That must end, so I’ve decided to learn Python. I just need something simple for number-crunching and graphics, and everyone in the know seems to have nice things to say about the language. (Secretly I would like to play around with genetic algorithms and cellular automata, but I’m not going to admit that.) I tried to get Fortran, my previous language of choice, up and running on my Mac … it didn’t go well.

So… any tips? Pointers to well-written resources and tutorials (online or in print) would be especially helpful. Keep in mind that the target audience is an aging theoretical physicist who hasn’t programmed in 20 years, and for that matter has been pretty much command-prompt free (working on my Mac) for the last five.

The things I admit in public on this blog, sheesh.

We present an analysis of Conficker Variant C, which emerged on the Internet at roughly 6 p.m. (PST) on 4 March 2009. This variant incorporates significant new functionality, including a new domain generation algorithm and a new peer-to-peer file sharing service. Absent from our discussion has been any reference to the well-known attack propagation vectors (RCP buffer overflow, USB, and NetBios Scans) that have allowed C’s predecessors to saturate so much of the Internet. Although not present in C, these attack propagation services are but one peer upload away from any C infected host, and may appear at any time. C is, in fact, a robust and secure distribution utility for distributing malicious content and binaries to millions of computers across the Internet. This utility incorporates a potent arsenal of methods to defend itself from security products, updates, and diagnosis tools. It further demonstrates the rapid development pace at which Conficker’s authors are maintaining their current foothold on a large number of Internet-connected hosts. Further, if organized into a coordinated offensive weapon, this multimillion-node botnet poses a serious and dire threat to the Internet.

Yikes! Whoever wrote this thing is not a very nice person…or persons. The C variant apparently managed to upgrade itself over the network, and disables security anti-virus software. If I were you (and I am apparently not because I use only OS X and Unix) I would update my antivirus software every day and scan my machine. And leave it off next Wednesday if possible.

Pass the word…

I want one, I want one! A new, totally tricked-out 17″ MacBook Pro with solid state drive:

2.93GHz Intel Core 2 Duo
8GB 1066MHz DDR3 SDRAM – 2X4GB
256GB Solid State Drive
SuperDrive 8x (DVD±R DL/DVD±RW/CD-RW)
MacBook Pro 17-inch Hi-Resolution Antiglare Widescreen Display
Backlit Keyboard (English) / User’s Guide
Apple Mini DisplayPort to DVI Adapter
iWork ’09 preinstalled
Aperture preinstalled
AppleCare Protection Plan for MacBook Pro (w/or w/o Display) – Auto-enroll

All for just $5,875.

But sometimes things get just plain silly! The Guardian is carrying a story of a real life couple who got divorced because the man was carrying on a platonic relationship with another woman in Second Life (I guess I should mention that his avatar also slept with a prostitute avatar also). So, first, while some things, like attending a talk by a cosmologist, may be almost as good in Second Life as in real life, I’m guessing sex isn’t one of them because it lacks the whole, you know, you getting laid part! Second, if you wanted to misbehave with a non-human toy form, put together from basic building blocks, you might as well make yourself a Lego partner – at least you could touch that.

Neither. I am an illiterate who has to reply on my wife for all of the assistance I can get.

Now come some even more impressive quotes in an interview with the New York Times.

He said, ruefully, that he had not mastered how to use the Internet and relied on his wife and aides like Mark Salter, a senior adviser, and Brooke Buchanan, his press secretary, to get him online to read newspapers (though he prefers reading those the old-fashioned way) and political Web sites and blogs.

“They go on for me,” he said. “I am learning to get online myself, and I will have that down fairly soon, getting on myself. I don’t expect to be a great communicator, I don’t expect to set up my own blog, but I am becoming computer literate to the point where I can get the information that I need.”

…

Mr. McCain said he did not use a BlackBerry, though he regularly reads messages on those of his aides. “I don’t e-mail, I’ve never felt the particular need to e-mail,” Mr. McCain said.

I know the internets are confusing and all, but I’m frankly a bit baffled by this. He needs help “getting on”??? To read newspapers? Hard to imagine that there’s not a computer he could use somewhere, already attached to the internet, and probably even with the browser already installed. I’m guessing he wouldn’t have to learn how to set his DNS servers in order to read the New York Times. Is it typing the URL that’s difficult? My grandmother, by the way, who is more than a decade older than McCain, seems to have figured this out just fine, even without a campaign staff to help.

