Archive for March, 2008

Espionage for the Information Age

Posted in Uncategorized on March 28, 2008 by quantummoxie

On April 15th I will be speaking at Colgate University, my grandfather’s alma mater (class of 1926).  Here’s the flier Colgate created to advertise it. I love the homage to Bond, especially considering the next film’s title.

More fun and games

Posted in Uncategorized on March 27, 2008 by quantummoxie

Allan Goff over at Allan Goff’s Entanglements linked back to a note I put up about a year ago concerning the possibility of using the game Quantum Tic-Tac-Toe (which Allan created) in my quantum mechanics class.  I had promised a report, but never put one up.  In any case, I’m thinking of using it again in my quantum cryptography class this spring.  It didn’t work too well as a pedagogical tool for everyday QM (even though I discussed entanglement in depth), but I suspect, considering the success I’ve been having with some of the cryptographic “games” (see previous post), it might prove more useful in my QCrypto class.  Ironically, I’m right at the point at which I would introduce it, almost to the very day.  So we’ll see how it goes and see what we can get out of it.  The problem with it in the QM class last spring was that the notion of the circularity of the entanglement apparently wasn’t all that intuitive from the game itself according to the students.  It made sense once I explained a bit more about what was happening, but it wasn’t as useful as a teaching tool as I had hoped.  However, I think it could prove very useful in teaching aspects of quantum cryptographic protocols, particularly in comparing the classical to the quantum cases.

Chaos Computer Club

Posted in Uncategorized on March 26, 2008 by quantummoxie

A student of mine alerted me to the following videos that describe some cryptographic protocols including some that are quantum.  In particular, they demonstrate some ‘games’ that can be ‘won’ with a quantum system but not with a classical system. The videos are by a German hacker group know as the Chaos Computer Club.

1st video

2nd video

3rd video

A further description of some interesting protocols as given by my student:

“Off the Record” (software) and the “Dining Cryptographers” protocol are cryptographic systems which are pretty much the opposite of “normal” crypto. For example, crypto is usually used to make sure that no one can read the data sent, and that no one can later forge documents using the same key. OTR, on the other hand, publishes *all* the keys used as soon as the conversation is over, ensuring that any message produced later as “evidence” could just as easily have been forged, granting the users plausible deniability.

The Dining Cryptographers protocol is a cryptosystem that ensures a level of anonymity for the sender(s). As far as I know it has not yet been seriously implemented, but the original idea goes like this: Some cryptographers are having dinner out together. When it’s time to pay the bill, the waiter says the meal is already paid for. Now, the cryptographers respect the donor’s anonymity, but they would like to know whether the person who paid is one of their group, or someone else. To do this, each person sitting at the table creates a random number and secretly shows it to the person on his right. The difference between one’s own number and the number of the person to one’s left is the key. The key is xor’d with the message (in this case just one bit, yes/no) and the result is published. The sum of all published numbers is the message. In this case, 1 means someone at the table paid, 0 means no one there did. (Note this requires at least three participants!)

The last videois a cursory introduction to quantum information, but it has a couple of cool games that can be “won” with entanglement that can’t be solved classically.

Add to this the Hat game in which three people agree on colored hats. We discussed this one in class today and I may write up a little something on it since I think one might be able to make a Bell inequality out of the classical case.

Sometimes people like crazy things…

Posted in Uncategorized on March 25, 2008 by quantummoxie

Woohoo!  My latest paper, as of last check, was sitting atop today’s SciRate entries with 4 SciTes – one ahead of a paper whose lead author is Ike Chuang, though, admittedly one of the four SciTes is my own.  I guess contemplating the intersection of quantum information and wormhole physics is just crazy enough to be interesting (though I guess it helps that my work builds on that of SciRate creator and Quantum Pontiff Dave Bacon who deserves credit for having the kahunas to be the first to consider this insane idea – thanks for stickin’ your neck out there, Dave).

Update: Up to 5 SciTes!

Two March Meeting highlights

Posted in Uncategorized on March 24, 2008 by quantummoxie

Having been under the weather and also inundated with family over the past week and a half I have not had a chance to put up some thoughts about the March Meeting talks until now. And, actually, I’m only going to summarize two at the moment that particularly interested me. I’ll summarize some more in the days to come, but I’ll start with these two.

Personally, I’ve always been particularly interested in the work the Vienna group is doing in the Canary Islands. This year they reported on progress with their 144 km relay in which they achieved a half-millisecond lifetime for the Bell state (the longest on record). The link attenuation, while better than weakly coherent transmission, is still pretty darn low. Nonetheless, these guys from Vienna are always pushing the envelope. I would love to spend some time working with them on something (Caslav Brukner has helped critique a paper of mine before, but I’d love to get into some of the experimental stuff as well).

