Author: dabacon

Posted on

Condensed Matter & Atomic Seminar

Today’s talk, powerpoint posted once I touch up the presentation:

04:00 PM
Condensed Matter & Atomic (CMA) Physics Seminar
Dave Bacon, University of Washington, Computer Science & Engineering
Building Robust Qubits Using Many-Body Strongly Interacting Quantum Systems
C-421, PAT (Physics)
The late Rolf Landauer liked to say that “information is physical.” By this he meant not that the abstract concept of information has anything to do with the laws of physics, but instead that it is physics which determines whether a device can robustly store and manipulate information. Thus, for instance, the robust storage of bits on hard drives is possible only because of the statistical physics of magnetic domains. In this talk I will discuss how this point of view should change the way we envision constructing devices which robustly store and manipulate quantum information. In particular I will discuss many-body quantum systems whose physics serves to replace the micro architecture of quantum error correction normally envisioned as necessary for building robust qubits. Along the way I will explain the basic ideas of topological quantum computing using anyons along with new ideas for self-correcting qubits in a three-dimensional quantum compass model.

Update: Talk is now posted here.

Posted on

Arxiv Links to Pontiff, Science at an End?

Alicki, Lidar, and Zanardi have put out version two of their paper critiqueing the assumptions of the threshold theorem for fault tolerant quantum computation. The new title of their paper is “Internal Consistency of Fault-Tolerant Quantum Error Correction in Light of Rigorous Derivations of the Quantum Markovian Limit” and is found at quant-ph/0506201. Discussions about the paper, can be found at the previous posts here and here. I’m a little streched write now to give it a good reading, but I do hope to do so in the next few days (after I finish the four talks I need to write, grade homeworks, and write the homework solution set.)
But I do think it is awesome that in the comment section on the abstract on arxiv.org, the following comment appears:

Comments: 19 pages. v2: Significantly expanded version. New title. Includes a debate section in response to comments on the previous version, many of which appeared here this http URL and here this http URL Contains a new derivation of the Markovian master equation with periodic driving

Which is now my favorite comment on an arxiv paper 🙂
Of course, it just isn’t fair competition for the greatest comment ever when you are battling up against the comment producing machines known as Chris Fuchs and Steven van Enk:

quant-ph/0205039 [abs, ps, pdf, other] :
Title: Quantum Mechanics as Quantum Information (and only a little more)
Authors: Christopher A. Fuchs (Bell Labs)
Comments: 59 pages, 5 figures, 140 equations, one simple idea

and

quant-ph/0204146 [abs, ps, pdf, other] :
Title: The Anti-Vaxjo Interpretation of Quantum Mechanics
Authors: Christopher A. Fuchs
Comments: 18 pages, not one equation. Requires sprocl.sty

and

quant-ph/0507189 [abs, ps, pdf, other] :
Title: |0>|1>+|1>|0>
Authors: S.J. van Enk
Comments: A more serious version, almost 2.36 pages, but still an unnormalized title
Journal-ref: Phys. Rev. A 72, 064306 (2005)

and

quant-ph/0410083 [abs, ps, pdf, other] :
Title: Quantifying the resource of sharing a reference frame
Authors: S.J. van Enk
Comments: Updated title as PRA did not accept the word “refbit” in the title: PRA accepts neither neologisms (=”a meaningless word coined by a psychotic”, according to Webster), nor novophasms
Journal-ref: Phys. Rev. A 71, 032339 (2005)

and

quant-ph/0207142 [abs, ps, pdf, other] :
Title: Phase measurements with weak reference pulses
Authors: S.J. van Enk
Comments: 5 pages, 5 figures. I apologize for this boring paper
Journal-ref: Phys. Rev. A 66, 042308 (2002)

