Quantum Optics
drorzel | April 8, 2008(This is the second of two background posts for a peer-reviewed research blogging post that has now slipped to tomorrow. I started writing it, but realized that it needed some more background information, which became this post. And now I don't have time to write the originally intended post...)
Making a quantum computer is a tricky business. The process of quantum computing requires the creation of both superposition states of individual quantum bits (in which the "qubit" is in some mixture of "0" and "1" at the same time) and also entangled states of different qubits (states where the state…
drorzel | March 17, 2008In one of his March Meeting posts, Doug Natelson writes about laser cooling experiments that explore condensed matter phenomena:
While the ultracold gases provide an exquisitely clean, tunable environment for studying some physics problems, it's increasingly clear to me that they also have some significant restrictions; for example, while optical lattices enable simulations of some model potentials from solid state physics, there doesn't seem to be any nice way to model phonons or the rich variety of real-life crystal structures that can provide so much rich phenomenology.
I would dissent…
drorzel | March 14, 2008The next lab visit experiments I want to talk about are really the epitome of what I called the "NIST Paradigm" in an earlier post. These are experiments on "four-wave mixing" done by Colin McCormick (who I TA'd in freshman physics, back in the day), a post-doc in Paul Lett's lab at NIST. As Paul said when I visited, if they had had a better idea of the field they were dabbling in, they would've thought that what they were trying was impossible; thanks to their relative ignorance, though, they just plowed ahead, and accomplished something pretty impressive.
The basic scheme is laid out in…
drorzel | March 10, 2008While Kate was off being all lawyerly at her NAAG workshop, I spent my time visiting my old group at NIST, and some colleagues at the University of Maryland. This wasn't just a matter of feeling like I ought to do something work-like while she was workshopping-- I genuinely enjoy touring other people's labs, and hearing about the cool things they're working on.
I figure that, having spent a day and a half talking about hot new physics experiments, I may as well mine them for blog fodder. I've managed to scrounge up papers related to a lot of the experiments in question on the arXiv, but the…
drorzel | February 18, 2008I gave a talk at Boskone in the prime Sunday 10 am slot, on quantum teleportation. I read the opening dialogue from Chapter 8 of the book, and then did a half-hour (or so) explanation of the real physics behind quantum teleportation.
If you weren't one of the thirty-ish people who watched at least part of the presentation, you don't know what you missed. But you can get a little flavor of it by looking at the PDF version of my PowerPoint slides (1.1 MB). I think they're mostly comprehensible on their own, but even if they're not, there are cute dog pictures galore. So, you know, there's that…
drorzel | December 7, 2007Kind of a technical question, but typing it out might provide some inspiration, or failing that, somebody might have a good suggestion in the comments.
Here's the issue: I'm starting on a chapter about quantum teleportation for the book, and one of the key steps in the teleportation scheme is an entangling measurement of two of the particles. If you're teleporting a photon polarization state, the easy way to do it is to make a joint measurement of the polarization of the photon whose polarization you want to "teleport" and one photon from the entangled pair you're using for the teleportation…
drorzel | September 26, 2007So, I've put myself into a position where I need to spend a substantial amount of time thinking about weird foundational issues in quantum mechanics. This has revealed to me just why it is that not that many people spend a substantial amount of time thinking about weird foundational issues in quantum mechanics.
Let's consider a Mach-Zehnder interferometer, of the type shown in the figure at left (click the figure to see the original source). A photon (or an electron, or an atom, or any quantum particle) enters the interferometer at the lower left, and is split onto two paths by a 50-50…
drorzel | September 12, 2007In a comment to the book announcement, "HI" makes a request:
Would you be able to summarize the recent paper "Progressive field-state collapse and quantum non-demolition photon counting" (Nature. 2007 Aug 23;448(7156):889-93) for non-specialists? How do you interpret it?
This probably would've slipped by me if not for this comment, but it's a really nice paper, and I'm happy to give it a shot. There's also a commentary by Luis Orozco that you won't be able to read without a subscription because Nature are bastards that way.
The basic idea of this paper is that they prepare a quantum system…
lundblad | August 22, 2007Lest this blog turn into a one-trick pony, let me tell you what I did today that's of a little different flavor.
I epoxied some stuff onto some other stuff. More importantly, I calculated a band structure.
This amazes me. Sure, all you squa^Wsolid-state types out there do this every day, over your cereal even, and (in some cases) just have it done for you by the undergrad, but I'm an AMO physicist. I haven't calculated a band structure since I first made sweet love to the Kronig-Penney potential back in the warrens of LeConte and Campbell, guided by the two-who-are-one, Cohen and…
drorzel | March 15, 2007After a short post-March Meeting lag, Physics World is back to announcing really cool physics results, this time highlighting a paper in Nature (subscription required) by a French group who have observed the birth and death of photons in a cavity. I'm not sure how it is that the French came to dominate quantum optics, but between Serge Haroche and Alain Aspect, most of the coolest experiments in the field seem to have been done in France.
