Introduction to the Quantum theory of computation Friday, Apr 28 2006 


Background : According to David Deutsch who gave these video lectures

This is a series of lectures designed to be used either

* as an introduction to the quantum theory of computation, by people intending to do research in the field; or
* as an introduction to quantum physics itself.

Very little knowledge of physics is assumed. Anyone who knows what a vector space is and what the eigenvalues of a matrix are will probably know enough mathematics to be able to follow the course.

Link :

I will just quote the site.

These lectures have a dual-use philosophy. They are designed to be an introduction to the quantum theory of computation for (say) graduate students intending to do research in the field.

Simultaneously, they are an introduction to quantum theory itself for (say) undergraduate physics students.

The links to the individual lectures are as follows.

Lecture 1: The Qubit
Introducing quantum theory, the quantum theory of computation, physical systems, observations, and the simplest quantum physical system,
the qubit.

Lecture 2: Interference Performing and analysing a single-photon interference experiment.

Lecture 3 : Measurement How to analyse pairs of interacting quantum systems.

Lecture 4 : The Schroedinger Picture Introducing the Schroedinger Picture, density matrices, state vectors, pure states and the Schroedinger equation.

Lecture 5 : A Quantum Algorithm The Deutsch Algorithm and how it works.

Lecture 6 : Grover’s Search Algorithm How to use quantum computation to search through N possibilities in a time proportional to the square root of N.

Deutsch has a very interesting perspective on Quantum mechanics ! So, even if you know quantum mechanics, you might just like to hear a different perspective.

Posted by : Loganayagam.R.(Tom)


Counting of States in a Micro-canonical ensamble Sunday, Apr 23 2006 

We (batch mates) were discussing about time reversibility and Karan pointed out an example of system that is not in equilibrium but seems stable: all the particles in a box are moving back and forth in one direction perpendicular to a wall. Now this system is not in equilibrium but in a meta stable state. 

My question is that there are many-many such possible states and during the counting of the states of micro-canonical ensemble we add all such states. Even though such states can never be achieved by a system in equilibrium. Why even then we have correct results for observables ? 

A hint of renormalization Friday, Apr 21 2006 

Background : Some amount of Quantum Field theory would help. Though the article doesnot go very much deep into quantum field theory as such, it is a bit difficult to understand the context of renormalisation, if you’ ve not seen it either in field theory or statistical mechanics.

Link :

A hint of renormalization
Authors: B. Delamotte
Comments: 17 pages, pedagogical article
Subj-class: High Energy Physics – Theory; Statistical Mechanics
Journal-ref: Am.J.Phys. 72 (2004) 170-184

An elementary introduction to perturbative renormalization and renormalization group is presented. No prior knowledge of field theory is necessary because we do not refer to a particular physical theory. We are thus able to disentangle what is specific to field theory and what is intrinsic to renormalization. We link the general arguments and results to real phenomena encountered in particle physics and statistical mechanics.

The abstract says it all. And yeah, all the best for endsems everyone 🙂

Update : See also

Renormalization of a model quantum field theory(should be accessible inside IITK)

Per Kraus and David J. Griffiths
Physics Department, Reed College, Portland, Oregon 97202

(Received 9 December 1991; accepted 30 April 1992)

Renormalization is the technique used to eliminate infinities that arise in quantum field theory. This paper shows how to renormalize a particularly simple model, in which a single mass counterterm of second order in the coupling constant suffices to cancel all divergences. The model serves as an accessible introduction to Feynman diagrams, covariant perturbation theory, and dimensional regularization, as well as the renormalization procedure itself. ©1992 American Association of Physics Teachers

Posted by : Loganayagam.R.(Tom)

The Net Advance of Physics Wednesday, Apr 19 2006 

Background : I guess this should be useful for all. Bookmark this links – even if you think it is above your level now, at some point of time you might find it very useful.

Link :

Review Articles and Tutorials in an Encyclopædic Format

Well, the name says it all. it is an MIT site.(Well, I am thinking of sitting down and creating a collection like that over here in this blog. Any help would be welcome…). These are some review articles and tutorials in physics arranged alphabetically – often very useful especially when you are doing termpapers 😉

Do have a look at the special review on condensed matter physics. It is quite a comprehensive collection of review articles in condensed matter physics.