Posted on

CSE 599d Lecture Notes 16,17,18, and 19

The latest additions will probably have lots of errors (well even more than my normal notes!) as I haven’t taught from these notes yet and I always find errors when I teach. (Plus they are on error correction!) But this completes this set of notes for this quarter. I’ll probably give these notes a good reading over sometime in the next month to correct all of the silly (and substantial) errors in the notes. I think I covered just about what I thought I would cover. We won’t get to quantum cryptography, but really to do this I’d need to spend some lectures on purification protocols and discuss some basic information theory to get at the Preskill-Shor proof of security. Unfortunately if I’m going to do this I probably would have to do it over a two quarter quantum computing course (for such a course I would add results on quantum communication complexity, and a lot of the basics of quantum information theory…certainly there is not a lack of subject to spend two quarters on!)
Actually the next class I really want to teach is a class on the representation theory of finite and Lie groups and quantum information science. Maybe next year (next quarter I teach “Introduction to Digital Design” No, not quantum digital design ;))
Lecture Notes
Lecture Notes 1: Introduction and Basics of Quantum Theory
Lecture Notes 2: Dirac Notation and Basic Linear Algebra for Quantum Computing
Lecture Notes 3: One Qubit, Two Qubit
Lecture Notes 4: The No-Cloning Theorem, Classical Teleportation and Quantum Teleportation, Superdense Coding
Lecture Notes 5: The Quantum Circuit Model and Universal Quantum Computation
Lecture Notes 6: Reversible Classical Circuits and the Deutsch-Jozsa Algorithm
Lecture Notes 7: The Recursive and Nonrecursive Bernstein-Vazirani Algorithm
Lecture Notes 8: Simon’s Algorithm
Lecture Notes 9: The Quantum Fourier Transform and Jordan’s Algorithm
Lecture Notes 10: Quantum Phase Estimation and Arbitrary Size Quantum Fourier Transforms
Lecture Notes 11: Shor’s Algorithm
Lecture Notes 12: Grover’s Algorithm
Lecture Notes 13: Mixed States and Open Quantum Systems
Lecture Notes 14: Quantum Entanglement and Bell’s Theorem
Lecture Notes 15: When Quantum Computers Fall Apart
Lecture Notes 16: Introduction to Quantum Error Correction
Lecture Notes 17: The Quantum Error Correcting Criteria
Lecture Notes 18: Stabilizer Quantum Error Correcting Codes
Lecture Notes 19: Fault-Tolerant Quantum Computation and the Threshold Theorem
Homework
Homework 1
Homework 2
Homework 3
Handouts
Syllabus

Posted on

2106…

Most people in quantum information science try to be sensitive to not overhyping the field. (Okay, so I get a little breathless sometimes!) This, however, is pretty amusing. I especially like

But could you imagine not using a Quantum Computer to come up with the most efficient sequence of nanobots to administer the cure to cancer.

Quantum-nano-bio!
Update: Jon brings up in the comments the word “quantum leap.” I have always found it amusing that in the Oxford English dictionary uses this example from 1977, as one of the early uses:

New Yorker 13 June 108/2 The imperial Presidency did not begin with Richard Nixon although under him abuses of the office took a quantum leap.

Of course once you find this out, you are at the OED website and you can’t help finding words like “quaquadrate” which means a sixteenth power.

Posted on

CSE 599d Lecture Notes 13,14 and 15

Hindsight I taught things a bit out of order. What I should have done was do entanglement after Grover’s algorithm. Then it would have been nice to have a lecture on quantum communication complexity, but seeing as how things are rapidly heading towards the end (four more lectures to go) and I want to get to the threshold for fault-tolerant quantum computing I decided not to keep this. So the next lectures will introduce quantum error correction, deduce the quantum error correcting criteria, discuss classical linear and then CSS codes, discuss stabilizer codes, and then more on to fault-tolerant constructions. We might just make it.
Lecture Notes
Lecture Notes 1: Introduction and Basics of Quantum Theory
Lecture Notes 2: Dirac Notation and Basic Linear Algebra for Quantum Computing
Lecture Notes 3: One Qubit, Two Qubit
Lecture Notes 4: The No-Cloning Theorem, Classical Teleportation and Quantum Teleportation, Superdense Coding
Lecture Notes 5: The Quantum Circuit Model and Universal Quantum Computation
Lecture Notes 6: Reversible Classical Circuits and the Deutsch-Jozsa Algorithm
Lecture Notes 7: The Recursive and Nonrecursive Bernstein-Vazirani Algorithm
Lecture Notes 8: Simon’s Algorithm
Lecture Notes 9: The Quantum Fourier Transform and Jordan’s Algorithm
Lecture Notes 10: Quantum Phase Estimation and Arbitrary Size Quantum Fourier Transforms
Lecture Notes 11: Shor’s Algorithm
Lecture Notes 12: Grover’s Algorithm
Lecture Notes 13: Mixed States and Open Quantum Systems
Lecture Notes 14: Quantum Entanglement and Bell’s Theorem
Lecture Notes 15: When Quantum Computers Fall Apart
Homework
Homework 1
Homework 2
Handouts
Syllabus

