Quantum entangled-photon Chinese satellite.

[Mirimir]

On 08/05/2016 12:14 PM, Zenaan Harkness wrote:
> On Fri, Aug 05, 2016 at 09:10:42AM -0600, Mirimir wrote:
> ...
>> Here, from <http://www.scottaaronson.com/blog/?p=2464>:
>>> The violation of the Bell inequality has a schizophrenic status in
>>> physics.  To many of the physicists I know, Nature’s violating the
>>> Bell inequality is so trivial and obvious that it’s barely even
>>> worth doing the experiment: if people had just understood and
>>> believed Bohr and Heisenberg back in 1925, there would’ve been no
>>> need for this whole tiresome discussion.
> 
> Seriously, I am none the wiser and cannot yet make sense of what they
> are saying.

First you create entangled electrons in two distant diamonds [separated
by 1.5 km in Hensen et al. (2015) and apparently 750 mi in the
Chinese-Austrian experiment described in the news article]. You do that
by exchanging photons, which travel at light-speed or less. Then you
measure the spins of those entangled electrons. And you find that the
spins are correlated in a way that's predicted by quantum mechanics, but
would be possible under classical mechanics (aka realism) only if the
entangled electrons could communicate at greater than light-speed.

So basically, they find that the classical model of reality is fucked.

Here's the abstract from Hensen et al. (2015)
<https://arxiv.org/abs/1508.05949>:

> For more than 80 years, the counterintuitive predictions of quantum
> theory have stimulated debate about the nature of reality. In his
> seminal work, John Bell proved that no theory of nature that obeys
> locality and realism can reproduce all the predictions of quantum
> theory. Bell showed that in any local realist theory the correlations
> between distant measurements satisfy an inequality and, moreover,
> that this inequality can be violated according to quantum theory.
> This provided a recipe for experimental tests of the fundamental
> principles underlying the laws of nature. In the past decades,
> numerous ingenious Bell inequality tests have been reported.
> However, because of experimental limitations, all experiments to
> date required additional assumptions to obtain a contradiction with
> local realism, resulting in loopholes. Here we report on a Bell
> experiment that is free of any such additional assumption and thus
> directly tests the principles underlying Bell's inequality. We
> employ an event-ready scheme that enables the generation of
> high-fidelity entanglement between distant electron spins.
> Efficient spin readout avoids the fair sampling assumption
> (detection loophole), while the use of fast random basis
> selection and readout combined with a spatial separation of 1.3
> km ensure the required locality conditions. We perform 245
> trials testing the CHSH-Bell inequality S≤2 and find S=2.42±0.20.
> A null hypothesis test yields a probability of p=0.039 that a
> local-realist model for space-like separated sites produces
> data with a violation at least as large as observed, even when
> allowing for memory in the devices. This result rules out large
> classes of local realist theories, and paves the way for
> implementing device-independent quantum-secure communication
> and randomness certification. 

The news article is full of bullshit.

> China apparently is putting this experiment in space - are they winning
> a game on prediction of one particular bit with > 75% probability, and
> if so, can they run that game numerous times to get that probability
> close to 100%, and if so, can the random inputs to each side be made not
> random so that the result of the game is transmission of information?
> 
> I cannot begin to answer any of these questions sorry...

As I understand it, they're just pushing the separation to 750 miles.
We're still a long way from transmitting useful data. And recall that
creating entanglement requires synchronization at light-speed or less.

>> Me, I like the many worlds interpretation. But it's just an
>> interpretation. What matters is the math.
> 
> That sounds much more interesting than the implications of 'dull'
> said to be arising from qubits :)
> 
> The hope is that since some say the experiment is pretty dull to begin
> with, then perhaps there is a soul alive who could answer the above
> questions... we can only hope.

In saying that it's dull, they're pointing out that what matters is the
math of quantum mechanics. It's just math. Equations. There's no mental
model, no story in words about how reality works. The interpretations
are just stories.