In this particular case, they set up a superconducting resonant cavity for microwaves. Basically, this is like two mirrors facing one another, and a photon…
drorzel | February 22, 2007This is an approximate transcription of my physics talk from Boskone, titled "Spooky Action at a Distance," in which I attempted to give a reasonable explanation of the Einstein-Podolsky-Rosen ("EPR" hereafter) paper and Bell's Theorem. This was sort of a follow-on from last year's "Weird Quantum Phenomena," meant to highlight a specific class of weird quantum phenomena.
There's some SF relevance to the ideas involved in EPR and Bell's Theorem. A number of authors have name-checked the idea, most notably Charlie Stross citing "entangled particles" as the mechanism for FTL communications in…
drorzel | February 19, 2007We're back from Boskone, which included lots of fun stuff, and not enough sleep. I also cleverly forgot to bring my lecture notes home from work, which means I need to go in early to figure out what the hell I'm talking about in class today, so there's not much time for blogging at the moment.
I would be remiss in my physics-blogging duties, though, if I failed to point people to this Physics Web story about a new single-photon interference experiment (you'll need a subscription to read the Science article). A French group including Alain Aspect (who else?) has done a beautifually clean…
drorzel | January 3, 2007A little bit before Christmas, I spent an afternoon swapping mirrors out of one line of the apparatus. I was losing too much of the laser light before it went into the chamber, and replacing the mirrors increased the power entering the apparatus by a factor of two or so.
Here's a picture of the two types of mirrors, side-by-side:
"Well, of course you had to replace them," you say. "The one on the left is a perfectly nice mirror, but the one on the right is utter crap. You dolt."
The thing is, the mirror on the right is the type I was putting in. The one on the left is the type that wasn't…
drorzel | January 2, 2007Some time back, Dave Munger called me out for the one sentence challenge, originally phrased thusly:
Physicist Richard Feynman once said that if all knowledge about physics was about to expire the one sentence he would tell the future is that "Everything is made of atoms". What one sentence would you tell the future about your own area?
Dave, as a writer, offers "Omit needless words." Over at Cosmic Variance, Risa responds with the much less elegant: "The Universe began, about 13.7 billion years ago, as a hot, dense soup of elementary particles, and has been expanding, cooling, and clumping…
drorzel | October 25, 2006The recent discussion of reviews of The God Delusion has been interesting and remarkably civil, and I am grateful to the participants for both of those facts. In thinking a bit more about this, I thought of a good and relatively non-controversial analogy to explain the point I've been trying to make about the reviews (I thought of several nasty and inflammatory analogies without much effort, but I'm trying to be a Good Person...). Unfortunately it requires me to explain a bit of physics... Please, please, don't throw me into that briar patch.
Some people say that the last really significant…
drorzel | October 6, 2006Third and final post in a series about "teleportation" from July 2002. This one is mostly dedicated to voicing the same complaints I have about the more recent stories that kicked this whole repost business off.
The more things change, the more I keep repeating myself.
So, having discussed how to do "quantum teleportation," how does this get us to "Beam me up, Scotty?" Well, that's the thing. It doesn't, not in any meaningful sense. What gets "teleported" is just the state of the initial quantum particle, not the particle itself. There's no reason why you couldn't do "teleportation" with…
drorzel | October 6, 2006Part two of three of an explanation of "quantum teleportation" experiments, from July of 2002. This one goes through the basics how teleportation works. I might be able to do better now, having worked through it in more detail in order to teach about it in my Quantum Optics class, but it's been a busy week, so I'll just repost the old entry for now.
So, the last whopping huge physics post here covered the idea of quantum entanglement-- how do you get from entanglement to "quantum teleportation", which is what the article that kicked the whole thing off was about?
The first step here is to…
drorzel | October 6, 2006As threatened in the previous post on new "quantum teleportation" results, here's the first of three old articles on teleportation. This one discusses EPR states and "entanglement." It's somewhat linkrotted-- in particular, the original news article is gone, but the explanation is still ok.
This dates from July of 2002, which is like 1840 in blog years.
Yet again, SciTech Daily provides me with weblog material, this time in the form of an oddball article in the Las Vegas City Life archives (how do they find this stuff? It never would've occurred to me to look there...). The article is mostly…
drorzel | October 6, 2006The latest physics news is an experimental demonstration of "teleportation" involving both light and atoms, done at the Niels Bohr Institute in Copenhagen, and reported on by the Institutes of Physics and CNN, among others, and remarked on by Dave, among others.
I wrote up some stuff about teleportation in the early days of this blog, and I'll Classic Edition those posts in a little while. "Teleportation" stories always kind of annoy me, though, because the reality isn't nearly as cool as the image that the term evokes. To some degree, it's a triumph of marketing more than a scientific…
drorzel | July 17, 2006It's not as sexy as Strings 2006, but it's easier to understand what the talks are about: Nathan Lundblad is blogging from the International Conference on Atomic Physics in Innsbruck, Austria (the bastard). Posts so far:
First day introduction.
First day talk recaps.
(The latter includes the announcement of the [Norman] Ramsey Prize, "to be given to the first credible measurement of a nonzero electron EDM, with the caveat that it be done in his lifetime." For those not in the field, Ramsey is 91, so that's an important caveat...)
Now that I've plugged this, Nathan will no doubt crumble under…