Wednesday, October 18, 2006

This week in cond-mat

Three papers this time out. The semester is very busy, so not much commentary for a while.

cond-mat/0610352 - Wu et al., Optical metamaterials at near and mid-IR range fabricated by nanoimprint lithography
There's been a lot of hubbub about making meso- and nanostructured materials that have negative permeability and permittivity over some limited frequency range. These materials can have very weird optical properties (obey a left-hand rule; refract in the opposite direction than conventional materials; can be used to try and beat the diffraction limit for imaging; can be hyped into Harry Potter-style invisibility cloaks). Here is the first example I've seen of someone making large-area 2d structures with these properties in an interesting frequency range (near-IR, close to the 1.5 micron telecommunications band).

610413 - Evers and Burke, Pride, prejudice, and penury of ab initio transport calculations for single molecules
I really like this paper, both for what it says and how it says it. The authors go into detail about different calculational approaches used to predict or retrodict electronic transport properties of single molecules. Very often people in this field crank out results using quantum chemistry techniques (density functional theory) and approximate methods without ever pointing out what those methods generally can't handle (strong correlation effects like Kondo; significant interaction corrections; Coulomb blockade). This paper really gets at what works, what doesn't work, why, and what can be done. Similar in topic is a recent preprint from Datta's group, where they look at Coulomb blockade in small molecules.

quant-ph/0610117 - Dyakonov, Is fault-tolerant quantum computation really possible?
I haven't read this one yet, but the abstract is attention-getting. It argues that the math upon which error correction schemes for quantum computers are based is unrealistic in terms of its relationship with real world systems. Therefore, it may be impossible in principle to scale up to large quantum computing systems. Anyone take a look at this and have an opinion?
Update: After reading Dave Bacon's comment, I actually looked at this preprint. Wow. The tone is very colloquial (it's based on a talk), and is hardly subtle, nor is it very convincing as reasoned technical argument. Is this the same Dyakonov as in the Dyakonov-Perel mechanism of spin relaxation? The initials are the same. Not that having something named after you necessarily means that you're right about everything; Brian Josephson's rather unorthodox views on telekinetics and levitation are the classic case in point.


Dave Bacon said...

I took a look quant-ph/0610117 and my head exploded. The author launches into an attack based on the fact that he has not understood the basic of fault-tolerance nor of quantum theory, proceeds to complain about issues which have certainly been addressed by the community, claims that most people working on fault-tolerance are computer scientists and that this makes the results wrong (which might be news to people like John Preskill who wins bets with Stephen Hawkings and also works on fault-tolerance), and, in general, puts forth a series of arguments which take about two seconds to refrute with a small working knowledge of the theory of fault-tolerant quantum computation. BTW.

But cond-mat/0610352 looks interesting!

Elia Diodati said...

You probably know this, but there are many, many quantum chemical techniques out there. DFT is but one of them. It may be the most popular one nowadays, but most people who know anything about quantum chemistry are either working hard on methodology or steering clear of it altogether when it comes to wanting accurate (milliHartree or better) results.

Reputation Managers said...

The author launches into an attack based on the fact that he has not understood the basic of fault-tolerance nor of quantum theory.