The level of cluelessness here is deep — not only does he admit that he’s completely illiterate, he demonstrates a basic lack of familiarity with the terminology (he also mentioned that his staff shows him Drudge, because “Everybody watches, for better or for worse, Drudge.”), much like his colleague Senator Ted “series of tubes” Stevens, opposer of net neutrality.

And it’s important. At the risk of stating the obvious: Internet policy has direct relevance for our most fundamental rights, including freedom of expression, privacy, and democratic access to information. Computing is increasingly critical to our increased understanding of the Universe, financial markets, and disease. The internet and social networking tools are rapidly revolutionizing the way we interact with each other, citizen’s access to and engagement in government, and government accountability. These things are central not only to innovation and the global economy, but to 21st century democracy in America and the world. It’s really hard to see how you can fully appreciate these issues if you don’t know the most basic things about operating a computer. Leadership matters.

Barack Obama, on the other hand, has a twitter account. (He also hired one of the Facebook founders to start his myBarackObama site, which has clearly been responsible for a good deal of his internet fundraising and organizing.) He gets it.

However, the other day, he nearly got me:

“Did you know it can emulate the HP-15C?”

Be. Still. My. Heart.

The HP-15C is simply the finest piece of handheld computing technology ever. (Take that Steve Jobs). I got my first 15C back in high school, and it was the only calculator I used for the next couple of decades. I could operate it in the dark. I lost it in an airplane seat back pocket and have never gotten over it.

I suppose in the intervening years we’ve gotten used to irrational devotion to electronic gadgets, but the 15C had to have been one of the first targets, at least in geeky circles. If you mention the 15C to a nerds of a certain age, our eyes grow misty at the utter perfection of it. It was a calculator that simply got everything right.

The genius of the 15C is multifold. First is the form factor. It’s essentially the same as an iPhone, held in landscape mode, with a nice weight that fits well in the hand. The buttons are large and well separated, and there are no more or no fewer than you could want. (In comparison, modern HP calculators are crammed with a thicket of unusable little buttons. Ick.) Second is the glory of reverse polish notation. The 15C operates with a memory stack, which when operating with RPN allows you to perform complex calculations with no need for parentheses. Third is the 15C’s unnatural durability. A former dog of mine literally mangled a friend’s 15C, and it continued to work in spite of the large teeth marks denting the keys. Fourth (and most critical for getting me through years of physics labs and observing runs) was that it’s programmable. That’s no big deal these days, but huge in the early 80′s. Spreadsheets were hardly widespread, and when one timed balls going down ramps or any other such repeated trial, doing repetitive calculations was a breeze on the 15C.

Now, am I alone if my love for the 15C? No, indeed. On Ebay, a 15C in good shape can go for hundreds of dollars. (And if you buy one, it’ll still work. I’m guessing one will not say the same about the iPod in 30 years.). There’s an on-line petition begging HP to bring the 15C back.

And, there are people out there writing emulators for it to run on the iPhone. If you ever see me with an iPhone, this will be why.

It’s a cute idea, though they should have chosen dark blue and gone for “Bloogle”.

This weekend I was at a Kavli Frontiers of Science meeting at the National Academies of Science office in Irvine, and one of the participants was Luis von Ahn — the guy who was responsible for inventing the CAPTCHA idea. He gave a great one-minute talk, in which he traced his personal feelings about being responsible for something that is so useful, yet so annoying.

CAPTCHA, you will not be surprised to hear, is ubiquitous. Luis figured out that the little buggers are filled out about sixty million times per day by someone on the web. So, as the inventer, he first felt a certain amount of pride at having exerted such a palpable influence on modern life. But after a bit of reflection, and multiplying sixty million times by the five seconds it might take to fill in the form, he became depressed at the enormous number of person-hours that were essentially wasted on this task.

Being a clever guy, Luis decided to make lemonade. What we have here is a huge number of people who are recognizing words that a computer can’t make out. Luis realized that there was a separate circumstance in which you would want the computer to recognize the words, even though it wasn’t quite up to the task — optical character recognition, and in particular the problem of digitizing old texts. Apparently, before the advent of the Internet, people would store information by binding together pieces of paper with words printed on them, forming compact volumes known as “books.” In the interest of preserving the products of this outmoded technology, various efforts around the world are attempting to scan in all of those books and store the results digitally. But often the text is not so clear, and the computers don’t do such a great job at translating the images into words.

