Engineering tour de force births programmable optical quantum computer

Re:Engineering tour de force births programmable optical qua... by foxes on Thursday September 06, 2018 @10:39AM (#17926626)

I like optical quantum computing, it feels hands on, like it's almost something you could build in your garage. Linear optical quantum computers just need waveguides, beam splitters, phase shifters and mirrors (no disrespect - I know it's not trivial to make work). You set up your circuit and fire your light through it and measure the system at the end.

It's a nice way to think about quantum computing. You aren't allowed to do any measurements half way or you will destroy your superposition. It's a bit like a pure function, no IO allowed until the very end.

Also I know three of the people on the paper, good to see them getting some mainstream attention for a nice result.

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Re:Engineering tour de force births programmable optical qua... by vtomole on Thursday September 06, 2018 @10:47AM (#17926674)

> You aren't allowed to do any measurements half way or you will destroy your superposition.

This is true of all quantum computations. It doesn't matter what the underlying hardware is.

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Re:Engineering tour de force births programmable optical qua... by Strilanc on Thursday September 06, 2018 @10:57AM (#17926736)

It's actually extremely common for quantum algorithms to have measurement operations halfway through. But they apply to individual qubits, not the whole system.

For example, error corrected quantum computation involves continuously measuring particular stabilizers in order to catch when they flip. Another example: measurement can reduce the cost of uncomputation (e.g. [1]).

[1]: https://quantum-journal.org/papers/q-2018-06-18-74/

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Re:Engineering tour de force births programmable optical qua... by foxes on Thursday September 06, 2018 @10:55AM (#17926722)

Yes you are right, I wasnt clear, just that it seems nicer to visualise as a physical thing in an optical circuit.

Also remember that you have to perform measurement multiple times. It produces a probability distribution, so you need to be confident you have the right answer.

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Re:Engineering tour de force births programmable optical qua... by de_watcher on Thursday September 06, 2018 @10:54AM (#17926716)

> This is true of all quantum computations.

And also for half of my non-quantum debugging...

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Re:Engineering tour de force births programmable optical qua... by deepnotderp on Thursday September 06, 2018 @11:29AM (#17926964)

I also like photonic quantum computing.

Unfortunately the success rate of two photon quantum gates is crushingly low.

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