Images of Bell-type non-local behaviour and 2√2 bound

Foundations of physics and/or philosophy of physics, and in particular, posts on unresolved or controversial issues

Images of Bell-type non-local behaviour and 2√2 bound

Postby Dirkman » Tue Oct 01, 2019 1:28 am

So I guess you're all aware of the highly media reported experiment done this year where they "took photos" of entagled particles.

https://advances.sciencemag.org/content/5/7/eaaw2563

But curiously enough , they say this

"Despite exceeding the classical limit of S > 2, the nonperfect contrast obtained on the graphs presented in Fig. 2 (B to E) explains that the ultimate two-dimensional 2√2 bound for S is not saturated."

What two dimensions are they talking about?
Last edited by Dirkman on Tue Oct 01, 2019 2:57 am, edited 1 time in total.
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Re: A photo of Bell-type non-local behaviour

Postby Joy Christian » Tue Oct 01, 2019 2:44 am

***
Ha Ha... The title of your thread made me laugh. :)

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Re: A photo of Bell-type non-local behaviour

Postby Dirkman » Tue Oct 01, 2019 2:51 am

Well yeah , but my question is serious.
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Re: A photo of Bell-type non-local behaviour

Postby gill1109 » Tue Oct 01, 2019 2:36 pm

Dirkman wrote:Well yeah , but my question is serious.

They are thinking of quantum systems built out of qubits - quantum systems with a two dimensional Hilbert space. Their remark shows that they have no idea at all of what they are talking about since the Tsirelson bound is the best that QM can do with two parties, binary setting choices, and binary measurement outcomes, but he actually optimises over all possible quantum systems (of any dimension whatsoever) and all possible binary measurements on those systems, and not just the rather special class of projective measurements corresponding to measurement of "observables" according to the Neumann-von Lüders projection postulate. It is just that the bound happens to be attained on with two dimensional Hilbert spaces, and the famous spin measurements of Bell, Aspect etc. [well ... Aspect moved from spin of spin half particles to polarization of photons but the abstract math is the same once you have figured out the mapping]

Anyway, it is a silly paper. Experimentally they are clever, their engineering is good and novel. They need to raise money to pay for their expensive experiments with many research assistants and PhD students, and they need to gain prestige within the academic world, so they write the kind of nonsense in Science or Nature which especially appeals to science journalists and the public. Academic publication is based on in-crowds and cliques promoting the work of their friends so as to promote their own work, keeping the science funding flowing and the scientific prestige and hence power and hence funding...
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Re: A photo of Bell-type non-local behaviour

Postby minkwe » Tue Oct 01, 2019 7:57 pm

gill1109 wrote:
Dirkman wrote:Well yeah , but my question is serious.

They are thinking of quantum systems built out of qubits - quantum systems with a two dimensional Hilbert space. Their remark shows that they have no idea at all of what they are talking about since the Tsirelson bound is the best that QM can do with two parties, binary setting choices, and binary measurement outcomes, but he actually optimises over all possible quantum systems (of any dimension whatsoever) and all possible binary measurements on those systems, and not just the rather special class of projective measurements corresponding to measurement of "observables" according to the Neumann-von Lüders projection postulate. It is just that the bound happens to be attained on with two dimensional Hilbert spaces, and the famous spin measurements of Bell, Aspect etc. [well ... Aspect moved from spin of spin half particles to polarization of photons but the abstract math is the same once you have figured out the mapping]

Anyway, it is a silly paper. Experimentally they are clever, their engineering is good and novel. They need to raise money to pay for their expensive experiments with many research assistants and PhD students, and they need to gain prestige within the academic world, so they write the kind of nonsense in Science or Nature which especially appeals to science journalists and the public. Academic publication is based on in-crowds and cliques promoting the work of their friends so as to promote their own work, keeping the science funding flowing and the scientific prestige and hence power and hence funding...


Wow, Joy, did Richard lend you his account? :shock:
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Re: A photo of Bell-type non-local behaviour

Postby Joy Christian » Tue Oct 01, 2019 10:48 pm

minkwe wrote:
gill1109 wrote:
Dirkman wrote:Well yeah , but my question is serious.

They are thinking of quantum systems built out of qubits - quantum systems with a two dimensional Hilbert space. Their remark shows that they have no idea at all of what they are talking about since the Tsirelson bound is the best that QM can do with two parties, binary setting choices, and binary measurement outcomes, but he actually optimises over all possible quantum systems (of any dimension whatsoever) and all possible binary measurements on those systems, and not just the rather special class of projective measurements corresponding to measurement of "observables" according to the Neumann-von Lüders projection postulate. It is just that the bound happens to be attained on with two dimensional Hilbert spaces, and the famous spin measurements of Bell, Aspect etc. [well ... Aspect moved from spin of spin half particles to polarization of photons but the abstract math is the same once you have figured out the mapping]

Anyway, it is a silly paper. Experimentally they are clever, their engineering is good and novel. They need to raise money to pay for their expensive experiments with many research assistants and PhD students, and they need to gain prestige within the academic world, so they write the kind of nonsense in Science or Nature which especially appeals to science journalists and the public. Academic publication is based on in-crowds and cliques promoting the work of their friends so as to promote their own work, keeping the science funding flowing and the scientific prestige and hence power and hence funding...


Wow, Joy, did Richard lend you his account? :shock:

Wow indeed! I agree with every word he has written in his post.

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