Quantum Bayesian Networks

October 3, 2017

A Microsoft Quantum Computing language by any other name would smell as badly

Filed under: Uncategorized — rrtucci @ 3:31 am

On September 25-29, 2017, Microsoft held its IGNITE conference at Orlando, FL. Arstechnica reported about IGNITE here. They usually publish quantum computing articles that are more balanced and well informed than the average sci-tech popular journal. This time though, I think Arstechnica dropped the ball badly. This article sounds to me like a glorified infomercial for MS. However, I did learn a few curious facts from it.

The article reports that MS intends to release by the end of this year a “quantum programming language—as yet unnamed” for programming quantum computers. The language will be distributed with Visual Studio and available on Azure, the MS cloud service. Let me henceforth call it language Q?#. The article gives the following snapshot of a quantum teleportation circuit written in this marvelous new language. A Rube Goldberg machine language if I ever saw one. Also, sounds like this ugly baby is going to be CLOSED SOURCE, just like LiquiD. (Click image to enlarge)

Mysteriously, no mention is made of Liqui|>, MS’s previous “quantum programming language”. Since Q?# comes a short time after Liqui|> and Dave Wecker is the main author of both, it is safe to assume that Q?# is just a new wrapper with Liqui|> under the hood. (Some have gone so far as to suggest that the new language should be called LiquidShit#).

But friends, Romans, countrymen, lend me your ears. I have come here to bury Q?#, not to praise it. Next, I will show the code for the same quantum Teleportation 3 qubit circuit, but written instead in IBM’s qasm language and in Qubiter’s language.

IBM’s github repository called qiskit-tutorial has a Jupyter notebook for this same teleportation circuit. Here is a snapshot taken from the notebook showing IBM qasm for the teleportation circuit.

The Qubiter repo at github also has a Jupyter notebook for the same teleportation circuit. Here is a snapshot taken from the notebook showing Qubiter’s English and Picture files for the teleportation circuit.

And now, let me indicate a few reasons why I think Qubiter (which I wrote) is nicer than the other two.

  • Qubiter allows one to write controlled gates with any number of controls, and the controls can be of two types T or F. (T controls are usually represented in latex pictures of quantum circuits by a solid dot, F controls by a hollow dot). Qubiter also has subroutines that allow one to expand each gate with multiple controls into a sequence of gates with only one or zero controls, because those simpler gates are the only type of gates that most hardware devices can perform physically. IBM’s qasm so far only allows one or two controls of type T only. They have CNOT and CCNOT and that’s it.
  • Qubiter automatically generates an ASCII picture of the circuit at the same time that it generates its English qasm-like file. IBM’s q-software and LiquiD do not write a picture of the circuit automatically. If they draw a circuit, it requires a separate run to generate it and the picture is in Latex. Also, their circuit pictures have time running from left to right instead of downwards. Qubiter’s English and Picture files, on the other hand, have the highly desirable properties–especially desirable for long circuits–that (1) time runs downward in both English and Picture files, and (2) line number n in the English file corresponds to line number n in the Picture file.
  • IBM qasm and LiquiD distinguish between quantum and classical registers. Qubiter only has quantum registers. Classical registers are an unnecessary, ugly complication because the information stored in them can be stored in the memory of your pc.

Two other languages, Rigetti’s PyQuil and ProjectQ, are similar to IBM qasm and suffer from some of the same architectural design flaws mentioned above.

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2 Comments »

  1. The motivation for classical registers in PyQuil, according to Rigetti’s Will Zeng, is because they want to bring those as close as possible to the quantum chip, i.e. you’d essentially program a hybrid quantum/classical “chip”.

    Comment by Quax — October 3, 2017 @ 4:55 am

  2. If you think about it, Will Zeng’s explanation makes no sense whatsoever. It’s as nonsensically as saying that Trump’s tax plan will not benefit the rich.

    The real reason why Will distinguishes between quantum and classical registers is that he was copying what other people have done before, pure and simple. He was copying IBM qasm, which was copying ProjectQ, which was copying probably Omer’s QCL or whatever.

    Comment by rrtucci — October 3, 2017 @ 5:18 am


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