Quantum Computing for Beginners

A class for quantum enthusiasts

Chapter 3 public release

Chapter 3 is now publicly available, in which Paul Dirac teaches you about vector spaces, inner products, and orthonormal bases.

Illustration by Stephen Rice.

Chapter 4 is also available for unlocking if you are registered for the class.


Chapter 2 public release

Chapter 2 is now available for public download, in which we meet our heroes, Alan Turing and Richard Feynman, and they have the seed of the idea to use quantum physics for building computing machines.

Chapter 3 available for unlocking

Chapter 3 is now available for unlocking, where we finally learn how to combine single qubits into a multi-qubit register, and Dirac arrives in Goettingen for Bohr’s lecture marathon. If you are in the class, please email me your solutions to unlock this chapter.

Nobel Prize in Physics

The Nobel Prize in Physics was announced today, and it was awarded to two experimental physicists working on quantum computing: Dave Wineland, an American at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, and Serge Haroche at the College de France. Wineland has done groundbreaking work on using trapped atomic ions as quantum bits, and Haroche has done analogous work for using photons, which are quanta of light.

The prize is well-deserved by both physicists, and this is exciting news for them and the entire field of quantum computing!

Bloch sphere simulators

There are two Bloch sphere simulators that I know of available on the internet to help you visualize what happens geometrically to a qubit as a point on the surface of a Bloch sphere as well as what happens algebraically to its complex matrix elements.

The first is written in Java by Stephen Shary and Marc Cahay at the University of Cincinnati.

The second is written in Wolfram’s Computable Docment Format and requires a plugin to run.

For the purposes of this class, we won’t be covering in more detail the relationship between the geometric rotation angle and the form of the 2×2 matrix which corresponds to a single-qubit quantum gate. However, interested readers can find out more in Dave Bacon’s lecture notes, under Section 1: One Qubit. In other sources, this relationship is called the homomorphism between the groups SU(2) and SO(3), if you want to research the topic on your own, on Wikipedia or in math textbooks.

Chapter 2 available for unlock

Chapter 2 (In which we meet Turing and Feynman) is now available for unlocking if you are in the class.

You have to successfully turn in Chapter 1 homework in order to plant the idea of a quantum computer in the minds of Alan Turing and Richard Feynman.

Here are some tantalizing illustrations by Stephen Rice.

Chapter 1 public release

I’ve decided to release the chapters publicly a week or two after the students have received them.

Here is chapter the first, in which Elina meets Ehrenfest, Planck, and a quantum bit.  I’ve included some of Stephen’s great illustrations below to entice you. Any and all feedback is welcome.

Anonymous feedback form

If you’d like to give me comments, questions, and suggestions about the class without revealing your identity, please use this nifty new Catalyst anonymous e-mail form. There’s no way for me to reply to you directly, but I’ll try to address any feedback I receive in class, on the mailing list, or on this blog if appropriate.

Otherwise, you can just e-mail me at my normal school address: ppham at cs dot washington dot edu.

First class meeting

Quantum computing for beginners has begun! I was very pleased with the first class meeting this past Tuesday. Students came up with really creative examples of analog computers (in nature and man-made), probabilistic machines, and systems which failed to operate outside of their designed environments. I’ll ask them to post some of their ideas in the comments. The main point of the lecture is that computation is physical.

What I want to do in the class is help develop physical intuition. As computer scientists, we are not used to dealing with physical objects that take up space, have mass, dissipate energy. We are used to creating virtual worlds, to defining the rules for the universe and executing a program for the computer to work out the consequences and enforce these rules. It may be frustrating or repetitive for you to see so many examples, when you are used to abstracting out the general principle. But details are powerful, and at the beginning it’s not clear what you are trying to abstract away and what is essential that you are trying to keep. Details add color and spice, details help you remember. Rather than giving you facts, I want you to have a felt experience of computation.

Here are the Lecture 1 slides (Chapter 0), and now some special bonus notes, like the extra features on a DVD. First, a correction. Aram pointed out that I said the FERMIAC was built before the ENIAC, but in reality, Fermi designed and built it during the period when the ENIAC was being moved and non-functional. Thanks to him, and also to Lukas Svec for telling me about the Fermiac in the first place and machining an actual replica in the UW Physics machine shop!

Some bibliography links:

Bloch sphereEnigma machine photographUW Blinov ion trap group photoPhotosynthesis photoFlock of birds photoReview article on functional quantum biology, including photosynthesisArticle on avian compassSteiner tree soap bubble analog computerSlime mold solving a mazeCrab nebula pulsar as taken by Chandra, Spirals in pine cone seeds follow the Fibonacci sequence

Some of you may be wondering why I am spending so much time talking about the people, stories, and events surrounding the birth of quantum physics and computer science. Isn’t it enough to learn the abstract models and mathematics and write some code? There are a few reasons to care about the history and culture surrounding scientific discoveries.

First of all, science doesn’t happen in a vacuum, and human beings in the 1940s are pretty much the same as human beings today. Learning about their motivations, fears, and desires, both in research and in their personal lives, can help us understand where their ideas came from, including their limitations. My two advisors, Dave and Aram, who taught previous quantum computing classes, are fond of saying that quantum computers would have happened much sooner if the very scientists developing it had not been so stubborn in clinging to classical intuitions and classical ways of thinking. But alas, it’s easy for us to say. Even today, quantum physics is still highly non-intuitive. We didn’t grow up with quantum at medium scale of human life, the way we experience a ball bouncing on the ground or an apple falling out of a tree. By the way, Chris Fuchs has a great book titled “Coming of age with quantum information” which I misremembered as “Growing up with quantum”. Dave lent it to me once, and it was a great spring break read.

Second of all, they can also inspire us to make new discoveries. These discoveries may be more recent, but they are not more modern. The scientific method, and the curiosity that drives it, are exactly the same today as they were during the Enlightenment and in the ancient world.

Third, scientists are human beings embedded in history. I’m sure some quantum physicists in the 1930s wanted to ignore politics and were very annoyed when WWII broke out and they could no longer freely travel and talk to their other scientist friends. We are embedded in the history of the future. Students in the year 2100 will wonder why we took so long to build a quantum computer, too. So pay attention!

And finally, history is fun, and I said so. Okay that’s all.

Chapter 1 released

I sent out Chapter 1 of the story and the corresponding homework out to the class mailing list. Students, please let me know if you don’t receive it!

Again, I’d like to give a shout out to our fantastic illustrator, Stephen Rice, who has been very understanding with my last-minute requests.

In the future, I’ll only bring printed copies to hand out in class after we have all discussed the homework and unlocked the next chapter.