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Quantum Class 5, Mon 2021-09-13

Source

1 Homework 4

here, due Thurs.

2 Quantum computing in the news

(or at least on Slashdot).

  1. https://yro.slashdot.org/story/21/09/04/2147245/americas-nsa-isnt-sure-quantum-computers-will-ever-break-public-key-encryption

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

5.2 IBM quantum computing

  1. A Qubit in the Making (2:01) https://www.youtube.com/watch?v=2pB87H3_F_c&list=PLOFEBzvs-VvpzQnlazij7cL1mjKvJTAwk&index=10&t=0s

  2. Behold the Mighty Qubit (2:51) https://www.youtube.com/watch?v=_P7K8jUbLU0&list=PLOFEBzvs-VvpzQnlazij7cL1mjKvJTAwk&index=10

  3. They have several quantum computers.

  4. The older ones are freely available on the web.

  5. Those have 5, 15 or more qbits; see https://quantum-computing.ibm.com/

  6. Note that you can put gates between only adjacent qbits.

  7. You submit a batch job and get emailed when it runs.

  8. IBM github site: https://github.com/Qiskit with

    1. a free simulator.

      It doesn't match all the physical complexity of the real computer, but it's a good start.

    2. and tutorials and presentations.

  9. and a SW development framework. https://qiskit.org/

  10. You can create a quantum computation program either by

    1. designing a circuit, or

    2. using a programming language.

5.2.1 Sites

  1. https://qiskit.org/

    1. You can install it on your machine.

    2. Create and run the demo program.

    3. Try the Getting Started tutorial.

      Since I'm still learning, I have to say circ.draw() not circ.draw('mpl')

  2. https://www.ibm.com/quantum-computing/

    1. Browse around the website.

    2. Look at the topologies of some machines.

    3. Create an account for yourself.

    4. Play with the graphical composer.

    5. Submit a job.

    6. Look at the output.