Quantum Chicanery

okay, I found that piece to be terribly written. Even though I am currently (literally as I type this) using lasers to manipulate cesium atoms, I still didn't know what they were talking about. And I couldn't even really tell who the group was, or how to look up their paper, because the article didn't point at all to a reference. I'm sure I could find it if I spent a little more time...but I shouldn't have to.

If they're talking about atom interferometers, there have been plenty of experiments that do this with much more than a few micron separation, for example, Holger Muller at Berkeley,wants to do a .1 square meter interferometer (something on the scale of 30cm rather than 10microns), or Mark Kasevich at Stanford's ridiculous 10m cesium fountain.

Basically any form of coherent control is capable of putting the atom into a superposition state. I.e. microwave pulses, RF pulses, or laser pulses which put them into spatially coherent superpositions as in interferometers. I didn't get anything from this article about what was 'new.'

Okay, I found the article. It's in the June 4th, PNAS doi: 10.1073/pnas.1204285109
Digital atom interferometer with single particle control on a discretized space-time geometry Andreas Steffena,Andrea Albertia,1,Wolfgang Alta,Noomen Belmechria,Sebastian Hilda,Michał Karskia,Artur Widerab, andDieter Meschedea

Basically, it is an atom interferometer in an optical lattice. Usually, atom interferometers are in free space. They put a Cesium atom into a superposition of the two hyperfine levels using a microwave pulse. Then to create the two arms of the interferometer, they use a lattice which is state dependent, meaning it will have a different effect on the two hyperfine levels, to drive them apart then back together again.



As far as atom interferometers are concerned, this does not compete with other interferometers. Free space interferometers are easily getting 1X10^-10 precision on measurements of g (local acceleration due to gravity). Where this one gets 5X10^-4. So it's about a million times less precise. And the free space interferometers have many improvements planned in the future. This article does claim that they'll get improvements to make them competitive with free space interferometers, so we'll see.



And the size of this trapped atom interferometer is interesting not because its 'big' but because it is small. Free space interferometers necessarily have longer atomic beam paths. It can sometimes be useful to have a measuring tool that is very small, so you could look for variations in g on very small distance scales. If your atoms have to travel half a meter in order to do your measurement, you certainly can't measure variations on the scale of a few mm. So I'm not trying to degrade the research or anything, because there can certainly be a place for this type of device.

I love AW.