Atoms and Molecules

I got forwarded a physics question last night asking about the connection between wind and temperature, which I'll paraphrase as: Temperature is related to the motion of the atoms and molecules making a substance up, with faster motion corresponding to higher temperature. So why does it feel warmer when the air is still and why does wind make you feel cold? This is a moderately common point of confusion, so while I responded to the question in email, I'll also appropriate it for a post topic. So, why doesn't "windy" equal "hot," given that wind consists of moving air molecules? The full…
Last week's series of posts on the hardware needed for laser cooling and trapping experiments dealt specifically with laser-cooling type experiments. It's possible, though, to make cold atoms without using laser cooling, using a number of techniques I described in two posts back in January. Those didn't go into the hardware required, though, so what's different about those techniques in terms of the gear? Less than you might think. In fact, most of the labs that do these experiments use exactly the same sorts of equipment that laser coolers do. Including some lasers. It's not all of them, but…
Following on yesterday's discussion of the vacuum hardware needed for cooling atoms, let's talk about the other main component of the apparatus: the optical system. The primary technique used for making cold atoms is laser cooling, and I'm sure it will come as no surprise that this requires lasers, and where there are lasers, there must also be optics. There are lots of different types of lasers used for laser cooling experiments, but they all need to have certain properties: tunability, stability, and adequate power. Tunability is important because laser cooling requires light at exactly…
Over in the reader request thread, Richard asks for experimental details: I'd be interested in (probably a series) of posts on how people practically actually do cold atoms experiments because I don't really know. I needed to take some new publicity photos of the lab anyway, so this is a good excuse to bust out some image-heavy posts-- lab porn, if you will. There are a lot of different components that go into making a cold-atom experiment, so we'll break this down by subsystems, starting with the most photogenic of them, the vacuum system: (Click on that for a much bigger version.) This…
So, last week, I talked about how superconductors work, and I have in the past talked about the idea of making cold atoms look like electrons. And obvious question, then, whould be: Do cold atoms systems allow us to learn anything about superconductivity? The answer here is, unfortunately, "Yes and no." That's pretty weaselly, dude. Yeah, well, there's nothing I can do about that. There are a huge number of experiments out there using ultracold atom systems to look at Bose Einstein Condensation, which is related to superconductivity, and that transition has been studied in great detail. Those…
A reader emailed me with a few questions regarding How to Teach Physics to Your Dog, one of which is too good not to turn into a blog post: What is a photon from an experimental perspective?... Could you perhaps provide me with a reference that discusses some experiments and these definitional issues? The short form of the experimental answer is "A photon is the smallest amount of light that will cause a detector to 'click.'" (For some reason, hypothetical light detector technology has never really advanced past the Geiger counter stage-- even though it's all electrical pulses these days, we…
Over at Unqualified Offerings, Thoreau proposes an an experimental test of Murphy's Law using the lottery. While amusing, it's ultimately flawed-- Murphy's Law is something of the form: Anything that can go wrong, will. Accordingly, it can only properly be applied to situations in which there is a reasonable expectation of success, unless something goes wrong. The odds of winning the lottery are sufficiently low that Murphy's Law doesn't come into play-- you have no reasonable expectation of picking the winning lottery numbers, so there's no need for anything to "go wrong" in order for you…
When one of the most recent issues of Physical Review Letters hit my inbox, I immediately flagged these two papers as something to write up for ResearchBlogging. This I looked at the accompanying viewpoint in Physics, and discovered that Chris Westbrook already did most of the work for me. And, as a bonus, you can get free PDF's of the two articles from the Physics link, in case you want to follow along at home. Since I spent a little time thinking about these already, though, and because it connects to the question of electron spin that I talked about yesterday, I think it's still worth…
The subject of the "spin" of the electron comes up again and again, so as pointed out in a comment, I really ought to do a post explaining what it is and how it works. As a bonus, this gives me the opportunity to do the dorkiest thing anyone has ever done with a cute-toddler video, namely this one: (That's an early version of SteelyKid's new favorite game. I'll put a clip of the final version of the game at the end of this post.) So, electron spin. Electrons, and all other fundamental particles, have a property known as "spin." This is an intrinsic angular momentum associated with the…
With the rumors of a Higgs Boson detected at Fermilab now getting the sort of official denial that in politics would mean the rumors were about to be confirmed in spectacular fashion, it's looking like we'll have to wait a little while longer before the next "Holy Grail" of physics gets discovered. Strictly speaking, the only thing I recall being officially dubbed a "Holy Grail" that's been discovered was Bose-Einstein Condensation (BEC), first produced by eventual Nobelists Carl Wieman and Eric Cornell in 1995. Somebody, I think it was Keith Burnett of Oxford, was quoted in the media calling…
