Danny and me just had our paper on quantum goblins published in PRA. This is the first publication from my Phd, and my first PRA.

After comments from the editor we changed the name from (the arXive version's) "Quantum discord and local demons" to "Quantum discord, local operations, and Maxwell’s demons"

In the paper we discuss three different types of quantum discord, the first is the original introduced by Zurek, the second was introduced by Zurek in relation to Maxwell's demons. We introduced the third in relation to a slightly different formulation of the same Maxwell's demon idea. During our conversations with various people we discovered that many people don't realize that  Zurek's second version of discord is different from the first one, so we used the opportunity to point out the difference. We also showed that all three versions of discord agree on which states have zero discord.

This work really started happening when I was too lazy to calculate discord in some 3x3 system, Danny and me then found that there is a very easy way to verify if a system has zero discord (it's in the paper). We then decided that maybe this method could give us a different version of discord, this different version of discord turned out to be very cool because it was related to thermodynamics.  We basically showed that this third version of discord is the difference in the amount of work that can be done by Maxwell's demons with access to the whole system (non local demons) and demons with access to just part of the system (local demons) since the local demons are not as "strong" as the non local ones , we called them goblins (It started the other way around, but Alex Terno told us that goblins are weaker then demons).

We have a few other results in the paper relating different types of discord to various other things,  generally trying to make the whole idea of different types of discord less confusing and showing the physics related to each one. Finally we also  showed that by looking at the discord of a density matrix (made up of probabilities of having different pure states)  we can't know if the  states which make up the density matrix are locally distinguishable.

Before we published I gave some talks on this work, one talk can be found here.

Yesterday at lunch Stojan and me were talking about the history of spin. Here is a very cool story about it

http://www.lorentz.leidenuniv.nl/history/spin/goudsmit.html

Just saw this...

http://www.youtube.com/watch?v=VeeXTmVGoxs&feature=fvsr

Now if I can can this for my iPhone I would have endless fun!

 

Easier than carrying around a copy of Gradshteyn and Ryzhik and more reliable than Wikipedia!

See:

http://dlmf.nist.gov/

I have now spent almost two months in research exchange in the University of Leeds and I thought it would be a good time to share some of my experiences.

I arrived in Leeds, West Yorkshire, UK in February from the summer climate of Australia. Being back in Europe after spending 12 months on the opposite side of the globe was pleasant but I was immediately reminded why I left the continent in the first place: the winters are cold and dark and people don't smile without a reason.

During the first 4 weeks I was accommodated in a student housing in the outskirts of Leeds. I had to walk about 10 minutes to get to the University and 20 to get to the city. This is not much but Leeds is a compact city and I preferred to live in the heart of the action so I started to look for alternative ways of accommodation.

During my first year in Sydney I had concentrated on anyon walks and compared their behaviour to classical random walks and quantum walks. My supervisor Gavin and my supervisor in Leeds, Jiannis Pachos, recently made some considerable progress in the study of anyon walks by considering "Ising" type anyons which have some special properties. These properties make them more easily tractable analytically and we could perform longer simulations than were earlier possible. I worked closely with a Master's student Vaclav Zatloukal from the University of Prague and we developed codes both in Matlab and C which calculate the dynamics of Ising anyon walkers. It appears that only a small portion of the total Hilbert space is relevant to the probability distribution of the walker. Thus by restricting the calculations to this subspace only we could double the amount of time steps in the numerical calculations. This gives more information about the asymptotic behaviour of the Ising anyon walks.

Previously we have observed the algorithmic performance of the non-Abelian anyon walks to be somewhere between that of the random walks and quantum walks. The numerical calculations hint that the asymptotic behaviour, when the number of time steps approaches infinity that is, is the same as in random walks. This means that the variance of the spatial probability distribution depends linearly on the number of time steps, whereas the dependence is quadratic in quantum walks. This is interesting in the context of anyon statistics: the more complex exchange statistics of anyons seems to mix the quantum correlations and decrease the speedup which the correlations deliver.

This progress with the research has naturally been nice for me, but of course it is not the reason I am here. The main reason is of course to see England and travel around as much as possible... So I have already visited my precious home country Finland for two times, and went skiing in the Swiss Alps for four days. I have also visited York a couple of times and I can say it is a very nice city with a huge history. I also found a nice flat in the Leeds city centre which I now occupy with Vaclav. I can still walk to the university in 10 minutes and there are several pubs in a 100 metres radius so what more can I ask for.

With the summer approaching life in Leeds doesn't seem bad to me at all. On the other hand, life in Australia never was bad either. Greetings to all at QISS and see you ... not soon but soon enough!

