An autonomous
Maxwell's demon. When the demon sees the electron enter the island (1.),
it traps the
electron with a positive charge (2.). When the electron leaves the island (3.),
the demon switches
back a negative charge (4.). Image: Jonne Koski.
(January 11, 2016) Scientists
created a nano-scale device that may facilitate the design of future computers,
for example.
In 1867, Scottish physicist James Clerk Maxwell challenged
the second law of thermodynamics according to which entropy in a closed system
must always increase. In his thought experiment, Maxwell took a closed gas
container, divided it into two parts with an inner wall and provided the wall
with a small trap door. By opening and closing the door, the creature – ‘demon’
– controlling it could separate slow cold and fast warm particles to their
respective sides, thus creating a temperature difference in contravention of
the laws of thermodynamics.
On theoretical level, the thought experiment has been an
object of consideration for nearly 150 years, but testing it experimentally has
been impossible until the last few years. Making use of nanotechnology,
scientists from Aalto University have now succeeded in constructing an
autonomous Maxwell’s demon that makes it possible to analyse the microscopic
changes in thermodynamics. The research results were recently published in
Physical Review Letters. The work is part of the forthcoming PhD thesis of MSc
Jonne Koski at Aalto University.
‘The system we constructed is a single-electron transistor
that is formed by a small metallic island connected to two leads by tunnel
junctions made of superconducting materials. The demon connected to the system
is also a single-electron transistor that monitors the movement of electrons in
the system. When an electron tunnels to the island, the demon traps it with a
positive charge. Conversely, when an electron leaves the island, the demon
repels it with a negative charge and forces it to move uphill contrary to its
potential, which lowers the temperature of the system,’ explains Professor
Jukka Pekola.
What makes the demon autonomous or self-contained is that it
performs the measurement and feedback operation without outside help. Changes
in temperature are indicative of correlation between the demon and the system,
or, in simple terms, of how much the demon ‘knows’ about the system. According
to Pekola, the research would not have been possible without the Low
Temperature Laboratory conditions.