The document discusses the concept of quantum entanglement, which involves particles interacting in a way that measuring one particle instantly affects the other particle, even when separated by large distances. This was proposed in the EPR paradox by Einstein, Podolsky, and Rosen to argue against the completeness of quantum mechanics. The two options to resolve the EPR paradox are hidden variable theory or quantum entanglement. John Bell proved that no local hidden variable theory can match all predictions of quantum mechanics. Experiments by Aspect in 1981 supported quantum entanglement and ruled out hidden variables. While entanglement allows instantaneous correlations between particles, it does not allow for superluminal information transfer.

1. Quantum Entanglement
a non-technical glimpse
Sreepadmanabh M
IISER - Bhopal

2. Hot Chocolate , anyone ?
A very practical example of a very unpractical concept
One cup is hot coffee , the other cold .Tasting any one is sufficient
to know both.
? ?

3. The Gospel
The Copenhagen Interpretation
▪ Formulated by Bohr and Heisenberg
▪ physical systems generally do not have definite properties prior to being
measured
▪ quantum mechanics can only predict the probabilities that measurements
will produce certain results
▪ measurement affects the system, causing the set of probabilities to reduce
to only one of the possible values immediately after the measurement –
wave function collapse

4. Enter Einstein

5. The EPR Paradox
▪ Proposed by Podolsky , Rosen and yes , of course , Einstein
▪ Basically a thought experiment in quantum mechanics
▪ the wave function does not provide a complete description of physical
reality
▪ The heart of the problem - particles can interact in such a way that it is
possible to measure both their position and their momentum more
accurately than Heisenberg's uncertainty principle allows, unless measuring
one particle instantaneously affects the other to prevent this accuracy,
which would involve information being transmitted faster than light as
forbidden by the theory of relativity

6. Answers please
How to resolve the EPR Paradox
▪ Option 1 : Hidden variables theory
( acceptable , conventional , essentially the easy way out )
▪ Option 2 : Quantum Entanglement
( outlandish , no available explanation)

7. For Whom the Bell Tolls
▪ The BellTheorem
▪ “No physical theory of local hidden variables can ever
reproduce all of the predictions of quantum mechanics “
▪ Bell proposed experiments to disprove hidden variables
theory
▪ Aspect ( 1981 ) - buried hidden variables

9. A Tangled Truth
▪ E.g. Angular momentum is conserved – spins must be opposite
▪ Independent description of quantum states is not possible
▪ Measurement of any one particle causes the wavefunction to
collapse
▪ The info regarding one particle is instantaneously transferred to
the other
▪ No apparent background mechansim

11. Why we won't have superluminal data transfer

12. Practical , we presume ?
▪ QuantumTeleportation
▪ Quantum computing
▪ Superdense coding - ( 2^n qubits output per qubit of input )
▪ Super fast , but NOT superluminal information transfer