Alexei Gilchrist customised a very good LaTeX thesis template for Macquarie University, Faculty of Science students. It can be found on his blog here http://ectropy.info/2009/03/latex-thesis-templates. I have made some minor changes to the template:

1) The "hyperref" macros package is now included in the class file and can be activated by using the option "foronline" in the document class options ( \documentclass[foronline]{mqthesis} ). Citations and references will then be hyperlinked within the document as will links to external sites and emails. The thesis index it also hyperlinked to the chapter and sections. All of this really only works if you are using pdflatex to make your pdf document. If you want to make a pdf copy for black and white printing just leave out "foronline".

2) A \pdfinfo section is also included in the thesis.tex file. This includes meta data into the pdf document, such as title, author and keywords.

For more info on the changes and how the template works, see the readme file and the documentation within the thesis.tex file and the mqthesis.cls (if you have to make changes) class file.

I think the LaTeX thesis template is pretty much perfect for Macquarie University students in the Faculty of Sciences as it is now. To use this thesis template for your faculty just get the right Macquarie University logo for your faculty. I tried to find these to include them, but gave up eventually. They were easy to find once, but now they are gone. WTF MQ?

Adapting the mqthesis LaTeX template to your university:

1) Get your university logo and slap it in the UNIlogos folder and rename it mqlogo.
2) Open the mqthesis.cls file in a text/tex editor.
   a) Search for all "Macquarie University" and change to your uni's name.
   b) If you want to change the bibliography style search for "\bibliographystyle" and change it to something you like.
3) Fiddle with the margin sizes if your uni is particular about these, other wise just leave as is.
4) Save your changes.    

Yep, and that's about it, you can change the way the chapter headings look by playing with  "\usepackage[grey,times]{quotchap}", enjoy and happy thesising.

The template can be downloaded from here:  http://members.iinet.net.au/~johannelna/mqthesis_v23.zip

Comments can also be left at http://howididitblog.blogspot.com/ where you don't need to log in. Please if you find any bugs/improvements let me know.

 

No  one solved the riddle from two weeks ago (hats), i'm still wating for the answer.

Light bulbs

You are standing in front of a wall with 100 light bulbs and 100 switches numbered 1 to 100.
the light bulbs  are all off, and the switches have the following effect:
flipping a switch will change the state of all the bulbs that are multiples of that switch (so flipping 10 will change the state of 10,20,30,40..100)
you decide to flip the switches one by one, how many light bulbs will be lit at the end?

flipping the first switch(1) will turn all the bulbs on, flipping the second (2) will then turn off all the even numbers etc... finally turning the 100th switch (100) will change the state of the 100th bulb.


enjoy.

No one solved last week's riddle yet so here's a small hint.
The answer is 1, but what's the algorithm?
For all those who asked, the prisoners cannot use any special methods
like timing their answers etc... the only information each prisoner can send is a single bit (i.e either black or white) but
that has to also be his guess for the hat.

In the mean while, here's a simple one

what are the next numbers in this series

18, 46, 94, 63, 52, ...

In a really harsh prison the sadistic warden decided to give 100 prisoners the following task:
They must stand in a line, and he will put a hat on each of their heads. The hats can be either black or white. Then each prisoner will be allowed to say one word, either "black" or "white", trying to guess what hat he has. At the end of the game, all prisoners who got their color right will be released, all the rest will be killed. If any prisoner brakes any rule (looks backwards, says any other word, jumps , pokes, etc..) everyone will be killed.

What is their best strategy to get the minimum amount of prisoners killed ? How many prisoners are risking their lives using such a strategy?
The can decide on the stratagy ahead of time.

Again the rules. They all follow the algorithm. They can all hear what the fellow prisoners say. Each prisoner can see all the guys ahead of him , but non of those behind. They can all say either "black" or "white" once but the order of talking is
whatever they want. The number of black and white hats is unknown (but there are  100 hats in total). 

 

 

A few people solved last week's murder mystery. It's quite obvious that Bill killed his brother hoping the girl would come to the funeral.
While the logical connection is simple, it takes a twisted mind to see the solution. The story is that this riddle was used to test psychopaths.
This makes this weeks hike very interesting since Lauri , Ingo and me all solved the riddle. (and it's on Halloween).
As for 2000!mod2003 Gavin is the only one who solved it. I guess i owe you a beer.

Today's riddle requires some thought although it seems easy at first sight.

What is the longest day on the equator, how long is it?
what is the shortest day, how long is that?

Think about your answer.