Quantum Bayesian Networks

April 29, 2011

Don’t Shut Up and Don’t Calculate

Filed under: Uncategorized — rrtucci @ 10:03 pm

Those practically-minded, results-oriented physicists who prefer spending their time working out the predictions of quantum mechanics (QM) and comparing those predictions to laboratory data, instead of rambling endlessly about the philosophical implications of QM, are often said to belong to the “shut up and calculate” school. It seems to me that the advocates of the multiverse “many-worlds interpretation” (MWI) of QM belong to the less desirable school of “don’t shut up and don’t calculate”.

MWI was first proposed in 1957 by Hugh Everett. More than half a century later, it still hasn’t spawned any useful results. And that, in my opinion, is the biggest flaw of MWI: that it’s not very useful. Is it possible to explain or predict or calculate any laboratory observations much more simply or elegantly using MWI than not using it? No. Like I said before, useless.

The vast majority of people working in quantum computing have never used MWI in their work. QM can easily stand without MWI. I can’t stress this fact enough. I hope that those new to the field of quantum computing don’t get turned off from the field because they get the mistaken impression that it’s based on MWI.

David Deutsch claims that MWI is necessary in order to “explain” a quantum computer. He has no mathematical proof of this claim. He argues that the claim must be true because of philosophy (his philosophy). Yawn. He even claims that he has devised a test that singles out MWI as the one and only possible interpretation of QM. His test requires a bizarre self-aware quantum computer artificial intelligence. Nothing like proposing an impossible-to-do, cryptic experiment to prove your point.

April 23, 2011

Quantum Computers according to the Bible

Filed under: Uncategorized — rrtucci @ 4:58 pm

It’s Holy Week right now, the holiest week of the year in the Christian tradition. According to Christian liturgy, Jesus Christ entered Jerusalem last Sunday (Palm Sunday), had his last supper on Thursday, was crucified on Friday, and resurrected on the Sunday which ends the week (Easter Sunday).

Being a Christian during Holy Week puts one in a religious mood. So it’s only appropriate for this blog to feature, on this Holy Week, a post discussing the biblical roots of quantum computing.

Many scientist believe that in order for a quantum computer hardware design to succeed, it must satisfy the 5 basic requirements that were first stated clearly by DiVincenzo circa 1997 in this paper. These 5 requirements, often called the DiVincenzo criteria, are as follows. A quantum computer must:

  1. (scalability) Be a scalable physical system with well-defined qubits
  2. (initialization) Be initializable to a simple fiducial state such as |000…>
  3. (decoherence) Have gate operation times that are much smaller than the decoherence time
  4. (universality) Have a universal set of quantum gates
  5. (measurement) Have qubit-specific high-fidelity measurement capability

According to biblical scholars, some laws very similar to the DiVincenzo criteria are mentioned in the Bible. Let me quote the relevant Bible passage. It’s quite clear from this passage that God intended man to build quantum computers.

(From The Holy Bible: King James Version)

The Second Book of Moses (Exodus 20)

The Five Commandments

And the quantum computer designer spake all these words to his quantum computer, saying, I am the LORD thy designer, which hath brought thee out of the land of Egypt, out of the bondage of classical computation.

  1. (scalability) Honor thy father |1> and thy mother |0>
  2. (initialization) Thou shalt have a graven state |000>, and thou shalt bow down thyself to that graven state on behest of the LORD, thy designer.
  3. (decoherence) Thou shalt do many good, coherent deeds before you die from decoherence. Goes without saying, this includes, Thou shalt not kill or steal or adulterate information or bear false witness with thy probabilities.
  4. (universality) All thy spins shalt covet their neighboring spins in a general and universal way.
  5. (measurement) Remember the sabbath day. Six days shalt thou labor, and do all thy work coherently: but the seventh day is the sabbath of the LORD, thy designer: in it thou shalt not do any work within thy quantum gates, for on that day thou shalt be measured by the LORD, thy designer, whereupon thou shalt confess thy information to him with high fidelity.

The People’s Fear

And all the people saw the thunderings, and the lightnings, and the noise of the quantum computer, a pile of smoking metal: and when the people saw it, they removed, and stood afar off.

And they said unto the IBM sales rep called Moses, Speak thou with us, and we will hear: but let not the quantum computer designer speak with us, lest we die.

And Moses said unto the people, Fear not, for the quantum computer designer just wants a research grant.

And the people stood afar off, and Moses drew near unto the thick darkness where the quantum computer and the quantum computer designer were.

And the quantum computer designer said unto Moses, Thus thou shalt say unto the children of Israel, Ye have seen that this quantum computer can do calculations that cannot be done by any classical computer in heaven or earth.

April 16, 2011

Honey, I shrunk the theory

Filed under: Uncategorized — rrtucci @ 4:11 am

I recently gave a talk at my local “physics club”. The talk was about renormalization group (RG) theory. It was just a brief introduction to the subject. With the help of LaTex, it was an easy and relatively painless exercise to write-up the talk as a pedagogical article. My pedagogical article is about as significant to the RG literature as a mosquito turd is to the New York city sewer system. Nevertheless, I’m posting it here, as a sort of extended blog post, hoping that a few people will find it useful. As I’m sure someone must have said before, “Those who can’t,… teach, and those who can’t teach, write blog posts”. (Also, those who can’t write, Tweet).

