Fwd: Guarding the Wall: tunnels, bridges and tendrils

[Prashant Kumar]

---------- Forwarded message ----------
From: *Prashant Kumar*
Date: Friday, April 26, 2013
Subject: Guarding the Wall: tunnels, bridges and tendrils
To: alice wellintown <alicewellintown at gmail.com>


Agree, though the specific problem here is less that than the fact that the
authors themselves seem to lack expert knowledge of the topic; their
repeated mention of Schrödinger's cat is the giveaway.

Having read a little more, I also take issue with their approach. Seems too
bottom up for me: there is a conspicuous lack of descriptions of phenomena
in that article.

P.

On Friday, April 26, 2013, alice wellintown wrote:

I doubt it. It is so poorly written that unless a reader is very familiar
with the topic he will have a great deal of difficulty making out what the
authors are trying to explain. Minor interference is now quite common in
science publications, but when it is compounded with grammar and usage and
punctuation errors or typos or copy errors, it often makes an article
unreadable, even for those who are expert in the subject matter and adept
at reading English with interference.

On Thursday, April 25, 2013, Prashant Kumar wrote:

It's not very well written. I looked at their
crash-course-in-quantum-mechanics section and it is very confused. I'm not
sure it's worth the effort.

P.

On Thursday, 25 April 2013, wrote:

Thank you for the Review Article (not attached here)- very approachable and
interesting. Next I'm going to try this:

http://arxiv.org/ftp/arxiv/papers/1304/1304.0683.pdf

Which was referenced in the Wikipedia article on Quantum Biology. Wish me
luck.


 -----Original Message-----
From: Prashant Kumar <siva.prashant.kumar at gmail.com>
To: bandwraith <bandwraith at aol.com>; pynchon -l <pynchon-l at waste.org>
Sent: Tue, Apr 23, 2013 1:28 am
Subject: Re: Guarding the Wall: tunnels, bridges and tendrils

 Good questions. Measurement erases the information stored in the
system (entropy
relates thermodynamics and information
theory<http://en.wikipedia.org/wiki/Maxwell%27s_demon#Criticism_and_development>).
And so yes, we know nothing about the system after measurement because the *act
*of* *measurement causes decoherence from quantum to classical. This why
quantum computing is so difficult to realise in practice.

 The system will have certain degrees of freedom; basically places where it
can store energy and information. The formalism differentiates between
classical (environment) and quantum (system) degrees of freedom. In an
actual experiment the system under study will usually be thermally isolated
from the apparatus. The equipment is separated into thermal stages, with
the quantum system at the lowest temperature stage. See
here<http://en.wikipedia.org/wiki/Dilution_refrigerator>:
the sample measured is in the section labelled "vacuum".

 As for photosynthesis, this is one of the things covered in the quantum
bio nature review. I've attached it. The first few sections are
surprisingly readable. The reason why quantum coherence is maintained is
rather complex. From the article:

 Evidence, both theoretical and experimental, does hint that the
non-perturbative and non-Markovian environment can enhance
both the coherence time[19] and the efficiency of the excitation
transport[39]. Similarly, a recent analysis argued that coherent vi-
bronic excitations may play an important role in the coherent oscil-
lations seen in experiments[40, 42]. However, the role of correlations
between the baths of different BChl molecules is still not fully un-
derstood. Recent work[39] showed that the correlations can in princi-
ple improve the efficiency in some cases, but can also decrease it, and
that there is an optimal overall noise level. In comparison, molec-
ular dynamics simulations[43, 44] indicated that the uncorrelated-bath
approximations may hold, and thus independent-bath models may
be sufficient to explain any enhancement in efficiency. Ultimately,
the real role of correlated-bath effects and vibronic excitations in
photosynthetic units, FMO and otherwise, is still not clear, and
requires further experimental studies.

 Basically it looks like the protein complex that is responsible for this
quantum coherent behaviour is a special kind of system ("non perturbative
and non-Markovian environment") which has a kind of coupling that may be
beneficial to coherence. I went to a conference last year where people were
doing this stuff and it looked then like the precise re
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