Thus, reCAPTCHA was born. At this point you should be able to guess what it does: takes scanned images from actual books, with which optical character recognition software are struggling, and uses them as the source material for CAPTCHA’s. The project is up and running, and can be implemented anywhere the ordinary CAPTCHA’s are used. Now, when you get annoyed at having to make out those squiggly words with lines slashed through them, you can take some solace in knowing that you’re making the world a better place. Or at least saving some books from the trash bin of history.

Computers often do the same thing over and over again. Microprocessors have become amazingly fast, but since they are general purpose, they are not as fast as dedicated circuits which just do one operation, but do it blazingly fast. Field-programmable gate arrays (FPGAs) have been used for over two decades for dedicated operations in high-speed electronics, and now Prof. Frank Vahid and his Ph.D. student Roman Lysecky at UC Riverside have married the FPGA to the microprocessor to create “warp speed” computing.

The idea, like many great ideas, is simple: when a computer program finds that it is executing the same instructions repeatedly, and these can be done faster in an FPGA, the program automatically moves that code section to an on-board FPGA, which will run that section up to a 1000 times faster than the microprocessor.

Lysecky’s dissertation on warp computing won the 2006 “Dissertation of the Year” prize at the European Design and Automation Association.

This is so obviously a great idea, and will speed up computing in so many circumstances that I expect we’ll see it in commercial systems very rapidly. This could be a huge breakthrough…

Suffering from its exorbitant price point and a dearth of titles, Sony’s PlayStation 3 isn’t exactly the most popular gaming platform on the block. But while the console flounders in the commercial space, the PS3 may be finding a new calling in the realm of science and research.

Right now, a cluster of eight interlinked PS3s is busy solving a celestial mystery involving gravitational waves and what happens when a super-massive black hole, about a million times the mass of our own sun, swallows up a star.

As the architect of this research, Dr. Gaurav Khanna is employing his so-called “gravity grid” of PS3s to help measure these theoretical gravity waves — ripples in space-time that travel at the speed of light — that Einstein’s Theory of Relativity predicted would emerge when such an event takes place.

It turns out that the PS3 is ideal for doing precisely the kind of heavy computational lifting Khanna requires for his project, and the fact that it’s a relatively open platform makes programming scientific applications feasible.

It all got thrown out of court, except the breach of contract part.

Huh? Well, she has a warning on her site, profanejustice.org that entering it and clicking on links etc. constitutes acceptance of her terms of service, which include not indexing it or downloading the contents, etc. You get the idea.

She sounds like something of a s**t diturber, anyway, refusing at one point to surrender a .38 in her carry-on, etc. Don’t get me wrong, I am gaining growing respect for the disturbers out there in this strange world. But, you know, pick your battles.

But to the issue: *do* internet search sites have the right, no matter what, to index you and send readers your way? Or index you and use the information for something else? Is it a bad thing to respect someone’s declared intent for you to not do that?

I think the whole argument about whether computer programs or agents or spiders or whatever are sentient is stupid. They are not, but someone hit that return key somewhere, and they are the ones responsible.

There is an informal agreement that robots should obey the restrictions in a robots.txt file on a site, but it’s no more than that, an informal agreement. So that’s not a good argument against the suit.

What happens if she wins this one all the way? Then, any time a site wanted to avoid being indexed, they could simply declare this on the page. The vagaries of our language being what they are, it would be hard to program a robot to be sensitive to any such disclaimers anywhere on a page. But, supposing that can be overcome, what uses might this be put to?

I suppose those might include online stores that don’t want their prices advertised elsewhere, because they are so high! It also might make it easier to protect copyrighted material. It certainly would put something of a damper, in the end, on the open and free nature of the web. But perhaps our diligent readers can think of other evil to do with such a new restriction.

For many people in this position (most of us, let’s be honest), part of their “free time” is spent trying to figure out who among their peers is being interviewed for which jobs, and, if it is a job for which they themselves have interviewed, whether the job has been offered to someone else yet.

Once, this might have been a lengthy task, involving surreptitious phone calls, sometimes through intermediaries, to glean whatever information one could from the organic “rumor mill”. However, by the time I started looking for jobs, the process had become much easier thanks, naturally, to the Internet.

