ARTICLES
Experiment shows Einstein’s Quantum (continued)
how about the motion of a macroscopic, massive object? Can we
make such an object behave according to the rules of quantum
physics, and observe that behaviour?
are more common than many people realise. The humble quartz
oscillator remains a crucial technology for some clocks. Surfaces
are imaged using the atomic force microscope, essentially a
suspended cantilever that deflects light. Gravitational waves are
observed by monitoring the motion of suspended mirrors using
laser light.
The answer, as we reported on 26th April, is yes.
In an experiment performed in the laboratory of Professor
Mika Sillanpää at Aalto University in Finland, we set up two
microfabricated vibrating circular membranes, like drumheads.
Each was about the width of a human hair, and we were able
to measure them in a state that exhibited the quantum property
of entanglement. The two drumheads were brought into an
entangled state through careful driving of a superconducting
electrical circuit to which both were coupled.
While quantum control of mechanical systems conceivably offers
an advantage in each of these scenarios, mechanical systems
offer another advantage – they move, and therefore they couple
to both microwaves and light.
While the processing power of a future quantum computer might
indeed rely on microwaves in a low-temperature laboratory
environment, all quantum communications systems will require
light propagating through optical fibres or free space, so
mechanical systems can act as intermediaries between these
worlds and thereby contribute to the realisation of a quantum
internet.
While these drumheads may seem small on the human scale,
they are huge on the atomic scale – each of the drumheads was
composed of trillions of atoms.
These drumheads are the largest objects to have been prepared
in such an entangled state, so this experiment was probably
the closest approach to the literal implementation of the famous
thought experiment of Einstein, Podolsky and Rosen that first
studied the phenomenon that became known as entanglement
back in 1935.
While it is hard to say exactly where these experiments might
ultimately lead, it is clear that the era of massive quantum
machines has arrived, and is here to stay.
Author:
Why we did it Dr Matt Woolley; Senior Lecturer in Electrical Engineering, UNSW
Why should we take the trouble to demonstrate quantum physics
with massive, macroscopic objects? There are two answers: one
fundamental and one applied. Disclosure statement
On the fundamental side, this demonstration gives us greater
confidence that the laws of quantum physics do indeed apply to
large objects. But will this continue to hold true as the size and
mass of the objects in such experiments is increased? We don’t
know. Tabletop experiments with massive objects bring forth the
possibility that such a question might one day be answered. This article was first published in ‘The Conversation’ on 26th
April, 2018. Science Education News and the Science Teachers’
Association of NSW are grateful to ‘The Conversation’ for its
generous policy of encouraging the republishing of its many fine
articles. We also thank the author, Dr Matt Woolley, for supplying
this article for general information, thereby supporting this policy.
Matt Woolley receives funding from the Australian Research
Council.
On the applied side, one may ask: what could mechanical quantum
systems offer in this electronic age? However, mechanical systems
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SCIENCE EDUCATIONAL NEWS VOL 67 NO 4