You can find the article in pdf format here.

It contains 19 short sections (a nice prime number). The titles of the sections are:

  1. Introduction
  2. Books and other references on RG
  3. RG theory- a big tent
  4. What is renormalization?
  5. A whiff of thermodynamics
  6. An essence of field theory
  7. Naive versus fractal “scaling” dimensions
  8. Real and momentum space RG
  9. Correlations rule the world
  10. Renormalization (semi-)group
  11. RG streamlines
  12. Fixed points of the trivial and critical kind
  13. Critical exponents and universality classes
  14. Relevant, marginal and irrelevant operators
  15. Self-similar coupling constants and beta functions
  16. The regulator and the fiducial mass scale
  17. RG theory has its pi-groups too! Callan-Symanzik type equations
  18. Forgetting initial conditions. Are we cheating with infinities? Where did the infinities go?
  19. The many faces of a renormalizable theory

Here is section 1 of the article:

1 Introduction
In this blog post, I will give a very brief introduction to Renormalization Group (RG) theory.

This blog is about quantum computing and more generally about quantum information science (QIS). So why should a person working in QIS be interested in RG theory? One reason is that RG theory describes how correlation functions scale, and correlation functions are crucial in: (1)the study of quantum entanglement (2)both classical and quantum Shannon information theory.

Physicists like to study how a theory transforms under a family of operations. Such families of operations usually constitute a mathematical group. The operations might be discrete, as with PTC (P=parity, T=time reversal, C=charge conjugation) or continuous (continuous transformations are a type of generalized rotation). In the case of the renormalization group, physicists consider how a theory transforms under an operation that “scales” the unit of length.

It’s useful (at least to me) to think of such scaling as a type of lossy data-compression or smoothing. Accordingly, RG theory can be viewed as a meta-theory that describes how theories change under lossy data-compression. Hence, a more precise but less catchy title for this blog post would have been “Honey, I applied lossy data-compression to the theory (and the kids).”

P.S. While looking for a picture for this blog post, I came across a webpage (for a plastic surgery practice?) that had the following image with the caption “Honey, I shrunk the kids”

April 1, 2011

OMG! OMG! OMG! Quantum Mechanics

Filed under: Uncategorized — rrtucci @ 12:01 am

This blog gets very few visitors. Thus, I was very glad when someone named Kimberley recently sent me the following email, giving me some advice on how to improve the blog so that I get more traffic. I think that she is right, and I’m going to follow her advice.

Hi rrtucci,
So, I’m like, Wow! I just red your blog for the first time. I think your blog is totally awesome, dude. Totally.

I am currently learning EVERYTHING about quantum mechanics and quantum computers. In fact, I have a Google Alert set up to notify me whenever there is a new web article with one of the phrases: “spooky action at a distance” or “quantum consciousness” or “the universe is a quantum computer” or “the multiverse”.

I think you should write a blog post explaining quantum entanglement in the brain, or about how Albert Einstein founded the first branch of String Theory.

Articles about quantum computers in educated publications like university press releases, the Huffington Post and Kaku’s blog (cofounder of String Theory) ALWAYS start with a one paragraph explanation of how a qubit can be in two states at once. Do journalists copy each other or what? LOL. It’s okay. I copy on tests too, especially in Inglish class. LOL.

I think all quantum computer articles should start that way because most people I know have never heard of quantum mechanics, so, it’s like, you know, a good idea to start with a complete, comprehensive one paragraph explanation of quantum mechanics and such.

The strange thing is that no matter how many times I read the same explanation of being in two states at once, I don’t quite get it. I wonder why. Hmm. I’m not dumb. LOL. Of course not. I read quite a lot, Tweets and all.

I’ve read in QuantumFactory, the official blog for the Institute for Quantum Computing at Waterloo, that nobody understands quantum mechanics. LOL. I’m like, that is sooo true. I love their blog because, even though it’s written by a scientific institute, it sounds like something I could have written myself. Those guys think just like me.

Unlike QuantumFactory, I see that you sometimes use weird arithmetic equashions, and that you suggest technical books and papers. That is sooo lame. Totally. You don’t really expect me to read equashions on my iPhone, while standing in line at the Mall or Cinema, do you? ROFL. Why can’t you be more like QuantumFactory? I’m sure any institute that can write an outstanding blog like that is quite capable of building a quantum computer.

Kimberley, Mall Goddess

P.S. For any uneducated people out there who might not know this: OMG=Oh My God, LOL=Laughing Out Loud, ROFL=Rolling On Floor Laughing.

P.S.2- I just received the following message as a comment to this blog post:

Mike Lazaridis <bigMike@rim.com> wrote:
OMG, is QuantumFactory all I got for my 100 million dollar investment? Sigh. At least I’ll recoup my money when the Blackberry outsells Android and iPhone.

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