PDF (double-sided) - Physics Department, UCSB - University of ...

Podolsky, and Rosen [Einstein et al., 1935] and is commonly referred to as the
“spooky action at a distance”, a term coined by Einstein.
As explained further in Chapter 10, this gedanken-experiment was eventually
formulated into mathematical inequalities, called “Bell’s Inequalities” [Bell,
1964, Clauser and Horne, 1974, Clauser et al., 1969], that could experimentally
test whether the apparently paradoxical predictions made by quantum mechanics
could be resolved by the introduction of a deterministic alternative theory, or
whether the ideas had to be accepted as true. These inequalities are based on the
definition of measures of correlation that can be shown to be limited to a certain
value in classical systems that do not require entanglement and superpositions to
explain their state. Quantum mechanical systems, though, with “access” to these
entanglements and superpositions, can show correlation values that exceed these
classical limits and are thus said to “violate Bell’s inequality”.
This makes the demonstration of a violation of Bell’s inequality in a system
of proposed quantum bits a strong proof that these quantum bits indeed show
behavior that goes beyond what is explainable by classical deterministic theories.
Such a demonstration could therefore be seen as very strong evidence that
the proposed architecture does promise the capability to eventually lead to the
exponential performance increases suggested by quantum mechanics.
This has made the violation of Bell’s inequality a major milestone for any
10