Passcode: please contact albertrico23 at gmail.com
seminar
Speaker: Albert Rico (UJ)
Abstract
Bell inequalities’s journey from rags to riches of quantum
theory was a long one. Proposed by John Bell in 1964, the inequalities
were designed to check whether quantum theory, with its inherent
statistical predictions, is a complete description of physical reality
or whether it is just a provisional construct, with an underlying
hidden structure which, once discovered, would offer precise
predictions. The subsequent pioneering experiments of outliers, such
as John Clauser (1972) and Alain Aspect (1982), showed that Bell’s
inequalities can be violated. However, these experiments were barely
noticed at that time. Quantum theory is admittedly strange, but it
worked and the research community just carried on using it in an
instrumental way, making successful statistical predictions while
avoiding anything related to their interpretations. Bell inequalities
were viewed as a philosophical topic with no practical value and hence
not worthy of the attention of serious scientists. When Bell
inequalities snagged my imagination, I was just a PhD student with
nothing to lose. In 1991, I reformulated Bell inequalities as the test
for eavesdropping in cryptography, paving the way for the most secure
communication systems to date, known as the device independent quantum
key distribution. The new narrative around Bell inequalities created
an additional motivation to close all possible loopholes in the
previous experiments. In the new context it seemed reasonable. Nature
would have to be very malicious if it were to cheat selectively; on
locality in some experiments and exploring detection loopholes in some
others. In contrast, an eavesdropper has all the rights to be
malicious. Closing the loopholes posed an experimental challenge but
gradually, due to the efforts of several experimental groups, to
mention only those of Anton Zeilinger (2015), the loopholes were
closed and device independent cryptography became a realistic
experimental proposition. Cryptography offered a lifeline to quantum
foundations and in return the experimental tools developed to pursue
esoteric philosophical questions gave cryptography unprecedented
security. The curiosity and perseverance of the few brave souls who
made this happen (and who are still alive) were finally rewarded with
the 2022 Nobel Prize in Physics.
