Synopsis: Reality, locality, and “free will”

By relaxing certain assumptions, it is possible to describe quantum correlations as both local and real.

In 1964, John Bell devised a testable prediction (now known as Bell’s inequality) based on two reasonable assumptions: that the measurement of one particle cannot instantaneously influence another, distant particle (locality) and that particles have properties before you measure them (reality).  Numerous experiments have since shown that Bell’s inequality is violated, forcing one to conclude that, contrary to the view held by Einstein, Podolsky, and Rosen, quantum mechanics cannot be both local and real.

But what of other assumptions built into Bell’s inequality?  In a paper appearing in Physical Review Letters, Michael Hall at the Australian National University in Canberra considers an assumption, called measurement independence, in the following experimental paradigm: A source emits two particles in an entangled state and sends them to two distant laboratories, where two experimenters randomly choose apparatus settings that measure a system property.  The measurement outcomes can be correlated in a way that violates Bell’s inequality, but measurement independence assumes that the experimenters freely choose apparatus settings, independent of any properties of the systems that they measure.  By relaxing this assumption, Michael Hall constructs a local and real model that describes the correlations of the experiment.  He shows that locality and reality can be retained with a 14% reduction of the experimenters’ “free will”—that is, the assumption of measurement independence need not be given up completely. – Sonja Grondalski


More Announcements »

Subject Areas

Quantum Information

Previous Synopsis

Nuclear Physics

Unequal parts

Read More »

Next Synopsis


Friction in a vacuum

Read More »

Related Articles

Viewpoint: Hiding a Quantum Cache in Diamonds
Quantum Information

Viewpoint: Hiding a Quantum Cache in Diamonds

Entanglement purification, a vital enabler for practical quantum networks, has been shown to be feasible with secluded nuclear memories in diamond. Read More »

Viewpoint: Classical Simulation of Quantum Systems?

Viewpoint: Classical Simulation of Quantum Systems?

Richard Feynman suggested that it takes a quantum computer to simulate large quantum systems, but a new study shows that a classical computer can work when the system has loss and noise. Read More »

Focus: <i>Landmarks</i>—Correcting Quantum Computer Errors
Quantum Physics

Focus: Landmarks—Correcting Quantum Computer Errors

In the mid-1990s, researchers proposed methods to preserve the integrity of quantum bits—techniques that may become the key to practical quantum computing on a large scale. Read More »

More Articles