Condensed Matter
drorzel | January 14, 2013Last week's post talked about the general idea of negative temperature, with reference to this much-talked-about Science paper (which also comes in a free arxiv version from which the figures used here are taken). I didn't go into the details of how they made a negative temperature gas, though, and as it's both very clever and hard to follow, I figure that deserves a post of its own.
Right, so last time you said that negative temperature just means you're more likely to find fast-moving atoms than slow ones, so all they need to do is whack these atoms in the right way? Right? No, it's more…
drorzel | January 8, 2013The most talked-about physics paper last week was probably Negative Absolute Temperature for Motional Degrees of Freedom (that link goes to the paywalled journal; there's also a free arxiv preprint from which the above figure is taken). It's a catchy but easily misinterpreted title-- Negative absolute temperature! Below Absolute Zero! Thermodynamics is wrong!-- that obscures the more subtle points of what's going on here. So, in the interest of clarity, I'm going to attempt an explanation, over the course of a few posts, but given my schedule these days, that might spread over a couple of…
drorzel | September 13, 2012Last week, in the post about fermion conduction, I left a reference hanging:
There’s nothing physically blocking the atoms from flying right through the channel– in fact, an atom that enters the channel will always exit the other side without slowing down along the way. This is termed “ballistic,” a term that will always have a special place in my heart thanks to an incident at my Ph.D. defense.
Which was what? Let’s just leave that hanging to see if anybody actually reads this far. I can explain it in a comment if people want to know.
A couple of people asked for the explanation in comments…
drorzel | September 6, 2012So, it's been a while, but let's see if we can't hit the ground running with a good physics post. There have been a few notable physics events since I went on hiatus, but for a return to physics ResearchBlogging, we'll go with something near and dear to my heart, ultracold atoms. Specifically, this Science paper (free arxiv version) about passing atoms through a narrow channel. This is a cool bit of subfield-crossing physics, so let's dust off the Q&A format, and go through it.
Hey, dude, long time no see. So, what's the deal with this paper? Well, the title pretty much tells you what's…
drorzel | March 13, 2012I finally got a copy of Cox and Forshaw's The Quantum Universe, and a little time to read it, in hopes that it would shed some light on the great electron state controversy. I haven't finished the book, but I got through the relevant chapter and, well, it doesn't, really. That is, the discussion in the book doesn't go into all that much more detail than the discussion on-line, and still requires a fair bit of work to extract a coherent scientific claim.
The argument basically boils down to the idea that the proper mathematical description of a universe containing more than one fermion is a…
drorzel | October 23, 2011It's been a while since I posted anything science-y, and I've got some time between flipping pancakes, so here's an odd thing from the last few weeks of science news. Last week, there was an article in Nature about the wonders of string theory applied to condensed matter physics. This uses the "AdS/CFT" relationship, by which theorists can take a theory describing a bunch of strongly interacting particles in three dimensions (such as the electrons inside a solid), and describe it mathematically as a theory involving a black hole in four dimensions. This might seem like a strange thing to do,…
drorzel | July 26, 2011One of the benefits of having joined AAAS in order to get a reduced registration fee at their meeting is that I now have online access to Science at home. Including the Science Express advance online papers, which I don't usually get on campus. Which means that I get the chance to talk about the few cool physics things they post when they first become available, without having to beg for a PDF on Twitter. This week's advance online publication list includes a good example of the sort of cool ultra-cold atom physics that I talked about at and after DAMOP, so let's take a look at this paper in…
drorzel | June 29, 2011The first of the five categories of active research at DAMOP that I described in yesterday's post is "Ultracold Matter." The starting point for this category of research is laser cooling to get a gas of atoms down to microkelvin temperatures (that is, a few millionths of a degree above absolute zero. Evaporative cooling can then be used to bring the atoms down to nanokelvin temperatures, reaching the regime of "quantum degeneracy." This is, very roughly speaking, the point where the quantum wavelength of the atoms becomes comparable to the spacing between atoms in the gas, at which point the…
drorzel | June 28, 2011That's the title of my slightly insane talk at the DAMOP (Division of Atomic, Molecular, and Optical Physics of the American Physical Society) conference a couple of weeks ago, summarizing current topics of interest in Atomic, Molecular, and Optical Physics. I'll re-embed the slides at the end of this post, for anyone who missed my earlier discussion.
