Tuesday, July 26, 2011

My Cat Is Dead! -- A Physics Problem

Let me start by saying that I am a physics nut who has been known to worship at the altar of Richard Feynman on occasion. So, you will not likely be surprised to discover that I was mesmerized by a recent article in the New Yorker by Rivka Galchen regarding quantum computing. You might be surprised that an old psychometrician reads the New Yorker (or even that I can read), but let me assure you I have had a subscription in one form or another since 1974.

Before I address quantum mechanics as they apply to computing and discuss Galchen’s article, it is best to attempt to present a little background on quantum physics such that we can have a context to evaluate its application. The world of quantum physics is bizarre if not unbelievable. For example, if you modify the traditional physics thought experiment commonly known as “Schrödinger's Cat” along the lines of Niels Bohr or Hugh Everett, you will understand its complexity.

Think of a box containing a cat. If I asked you “Is the cat alive or dead?” you would probably say it is one or the other but certainly not both. Well, with one interpretation of quantum physics (the “many-worlds interpretation of quantum mechanics”), the cat is both alive and dead simultaneously. The cat is alive in one universe while dead in another (or many) based on the cumulative probabilities of such events across all universes. Hence, depending upon what universe you are in when you observe the cat (read “universe” as “dimension” if you are struggling—like in the Twilight Zone television shows), you will see the cat either alive or dead.

But wait! There is a catch according to the quantum physicists—as soon as you look at the cat you become “entangled” and the cat’s state (dimension or world) is no longer separate from yours. Hence, if you see a dead cat, there is another universe (or dimension) where you are looking at a live cat! Makes great sense, right?

Before you dismiss this quantum stuff as all nonsense, let’s look at a separate but analogous concept in probability theory that is not so controversial—called Let’s Make a Deal or “the Monty Hall Problem.” Suppose there are three curtains; behind one waits a prize and behind the other two a rock. You don’t have to be a statistical genius to know that the probability of selecting the correct curtain is one out of three or 1/3 (0.3333…), at least at the onset of the experiment. However, once you pick a curtain, (even before it is revealed to you) you either won (1.0) or lost (0.0). Only over the long run or accumulation of probabilities will your “sampling distribution” average out to 1/3 and only if the game is played fairly.

However, when Monty eliminates a curtain and gives you a chance to keep your selection or switch, your probability of winning goes up substantially if you switch to the other curtain! Hence, even in current probability theory there seem to be separate dimensions—you have one probability of winning when you selected the first curtain and a different one if you switch. Notice also that once you make a final choice (i.e., once you become “entangled” with the probability) you either win or lose.

If you are still reading :), a logical question you might be asking is: “What does this quantum stuff and simultaneous probabilities have to do with computing and technology?” Galchen introduces us to a professor from Oxford by the name of David Deutsch. David is an odd professor because he hates to teach—rather, he hates to teach people who do not want to learn and sees this as one of the biggest problems of our educational systems—but I digress. Professor Deutsch “works” (to the extent you define just what it is a professor does) at the Oxford Centre for Quantum Computation, which is part of Oxford’s Clarendon Physics Laboratory (this is the same university hosting the Oxford University Centre for Educational Assessment established with a grant from Pearson.

As Galchen describes it, quantum computing is based on quantum mechanics, which simply states that particles exist in two places at once—a quality called superposition. Furthermore, these particles are related in a “spooky” way, or are entangled, such that they can coordinate their properties regardless of their distance apart in space or time. Finally, when we actually observe these particles, we obliterate them! This last case is analogous to looking at the cat in the box and seeing it is dead—because the sheer fact of looking at it caused the result to be a specific outcome!

Unlike a traditional computer that uses bits (“0” and “1”) to represent states, the quantum computer uses qubits (“0,” “1” and “0 and 1”). Hence, these entangled particles can share information, resulting in the ultimate “distributed computing” model. Conceptually, if we set a qubit to “0” in this state, we know that it has another particle in “another world” that can carry a “1” because it is entangled with this world. Hence qubits perform “double duty” across dimensions. One way to understand this is to think about what Everett says about this concept: in quantum computing when there is more than one possible outcome, ALL of the outcomes exist simultaneously, each in different universes. As such, all we have to do is figure out which one is the “correct one” and look only at that one.

If it works, we will unleash computing power never realized before. For example, it would take a current computer a lifetime to factor a 200-digit number whereas, depending upon the number of qubits in the quantum computer, it would take a fraction of a second to compute. This is not as fantastic to believe as it sounds. The Oxford Centre has an eight-qubit computer that looks like an “air hockey table,” according to Galchen, but with added lasers, optics and magnetic fields to control for contamination--as do other centers in Canada, Singapore and New Haven.

Outside of the power such enhanced computing would provide to us, why would we care? Well, to begin with, one of the organizations paying for and experimenting with quantum computing is Google. If Google invents and/or holds a patent on quantum computing, I am sure they can bring it to market and we could use it. I think it would be much better though, if we could see the same future Google sees, get in on the ground floor (particularly with a place as prestigious as Oxford) and allow them to help us open our eyes to the types of innovation the future will require.

Let me know what you think.

Jon S. Twing, Ph.D.
Executive Vice President & Chief Measurement Officer
Test, Measurement & Research Services
Assessment & Information

1 comment:

HVernon said...


Thanks for sharing.

I've read both of Hawking's books twice, and get twisted around on myself each time(Brief History of Time and Briefer History of Time). Your blog motivates me to go back and try to slug through them again. The "Let's Make Deal" analogy was the trigger for me. I'd be interested in your thoughts about the book, "The Zen and Art of Motorcycle Maintenance," if you have read it. The concept of situational quality seems like a theme I have run into throughout my entire career. "Zen" had the same effect on me that Hawking's books did.