Monthly Archives: May 2012

SUSY Matrix Blues

Popular Science, Quantum Computing
The Gentleman to the right places you into the Matrix. His buddy could help, if only he wasn’t a fictional character.

Dr. Gates, a distinguished theoretical physicist (with a truly inspiring biography), recently made an astounding statement during an interview on NPR (the clip from the On Being show can be found here – a transcript is also online).  It gave the listener the distinct impression that he uncovered empirical evidence in his work that we live in a simulated reality.  In his own words:

(…) I remember watching the movies, The Matrix. And so, the thought occurred to me, suppose there were physicists in this movie. How would they figure out that they lived in the matrix? One way they might do that is to look for evidence of codes in the laws of their physics. But, you see, that’s what had happened to me already.

I, and my colleagues indeed, we had found the presence of codes in the equations of physics. Not that we’re trying to compute something. It’s a little bit like doing biology where, if you studied an animal, you’d eventually run into DNA, and that’s essentially what happened to us. These codes that we found, they’re like the DNA that sits inside of the equations that we study.

Of course Dr. Gates made additional qualifying statements that cautioned against reading too much into this, but media, even the more even-handed NPR, feeds off sensationalism. And so they of course had to end the segment with a short excerpt from the Matrix to drive this home.  It would be interesting to know how many physicists were subsequently badgered by family and friends to explain if we really live in the Matrix. So here’s how I tackled this reality distortion for my non-physicist mother-in-law:

  • Dr. Gates has been a pioneer in Supersymmetry research (affectionately abbreviated SUSY) but just as with String theory there is an absolute dearth of experimental verification (absolute dearth meaning not a single one).  While SUSY proved to be of almost intoxicating mathematical beauty the recent results from LHC have been especially brutal. Obviously, if nature doesn’t play by SUSY’s rules it will be of no physical consequence if Dr. Gates finds block codes in these equations (although it certainly is still mathematically intriguing).
  • The codes uncovered in the SUSY equations are classic error correction bit codes. The bit, being the smallest informational unit, hints at a Matrix style reality simulated on a massive Turing complete machine.  There are certainly other smart people who actually believe in such (or a very similar) scenario – e.g. Stephen Wolfram advocated something along these lines in his controversial book.  The one massive problem with such a world view is that we rather conclusively know that classic computers are no good at simulating quantum mechanical systems, and that quantum computers can outperform classical Turing machines (the same holds in the world of cellular automatons, where it can be shown that quantum cellular automatons can emulate their Turing equivalent and vice versa).

If Dr. Gates had discovered qbits and a quantum error correction code hidden in SUSY, that would have been significantly more convincing.  I could entertain the idea of a Matrix world simulated on a quantum computer.

At any rate, his equations didn’t provide a better answer to the question of why anyone would go to the trouble of running a simulation like the Matrix.  In the movie, the explanation is that human bodies perform as an energy source just like a battery.  Always thought this explanation fell rather flat.  If a mammalian body was all it took, why not use cows, for example?  That should make for a significantly easier world simulation – an endless field of green should suffice. Probably wouldn’t even require a quantum computer to simulate a happy cow world.

A Picture is Worth More Than a Thousand Lines of Code

Quantum Computing

Imagine a world before the advent of the steam engine that nevertheless imminently anticipates this marvelous machine’s arrival. Although no locomotive has been built, civil engineers are already busy discussing how to build rail-road bridges, architects try to determine the optimal layout of train stations, and the logistics of scheduling and maintaining passenger and freight traffic over the same tracks is heavily researched.

To some extent this seemingly absurd scenario is playing out in the world of quantum computing.  For instance, take a look at this intriguing presentation by Rodney Van Meter:

While watching it I had to pinch myself a couple of times to make sure I wasn’t just hallucinating a beamed broadcast from the future. In fact it is more two years old. All this impressive infrastructure work is being performed while we are still years away from an actual scalable universal quantum computer.