In a somewhat related problem (i.e. the lifetime of the entangled Bell states), there was some progress reported by Zhen-Sheng Yuan on quantum memory in which a quantum repeater is used. So, not only is decoherence a problem for the distance of information transmission, it is also a problem for storing the information for long periods of time (as we saw above, 0.5 ms is considered long). So Yuan’s group employed these repeaters and essentially entangled photons with atoms which is essentially a swap of information between two different types of storage “device,” so-to-speak. The photonic states, then, get stored in atomic states which have a longer lifetime. Not only does this improve the lifetime and efficiency, it also improves the scalability issue for quantum computers.

I found these two particularly interesting because they represent significant progress towards practical quantum communication and computing. This is truly exciting stuff!

Qubit, qubit, qbit, or q-bit?

Posted in Uncategorized on March 19, 2008 by quantummoxie

Dave Bacon (The Pontifftook on David Mermin in the latest issue of Physics Today over the spelling of the word ‘qubit.’  In his recently published book Quantum Computer Science Mermin takes issue with the conventional spelling, suggesting that ‘qbit’ is more appropriate.  Dave and David, in their dueling letters, also debate the merits of ‘q-bit’ which sounds too much like ‘Q-tip’ for some people.  At one point Mermin suggests ‘Qbit’ is perhaps the most appropriate.  However, there is one serious problem with that argument.  van Enk has actually proposed a definitional difference between ‘qubit’ and ‘Qubit’ and even ‘qubit.’  The first is an actual physical qubit – a photon, a spin-1/2 particle, etc.  The last is defined as being a physical qubit on a noiseless channel.  That is, the italics denote an information resource.  The middle form employing capitalization (which van Enk applies to cbits, ebits, refbits, etc.) is a way to represent the encoding of a single logical qubit with two physical qubits.  So suppose we have the following:

|0>(L) = |0>|1>
|1>(L) = |1>|0>

Alice can encode the logical qubit by performing

|0>(a|0>+b[exp{iP}]|1>) ->  exp{iP}(a|0>(L)+b|1>(L))

If you can’t read that, read the paper

March Meeting highlights (or, Deepak Chopra drank the milk!)

Posted in Uncategorized on March 14, 2008 by quantummoxie

Well, I never got to blog in the evenings due largely in part to the fact that I wasn’t getting back to my room until late due to dinner meetings.  I managed to eat at BayonaBroussard’s, and Antoine’s (the first two on the APS’ dime).  I played Matt Leifer for a morning since he couldn’t make it (I skipped the London accent, though) and, due to Howard Barnum’s invitation, spent an afternoon at the Clifford Lectures at Tulane.  Here’s a short summary of some random things I learned at the March Meeting, in the spirit of The Pontiff.  I might give more detailed summaries of some of the talks later.

 – Dave Bacon honored me in his talk by listing me as one of the handful of people as crazy as he is. 

 – Dave’s father once sent him an “itsy-bitsy, teeny-weeny, yellow polka dot zucchini” in the mail. 

 – Dave is very, very funny (and a nice guy, too). 

 – Gravitational fields degrade entanglement. 

 – Seth Lloyd has cheered on Haruki Murakami, one of my favorite authors, in the Boston Marathon (Seth’s wife is a Prof. of Japanese Lit.).

 – Seth’s father hid their TV once, claiming he’d shot it with his .22 while Nixon was talking one day (turns out he
only hid it in the attic).

 – Deepak Chopra drank all of John Preskill’s milk once, without asking.

 – Mathematicians have very little physical intuition (oddly, I have a PhD in Mathematics – hmmm…).

 – There are way too many sessions on superconducting qubits at the March Meeting.

 – Too much of physics has become engineering in disguise (Frank Schroeck agrees with me on this).

 – New Orleans has awesome street musicians.

 – While physicists are still very easy to pick out of a crowd, they’re getting a little better at blending in, e.g. Bob Coecke looks like he ought to be riding a Harley.

 – Barry Sanders owns at least two ties.

 – My result on Cerf-Adami inequalities sent one dude into an incoherent tirade that no one seemed to understand.

 – I seem to have a better memory of the non-scientific results from this week than everything else.  I wonder why.

 Well, we’ll see where that gets us.  I did take some notes at some of the sessions and will report on them at some point (of course, they’re all going to be summarized in The Quantum Times’ next issue).