Marissa Giustina: Significant loophole-free test of Bell’s theorem with entangled photons

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell’s theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell’s inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. In this paper, I will discuss the recent results from my laboratory, in which we designed an experiment that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism is exceedingly unlikely, corresponding to an 11.5 standard deviation effect.

Marissa Giustina University of Vienna, Physics
Information-Theoretic Interpretations of Quantum Mechanics: 2016 Annual Philosophy of Physics Conference
June 11-12, 2016

[SkyNelson]

This was a great paper and great experiment. Thanks for moving the field forward.

[oofbruh]

Something about listening to smart people talk about complex things is mind boggling and relaxing at the same time

[nathanokun]

It is interesting that while Bell proved (so far with our current knowledge) that the two entangled particles are INTERNALLY communicating with one-another in some manner, Einstein is STILL CORRECT in that you cannot get any EXTERNALLY OVERLAID information into this communication (the results, though correlated as matching pairs, are still random as to what they are at any time, so you cannot send any useful data on this link, as far as we know now). This "ghostly" super-luminal connection is what made Einstein "agin it", though it still respected his overall rules. This is what makes this effect so frustrating: It is staring you in the face, but you cannot use it for anything that YOU want to do! Is God laughing?

[AkamiChannel]

I’m just an interested amateur but this was great, thank you. Wonderful to have stuff like this on YouTube.

[dixithanoop]

It's mind-blowing to just look at the experiment setup!

[KeithMakank]

"Photons are easy to loose" - some LIGHT humour

[MarcusMorgan]

Excellent presentation. Thanks for your careful work.

[CandidDate]

I'm glad I'm not at the experimental end of things. It takes a lot of willpower and determination to fight the elements (and dust) and get this thing we call reality to yield its secrets. I applaud your research as it is on the cutting edge of the field. I am working on the theoretical end of things, but I hope we will find out someday if Shrodinger's cat is alive or dead. :)

[make.and.believe]

Fantastic work. Wonderful presentation. Well constructed experiment.

[robbie_]

Great presentation. Thanks for sharing.

[indiadad]

There was a gentleman in the audience who asked at the end if entanglement is necessary for such experiments to be meaningful, and Marissa said "no". I don't understand that. I thought entanglement was at the heart of Bell's result.

[ivanscottw]

Way over my paygrade ! At this point at 24:31 when she states 'when the apparatus knows what you're doing" is when I got lost ! (since when does a mechanical construct *knows* anything ?)

[holdenrobbins]

I'm still confused why people assume there is some sort of non-local communication occurring. Why is entanglement not like two spinning balls bouncing off each other in different directions? ie. the initial conditions for the "entangled system" is what makes the spin opposite. (not some 'spooky' communcation) I assume this was Einstien's point... there is more likely something more mechanical at work fundamentally, not that the spin isn't set until someone actually observes it.

[vancamjr]

There’s always seems to be that guy (1:16) who smugly rolls a statement into the form of a question for his own edification. His face, an easy read, speaks volumes.

[Fransamsterdam]

So the result is - as expected I think - a violation of Bell's inequality, which means that we cannot explain quantum theory with hidden variables. Please correct me if I am wrong...

[robertharlton]

I'm also thinking that for entanglement to work, everything, at some level, must be single point.

[grandunifier]

I can't wait for the new generation of particle physicists to replace the old guard...

All photons are capable of fusion & fission, it's not that hard to understand...

[TheNorgesOption]

Okay, heard enough of the mystical "Spooky Action at a Distance" Quantum Mumbo Jumbo. Here is a No-Go challenge for Bell’s Theorem.


The Bell’s Inequalities Challenge -


Can one by combining Macroscopic Real Objects with classical wave functions violate Bell’s Inequalities?


This can be achieved by using a large pool, small self-propelled model boats that do not have a steering system and a series of short parallel walls that can vibrate and produce waves.


First one has to create the parallel walls that are just wide enough so that if a boat is sent on a parallel direction to the canals created that they can reasonably pass through without the boats touching the wall (which would be a fail). Then send the boats on slightly canted angles and using classical wave mechanics most should hit the wall and fail the test and not violate Bell’s Inequalities.


Now vibrate those walls in which pressure from the waves creates a low-pressure zone in the center of those walls so that the boats will head that direction in a path that is parallel to the walls. The boats should then be able to Violate Bell’s Inequalities.


If that is achievable, then virtually every experiment in quantum physics should be reproducible using just local wave functions.

[BarryKort]

In the derivation of Bell's Inequality, he posits a presumptive hidden variable, λ(x, t). In this view, one member of the twin particles has a position +x at time t, while the twin has a position -x at time t. But note that Bell blithely adopts a common master clock, t, so that λ(x, t) can be algebraically canceled out by λ(-x, t), regardless of the function λ(•).

If you appreciate that a gravitational gradient perturbs timekeeping so that the particles speeding off in opposite directions age at their own idiosyncratic rates, then one can no longer algebraically cancel out λ. That is, the derivation of Bell's Inequality breaks down; the presumptive hidden variable λ(x, t) remains present. Indeed one can say the hidden variable is time itself. That is, in reality, each particle ages according to its own local clock, rather than being governed by a common master clock.

In Aspect's experiment, λ(x, t) could be Maxwell's Equation for the photon, or (equivalently) Feynman's rotating vectors. But recall that photons traversing a gravitational gradient gain or lose energy and thus change their wavelength (or color) accordingly. The two photons are thus represented by sinusoids which are not perfect mirrors of each other and thus cannot be algebraically canceled out. They will have a residual nonzero "beat frequency" which remains present, thus spoiling Bell's convenient cancellation of λ(x, t) midway through his derivation.

That's why Bell's Inequality doesn't hold in the real cosmos where there is no universal master clock that keeps identical time everywhere and everywhen.

The not-so-hidden variable is time, itself.

[robertbarta]

Super interesting. And next time I walk by the Hofburg I will tread more carefully :)