The big physics story at the moment is probably the new measurement of the size of the proton, which is reported in this Nature paper (which does not seem to be on the arxiv, alas). This is kind of a hybrid of nuclear and atomic physics, as it's a spectroscopic measurement of a quasi-atom involving an exotic particle produced in an accelerator. In a technical sense, it's a really impressive piece of work, and as a bonus, the result is surprising. This is worth a little explanation, in the usual Q&A format. So, what did they do to measure the size of a proton? Can you get rulers that small…
Last week, Dmitry Budker's group at Berkeley published a paper in Physical Review Letters (also free on the arxiv) with the somewhat drab title "Spectroscopic Test of Bose-Einsten Statistics for Photons." Honestly, I probably wouldn't've noticed it, even though this is the sort of precision AMO test of physics that I love, had it not been for the awesome press release Berkeley put together, and this image in particular (grabbed with its caption): This is a nifty paper, and deserves a little explanation in Q&A format: Is this another New Scientist style "Einstein was wrong" paper? No. If…
A press release from Harvard caught my eye last week, announcing results from Markus Greiner's group that were, according to the release, published in Science. The press release seems to have gotten the date wrong, though-- the article didn't appear in Science last week. It is, however, available on the arxiv, so you get the ResearchBlogging for the free version a few days before you can pay an exorbitant amount to read it in the journal. The title of the paper is "Probing the Superfluid to Mott Insulator Transition at the Single Atom Level," which is kind of a lot of jargon. The key image is…
An experiment in Germany has generated a good deal of publicity by dropping their Bose-Einstein Cendensate (BEC) apparatus from a 146 meter tower. This wasn't an act of frustration by an enraged graduate student (anybody who has worked with BEC has probably fantasized about throwing at least part of their apparatus down a deep hole), but a deliberate act of science: They built a BEC apparatus that is entirely contained within a two-meter long capsule inside the evacuated drop tower at the Center of Applied Space Technology and Microgravity (which in German leads to the acronym ZARM, which…
A number of SF-related sites have been talking about the "Periodic Table of Women in SF" put together by Sandra McDonald, presumably passed around at Wiscon. James Nicoll has a list of the authors, and SFSignal has a link to the table, which I will reproduce here to save you the annoyance of opening a PDF: This is an area where my nerdiness gets the best of me, because while I appreciate the concept-- listing a whole bunch of really good female authors as a way to draw attention to them-- the execution is dreadful. It's particularly disappointing given that the whole project is in reference…
I mentioned in a previous post that one of the cool talks I saw at DAMOP had to do with generation of coherent X-Ray beams using ultra-fast lasers. What's particualrly cool about this work is that it doesn't require gigantic accelerators or nuclear explosions to produce a laser-like beam of x-rays-- it's all done with lasers that fit on a normal-size optical table in an ordinary lab room. The specific talk I saw was by Margaret Murnane of JILA, who co-leads their ultra-fast laser group, and dealt with a new technique for producing soft-x-rays (~500 eV photons) with ultrafast lasers. We'll do…
Some late nights and wireless problems conspired to keep me from posting anything Friday or Saturday, but I was still at the meeting, and saw some cool talks on coherent X-ray production with lasers, opto-mechanics, and ridiculously good atomic clocks, some of which I hope to talk about later. For the moment, I'm just enjoying being home with Kate and SteelyKid and Emmy, so a real wrap-up post with physics content will have to wait a bit. I will put up a quick note that I'll be signing books one week from today as part of the Authors Alley program at the World Science Festival. More on that…
Since I sort of implied a series in the previous post, and I have no better ideas, here's a look at Thursday's DAMOP program: Thursday Morning, 8am (yes, they start having talks at 8am. It's a great trial.) Session J1 Novel Probes of Ultracold Atom Gases Chair: David Weiss, Pennsylvania State University Room: Imperial East Invited Speakers:  Cheng Chin,  Markus Greiner,  Kaden Hazzard,  Tin-Lun Ho  Session J2 Coherent Control with Optical Frequency Combs Chair: Linda Young, Argonne National Laboratory Room: Imperial Center Invited Speakers:  J. Ye,  Moshe Shapiro,  W. Campbell,  …
I was pretty sedentary on Wednesday, going to only two sessions, and staying for most of the talks in each. I spent most of the initial prize session getting my bearings in the conference areas, and talking to people I know from my NIST days. In the 10:30 block, I went to the session on Alkaline Earth Quantum Fluids and Quantum Computation. Tom Killian of Rice opened with a nice talk on work his group has done on trapping and Bose condensing several isotopes of strontium; somebody near me pooh-poohed it as just a technical talk on evaporative cooling issues, but I thought Tom did a nice job…
The conference I'm at this week is the annual meeting of the Division of Atomic, Molecular, and Optical Physics of the American Physical Society (which this year is joint with the Canadian version, the Division of Atomic and Molecular Physics and Photon Interactions, or "DAMPΦ." The Greek letter is a recent addition-- as recently as 2001, they were just DAMP.). As the name suggests, this is a meeting covering a wide range of topics, and in some ways is like two or three meetings running in parallel in the same space. You can see the different threads very clearly if you look at the different…