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Quantum Class 5, Mon 2022-09-12

1 Homework 4

You talk next Mon. See here.

2 Quantum computing in the news

(or at least on Slashdot).


3 Abstract computation models ctd

  1. Original motivation was to discover an algorithm for proving (or disproving) theorems.

  2. That can be done in some simple cases, like first order predicate calculus with addition over the integers.

    1. and first order predicate calculus with addition and multiplication over the rationals or reals.

  3. This goal failed because it was proved that it is undecidable in some cases.

    1. like first order predicate calculus with addition and multiplication over the integers.

    2. Some theorems truth or falsity depends on the allowable domain of their variables.

    3. in a deep sense, ints are harder than reals.

    4. Long time ago I wrote a paper on this, in the context of computer graphics. Problems with Raster Graphics Algorithms.

4 Complexity classes

  1. Group problems into broad classes of considerably differing difficulty.

  2. P vs NP.

  3. Steve Cooks's paper first describing this was rejected.

  4. Quantum complexity classes.

5 Hardware implementations

  1. Quantum computation was theoretically started decades before actual quantum computers were designed.

  2. Just like classical computers.

  3. Many competing technologies.

  4. Let the strongest win.

5.1 Superconducting qubits

  1. Dilution fridge: cool by mixing He3 into He4.

  2. Cooper pairs of electrons: pairs of electrons in a metal weakly attract each other. It's a quantum effect.

  3. Josephson Junction.

  4. good ref: A Quantum Engineer's Guide to Superconducting Qubits

5.1.1 Transmon qubit

  1. Sutor: Under the hood of IBM Q

  2. The transmon qubit | QuTech Academy 6:03.

  3. Alexandre Blais - Quantum Computing with Superconducting Qubits (Part 1) - CSSQI 2012 45:11.

  4. Control of transmon qubits using a cryogenic CMOS integrated circuit (QuantumCasts) 35:47.

5.2 Trapped Ion


  2. Proponents say that it's better than transmon qbits.

  3. Trapped-ion qubit, the maglev train of a quantum computer, 9:34, 2021-08-24.


    "To date, we’ve run single-qubit gates on a 79 ion chain, and complex algorithms on chains of up to 11 ions."

5.3 Quantum annealing

  1. This is not comparable to quantum gates and circuits like IBM has.

  2. It minimizes a function by testing many solutions in parallel.

  3. See details in the D-Wave section.

  4. Qbit count is not comparable to gate models.


  6. They make a different type of quantum computer, called a quantum annealer. They have been in the news lately, e.g.,


  8. What is Quantum Annealing? 6:14.

  9. How The Quantum Annealing Process Works 6:09.

  10. Quantum Programming 101: Solving a Problem From End to End | D-Wave Webinar 54:25.

    "Want to learn how to program a quantum computer? In this webinar, we explain how to do so by running through a complete, simple example. We explain how to formulate the problem, how to write it, and how to tune it for best results. "

    "This webinar is intended for those with little or no experience programming on a D-Wave quantum computer. After watching, get free time on Leap, the quantum cloud service at "

  11. Slides from Programming Quantum Computers: A Primer with IBM Q and D-Wave Exercises by Frank Mueller, Patrick Dreher, Greg Byrd held at PPoPP (Feb 2019) ASPLOS'19 (Apr 2019),

    Part 3: D-Wave -- Adiabatic Quantum Programming

  12. D-Wave factoring tutorial and other demos

    including Jupyter notebooks (you have to login for them).

5.4 Photonics

  1. Xanadu Quantum Cloud


  3. Uses photonics.

  4. Operates primarily at room temperature.

  5. Up to 24 qbits, gate depth of 12.

  6. Has free SW tools, some of which can compile to other quantum technologies.

  7. Expected good applications: graphs and networks, machine learning, and quantum chemistry.

  8. They expect to scale up better than competing technologies.

  9. Operates at room temperature.