The prime source for information about jobs in theoretical particle physics groups is the Theoretical Particle Physics Jobs Rumor Mill, which was the main site I would visit for gossip when I was on the market. I think it was somewhat later that the Astrophysics Jobs Rumor Mill came along, which was also occasionally relevant to me and certainly involved a lot of people I know. Since then, rumor sites have sprung up in Austria/Germany/Switzerland/Denmark, Greece, New Zealand and the U.K.. Other subfields have also followed suit, in Nuclear Physics and Condensed Matter/AMO Physics.

The rumor mill sites elicit mixed reactions in the community. Most people who are on the market seem to like them and find them to provide a desirable service. Among search committee members feelings are less homogeneous; some are unperturbed about their, and others’, shortlists being public, while some clearly feel they have a right to keep the information secret.

There are a couple of different worries that I have heard some candidates and more people on the other side express about the rumor mills. The first is merely that the deliberations of hiring committees and the resulting offers they make are the private business of the universities and the candidates and nobody else’s business. They understandably don’t like the idea that, for example, if they make an offer to their first choice candidate and are turned down, then when they make their next offer it will be to someone who knows they weren’t the first choice.

The second worry is that there is a fear of a herd mentality developing, in which once it becomes clear that a couple of universities have decided on the same number one choice, this may influence the decisions at other institutions. After all, several fine institutions can’t all be wrong about a particular person being the best choice, can they?

From my perspective, having been on both sides of the hiring process, there is some merit to each of these worries. There is often very little separating the exceptional people who make it to an ordered list of people to whom a position will be offered, and if one is, say, third on the list and is ultimately offered the job, it is seldom a reflection on your absolute talent. I think the rumor mills can make it harder to see past that, when the information is clearly out there for anyone to see.

A herd mentality can sometimes develop, it is true. Often its only effect is to slow down the process as one person garners multiple offers and then sits on them for a while negotiating with the various institutions. Sometimes, however, this can derail the hiring process at some places. On the other hand, if an institution does not follow the herd, the information provided by the rumor mill can be invaluable, enabling the hiring committee to make an attractive offer to someone else, and to snap them up while other institutions are tied up playing the waiting game.

However, my attitude to the rumor mills has always been that the various pros and cons I’ve identified above are, at the end of the day, irrelevant. If one thing is clear on the Internet, it is that information that is out there will be made public whether one likes it or not. All that technology does in this situation is to formalize, simplify and make very efficient, the dissemination of the kind of gossip that people have always shared in the community. Like it or not, one just has to live with it – what are you gonna do?

This week, I learned from my friends at Berkeley – cosmologists Martin White and Joanne Cohn – that rumor mill technology is taking another leap forward. Joanne and Martin have set up an Astrophysics Job Rumor Mill wiki which, rather than individuals emailing in their information to a moderator, as they do now, can be directly edited by all contributors. As Martin put it

The idea is to take some of the burden off of the person(s) running the Astrophysics Job Rumour Mill by letting lots of different people edit a Wiki. A successful Wiki could result in an accurate and up-to-date page with little work for any one person if the community embraces it.

If you’re interested in how our rumors get propagated, take a look; and if you’re in the field and use the rumor mills, I’m sure Martin and Joanne would be interested in any feedback you might have.

Anyway, I just learned of another excellent tool. Many of you may know of it already, but those of you who don’t might find it a major boost to communications. I use Instant Messaging a lot to communicate a lot with collaborators, students, and friends and family. I use iChat for IM, adding iSight for video sometimes.

Well, my undergraduate student Jeff Pennington IM-ed me last night to tell me about Adium X. It is a new (at least to me) IM program for Mac OS X, and if you have Equation Service installed (don’t tell me you don’t have Equation Service installed!!!), when you type an equation in LaTeX (enclose it inside double dollar signs, e.g., $$\LaTeX$$), it shows up fully processed in the IM window!

Here’s a screen shot of a chat I did with…er…. myself, which explains the repetition in the dialogue (well, nobody else seemed to be awake when I wanted to generate the test chat….sigh):

This is just so great for those more technical collaborative conversations…..cuts down on faxing equations, or trying to point your camera at your notebook (especially if you don’t have it with you on your travels, etc….) And of course you can save the whole conversation. I’ll bet there are a lot of other features I don’t know about…but the instant LaTeX-ability just makes it click for me. Now if only they’d allow me to connect my iSight camera into it as well….

