ARTICLES
Experiment shows Einstein’s Quantum ‘Spooky Action’
Approaches the Human Scale
By Dr Matt Woolley
There are perhaps two ingredients required for the observation of
quantum behaviour in an object.
The first is isolation. The world outside is full of sound and fury,
such as other matter and radiation. If the object can find a way to
isolate itself from this fury, it can evolve according to the simple
rules of quantum mechanics.
An object that cannot isolate itself from the fury will find that the
richness of quantum dynamics cannot be accessed, so its motion
will be well described by the familiar rules of classical physics.
A thrown ball will follow a well-defined trajectory; it will not spread
out as one might expect from quantum physics. A rolling stone
will go up a hill until the supply of the energy of motion it had at
the bottom of the hill is exhausted; it cannot possibly emerge
on the other side of the hill as it might according to the rules of
quantum tunnelling.
Einsteins Spooky Action approaches Human Scale
Quantum physics is often defined to be the physics of the
very small – think atoms, electrons and photons. But we have
managed to demonstrate one of the quirky features of quantum
physics at a much larger scale. In a paper published on 26th
April, 2018 in ‘Nature’, we describe how we were able to create
‘quantum entanglement’ of the motion of objects composed of
many billions of atoms.
The second ingredient is frequency, the rate at which a confined
object vibrates. The emergence of quantum behaviour typically
requires that the energy associated with the object (which
is related to its frequency of vibration) exceeds the energy
associated with the object’s environment (which is related to
its temperature). So, even if an object is well isolated from its
environment, it will not be perfectly isolated, so the properties of
the object’s environment still matter.
Entanglement is where two objects that may be separated by
an arbitrary distance are somehow connected: a measurement
on one object leads to a change in the results of measurements
made on the other – what Albert Einstein called “spooky action
at a distance”.
Consider light: photons of light interact only weakly with other
photons, so that if we consider light propagating in near vacuum
conditions we have a well-isolated system. That’s the first
ingredient.
Entanglement for microscopic-scale systems, such as those
involving photons, ions and electron spins, has already been
demonstrated in a number of experiments, but there were
of challenges still remained before we could demonstrate
entanglement on a larger scale.
What about frequency? Well, the electric and magnetic fields
associated with visible light go up and down around 6×10 14 times
per second.
Before I look at how we solved some of those challenges we
need to understand a bit more about quantum physics.
In cases like this the energy associated with a photon of light
vastly exceeds the energy scale of the likely thermal environment.
One can tell a similar story for the electronic levels of isolated
atoms. Thus very small objects are more likely to possess the
ingredients required for the observation of quantum phenomena.
The size of things
Does size really matter in quantum physics? Kind of; in fact there
is nothing in the formulation of quantum mechanics that mandates
that it should apply only to the very small. In which case, what
really matters in determining whether a particular object will
behave according to the strange rules of quantum physics, or
according to the familiar rules of classical physics?
Scale things up a bit
Let’s go bigger and more tangible. Instead of thinking about the
electromagnetic fields of light, or the electronic levels of an atom,
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SCIENCE EDUCATIONAL NEWS VOL 67 NO 4