Quantum Entanglementa non-technical glimpse

Sreepadmanabh MIISER - Bhopal

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.

? ?

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

Enter Einstein

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

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)

For Whom the Bell Tolls

▪ The Bell Theorem

▪ “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

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

Why we won't have superluminal data transfer

Practical , we presume ?

▪ Quantum Teleportation

▪ Quantum computing

▪ Superdense coding - ( 2^n qubits output per qubit of input )

▪ Super fast , but NOT superluminal information transfer