Posted on

CSE 599d Lecture Notes 11 and 12

We’ve reached the Shor and then searched for a needle in a quantum haystack.
Lecture Notes
Lecture Notes 1: Introduction and Basics of Quantum Theory
Lecture Notes 2: Dirac Notation and Basic Linear Algebra for Quantum Computing
Lecture Notes 3: One Qubit, Two Qubit
Lecture Notes 4: The No-Cloning Theorem, Classical Teleportation and Quantum Teleportation, Superdense Coding
Lecture Notes 5: The Quantum Circuit Model and Universal Quantum Computation
Lecture Notes 6: Reversible Classical Circuits and the Deutsch-Jozsa Algorithm
Lecture Notes 7: The Recursive and Nonrecursive Bernstein-Vazirani Algorithm
Lecture Notes 8: Simon’s Algorithm
Lecture Notes 9: The Quantum Fourier Transform and Jordan’s Algorithm
Lecture Notes 10: Quantum Phase Estimation and Arbitrary Size Quantum Fourier Transforms
Lecture Notes 11: Shor’s Algorithm
Lecture Notes 12: Grover’s Algorithm
Homework
Homework 1
Homework 2
Handouts
Syllabus

Posted on

Jesi

And now for something inappropriate.
Tonight I was watching the Stephen Colbert Report and his word of the day was “Jesi.” Damnit I have been using that word for years, and now Colbert has stolen it from me! Stolen, you ask? Indeed, if you look at Wikipedia it says that “Jesi is also the plural form of Jesus, according to Stephen Colbert.” (oh and it is also town in Italy.) But I’ve been using Jesi for ages to describe what would happen if you cloned Jesus from the Shroud of Turin. The result of this experiment is that you would have lots of Jesi. Actually you would be amazed at how useful this word is in theological arguments (of which I’m usually on the losing end, so what do I know.)

Posted on

Did He Just Say "Quantum Coherence"?

As noted by JoAnne at Cosmic Varience, the Director of the Office of Science and Technology Policy took emailed questions about last night’s comments concerning science funding made by U.S. President George Bush in his state of the union speech. Not since Al Gore explicitly mentioned quantum computers have quantum computers made it so close to the spotlight! In particular we read:

Collin, from Chicago writes:
What is the White House definition of ‘Basic Science’ the funding of which the president proposed to double in 10 years? For example, does the definition (and proposed doubling) include particle physics? What about nano technology? And a mission to Mars? Thanks.
John Marburger
The American Competitiveness Initiative identifies three priority agencies that are critical to basic research in the physical sciences that provides the foundation for future economic competitiveness. Areas like nanotechnology, information technology, materials science, and quantum coherence will be an important part of the initiative. Particle physics and space exploration are important, but not necessarily a focus of the Initiative.

Quantum coherence. That’s like almost quantum computing, right? (My favorite description along those lines are the words “quantum manipulation”…reminds me of someone trying to manipulate someone else’s wave function.)
On the same topic, you can find, here a press conference with a few more details. My favorite part of that press conference is

Q Is our Secretary of Education ill-equipped to help her own daughter with algebra? (Laughter.)
SECRETARY SPELLINGS: There’s the point, Ken. We need a math initiative for grown-ups like me. I’m going to see you like that, Elaine. (Laughter.)

Posted on

Physics Blogs

Click here to find, at PhysicsWeb, the Quantum Pontiff making an idiot of himself:

“It often becomes necessary, in a world where there is so much garbage floating around, to advertise your work,” says Bacon. “Blogging, to me, is no worse than giving a talk at a conference.”

Okay, that didn’t come out exactly as I wanted it too.