Quantum Mechanics and BEC

Chandra Raman's talk

2006-05-10T20:30:00.000-07:00

Yesterday we had a talk by Chandra Raman, from Georgia Tech. He showed pictures of vortex lattices in a Bose-Einstein condensate, which he created by stirring the BEC, for example via a laser.

He also discussed their use of Bragg scattering to characterize the condensate, and also how they plugged the trap for Na BECs to counteract Majorana transitions.

Sadly, this was the last talk and lunch of the academic year...and I think it's also my last blog posting for a while, as my hit counter says that this blog has had zero hits thus far, except for a few hits coming from Harvard (i.e., me). :)

I suppose I could discuss Britney Spears in order to stimulate some discussion. :) But that's OK.

Weird

2006-05-02T21:52:00.000-07:00

Here is a link to the Sarong Theorem Archive, a collection of pictures of people wearing sarongs while proving theorems. You too can be immortalized; just send them your picture while proving a theorem, and wearing a sarong.

More Jobs

2006-05-02T18:16:00.000-07:00

I just came across another list of jobs available in quantum control/quantum information and related fields.

In the Harvard advertisement, many of the professors listed work at the interface of AMO and condensed matter, which seems to be a very promising field: one reason people are so interested in optical lattices is their potential for exploring phenomena in condensed matter.

Charlie Marcus' group, and in particular Jason Petta, whom I don't know personally, has recently done some incredible experimental work on manipulating electron spins in double quantum dots--worth a look!

Preprint of the day--Quantum chemistry meets quantum computing

2006-05-02T14:46:00.002-07:00

Here is the preprint which I would like to highlight today, by Alán Aspuru-Guzik, Anthony Dutoi, Peter Love, and Martin Head-Gordon.

Alán Aspuru-Guzik is coming to Harvard in July, which I think will make him the first real electronic structure theorist here. Electronic structure has been a very hot, and useful, field for a very long time, and I have always been surprised that Harvard did not have anyone in the chemistry department working on it.

The theme of recent research by Alán and some others in the Head-Gordon group has been to use classical computers to simulate quantum computers, and show that quantum computational algorithms can be useful and accurate for determining ground-state energies of small molecules. For example, they have simulated calculations of the ground state energies of both water and lithium hydride. It seems that only a few hundred qubits can give extremely accurate results. Another use for quantum computing!

Now if we AMO people could just get the quantum computer running... :)

Upcoming AMO Conferences

2006-04-27T21:29:00.001-07:00

Upcoming AMO conferences (including theory) are DAMOP (Knoxville, TN) and ICAP (Innsbruck, Austria). Note that the ICAP chairs include Rudolf Grimm, whose work on Efimov states I had mentioned earlier this month.

I unfortunately have to skip DAMOP this time around, as I'm busy in the last few months of my Ph.D. I'm sad about missing DAMOP--like March Meeting, it's very big, but the upshot is that something interesting is always going on, and absolutely everyone you could possibly want to talk to in AMO physics is there. It's therefore great fun to go.

DAMOP 2004 was in Tucson, Arizona in May. The desert was gorgeous--and the U of Arizona is world reknowned for optics. But boy, was it HOT! Those of us from Boston who had forgotten what the sun looked like had to scurry from building to building trying not to melt. :)

DAMOP 2005 was in Lincoln, Nebraska. This year DAMOP is in Knoxville, Tennessee.

This particular atomic physicist hopes for DAMOP 2007 (which I will definitely attend) in Hawaii. :)

Graduate Student Etiquette

2006-04-26T16:32:00.000-07:00

We recently had a fun (and crowded) talk here by Jorge Cham from Caltech about his comic strip, "Piled Higher and Deeper". (The comic is about graduate school--talk about a niche audience!)

I guess Dr. Cham will never have any trouble filling out the "outreach" section on his grant applications! :)

Anyway, my personal rules of physics graduate student etiquette are this:

Thou shalt not...

1. Ask any physics graduate student what year s/he is in
2. Ask any physics graduate student when s/he is graduating

If the student is eager to volunteer this information, s/he will!

Today's talk on Matter Wave Optics

2006-04-25T18:59:00.000-07:00

Today we had lunch with, and then attended a talk by, Markus Oberthaler from Heidelberg.

Oberthaler's group is doing very interesting work in BEC dynamics. Today's talk discussed, among other things, dynamics of BECs in shallow and deep periodic potentials, as well as tunneling of a BEC trapped in a double well potential (see cond-mat/0411757). I particularly liked the analogy of the wavefunction in a well to a pendulum with a length dependent on the angular momentum. The double well was created by superimposing a harmonic and periodic potential. Double wells seem quite popular lately, and are also a focus of research by Bill Phillips' group at NIST.

