Is all correlation related to quantum entanglement?

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Discussion Overview

The discussion explores the relationship between correlation and quantum entanglement, questioning whether all correlation implies entanglement and examining the nature of classical versus quantum correlations. The scope includes theoretical considerations and conceptual clarifications related to quantum mechanics.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants propose that entanglement necessarily leads to correlation in measured properties, while questioning if correlation alone implies entanglement.
  • Others argue that correlation can exist without entanglement, using the example of a coin where heads and tails are correlated but not entangled.
  • A participant challenges the notion of correlation without entanglement, suggesting that measurement requires correlation and questioning if correlation is a measure of entanglement.
  • Another participant asserts that entanglement is a specific mathematical property of the wave function, which does not apply to the classical example of a tossed coin.
  • There is a discussion about the necessity of superposition for entanglement, with some participants agreeing that superposition is part of the definition of entanglement.

Areas of Agreement / Disagreement

Participants express disagreement regarding whether correlation can exist independently of entanglement, with some asserting that it can while others maintain that entanglement is required for correlation in a quantum context. The discussion remains unresolved.

Contextual Notes

The discussion highlights the dependence on definitions of correlation and entanglement, as well as the distinction between classical and quantum frameworks. There are unresolved questions about the implications of measurement and the nature of superposition in relation to entanglement.

friend
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In other words, it seems that if you have entanglement, then you have correlation (of measured properties). But is it true that if you have correlation, then you have quantum entanglement? Classically, correlation is between macro-events. But macro-events are made of micro-events. So is classical correlation the classical limit of quantum entanglement?

Thinking further, we can only measure something if there is correlation. e.g. correlation between the needle on the meter and the voltage in the circuit. Even a quantum measurement only exists if there is a correlation. For it takes an interaction to make a measurement, and we only know something about the particle being measured because it is somehow correlated with the particles interacting with it. So can you have correlation without entanglement? Isn't correlation the measure of entanglement (always)?

Thanks.
 
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It is easy to produce correlation without entanglement. An ordinary coin provides a good example: observations of heads on one face are strongly correlated with observations of tails on the other side.
 
Nugatory said:
It is easy to produce correlation without entanglement. An ordinary coin provides a good example: observations of heads on one face are strongly correlated with observations of tails on the other side.
Are you saying that the heads on one side are not entangled with the tails on the other when they are both part of the whole coin? I suppose there is no superposition. Does entanglement only exist between states that are superposed?
 
friend said:
Are you saying that the heads on one side are not entangled with the tails on the other when they are both part of the whole coin?
Yes, I am saying they are not entangled. Entanglement is a precisely defined mathematical property of the wave function, and a tossed coin doesn't have that property.
I suppose there is no superposition. Must there be superposition to get entanglement?
Yes. That's part of the definition.
 

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