Cryogenic dark matter search (CDMS) signals converted into visual and audio
(OK, who didn’t have one of these in their dorm rooms in college? 🙂 )
There’s a pepsi-through-the-nose funny part, too, (at least according to my calibrations) about halfway through. What a dark sense of humor!
From the Fermilab newsletter, via physics and physicists
One thing about R & D is that the project eventually moves you from physics (the “R” part) over to something that’s more engineering in nature (the “D” part). Here’s a quick example. Here’s the laser system for the caesium fountain, which is a research device. It’s spread out to be optimized for getting your hands in and tweaking on knobs, since you don’t know ahead of time what is going to work best. Lots of mirrors and other optics that need to be adjusted, and there has to be room to change things around and/or add things that might work better. You have to generate six beams for trapping (this is done at the table under the big cylinder, splitting two beams from the main table), plus a beam for optical pumping and another for probing the atoms. That’s four different beams on the table, at various (and for the MOT, adjustable) frequencies. The long paths meant that the beams would only stay aligned into the fiber couplers for, at best, weeks at a time.
Eventually you decide on a design that works, and since our production devices need to fit into a smaller space, and aren’t meant to be adjusted much (ideally, not at all) after the initial setup, you make everything smaller. Pretty much everything except the lasers (the 2 blue boxes on the left and 3 black boxes; one center-front and two right-rear) and the spectroscopy (which ends up on a different table) are compacted to fit on a much smaller table.
Everything is fiber-coupled, so it’s modular — it doesn’t matter which particular laser you use, or what you do with the beams after they leave the box. As you can see, it’s rack-mounted, and about 4u high. (You can just see another table at the top of the picture; this houses the spectroscopy/locking hardware)
Chad’s been busy blogging about his recent lab visits to NIST and U. Maryland, and the writeups are, as usual, top-notch. Cavity QED (a subfield I find fascinating and something I might have pursued had the right opportunities arisen when I was looking for a postdoc), Cold Plasmas, Biophysics (you might have a “what the?” reaction, but it uses optical tweezers, which is why this doesn’t really fall under “one of these things is not like the other,” Four-Wave Mixing (another field I find interesting, and the summary is definitely worth a read if you’ve ever wondered if things you learned in QM were ever actually applied to anything. You’ve got electrons moving between states without ever exciting the atom, and squeezed states, which is an exploitation of the Heisenberg Uncertainty Principle)
Last but not least one on this list (so far, anyway) is about trapping Francium. As I mentioned in the U.P. comments, I was a postdoc in the group that tried to trap Francium at TRIUMF several years back, and when we started discussing plans to do it, we were hoping to trap before the Stony Brook lab did so. Well, they succeeded while we … met some obstacles. As I recall, we weren’t the first in line to use the target; there was another experiment that went first, and so we only had a short time to try. And trying to trap something that has no stable isotopes is a special challenge. You have to reference your laser to something, so that you know he frequency of the light you are generating. With an existing stable isotope that’s straightforward, since you can use an absorption line, and the frequency of the radioactive isotope would be close by. Otherwise you do something like locking to an iodine transition, or some other reference cell used in spectroscopy. And you have to know the frequency you want to generate — with no stable or at least naturally-occurring isotopes the spectroscopy information would be very sparse in comparison to other alkalis, so your calculation of where you expect the transition to be has some uncertainties, meaning you have to search frequency-space until you find something. And we ran out of beam time before we saw anything.
And, as I had mentioned, we (well, someone at TRIUMF) got a call from a watchdog station that tries to detect nuclear fallout, wanting to double-check on things. They knew the signature they were reading wasn’t from a bomb, but they knew something was up and guessed our target material: Thorium. When you blast that with energetic protons, you get lots of heavy isotopes.
Over at Physics and Physicists, ZapperZ has a short post on an interference experiment that looks like a useful apparatus to demonstrate some of the quirkiness of QM. It shows both single-photon interference and, since it’s a Mach-Zehnder interferometer, it’s also easy to show the “which-path” effect that washes away the fringes.
No, just a coathanger.
A small exercise in seeing whether people can tell the difference between Monster cables and coat hangers.
via Daring Fireball
Trivia about time, to be precise. Prior to my current job, my knowledge of timekeeping was pretty much knowing how to read and adjust a clock, and because I’m a physicist, Einstein synchronization (basically accounting for propagation delay of light) and the effects of general and special relativity. All of the physics-related exercises with time conjure up a perfect clock, so you don’t have to worry about all the little details that arise when dealing with real-world hardware. Now, I don’t actually do time measurements, I “just” work on building clocks, but there are some things I’ve picked up.
A clock will have an oscillator in it, and some way of counting the oscillations. Time is the phase of these oscillations — one “tick” represents one cycle or some number of cycles. The derivative is the frequency, and if you take another derivative you get the rate of change of the frequency, which is the drift. Which sounds just like kinematics — the basic equation that describes all of this looks just like basic kinematics, as long as the rate of change of your frequency is a constant. And that brings up a point commonly fumbled by the popular press: leap seconds are often described as being added because the earth’s rotation is slowing. And while it’s true that over long times, the rate is slowing, that term could be zero and you’d still have to add leap seconds. The frequency represented by an earth that has slowed (but is no longer slowing) is different than that of atomic time, and so one will accumulate a phase difference (i.e. one will run slow compared to the other). That the rotation rate is slowing means that we will add leap seconds more often, assuming other effects on the rotation rate don’t mask this.
The above assumes “perfect” clocks. However, in all real processes that we measure, there is noise. Different kinds of noise, too, depending on the systems being measured. The best you can hope for is random, (i.e. white) noise, which gets averaged down as you take more measurements, and varies with the inverse square root of the number of data points (in this case, time). There are noise processes that average down faster, but eventually white frequency noise will dominate, and then the best case is that there are no other noise processes that dominate at longer times (like flicker or drift).
You integrate white frequency noise to get the effect on the phase, or time. The integral of this white noise gives you a random walk. That is, for any two real clocks, with exactly the same frequency, the best you can do is have them random-walk with respect to each other. They will never stay synchronized.
Science After Sunclipse has some links to Conan O’Brien spinning his wedding ring and getting help from an MIT professor to maximize the spin time.
(BTW, I have colleagues who use the term “nutate” on a regular basis.)
“Trapping of Neutral Mercury Atoms and Prospects for Optical Lattice Clocks” Hachisu et al., PRL, 100(5). I haven’t had time to read the paper, but Chad at Uncertain Principles has a summary of it.
My personal nit is that everybody calls these clocks, and they are really frequency standards/references. But almost nobody cares about that.
Every so often a nanotechnology discussion pops up on the SFN forums (one of several recurring themes), and invariably there is a comment or two in the direction of pop-sci topics like nanobots, and the implication that nanofabrication is a future technology. While the length scales have gotten smaller and manipulation techniques have certainly gotten better over time, nanofabrication has been around for a while.
The photos shown below the fold are from some grad school work I did at the Cornell NanoScale Science & Technology Facility in the early 90’s (back then there was no network of such labs, it was the National Nanofabrication Facility. Notice that they’ve been in existence for more than 30 years.) I was fabricating some transmission gratings for an atom-optics experiment to show atomic interference. The structures (grating wire and gap) were each about 125 nanometers across. The basic fabrication process was this: Continue reading