Of course there is ample reason for all this activity, as has been documented on this humble blog.  To recap: As our conventional computing inevitably arrives at structure sizes where undesired quantum effects can no longer be ignored. On the other hand harnessing the peculiarities of quantum mechanics will supercharge Moor’s law. It will enable us to tackle problems that are too complex for conventional computing.

Specialized quantum computing devices such as D-Wave’s machine or NIST’s impressive ion based quantum simulator already allow us a glance at the potential that this new approach to computing will unleash (btw. the NIST article makes it sound as if a “crystal” was contained in the Penning trap.  This of course is nonsense.  What is meant is that the ions are arranged in a 2d crystal like grid).

It is encouraging that this core technology is so feverishly anticipated and that considerable efforts to lay the groundwork for it are in progress.  After all, conventional programming techniques won’t cut it if the goal is to leverage the additional power of a quantum computer. It will be key to empower software engineers to program these devices without forcing them to go through a quantum mechanics boot camp.

When picking up a textbook on the subject, the reader will very quickly be confronted with diagrams typically following the circuit model, where every line corresponds to a qbit. Such as:

Only good to beam up qbits.
Teleportation of the kind that’s only good to beam up qbits.

While this is useful to introduce a reader to the peculiarities of entanglements and how this can be leveraged as a computational resource, it is obviously of limited use once you have a meaningful device that offers hundreds of qbits.  Even for a dedicated (Ising model solving) system such as D-Wave, you can no longer draw a complete graph (although it helps to introduce a matrix notation to the uninitiated).

A purist might stop there and observe that quantum computation just means working with density matrices, and hence brushing up on your linear algebra is what it takes.  The conventional programming analog would be to observe that Boolean logic is all you need to program a conventional chip.  Obviously, higher levels of abstraction serve us well in this area.

The current state of affairs in quantum computing remind me of the early days of visual programming research long before the advent of UML to provide a unified framework.

For instance, there is Robert Tucci’s remarkable work to extend Bayesian Network diagrams into the quantum computing realm.  There are also considerable efforts underway to develop a universal visual Tensor Network “language”.  Last but not least, there are some convincing arguments that topological quantum computers are most amenable to a schema dubbed “quantum picturalism“. A nice talk on this is also available online (courtesy of Microsoft’s research division).

As this industry matures, expect a similar process as that which played out in the old world of visual programming.  There is one important twist, though: Although UML is an excellent way to approach coding in a structured way (one  that actually deserves to be called engineering), its adoption is lackluster, and sloppy coding still rules supreme.

To the extent that pictoral languages are at the heart of quantum computing programming, maybe another beneficial side effect of the coming quantum computing age will be to accelerate the maturing of the computer industry’s approaches towards software development.

Modern and ancient pictograms. Sometimes hard to piece together what a graphical representation is supposed to convey.

 

Regular Blogging Will Resume Shortly

Uncategorized

Currently I am spending way too much time commenting on Scott Aaronson’s blog where the Joy Christian “Bell Inequality Disproof” controversy is still in full swing.  The latter also inpsired me to the new “QC Bet Tracker” page on this humble blog of mine.

Head over if you want to see a first class science imbroglio.

About Time – Blogroll Memory Hole Rescue

Blogroll Rescue, Popular Science, Quantum Computing

One of the most fascinating aspects of quantum information research is that it sheds light on the connections between informational and thermodynamic entropy, as well as how time factors into quantum dynamics.

I.e. Schroedinger Equation and Heisenberg picture are equivalent. Although in the former the wave-function changes with time in the latter the operator. Yet, we don’t actually have any experimental insight in when the changes under adiabatic development are actually realized, since by its very nature we only have discrete observations to work with. This opens up room for various speculations such as that the “passage of time” is actually an unphyiscal notion for an isolated quantum system between measurements (i.e. as expressed by Ulrich Mohrhoff in this paper).

Lot’s of material there for future posts. But before going there it’s a good idea to to revisit the oldest paradox on time with this fresh take on it by Perry Hooker.