Posted by :

Structure and Interpretation of Classical Mechanics Wednesday, Apr 19 2006 

Background : I guess classical mechanics at the level of Goldstein is enough. And yeah some patience to read and understand abstract math-lingo.

Link : Structure and Interpretation of Classical Mechanics

The first thing – this book has some crazy notation ! Apart from that these are some good lecture notes on mathematical aspects of classical mechanics. They require some math-maturity but once you get used to all the weird looking equations and awkward conventions, it is readable. I will not recommend it for the first reading- rather read it along with somethoing else like Landau or Jose & Saletan

You can see a book review of this book that appeared in American Scientist here.

Posted by : Loganayagam.R.(Tom)

Blog Theme Tuesday, Apr 18 2006 

As Tom mentioned, I've changed the theme to one which automatically displays the author of each post.  I tried reading up on the stuff, but wordpress is weird and doesn't allow us to tweak the themes, because as wordpress puts it

We are definitely mindful of making everything more customizable for our users, but at the same time we don’t want people to have to look at HTML and CSS code, which is antithetical to the purpose of If you want complete control over your enviroment, you’re probably better off running WordPress on a great web host of your own

Quite stupid actually, but, unless some of you can tweak something under the hood, we'll have to stick to this theme, which is a shame because I actually liked the old theme more.

 Also, to all the other contributors (mainly Ajay and Venky I think), I think it shouldn't be much of a pain to create your own wordpress account, signup here: and let me know your wordpress username, so that I can add you to the blog team, and then you can post while you are logged in under your own login.  That way the confusion with everyone using the blogphysica id will end. 

And I would suggest that we mail everyone to create their id's now, or whenever they feel like posting and mail one of us here about it if they want to join in as authors.  If you are all ok with it, then we could lock the blogphysica id in, say, a week's time?

P.S. : Since this post is relevant to the about page and how to post in this blog page, I am adding a trackback to those pages – Tom.

Life on the Lattice Monday, Apr 17 2006 

Background: This is a blog by two Physicists working on Lattice QCD, and although I can't exactly descibe a clear set of prerequisites, it is technical – a little background in QFT and related stuff is kind of required, I guess, though there's no harm in perusing through it and reading what you like or understand.

Link: Life on the Lattice

One good thing about this blog is that it prides itself on being a Physics blog and not a Physicist's blog

Posted by: Shanth

PS: Tom/Ravi do you guys know of a way that we can enable wordpress to automatically display the login name from which the post was made? If we get that done, then the three of us who have seperate wordpress logins can just post articles and the posted by thing will become automatic, and even the others can probably get accounts soon?




Posted By : Ajay Singh

P.S. : Added hyperlinks and uploaded the post. By the way, Ajay, what exactly was the problem in you accessing the site ? -Tom

P.P.S. : Ravi/Shanth, I think we have to come up with a “How to post ?” page. I’ve come up with a preliminary version of it. Feel free to edit it.- Tom

Review of Particle Physics Friday, Apr 14 2006 

Background : It is a concise review of the whole field of particle physics as it stands now. It also has some good review articles on cosmology.

Link : Reviews, Tables, and Plots
in the 2005 web update of Review of Particle Physics

Just to give a taste of links there you can see the articles on Big-Bang cosmology (Rev.) , Neutrino mass, mixing, and flavor change (Rev.) , Cabibbo-Kobayashi-Maskawa quark-mixing matrix and Quantum chromodynamics (Rev.)
I guess it would be quite useful for those who are giving their particle physics presentations in this weekend 🙂

All the best for the presentations !

Posted by : Loganayagam.R.(Tom)

Poems By James Clerk Maxwell Tuesday, Apr 11 2006 

Background : Nothing at all ! just for fun !


Link : Poems by James Clerk Maxwell

The title is self-explanatory 😉 On the same vain, have a look at The Love Song of the Electric Field , a song on Bravais lattices and a song about Faraday’s law

And yeah, if you have more links like this one, do post it in the comments below. 🙂

Posted By : Loganayagam.R.

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