(Oh, yes, I’d be very happy if someone wrote in and told me that LaTeX works just as well for iChat too…. if so, how do you switch it on?)

You can get Adium X (and read more about it) here.

Enjoy!

-cvj

So I’d like to broach a more controversial topic. I’m thinking of buying a new laptop. Tell me: Mac or PC? I’ve used both quite a bit, so I’m not a fundamentalist either way. The Macs are of course Linux FreeBSD-based, which is useful if you’re a scientist. And there’s the fight-the-evil-empire business. But one cannot deny that there is useful software that isn’t available for Macs. And the variety of laptop hardware is much more diverse in the PC world, including attractively thin ultralights. So — reasonable cost-benefit analyses on either side? Your thoughts are welcome.

And play nice.

Progress understanding the fate of the Universe lies in your hands! Thanks in advance for any advice.

Yes, I’m still here at the Aspen Center for Physics, attending the SuperCosmology workshop. I’ve been attending some Cosmology discussions, but also doing some computations on another project (which I ought to tell you about some time) and thinking. This has been helped a lot by the Aspen Music Festival and School, since I’ve gone and sat in the nearby giant music tent in the mornings where the student orchestra is rehearsing pieces they’ll play in the concerts later in the evening. I love listening to orchestras rehearse. Especially large orchestral pieces (such as yesterday’s Shostakovich’s 1st Symphony) where the rehearsal entails deconstructing certain difficult passages by section. So you hear all the strands of a chord played separately by different bits of the orchestra and then put back together. You really appreciate a chord constructed by a master when you’ve heard it this way. Often more fun than going to the concert.

The Center is a wonderful place to do physics for so many reasons. One of them is the fact that there is a weekly colloquium given by one of the physicists from one of the workshops going on. You learn so much about what is going on in other fields.
(and they have really good cheese, wine, crackers and conversation after.)

So I’m supposed to sit here and write a second installment about stringy cosmology, following on from the first installment I gave here. Since there did not seem to be that much in the way of interest in it, as far as I can tell, I’ll instead tell you about this great colloquium I went to. “Topological Quantum Computation”, by Chetan Nayak.

Chetan told us about new ideas and approaches in quantum computers. So those of you who might know Chetan might wonder what on earth he’s doing talking about that stuff. Was he not working on matters to do with condensed matter physics, and topological quantum field theories showing up in strongly correlated electron systems? Yes, but that’s the point!

Let me back up (and turn off the pilaf).

First, what is a quantum computer? Well, such a thing does not exist, as far as we know. It is a dream that physicists would like to turn into a reality. The idea is often attributed to Feynman, and significant key refinements in the important concepts towards making it a reality were made by Deutch, and by Shor. You might start (as Feynman did) by wondering how well an ordinary computer will do in simulating a quantum system, and you quickly realize it would be highly inefficient. For example, to simulate N spins would require diagonalisations of matrices of size 2^N times 2^N. (That’s 2 to the power N, if some browsers miss the crucial character) This is very slow, and gets really bad as N grows. So you begin to think that maybe a computer that uses Quantum mechanics to do its actual computations is the way to go in simulating quantum processes. This is how it all began.

How might you get one to work? A “classical” computer (the one you’re reading this on now, unless you’re way in the future reading old historical records -Hi!) manipulates “bits”, which are realized and manipulated using transistor technology to do the various logical operations (NOT, OR, AND, etc) which build up everything your computer is doing. The basic bit takes two values, “0″ or “1″. (Or “up” and “down”, “pink” or “blue”, etc). The logical operations are then various manipulations you can do on a bit, or collection of bits, and then out comes an answer. A quantum computer uses instead a “q-bit”. A q-bit is rather different since it is inherently quantum mechanical in that it takes two quantum states, which I’ll call |0> and |1>, and forms a superposition of them. That’s your bit. Another example, (since you can’t have a QM discussion without it) is your basic Schrodinger’s Cat example. The q-bit there would be a superposition of the |dead> and |alive> states: |q-bit>=|dead> + a*|alive> where a is some complex number. So you build your computer out of these bits. You do manipulations on the bits with quantum mechanical operators which are in general some unitary operation. (In an N-dimensional Hilbert space, it would be U(N)). When you’re done, you read out your result. Since you’re working with a continuum of linear combinations of bits, it is rather like doing some humongously parallel computation, and this is (roughly) why this is such a potentially radical idea.

