1+1=3
Monday, July 31, 2006
An article about vanishing decoherence for certain parameters of an environment. In this paper, the authors study an environment that can undergo a quantum phase transition depending on the value of the coupling to the system (similar to Quan et al and Cucchietti et al ). The authors are surprised that the environment (an XY spin chain where gamma is the anisotropy parameter) does not produce decoherence for gamma=0. Actually, this is a trivial finding: for gamma=0 the model conserves the Z projection of the spin, so it commutes with the system-environment interaction and only the eigenenergies change. This is all because at gamma=0 the XY model belongs to a different class than for gamma .not.= 0 (the Ising universality class), and does not have a quantum phase transition as far as I know. 

The only thing I like about the paper is at the end there are some comments about starting with excited states (not the ground) which would be useful (if true) for some calculations I am doing.

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Posted by fercook to Science at 7/31/2006 01:48:42 PM

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posted by fercook @ 1:53 PM   0 comments links to this post
Friday, July 14, 2006
Couldn't read anything while on travel, so a long backlog to put up to date.

  • Quantum baker map from Marcos Saraceno and Leonardo Ermann. Marcos writes very nice and has deep intuition on quantum chaos, so I make a point on reading his papers. Plus, I made friends with Leo in Benasque which is another reason to read this.

  • Unifyind decoherence and Heisenberg principle. This appears to go in line with Bub and Clifton's relation between information constrains and quantum mechanics. It is a little mathematical though.

  • Finally, an Introduction to entanglement measures!!!

  • This paper by Schack, Caves and others, is a very nice paper indeed. It shows very interesting relations between quantum and classical chaos, pointing to the direction of characterizing the former. However, I am disappointed at the way the authors jump around the studies on the Loschmidt echo, since 2001 up to the present. Their newest reference on decay of fidelity is in the 90s. I am sure Carl has seen my talks at least, so he knows very well the subject. Are the authors pissed at the Loschmidt echo community? They were working on the problem but never quite got to the point of identifying Lyapunov exponents in their quantum decays. This is not enough reason to "not-cite" a huge bunch of papers that are obviously related.

  • Yet, another paper on entanglement and quantum phase transitions (static).

  • A huge, long, and obsessively detailed review on quantum simulations using cold atoms. Very nice. What's with the formatting though?

  • This is a very nice paper. A little technical at some points, but the ideas and results are beautiful.

  • A useful paper

  • Could this have some numerical testing? I think so, but I failed to have good numerics in a reasonable time for J. Emerson with an older algorithm (it is still running though...)

  • Nice, could NP-complete problems be not so NP then?

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Posted by fercook to Science at 7/14/2006 11:34:16 AM

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posted by fercook @ 11:38 AM   1 comments links to this post
For large values of 1.