Speaker
Rainer Kaltenbaek
Description
Since its development, quantum physics has quickly
become one of the most successful physical theories
ever devised. Despite of that, some of the most basic
concepts of quantum physics even today remain a topic
of discussion. One of these central concepts is that of
quantum superposition, which will be the main topic of a
second talk. However, it also is a prerequisite for
quantum entanglement. The notion of entanglement
was originally coined by Erwin Schrödinger, and the
concept was immediately seized by Einstein, Podolsky
and Rosen (EPR) in an argument for what they called the
“incompleteness” of quantum theory. Bell and others
later formalized this argument in what is now known as
Bell-type inequalities. This inequality has to be fulfilled by
the predictions of any theory fulfilling the two basic
assumptions of EPR's definition of a complete physical
theory: locality and realism. Such theories are therefore
called local-realistic models. Yet, quantum theory can
violate those inequalities and, by now, many
experiments have shown that nature itself also violates
Bell-type inequalities, confirming the predictions of
quantum theory. Due to this fact, quantum theory and
any theory that wants to accurately predict experimental
results has to violate at least one of the two
assumptions of local-realistic models: either realism or
locality. Because many physicists still find it hard to part
with the classical notion of realism, the notion of
quantum non-locality appeared. Here, we will discuss
the concepts, the realization and the implications of
experiments testing quantum theory against local
realism.