So, you ask, “why isn’t my Mac using this wonderful, truly innovative science?” No, it’s not because they’re not called “i-bits” but because there are problems making it a reality. Not just engineering problems, but physics ones. Just as with classical bits, you can implement q-bits and make a computer in a variety of ways (I hope there will be a pink-blue classical computer one day, perhaps based on pink and blue sugared almonds…). The trick is to do it in a way that allows you to do lots of basic computations in a fast and error-free way. And maybe not take up too much space. (There goes my almond computer, on all three counts.).

This is hard. The biggest problem people are worried about is errors. They basically kill your q-bit computation’s integrity way faster than for a classical analogue. There are several reasons for this, and among those are the fact that you have many more (an infinite set of: consider the complex number a) delicate numbers making up the q-bit. If you realized your bit as a tiny spin, say, it is really very sensitive to being knocked about by tiny environmental variations in the local magnetic field. Worse than that, you can’t peek into the computer’s computation half way and check to see if there are errors accumulating and then fix them: That would require you to read one of the intermediate quantum states which would (in the old language) collapse the wave-function and kill your superposition. So basically your mobile phone rings and your computer spits out nonsense. Not good. Well, it’s a lot worse than that, but you get the idea.

Well, there is a huge effort around the world in various universities trying to beat this error-correction problem (as it is called) both theoretically and experimentally. There actually are ways of introducing means of reading off errors and doing corrections (Shor ’95, Gottesman ’97 ….), by introducing a type of redundancy into the realizations of the q-bits, and people are trying to implement them in various
ways experimentally. Apparently, a tolerable error rate is about 1 in 10^5 operations. (That’s 10 to the power 5 if some browsers miss the crucial character) Current estimates of what is possible experimentally right now using “conventional” systems (Silicon, Gallium Arsenide, etc), come in at about 1 in 10^4 at best. (I’m sure there are those who would argue these numbers, but you get the idea.).

So far, in a colloquium about quantum computers, a physicist has been nodding and paying attention. Then the talk degenerates into (depending upon whether the speaker is a physicist, computer scientist, or engineer) rather dry and muddy discussion of various engineering solutions to the problem. All very interesting and important in fact, but if you don’t work on that stuff its dry, dry, dry as a….really dry thing. Instead, Chetan shifts gears and the talk gets *more* interesting.

What do we want? We want to have q-bits that are rather robust against local perturbations. This is where topology comes in. Topology is the study of properties of geometrical shapes which persist even after you do local deformations of it. The classic example is a donut (doughnut?) and a teacup. Imagine making them out of playdough or plasticine (do kids still play with that stuff? I hope so.) Well you could deform one into the other without ever tearing the playdough. You just do local deformations, squeezing and pushing here and there. The “hole” is the thing that is preserved. It is in the middle of the donut, and then it moves to the middle of the loop formed by the handle of the cup. Topology is all about the study of such persistent features. Another example is the study of knots, or how things are tangled or braided together. There are important features that stay the same about a knot tying together loops of string even if you locally waggle the strings a bit. You can classify different knots, or braids, or different surfaces (such as that of the cup and the pastry) according to what features are preserved under local deformations. It is a beautiful area of pure mathematics, and certain areas of physics (such as particle physics and string theory) But so what?

Ah! What if we represent our q-bits topologically instead?! Then they’d be less inclined to care about local environmental disturbances: They’d be really really robust. So how to do that? This is why Chetan is giving this talk, and not an engineer (not that there’s anything wrong with being an engineer; some of my best friends and colleagues are engineers). What you want is a physically realizable system (because you want to build it, right?) where the basic degrees of freedom -things that you want to manipulate and form superpositions of, like we were doing with spins and cats earlier- are topological. Well such systems are known. An example is the Fractional Quantum Hall Effect (Nobel prize 1998 to Laughlin, Störmer, and Tsui by the way ). In very high magnetic fields and a low temperature, you can get what’s called a Hall current of charge carriers flowing perpendicular to the applied potential and applied magnetic field (which are themselves mutually perpendicular). You can measure a Hall resistance associated to this effect, and it varies in a way which is proportional to the applied magnetic field. The quantum Hall effect occurs when the variation is no longer linear, but there are plateaux in the resistance-field curve, resulting in a sort of quantized resistance. At those plateaux, the resistance associated to the other current, the one flowing due to the
applied electric field, actually drops to zero. The unit of quantization is essentially set by the basic fundamental unit of charge of the basic charge carriers, e.g. electrons. The fractional Quantum Hall effect is like the Quantum Hall effect but the plateaux occur at steps which imply a fractional charge carrier. This is very puzzling indeed if you think your basic charge carriers are things like electrons. What Laughlin showed is that the effective theory is different for the FQHE plateaux, and the electrons interact so strongly that they form a phase of matter called a “quantum fluid”, whose basic degrees of freedom are now new localized particles of fractional charge called “quasiparticles”.

