[ExI] John Preskill on Quantum Computing

John Clark johnkclark at gmail.com
Thu Jun 14 16:55:59 UTC 2018

On Wed, Jun 13, 2018 at 10:03 PM, Adrian Tymes <atymes at gmail.com> wrote:

>> Given that Preskill is one of the world's leading experts on
>> quantum information and is the Richard J Feynman Professor of
>> Theoretical Physics at the California Institute of Technology

> ...*is an appeal to authority, and says nothing about the statements
> to which I objected.*

An appeal to authority is not always without merit. If a professor of
physics at Caltech says something about physics and Adrian Tymes says he's
dead wrong and is just spewing pablum I think it is a tad more likely
that Mr. Tymes has misunderstood the professor than that the professor has
misunderstood physics.

*> Anything that is initially shocking fades from that status as it becomes
> more familiar.  This is true even of quantum theory.*

I guess you're smarter than Feynman because he admitted me didn't
understand quantum mechanics and didn't think anybody else did either. But
then he never met you.

> >> That is the simplest possible example of quantum entanglement involving
>> a single Qbit, Preskill was talking about far more complex systems where
>> thousands or millions of Qbits are entangled, the sort of thing you'd need
>> for a quantum computer.

*>And?  Each and every one of them is entangled with another
> particle; perhaps some pairs might be among that thousands or millions.
> This does not render the whole collection immeasurable.*

Preskill never said the information in the whole collection was
immeasurable, if it was it would be useless for quantum computers; he was
trying to explain how to make things more robust with quantum error
correction; if the particles are entangled in a clever way and the outside
environment interacts with just one particle in a many particle system the
quantum information in the entire system will not be lost. And that’s
vitally important because you’re never going to able to isolate the
computer completely from interacting with the environment.

*> Unless he is trying to redefine the term "quantum entanglement".  If so,
> that is far closer to "hyping up the spooky and mysterious” than "clearly
> explaining", and thus is not worth listening to if one is​ ​seeking an
> explanation.*

Nobody has an explanation why things behave the way they do in the quantum
world, but some people know rules that allow them to make statistical
predictions about what will happen. Nobody is very happy about these rules
because they make little sense and would be universally rejected except for
one thing, they work. In fact most physicists have given up trying to
figure out why they work and thus aren’t interested in Copenhagen or Many
Worlds, they are adherents of the “Shut Up And Calculate” quantum
interpretation. A quantum computer engineer need not understand why the
rules work he just needs to know that they do.

John K Clark

If you always assume you know more than your teacher how can you ever
learn? I think you could use a dash of humility

, maybe just maybe other people know things you don't.

John K Clark
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