## We’re on GitHub!

May 15, 2012

The open science movement seems to be picking up steam these days thanks, in no small part, to Michael Nielsen’s “Reinventing Discovery“. Complementary to this has been an increasing clamor for scientists to open up and release the computer codes involved in scientific papers. This is an issue I feel strongly about: it is rather hard for a scientific result to be called “reproducible” if the code the result is based on is withheld.

Strongly motivated by these issues I’ve recently been investigating ways to share and open the source code for the numerical quantum many body projects I’m involved in here in the quantum information group, Hannover. The social coding website GitHub provides a great platform to do exactly this. Thus I’d like to take this opportunity to introduce a new open science open source project evoMPS, led by Ash Milsted, and hosted on GitHub.

EvoMPS is an actively developed implementation of some of the new methods to simulate quantum many body systems using the time-dependent variational principle reported on in these papers.

EvoMPS is also partly the result of our frustration with the expensive licenses required by commercial scientific software (e.g., Matlab and Mathematica) and the irritations of maintaining connections to license servers etc. We wanted that anyone could download the code and experiment with it without having to pay exorbitant fees for commercial software. Thus, to implement the project we looked around for open source alternatives to Matlab and eventually settled on Python + Scipy/Numpy, (although I must say, the new Julia language looks extremely interesting). Python seems really well suited to numerical quantum many body calculations as it allows one to swap in highly optimised LAPACK/BLAS libraries and also one can insert optimised c code using cython.

I am very excited by the results, so please do clone/fork evoMPS today and take a look.

## Translation-invariant quantum states

March 12, 2009

In making my research open I’ve continually encountered the difficulty of working out what to actually post. My typing speed doesn’t really match the speed at which I write down notes. In order to overcome this I’ve already censored most of the worst mistakes in my handwritten notes: i.e., I’ve spared you all of the crossed-out calculations where I made, eg., a minus-sign error and just written up the corrected notes. But apart from this you are pretty much getting what I’m thinking. There is an exception: I am involved in several projects where my co-authors have, for good reasons, requested I not post on them.

In writing my notes for a wider audience I also attempt to preface each post with some kind of general discussion. This seems to be a useful device, not unlike when using del.icio.us where you are forced to write a description. These little extra tasks seem like a useful mental filing device. Also, I think of the prefaces and tags etc. as a way to enthuse a wider audience to work on the problems I’m working on. (Not entirely clear if this is working yet…)

In this post I’d like to talk about a problem that I’m not really working on, but plan one day to work on if I have an idea. I guess most researchers have these kind of “to do” lists of problems waiting for time/inspiration. I find that these problems take up a lot of mental space (even when I’m not thinking about them directly: eg. “I must remember to think about problem X”) and I’d like to experiment by posting about one of them here in an attempt to clear out this to-do list, so to speak.

The problem/idea I’d like to talk about today is principally motivated by a single figure (Figure 1) in a paper of Cirac and Verstraete. Read the rest of this entry »

## Visit to to the AMOPP group at UCL

February 11, 2009

Today I was invited to give a talk to the AMOPP group at UCL. While I was visiting I was given a lab tour of the LCN, and I got to see all their fancy stainless steel lab equipment including big magnets and other stuff to move and measure small cold things.  During the visit I heard about the latest stuff they are doing there, including some very exciting implementations of electrical spin-trap readout of coherence in silicon.

I heard from the group of Sougato Bose, and I learnt about some counterintuitive results showing that after a quench of interactions in the XXZ chain there can be a substantial generation of entanglement from an initial thermal state. I also heard about the some other results about entanglement generation after a quench, but this time where only one or two interactions are quenched. Both of these papers are intimately linked with how quasiparticles propagate through interacting quantum spin systems and, by focussing on entanglement generation, expose subtle transport physics in these models. Eg. check out figure 4 in this paper where some kind of interesting transition (probably not a quantum phase transition) is occurring at $\Delta = -0.5$.

The slides for the talk I gave are here. I spoke about the some of the known results concerning the computational complexity of simulating interacting quantum systems, in particular, quantum spin systems.