What is really interesting for our purposes is the topological facts hiding here. It turns out that the quasiparticles have very interesting properties when you interchange them, or if you take one and encircle another with it. Their wavefunctions come back multiplied by phases with fractional exponents (complex numbers arising from taking n-th roots of unity, for example). These phases are measurable (using e.g. the Bohm-Aharanov effect), but because they arise from taking various paths, or doing certain exchanges, they are tolopogical data. In fact, you can represent the basic degrees of freedom of the system in terms of braiding, or knot theory. (You can see the braids if you imagine little threads attached to the particles, and then you exchange the particles in various ways. You start braiding the threads.) These paths, these entanglements, are the quantum states to use as q-bits, and these are really things that you can make and study! It turns out that there are rather nice quantum field theories that you can write down which model the topological essence of these systems rather nicely. Moreover, they are inherently topological in their definition and rather clean to study. The Chern-Simons theory is an example.

Actually, there’s a more technical point: to make them useful q-bits you need to make sure that your have a full representation of the unitary action on the associated Hilbert space. Move on if you don’t care about the details, but the issue is that you need to have a more subtle braiding such that the monodromy matrices that you get by doing various exchanges are non-Abelian, and that they furnish a representation of the Unitary group U(N) for an N-dimensional Hilbert space. Then, your Chern-Simons effective theory is in fact a non-Abelian one. It is believed (but still being worked on that the 5/2 plateau has such an effective theory (as suggested by Moore and Reade in 91).

These theories are well-studied in the context of both formal field theory and string theory, and both fields have been enriched by work in this area. Also, the field of mathematics has been enriched in this area due to some of Witten’s Fields Medal work, on topological quantum field theory and Knots. Also, real condensed matter theorists like Chetan and his phd advisor of several years ago, Frank Wilczek (Nobel prize last year, by the way, for something else, with Gross and Politzer) have been applying these models to real physical systems. (There are unfortunately three different uses of the word “field” in this paragraph. Anybody care to point them out? Still with me?)

Ok, this post is way too long and my pilaf needs to start heating all over again. So I’d better get to the punchline. Story so far: It would be great to make a quantum computer as it will transform our world. It is hard because q-bit computations are really sensitive to little perturbations in the environment. Topological states are not. So make q-bits out of topological degrees of freedom of a physical system.

So what you’ve got to do is start looking out for ways to engineer it so that you can prepare, manipulate and read out the data from the topological degrees of freedom of a q-bit that you make in the lab. Chetan outlined a number of ways of doing this, involving very clever uses of Josephson junctions (another Nobel, 1973, with Esaki and Giaever) to have the various currents tunneling between various readouts to make gates, and the topological features are the paths the quasiparticles take around various trapped quasiparticles that have been prepared to make the q-bit.

I imagine that you get the idea now. Use topology in an essential way to furnish quantum states upon which to build q-bits from which to build a quantum computer. It turns out that the error in this realization of the system is better than 1 in 10^30 (10 to the power 30…it is controlled essentially by the resistance, which you’ll recall drops precipitously to zero at the plateau).

There’s a long way to go in this program, Chetan tells us, not the least because we’re not going to be making practical computers with devices that only work at about 5 milliKelvin with and applied magnetic field of 10 Tesla! But the point is that there are probably several other systems (for example in high temperature superconductors) that might have accessible topological degrees of freedom, and so this is a program that has a lot of exciting exploration ahead. Have a look at the paper of Freedman, Nayak and Shtengel, Phys. Rev. Lett. 94, 066401 (2005), and references therein for more information. (And note that these guys are working for Microsoft, so you Apple people should make sure Apple’s in on the act. I’ll cry bitterly to see the Windows operating system slowing a quantum computer down to classical speeds after years of innovative research. )

This is a really fascinating combination of very practical concerns with seemingly esoteric things that we string theories work on – like topological field theories – all done in a very satisfyingly clever way. It was also great to see several of my stringy colleagues suddenly start sitting at the edge of their seats during during the colloquium (some of them stopped playing -or whatever- on their wireless-web-connected laptops and sat up), just as I was.