The phenomenon that Oberthaler discussed in connection with the deep potential well was "nonlinear self-trapping," where a wavepacket expands initially, but then stops.

Vidal's Method

2006-04-23T20:57:00.000-07:00

The problem with simulating a quantum lattice system is the exponential growth of the Hilbert space with the system's size. One way of treating such a system is known as the DMRG (Density Matrix Renormalization Group).

Another fairly new method is Vidal's method, which provides a way of calculating the time evolution of 1D systems. The reference is Phys. Rev. Lett. 91, 147902 (2003), and the preprint is available at quant-ph/0310089. Vidal's method is becoming more and more popular in the AMO community, and is often used to solve 1D Bose-Hubbard models, in the context of optical lattices.

I hope to discuss Vidal's method in some detail in coming days; I think it is one of the more important developments in AMO theory. But for now, back to thesis-land! (Argh).

On a personal note, I'm giving our group meeting on Tuesday. I am not sure that the shift to PowerPoint/Keynote talks has been good for physics as a whole. Anyway I guess I use Keynote too, so I'm not one to talk. :)

Harvard Physics Building an historical site

2006-04-21T22:05:00.000-07:00

In a note unrelated to AMO physics, our bullding, Jefferson Lab, was officially declared an historic physics site today by the APS. Among other experiments performed there was the famous experiment by Pound, Rebka, and Snyder to measure the gravitational redshift.

It is quite fun to have an office in a building where so much history has happened!

Cabot Library has been holding a book sale during which they have been selling many very old physics books, including books by Mott, Bragg and Bragg, etc. The sale included some large books of refractive indices and special functions. It is amazing how much technology (e.g. Mathematica, the web) has affected physics, and made so many things obsolete.

Jobs

2006-04-21T01:06:00.000-07:00

I wanted today to link to some sites that might be of use for folks trying to find a job.

This is the web page for TAMOC, an association of AMO theorists. Check out the list of job postings...it isn't updated very often but my friend got a postdoc through it.

Here is a page at the Weizmann Institute which points mainly to jobs outside the US in AMO physics.

USC is looking for a quantum information theorist, which is an unusual thing to look for, so I thought I'd mention it.

An interesting article on the ArXiV

2006-04-19T18:45:00.000-07:00

As my advisor once said, "any time you see a paper by Q. Niu, you should read it." I followed his advice and read one of Niu's papers on the idea of atom tweezers; it was indeed a very nice paper--I appreciated the clarity as well as the connection to experiment.

So, here is a link to today's preprint by Y. Shi and Q. Niu.

The authors discuss a BEC made of two different species of atoms; they find a ground state which is not a mean-field ground state and relates to interspecies entanglement. They introduce the idea of entanglement of the order parameter, and further derive some single-particle orbital equations which have extra interference terms.

I'm a bit busy right now trying to graduate, but when I have time I hope to come back and comment on this paper in more detail.

Cool physics

2006-04-18T02:35:00.000-07:00

To digress from AMO physics for a moment, I want to talk about scattering. AMO theory is cool; I guess to be more precise, it's ultracool. ;) But let's face it--BECs, and quantum corrals, and all the things we study are pretty exotic. Every now and then I like to pause, and look at scattering problems which occur in the everyday world (I mean, outside of the physics building).

This article in Physics Today deals with the use of sonar scattering to take a census of fish populations!

Multiple scattering has also found applications in ornithology, in the groups of Richard Prum, a biologist at Yale, and Rodolfo H. Torres who is in the math department at the University of Kansas. In collaboration, the two study scattering from "quasi-ordered arrays," but the arrays are biological ones--parallel collagen fibers. In their research they examine how interference leads to structural coloration in bird feathers, mammalian skin, etc. and they conclude that the scattering is coherent rather than incoherent.

See also this web page on the scattering of sound by zooplankton.

This is one of the things I love most about physics, that similar physical phenomena occur in an incredible range of systems.

NIST Atomic Clock Uses Yb 'Pancakes'

2006-04-17T12:17:00.000-07:00

See this article at photonics.com, which discusses an optical-lattice based atomic clock.

Efimov states in Cesium

2006-04-16T20:25:00.000-07:00

Check out the article in this month's Physics Today (April 2006, p. 19) on experimental observation of Efimov states in Cesium by Rudolf Grimm and others at Innsbruck. In order to clearly observe the states, they had to reduce the temperature to 10 nK.

The article reviews some theoretical studies also. Interestingly, it seems there are two predicted Efimov resonances in Cs, one of which is masked by breakdown of the scattering length approximation.

A nice summary of the Efimov results is here...