Screwing Up on Quantum Computing

Well, I screwed that up.

In the next Physics Frontiers podcast, recorded about six months ago (approx. 1/27), Randy and I talked about photonics and quantum computing. The papers we read were very interesting and we had a good time talking about them, although we got a little bit confused (as my memory serves me, I believe that happens in the next episode as well). During the episode I went off on three digressions that I probably shouldn't have: science fiction, quantum computing, and economics and politics. I cut out all of the economics and politics bits (again). I left in the quantum computing, and that's what this is about.

I first read a journal article and had discussions with reasonably technical people about quantum computing in the 90's, before 1998 and after 1995 based on the people I was talking to. The whole idea that someone could construct an algorithm for a computer of a type that didn't exist yet really intrigued me at that point, and since one of my majors was "theoretical mathematics" (I think that's what the track name for all that abstract algebra and number theory stuff was at that school), figuring things about like how to factor large numbers very quickly was interesting to me. The applications to cryptography, not so much. But, the state of the art at that time was a sheet of paper and a proof, so my marginal interest in the subject didn't really go anywhere.

I've occasionally looked in on quantum computing from time to time since then. I've read a couple of technical books on the subject, for example, and I'll read articles about it when I actually have time to crack open one or two the Science and Nature magazines that clutter up my office. So, although I'm certainly not an expert (I'm not an expert about anything we talk about on Physics Frontiers), I certainly didn't think anything really astounding had happened. I was pretty sure a couple of people had put together a small number of qubits in one or the other of the ultracold settings.

I had no idea that Google and IBM had them up and running.

That's what my phone told me today, about lunchtime.

I think that I had heard that quantum computer simulators existed, and so some of my comments were just thoughtless ("people who design algorithms for computers that don't exist and then mathematically prove they'll run correctly" or something like that), but the fact that IBM has a 17 bit quantum processor up and running and they're giving people beta access with an SDK for Python makes some of my comments laughable. And of course, Google's up to the same thing.

It's amazing how fast these things are developing.

Oh well. The episode's already short, so I won't edit anything more out. You can just hear me babble from the past about things in the future.

Now, how can I get into that IBM beta?

List of Requirements for Gravitational Theories

Here it is without fanfare. If you have any questions about any part of it, please comment in the comments:


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To be theoretically consistent and compatible with experiment, a theory of gravitation must:

1. Predict correct cosmological dynamics
1. Big bang nucleosynthesis
2. Produce the correct evolution of cosmological perturbations
1. Cosmic microwave background
2. Large scale structure
3. Have the correct weak-field limits
1. Reproduces Newtonian Mechanics
2. Predicts post-Newtonian experiments in weak field
3. Produces stable solutions
1. Matter-side instabilities (Dolgov-Kawasaki)
1. Ground states should be highly symmetric
2. Gravity-side instabilities
1. Stable de Sitter solutions
3. Stability of the first loop in quantum gravity
4. Stability in the face of inhomogeneous but isotropic perturbations
5. Black hole nucleation
4. Not contain any ghost fields
5. Admit a well-posed Cauchy problem
6. Reasonable theory of gravity waves
   

Physics Frontiers

Randy and I have started up a companion podcast, Physics Frontiers, with shorter discussions of topics in physics. Check it out! Show notes at the Physics Frontiers website.

Schrodinger's Cat

I've put together a video describing Schrodinger's cat and explaining why its important to have an interpretation of quantum mechanics.  It doesn't give any answers, just explains why the question is so important.  We overview some of the answers in the next podcast, which I will hopefully get up tomorrow (I'm putting in the breaks right now.  I need to record the intro and upload it, so it's pretty likely).

Plus, I drew the pictures.

Videos

I've got the first of the explanatory videos up. Randy and I have talked about putting up videos to help explain what is going on in the experiments for almost a year now. It can be really hard for someone to visualize what's happening in the experiments for the paradoxes just from our description. I've even found that in writing descriptions: the more precise someone describes something, the harder it is for someone else to understand it.

That's just not how we talk.

Unfortunately, the vaguer the description the more easily the listener misconstrues what is being said. And it turns out it's not an easy needle to thread: it takes many years for someone to be able to reliably read a geometrical description of a problem without getting confused.

But never fear, video is here! I can draw out what I want to talk about for you, as I have in this video.

Measurement and Compensation

Unfortunately, I deleted much of the intro. I'll fix it later.

e-mail me if this is still here after September. Thanks!

In this episode, we talk about Aharonov and Rohrlich's Quantum Paradoxes, chapter 8: "Measurement and Compensation":



Please comment on our subreddit! It will help us respond to what you're saying if we can collect all the comments in the same place.

We're reading Quantum Paradoxes by Yakir Aharonov and Daniel Rohrlich. This is a technical book that is making an argument for a specific interpretation of quantum theory. The first half of the book uses paradoxes to explore the meaning of quantum theory and describe its mathematics, then after interpretations are discussed in the middle chapter, an interpretation of quantum mechanics is explored with paradoxes based on weak quantum measurements.

Early Edition Is Up!

I finally got Show 8 mostly edited and uploaded to Patreon. As per my promise there, I won't publish it here for a day or two, but I've got both of those working. Last month I tried to put up the special discussion we had on quantum interpretations and had a lot of problems for no known reason. Now that I've got that working, I'll try putting that up again in about two weeks. Show 8 is the first show that goes up early, so I wanted to inform people that I'd made the Patreon feed work the way it's supposed to. This is the last time I'll post about Patreon here unless there is some important change.