Really, really great stuff. (Which reminds me….Chicken pilaf time!)

-cvj

Well, a number of things did come up as interesting and fun to try, and the following is one of them. I’ve already said on this blog that our particular field (string theory and related topics) could do with more ways of having discussion, both general and specific. We have already accelerated the primary way in which we exchange research results (revolutionizing scientific publishing in the process) by establishing the Archive (see writing about this by Paul Ginsparg), and it undeniably helped drive the field’s rapid developments in the middle 90s while also democratising it by enabling serious papers from the traditional large and famous institutions to be seen on everybody’s computer screen right alongside the serious papers from smaller less well known institutions, often within minutes or hours of the completion of the work.

Imagine if we could do the same with discussions. How might a blog help? Well, of course, we could just have a blog (like this one) with lots of topics up from time to time and people come in and make comments and throw around ideas. This is great, and valuable, respectful and balanced discussion (e.g. here and here) has already been happening here at Cosmicvariance on general and technical aspects of string theory and long may it continue. But I think that it can be better. Way better. The model is as follows:

If you are an individual researcher or group at an institution somewhere, that wants to be a full participant in the process, you register with the System. The System then randomly picks a schedule which determines which group (from wherever in the world they are from) gets to be the hosts of the blog. As hosts, they choose the topics of discussion (perhaps some of the topics they are working on in that group) and put up posts on these matters. Everybody else reads and makes comments as usual on several threads, just as on any busy blog. Discussion happens. After the predetermined period ends, it is the turn of the next randomly chosen group to take the baton, choosing their topics of interest, and sparking off the topics for discussion. This just keeps cycling on and on. Full participants get to contribute and host, while others can simply lurk and listen, or listen and post comment.

Advantages?

1) Ideas are thrown around, both good and bad, general and technical. Nuggets of value are panned out of the mud and incorporated into research in the usual manner.
2) Senior people as well as junior get to contribute, and learn from each other.
3) Smaller groups or individuals at more isolated institutions get to have regular conversations with the entire field. Everybody benefits.
4) By changing the host every so often, everyone gets a chance to participate and to change the perspective and the agenda.
5) No one group, no matter how big or powerful, gets to dominate the scene.
6) There will be a permanent archive of these discussions which will be fully searchable. It can be mined for information at later times.
7) Flexibility: It is up to the group how they choose to participate. Just one person from the group can run the show, or it could be a group blog from that whole research group.

Disadvantages?

1) Someone has to design the system, but there are so many clever people to write some software to implement the System and there are excellent standard blogging resources for making it easier. Once set up, it will run itself with minimal effort. I bet there are several such clever people out there who could collaborate on setting it up.
2) Lots of random comment might come from people not working in the field that could be distracting. I’m not really convinced that this is a problem, but I’m sure that it will be mentioned as one. Easy solution is to have three levels of participation. The basic level is that everyone can see it and search on it as a resource. Next level is that you are a registered contributor that can comment. Next is that you are a group or individual that can be chosen by the system (with ample warning of course!) to be a host for a period.
3) Too much talk not enough equations? Not convinced this is a problem either. It is trivially easy to post up equations as images, raw TeX, or whatever, and also I think that people like Jacques Distler have been playing with other equation plugins for serious research use.
4) Can’t think of any more downers. What are we waiting for?!

I think this could work for several fields of endeavour where exchange of ideas is a key component. It is very well-suited to theoretical physics indeed. It will not and should not replace blogs like this (which have discussions of all types on all sorts of subjects, scientific or not), and will not replace all the other more “traditional” modes of discussion that already happen. It will enhance them.

I’d really like to hear people’s thoughts about this. For example:

1) Maybe it has been tried before by someone else? If so, point it out and we can learn from their experience.
2) Maybe it has been thought about before and not implemented for some reason I’ve missed?
3) Would you take part in something like that? Or not at all? What are your reasons?

Please share your thoughts (and ask others to come here and share theirs too), and let’s see if it’s worth taking further. Maybe even if we talk about it but don’t do it, the model might be useful to others.

-cvj