Entanglement and Bell’s Inequality | Qiskit in the Classroom

[@Thomas-mj1dv]

I used to read your articles in Quantamagazine and now I watch your short but substantive lectures on quatum physics with the same pleasure. Great job, Katie... Merry Christmas 🙂

[@beeris]

Great explanation of Bell's inequality !!

[@physicsouruniverse2798]

I used to watch all the lectures but for me this lecture is more fruitful.Thank you!!!

[@cyclonasaurusrex1525]

Did Bob and Alice finally retire?

[@Simulera]

To tell you the truth, no one knows for sure.

[@DSAK55]

they switched partners Bob and Carol, and Ted and Alice

[@pauldirac6243]

Lucas and Rhianna?! That's simply irresponsible.

[@enriquantum]

Thank you, Katie, very good video and with the bonus of the Python notebook to continue deepening. The duality (only mathematical?) between entangled particles and wormholes is something that has left me thinking since I heard Juan Maldacena in a talk he gave in Buenos Aires some time ago... Cheers!

[@sylvainbougie7269]

This is so important ❤

[@arunms8696]

Thank you👍🏻

[@NeerajKumar-ld8ht]

I may agree that the measurement doesn’t affect the other particle’s state but there is some connection which somehow causes these particles communicate, no matter how far apart they in universe and why i’m seeing this because change in one’s state changes other’s state too and that too happens instantaneously.

[@classicalmechanic8914]

Entanglement and action at the distance are not the same. Entanglement is just particle correlation while action at the distance imply causation.

[@messapatingy]

Entanglement is a phenomenon in quantum mechanics where two or more particles are connected such that when the state of one is measured, it instantly determines the state of the other, no matter how far apart they are. That's it.

[@poshsims4016]

No one asked you let her explain in detail.

[@decretingredient6892]

what does " - + > " mean at 5:04?

[@katiemcc89]

Sorry, that wasn't super clear. In this case, the "+" and "-" signify whether each particle's spin is +1/2 or -1/2, respectively. The joint state of the particles is an entangled state (the" \Psi" in the next line) in which each particle's spin must have the opposite sign of its partner. So "|-+>" is the term that signifies that the first particle's spin is -1/2, and the second particle's spin is +1/2. Note that in standard quantum computing convention, |+> and |-> are usually reserved to represent the eigenstates of the X basis, so this choice of notation wasn't my best decision.

[@jamesruscheinski8602]

could entanglement happen with cosmological constant expansion of space (faster than light)?

[@brickchains1]

bell's theorem and EPR isn't about intrinsic probability, but non-locality.

[@DevanConrad]

I didn't get why we can measure in 3 directions to get 4/9 then only use 2 dimensions to get 1/2... feels like slight of hand in math.

[@andrewcraig11781]

Why is the co-sign squared?

[@anywallsocket]

Because cos(theta/2) represents the amplitude, which needs to be squared to give the probability.

[@andrewcraig11781]

@ thanks!

[@anywallsocket]

@@andrewcraig11781 yeah it’s just the Born rule if you wanna look it up - pretty central to QM

[@mahasamatman12]

How can you confuse Max Born with Niels Bohr ?

[@radfordmcawesome7947]

Bohr may have been the most vocal (ironic because he was famous mumbler) proponent of the Copenhagen Interpretation, but Born was also documented as being against hidden variables. For example, he gave a talk with Heisenberg at the '27 Solvay Conference (you know, the one where that famous group photo was taken) where he stated, "we consider quantum mechanics to be a closed theory, whose fundamental physical and mathematical assumptions are no longer susceptible of any modification".

[@mahasamatman12]

@@radfordmcawesome7947 Now that you have shown off your knowledge and hopefully contented your ego, you can watch the video and find that she's confusing Born with Bohr.

[@radfordmcawesome7947]

@mahasamatman12 What part are you referring to? The one where she contrasted Einstein's views with Born's?

[@radfordmcawesome7947]

​@@mahasamatman121:30, she states that Max Born was "in the other camp", which is 100% correct, even though Niels Bohr was also in that camp. You're attacking me for no good reason, have a nice life.

[@mahasamatman12]

@@radfordmcawesome7947 Yes

[@JustNow42]

Verry nice, better than most, but some small slips. Also I do not like that the definition of what hidden variables is is not complete.

[@anywallsocket]

Why do the first and last rows not violate the equality??

[@radfordmcawesome7947]

Assuming you are talking about 10:41, it’s because L and R (oh, I just understood why they used those names lol) always measure opposite signs in those scenarios.

