# Quantum Bayesian Networks

## May 23, 2013

### Déjà Vu???

Filed under: Uncategorized — rrtucci @ 1:36 pm

“The way I thought about it was that we’d have succeeded if: (a) someone bought one for more than $10M; (b) it was clearly using quantum mechanics to do its thing; and (c) it was better at something than any other option available. Now all of these have been accomplished, and the original objectives that we’d set for ourselves have all been met.” (Geordie Rose, 2013, source) While D-Wave investor Steve Jurvetson predicts that D-Wave’s computers will soon run “faster than the universe”, in a different planet, Scott Aaronson and Greg Kuperberg claim D-wave’s computers show no speedups and are “worth$0”. Luckily for D-Wave, the public will never read 300++ blog comments. I confess I have no life, so I’ve read most of them.

We’ll soon find out who’s right, probably in less than a year’s time.

Personally, my opinion on the matter is very bland and boring. I believe that in the future, gate model QCs will outshine D-wave’s QCs (because they allow better error correction), but for now we can learn some interesting physics and engineering from D-wave’s QCs.

(Prediction is very hard, especially about the future – Yogi Berra)

## May 21, 2013

### Faster Than the Universe!

Filed under: Uncategorized — rrtucci @ 5:36 pm

“A year later, it outperforms all computers on Earth combined. Double qubits again the following year, and it outperforms the universe.”
Steve Jurvetson 2012, describing his Rosy Law.

This quote comes from an awesome essay entitled “Rose’s Law for Quantum Computers” that I think should be required reading for all QC aficionados, especially Californians. Scott Aaronson reads it during fairy tale reading time to his 2 year old daughter Lily every night before going to sleep. She loves it. It’s that good!

Jurvetson is a partner in Draper Fisher Jurvetson, a venture capital firm that has invested a lot of moolah in D-Wave. Jurvetson posted this essay on something called Flickr, an internet company in which his VC firm has also invested. Flickr is owned by Yahoo, another internet company that you probably never use either. The full essay is posted in the comments below, in case Flickr vanishes long before WordPress does.

## May 7, 2013

### Fox News Poll: Who Won (or is Winning) the Aaronson/Lubos Debate

Filed under: Uncategorized — rrtucci @ 2:21 pm

Remember: Vote early and vote often!

The debate of the century!
The debate that polarized the world and tore countless families apart.

The debaters: Scott Aaronson Versus Lubos Motl
Topics being debated tonight: Is Complexity Theory just a science based on conjectures? Are those conjectures even right, or that fundamental, or of any importance to Physics? Are Complexity Theorists too political, clannish and dismissive of others? Do they sometimes give themselves all the credit for inventing the wheel? Did they really invent physics? Which one would you hire: a complexity theorist, a computer programmer or a string theorist? Would you hire Lubos? Would you hire Aaronson?
Topics not being debated tonight: Will (gate model) quantum computers ever be built? Both debaters believe that they will be.
Venues (in inverse chronological order): (sorry for the preponderance of Lubos links, but, shit!, the guy does have stamina, and, unlike Lubos, no complexity theorist has reviewed Scott’s book in their blog, so far, that I know of)

## May 1, 2013

### “Quantum Computing Since Democritus” (Cover of Czech Edition, the Lubos Motl translation)

Filed under: Uncategorized — rrtucci @ 9:47 pm

Scott Aaronson at Work

### Pooch Interpretation of Quantum Mechanics and Doggie Q-Spectacles

Filed under: Uncategorized — rrtucci @ 5:58 pm

For more than a decade, John Preskill has been illustrating Bell’s inequality and related concepts with pictures of balls of two colors (red and green) that can be inserted into a box with two doors, door 1 on the top side, and door 2 on the front side. Here is a small sample of his art work:

Personally, I prefer explaining Bell’s inequality using Bayesian networks. It’s clearer that way, at least to me. I’ve been explaining Bell’s inequalities that way ever since I wrote the manual for my software Quantum Fog more than a decade ago. I’ve also explained them that way previously in this blog in the post entitled “Bell’s inequality for the Bayesian statistician“. Here is a sample of my art work from that previous blog post of mine:

John’s fine art work has made me realize that mine is grievously lacking in empathic cues (i.e., it’s pretty dull). If I had to give a public lecture accessible to non-scientists, I would fail miserably, unless…I enhanced the bayesian networks experience by adding some dog pictures. (if you are a quantum complexity theorist, instead of dogs, you might prefer to add some pictures of yourself in various dashing poses.)

As shown by the above figure of a Bayesian network, Bell’s inequality leads us to consider a variable $x_j^{\alpha_1}\in \{0,1\}$ where $j=1$ for Alice and $j=2$ for Bob. $\alpha_1\in \{A,B,C\}$ denotes the axis along which Alice measures the spin and $\alpha_2\in \{A,B,C\}$ the one for Bob. (For the CHSH inequality, one has $\alpha_1\in \{A,B\}$ and $\alpha_2\in \{A',B'\}$ instead.)

The pooch interpretation of quantum mechanics posits that there are three dogs named Alice, Bob and Mimi that have poor eyesight and require spectacles in order to see/measure an atom, which looks to them like a fuzzy glob without their spectacles on, but which looks like either a cat or a squirrel with the spectacles on. Each dog can wear either spectacles A, B or C, but each of those spectacles gives a different ratio of squirrel to cat sightings for the same neighborhood!

(Previous work: Dogs Playing Poker)

The “Preskill’s 2 balls” model can be mapped into the pooch model as follows.

Replace persons Alice, Bob and Eve by spectacle-wearing dogs named Alice, Bob and Mimi.

Alice

Bob

Mimi

Replace doors 1,2,3… by spectacles with lens types labeled A,B,C, etc. A and B might correspond to linearly polarized and circularly polarized.

Replace red and green balls by pictures of a cat and squirrel. These might correspond to the measurement values of 0 or 1 for the state of a qubit.

Squirrel!! Ruff, Ruff

Cat!! Ruff, Ruff

Here is a summary in tabular form of these 2 leading interpretations of quantum mechanics

 Variables Preskill’s model Pooch model $j\in \{1,2, M\}$ (Persons) Alice, Bob, Eve (Dogs) Alice, Bob, Mimi $\alpha\in \{A,B,C\}$ doors 1,2,3 spectacles A, B, C $x_j^\alpha\in\{0,1\}$ green, red balls cat, squirrel

And here is monogamy for dogs:

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