I put a ton of work into that talk, and had a huge amount of material that I didn't have time to include. I'd hate for that to go to waste, so I'm going to repurpose it for blog content over the next week or so. It'll probably be about a half-…
drorzel | June 14, 2011That's the title of my talk this morning at DAMOP, where I attempt the slightly insane feat of summarizing a meeting with over 1000 presentations in a single 30-minute talk. This will necessarily involve talking a little bit like the person reading the legal notices at the end of a car commercial, and a few of the guide-to-the-meeting slides will have to flash by pretty quickly. Thus, for the benefit of those who have smartphones and care about my categorization of talks, I have put the slides on SlideShare in advance, and will embed them here:
What's So Interesting About AMO Phyiscs?…
drorzel | June 13, 2011You may or may not have noticed that I've been making a concerted effort to do more ResearchBlogging posts explaining notable recent results. I've been trying to get at least one per week posted, and coming fairly close to that. I've been pretty happy with the fake Q&A format that I've settled into, and while they're time-consuming to write, they're also kind of fun.
This past week, alas, was kind of brutal, as I was doing a ton of reading in preparation for my DAMOP talk tomorrow, which, in retrospect, is kind of insane, and SteelyKid's day care being closed for two days didn't help (…
drorzel | May 16, 2011Several years ago, now, a group at Penn State announced a weird finding in helium at extremely low temperatures and high pressures (which is what you need to make helium solidify): when they made a pendulum out of a cylindrical container with a thin shell of solid He toward the outside edge, twisting about its axis, they saw a small but dramatic change in the oscillation frequency as they cooled the system below a particular temperature. They interpreted this as a "supersolid" phase of helium, with a quantum phase transition taking place that caused the "supersolid" to stop rotating with the…
drorzel | January 12, 2011Another response copied/adapted from the Physics Stack Exchange. The question was:
What are the main practical applications that a Bose-Einstein condensate can have?
Bose Einstein Condensation, for those who aren't familiar with it, is a phenomenon where a gas of particles with the right spin properties cooled to a very low temeprature will suddenly "condense" into a state where all of the atoms in the sample occupy the same quantum wavefunction. This is not the same as cooling everything to absolute zero, where you would also have everything in the lowest energy state-- at the temperatures…
drorzel | December 28, 2010It's the last week of the (calendar) year, which means it's a good time to recap the previous twelve months worth of scientific news. Typically, publications like Physics World will publish a list of top ten physics stories of 2010, but we're all Web 2.0 these days, so it seems more appropriate to put this to a poll:
What is the top physics story of 2010?survey software
I've used the Physics World list as a starting point, because you have to start somewhere. I added a few options to cover the possibility that they left something out, and, of course, you know where the comments are.
This…
drorzel | November 5, 2010Regular commenter onymous left a comment to my review of Warped Passages that struck me as a little odd:
The extended analogy between the renormalization group and a bureaucracy convinced me that she was trying way too hard to make sophisticated concepts comprehensible. Also, I'm not really sure that analogies are the best way to explain concepts to people without using mathematics.
I'm not talking about the implication that making sophisticated concepts comprehensible is not worth doing, but rather the negativity toward analogies. It's odd because, if you think about it, a huge chunk of…
drorzel | October 5, 2010The 2010 Nobel Prize in Physics goes to Geim and Novoselov for their work on graphene, a material consisting of one-atom-thick sheets of carbon atoms in a hexagonal array. This is one of those prizes that was basically inevitable, as graphene is one of the hot materials of the last couple of years. Hardly a week goes by without a couple of press releases touting some amazing new potential application.
Joerg Heber has a nice explanation of the basics of graphene, including some cautionary notes about overhype. From an experimentalist's perspective, the really cool thing about this prize is…
drorzel | August 25, 2010The Joerg Heber post that provided one of the two papers for yesterday's Hanbury Brown Twiss-travaganza also included a write-up of a new paper in Nature on Mott insulators, which was also written up in Physics World.
Most of the experimental details are quite similar to a paper by Markus Greiner's group I wrote up in June: They make a Bose-Einstein Condensate, load it into an optical lattice, and use a fancy lens system to detect individual atoms at sites of the lattice. This lattice can be prepared in a "Mott insulator" state, where each site is occupied by a definite number of atoms. As…
drorzel | August 15, 2010A couple of new-to-me but good physics blogs to point out this week:
All That Matters by Joerg Heber. This looks like it will be updated weekly-ish, and has a couple of good entries, including a nice write-up of an ultrafast laser experiment that I had flagged to write about before I got distracted by crazy people and lab porn this week.
The Dayside by charles Day of Physics Today. This has roughly daily updates, on a wide range of stuff.
Both of these cover physics beyond the default particle-physics-and-cosmology that you can find in dozens of places, and Day even has a post titled Why I…
drorzel | August 9, 2010So, 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…
drorzel | August 4, 2010I had the tab open and everything, and still somehow forgot to include a link to John Baez's blog post reporting on a talk by Tony Leggett which directly addresses some of the questions asked about yesterday's superconductivity post. It's about a talk called "Cuprate superconductivity: the current state of play" ("state of play" apparently being a favorite phrase of Leggett's), and directly addresses what's weird about high-temperature superconductors and why they haven't been explained theoretically.
These are notes from a talk, and thus somewhat compressed, but it's a good summary of the…