# Bell's Inequality: The weirdest theorem in the world | Nobel Prize 2022

TLDRThe 2022 Nobel Prize in Physics was awarded to pioneers in quantum mechanics who proved Einstein's assumptions about local realism wrong. Their groundbreaking experiments on quantum entanglement, built on John Bell's theorems, demonstrated that quantum particles can be correlated in ways unexplainable by classical physics. By testing Bell's inequalities, they showed conclusively that nature behaves according to the strange predictions of quantum theory. Their work paved the way for innovations like quantum teleportation and computing that rely on entanglement and disproved hidden variable explanations, deepening our understanding of quantum weirdness.

###### Takeaways

- ๐ฒ The 2022 Nobel Prize in Physics was awarded for groundbreaking research on quantum mechanics and testing Bell's theorem experimentally.
- ๐ John Stewart Bell theorized that quantum mechanics is incompatible with local realism in what became known as Bell's theorem.
- ๐คฏ John Clauser first demonstrated experimentally that nature violates Bell's inequalities, proving that quantum mechanics does not obey local realism.
- ๐ Alain Aspect performed more stringent tests of Bell's theorem and closed experimental loopholes.
- ๐ก Anton Zeilinger demonstrated quantum teleportation experimentally for the first time.
- ๐ฎ The CHSH inequality sets an upper limit of 2 on certain measurable quantities, assuming local realism holds true.
- ๐ค Entangled quantum particles can violate the CHSH inequality with a value of ~2.8, proving Bell's theorem and quantum mechanics correct.
- ๐ง Quantum mechanics requires giving up either locality or realism - the results can't be explained classically.
- ๐ฉโ๐ฌ The Qiskit textbook has a tutorial to demonstrate a violation of the CHSH inequality yourself.
- ๐๐ป The Nobel laureates showed that quantum mechanics is practical and fundamentally different from classical physics.

###### Q & A

### Who were the three gentlemen that won the 2022 Nobel Prize in Physics?

-John Clauser, Alain Aspect, and Anton Zeilinger.

### What theorem did John Bell prove that showed the incompatibility between quantum mechanics and local realism?

-Bell's theorem.

### What are the two main assumptions of Bell's theorem?

-Locality - information cannot travel faster than the speed of light. Realism - objects have definite properties independent of measurement.

### What experiment did John Clauser perform that provided the first experimental demonstration of a violation of Bell's inequalities?

-The CHSH experiment.

### What is quantum teleportation and who first demonstrated it experimentally?

-Quantum teleportation is a technique for transferring quantum information between entangled particles without transmitting the actual particles themselves. It was first demonstrated experimentally by Anton Zeilinger.

### What is the CHSH inequality and what is the maximum value it can take in classical physics?

-The CHSH inequality puts an upper bound on the correlations between measurements on two spatially separated systems under the assumptions of locality and realism. In classical physics, it can have a maximum value of 2.

### What is the approximate CHSH value that is observed when performing the experiment on entangled quantum particles?

-2.8

### Does violating Bell's inequalities imply faster-than-light communication is possible?

-No. Although the entanglement between particles implies instantaneous correlations at a distance, no useful information can be transmitted faster than the speed of light this way.

### How do scientists interpret the violation of Bell's inequalities?

-As evidence against local realism - either locality or realism (or both) must be given up. The common interpretation is to abandon realism and accept that quantum systems do not have well-defined properties prior to measurement.

### Where can you find tutorials to try Bell test experiments yourself?

-The Qiskit textbook has tutorials on testing Bell's inequalities using quantum circuits you can run online.

###### Outlines

##### ๐ค Introducing the 2022 Physics Nobel Prize and its significance

Olivia from IBM Quantum introduces the 2022 Physics Nobel Prize awarded to John Clauser, Alain Aspect, and Anton Zeilinger for their groundbreaking research on quantum entanglement. She provides background on John Bell's theorem which showed that quantum mechanics is incompatible with local realism, and how the prize winners' experiments proved this experimentally.

##### โ Demonstrating quantum weirdness through the CHSH inequality

Olivia explains the CHSH inequality thought experiment with entangled particles sent to Alice and Bob who make measurements. She shows how the CHSH value violates the upper bound predicted by classical physics, proving that quantum mechanics violates local realism.

##### ๐คฏ Interpreting the meaning and implications of quantum entanglement

Olivia clarifies that quantum entanglement does not allow faster-than-light communication, a common misconception. She emphasizes that the experiments show particles do not have definite properties before measurement, only probabilities described by the wavefunction. Olivia concludes by highlighting how fundamental quantum entanglement is for quantum technologies today.

###### Mindmap

###### Keywords

##### ๐กQuantum mechanics

##### ๐กEntanglement

##### ๐กBell's Theorem

##### ๐กBell's inequality

##### ๐กCHSH inequality

##### ๐กQuantum teleportation

##### ๐กLocal realism

##### ๐กEPR paradox

##### ๐กWave function

##### ๐กHidden variables

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###### Transcripts

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