[@radfordmcawesome7947]

Oh wait, I understand what you are asking now. It’s because 4/9 is the upper bound for measuring the same sign, and those rows have 0 chance, thus not violating the bound.

[@anywallsocket]

@@radfordmcawesome7947 I thought those rows have a 100% chance, ie of getting opposite spins.

[@radfordmcawesome7947]

@ They do, didn’t the video say they were talking about the probability to measure the same spin sign? edit: yeah, check out 9:30. You probably just misheard the first time around

[@ChimeraZone]

A lack of hidden variables disproves superdeterminism true story.

[@anywallsocket]

False story. You forgot to qualify local hidden variables.

[@davidrandell2224]

QM classicalized in 2010. Forgotten Physics website uncovers the hidden variables and constants and the bad math of Wien, Schrodinger, Heisenberg, Einstein, Debroglie, Planck, Bohr etc. So,no.

[@vadim32]

Einstein said God doesn't play dice using telepathic methods. Which means there's either hidden parameters or there's spooky action at a distance. In 1964, it turned out that there are no hidden parameters, but there is spooky action at a distance. If we find the probabilities corresponding to the correlations of entangled particles at angles 0, 120, 240, they are P(+a,+b,+c)=P(-a,-b,-c)=-1/16 the other 6 states P(+a,+b,-c)=P(+a,-b,-c)=P(+a,-b,-c)=...=3/16. This means that there is no wave function describing an entangled state. There are no such complex numbers, the square of the modulus of which is equal to a negative number (Born rule). Therefore, the wave function will never be written in numbers, it can only be drawn with arrows.

[@anywallsocket]

Bro just had a stroke

[@benyoyyoyo8381]

your right albert einstein was so wrong, but to be smartenef to guest

[@dissaid]

😎☕️🇺🇲

[@SciD1]

That was the one time Einstein was actually right.

[@connormcmk]

hey a fellow McCormick that enjoys quantum mechanics maybe we're related

[@lilep666]

particles don't know anything. humans do

[@sami-q4m]

First

[@jjjccc728]

This source uses the analogy of a map and a territory to discuss the relationship between **quantum mechanics** (the territory) and **hidden variable theories** (the maps). * **The Territory:** The territory in this analogy represents the true nature of reality at the quantum level. This territory is characterized by strange and counterintuitive phenomena like quantum entanglement. It's a landscape where particles can be linked regardless of distance, defying our everyday experiences of space and time. This territory is full of mystery and complexity, and our understanding of it is still evolving. * **The Maps:** The maps in this analogy represent different theoretical frameworks that attempt to describe and explain the territory of quantum mechanics. * **Map 1: Quantum Mechanics** - This map, based on the principles of quantum superposition and entanglement, suggests that the properties of particles are not determined until they are measured. This map embraces the probabilistic nature of quantum phenomena and accepts that there is inherent uncertainty at the heart of reality. * **Map 2: Hidden Variable Theories** - These maps, favored by Einstein and others, propose that there are underlying, unseen variables that predetermine the outcome of quantum measurements. These maps aim to restore a sense of determinism to the quantum world, arguing that the apparent randomness is simply due to our lack of knowledge about these hidden variables. ### Analyzing the Analogy with Examples: 1. **Example 1: Entanglement:** Imagine the territory has two mountains that always have opposite weather. If one mountain is sunny, the other is instantly stormy. This is like entanglement. * **Quantum Mechanics map** accepts this strange weather pattern as a fundamental feature of the territory. * **Hidden Variable map** might suggest there's an underground weather control system connecting the mountains that we haven't discovered yet, explaining the correlation. 2. **Example 2: Bell's Theorem:** Imagine a map that claims there's a limit to how high the mountains in the territory can be. This is like Bell's inequality. * Experiments, like exploring the territory, reveal that some mountains exceed this predicted height. * This suggests the **Hidden Variable map** is inaccurate and the territory is more complex than initially thought. 3. **Example 3: Measurement Problem:** Imagine trying to draw a map of a constantly shifting sand dune. Every time you try to pinpoint a specific grain of sand, the dune changes shape. This is like the measurement problem in quantum mechanics. * The act of observation, or measurement, alters the state of the quantum system, making it difficult to create a definitive map of the territory. ### Conclusion: The map and territory analogy helps us understand the ongoing debate about the nature of reality at the quantum level. Bell's theorem and subsequent experiments have shown that the "Hidden Variable maps," at least in their simplest forms, do not accurately represent the territory. While the "Quantum Mechanics map" currently seems to be the most accurate representation, it still leaves many questions unanswered. The exploration of the quantum territory continues, and new maps are constantly being drawn as we delve deeper into the mysteries of the quantum world.