amenable to my ideas.)

As for the point you actually raised here, I agree with you. I spend tons of time in front of a computer (although I try to do most of my blogging at night, unless there's something I see during a break in my work that I want to post), and this is one way to take a break from the stuff I should be doing.

Posted by: Mason | January 22, 2006 12:32 AM
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