The 2022 Nobel prize for physics
has been awarded
to a trio of scientists for pioneering experiments in quantum mechanics, the
theory covering the micro-world of atoms and particles.
Alain Aspect from Université Paris-Saclay in France, John Clauser from J.F.
Clauser & Associates in the US, and Anton Zeilinger from University of
Vienna in Austria, will share the prize sum of 10 million Swedish kronor
(US$915,000) "for experiments with entangled photons, establishing the
violation of Bell inequalities and pioneering quantum information science".
The world of quantum mechanics appears very odd indeed. In school, we are
taught that we can use equations in physics to predict exactly how things
will behave in the future – where a ball will go if we roll it down a hill,
for example.
Quantum mechanics is different from this. Rather than predicting individual
outcomes, it tells us the probability of finding subatomic particles in
particular places. A particle can actually be in several places at the same
time, before "picking" one location at random when we measure it.
Even the great Albert Einstein himself was unsettled by this – to the point
where he was
convinced that it was wrong. Rather than outcomes being random, he thought there must be some "hidden
variables" – forces or laws that we can't see – which predictably influence
the results of our measurements.
Some physicists, however, embraced the consequences of quantum mechanics.
John Bell, a physicist from Northern Ireland, made an important breakthrough
in 1964, devising a
theoretical test
to show that the hidden variables Einstein had in mind don't exist.
According to quantum mechanics, particles can be "entangled", spookily
connected so that if you manipulate one then you automatically and
immediately also manipulate the other.
If this spookiness – particles far apart mysteriously influencing each other
instantaneously – were to be explained by the particles communicating with
each other through hidden variables, it would require faster-than-light
communication between the two, which Einstein's theories forbid.
Quantum entanglement is a challenging concept to understand, essentially
linking the properties of particles no matter how far apart they are.
Imagine a light bulb that emits two photons (light particles) that travel in
opposite directions away from it.
If these photons are entangled, then they can share a property, such as
their polarization, no matter their distance. Bell imagined doing
experiments on these two photons separately and comparing the results of
them to prove that they were entangled (truly and mysteriously linked).
Clauser put Bell's theory into practice at a time when doing experiments on
single photons was almost unthinkable. In 1972, just eight years after
Bell's famous thought experiment, Clauser showed that light could indeed be
entangled.
While
Clauser's results
were groundbreaking, there were a few alternative, more exotic explanations
for the results
he obtained.
If light didn't behave quite as the physicists thought, perhaps his results
could be explained without entanglement. These explanations are known as
loopholes in Bell's test, and Aspect was the first to challenge this.
Aspect came up with an ingenious experiment to rule out one of the most
important potential loopholes in Bell's test. He showed that the entangled
photons in the experiment aren't actually communicating with each other
through hidden variables to decide the outcome of Bell's test.
This means they
really are spookily linked.
In science it is incredibly important to test the concepts that we believe
to be correct. And few have played a more important role in doing this than
Aspect. Quantum mechanics has been tested time and again over the past
century and survived unscathed.
Quantum technology
At this point, you may be forgiven for wondering why it matters how the
microscopic world behaves, or that photons can be entangled. This is where
the vision of Zeilinger really shines.
We once harnessed our knowledge of classical mechanics to build machines, to
make factories, leading to the industrial revolution. Knowledge of the
behavior of electronics and semiconductors has driven the digital
revolution.
But understanding quantum mechanics allows us to exploit it, to build
devices that are capable of doing new things. Indeed, many believe that it
will drive the next revolution, of quantum technology.
Quantum entanglement can be harnessed in computing to process information in
ways that were not possible before. Detecting small changes in entanglement
can allow sensors to detect things with greater precision than ever before.
Communicating with entangled light can also guarantee security, as
measurements of quantum systems can reveal the presence of the eavesdropper.
Zeilinger's work paved the way for the quantum technological revolution by
showing how it is possible to link a series of entangled systems together,
to build the quantum equivalent of a network.
In 2022, these applications of quantum mechanics are not science fiction. We
have the first quantum computers. The Micius satellite uses entanglement to
enable secure communications across the world. And quantum sensors are being
used in applications from medical imaging to detecting submarines.
Ultimately, the 2022 Nobel panel have recognized the importance of the
practical foundations producing, manipulating, and testing quantum
entanglement and the revolution it is helping to drive.
I am pleased to see this trio receiving the award. In 2002, I started a PhD
at the University of Cambridge that was inspired by their work. The aim of
my project was to make a simple semiconductor device to generate entangled
light.
This was to greatly simplify the equipment needed to do quantum experiments
and to allow practical devices for real-world applications to be built. Our
work was successful
and it amazes and excites me to see the leaps and bounds that have been made
in the field since.
This article is republished from The Conversation under a Creative
Commons license. Read the
original article.
Tags:
Physics