Sometimes, as I have, you'll find yourself working with colleagues who, through no fault of their own, are either not acquainted with the etiquette of Subversion repository use, or simply have an accident. What you may then end up with is a repository that contains one or more giant blobs of useless data that, really, should never have been added in the first place. Whether or not the culprit well-intentionedly removes these giant blobs in subsequent revisions, you're still left with a huge chunk of nothing-much wasting space on your server's hard drive.

Though a long-standing item on Subversion's wishlist, there is no command that will simply obliterate files from the repository's history. Nevertheless, there is a way to achieve this. Here's how.

The first step of the process is to determine which files need to go. (Some snippets in the following are derived from StackOverflow and Christosoft blog.) First, find the size of each revision in the repository. Replacing REPO appropriately, run this on your server:

REPO=[/absolute/path/to/repo]
for r in `svn log -q file://$REPO | grep ^r | cut -d ' ' -f 1 | tr -d r`
do
    echo "revision $r is " `svn diff -c $r file://$REPO [...]

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Some time ago in a far off land, I kept a website. It was a cozy little website, housing a few bits and bobs that I had made and thought to share should other people find them at all useful. It was hosted with my ISP, accessible via a free domain, which made things cheap and easy for me, but also meant that if I were ever to move I'd have to find a new host, or lose my site.

Of course I moved and I lost my site. This was a couple of years ago, now. From then until now I've been meaning to get this thing back up and running at some point, but lack of time and real impetus meant that it didn't happen. Recently I got my butt into gear and began a focused effort to finally get it off the ground, getting myself some cheap hardware and a new domain name for the purpose.

What you see here is the result—welcome to Quantum Furball! Over the next little while I'll be reposting old things (backdated as accurately as I can guess), along with things I should've posted at the time, and I hope to [...]

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Generating entangled photon states is vital for numerous quantum communications and quantum computation primitives. Here we pioneer a new approach to in-fiber generation of entangled photon pairs. We take inspiration from a technique in bulk-optics, where two nonlinear crystals are sandwiched close together, and splice two pieces of birefringent optical fiber together at 90 degree orientation. With suitable compensation optics, all of which could be implemented in fiber, we show fidelity with a maximally-entangled Bell state of better than 92%.

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Here we detail our work on optoelectronics implementing a high-speed high-fidelity source of optical quantum states for quantum encryption.

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We perform a thorough theoretical analysis of the expected key rate, success of Bell test, and teleportation distance of experiments performed between the ground and a satellite in low Earth orbit. Our findings demonstrate that successful, regularly repeatable demonstrations are feasible with current technologies and relatively small telescopes.

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An ensemble cast detail the new physics that could be explored by taking quantum optics experiments into space. My first publication as part of Prof. Thomas Jennewein's group, I contributed details about near-term tests and our present work at the Institute for Quantum Computing, and helped out with logistics and proofing.

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