Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km

Understand

For more than 80 years, the counterintuitive predictions of quantum theory have stimulated debate about the nature of reality.

• In his seminal work, John Bell proved that no theory of nature that obeys locality and realism can reproduce all the predictions of quantum theory.
• Bell showed that in any local realist theory the correlations between distant measurements satisfy an inequality and, moreover, that this inequality can be violated according to quantum theory.
• This provided a recipe for experimental tests of the fundamental principles underlying the laws of nature.