Efficiency
Fluctuations at maximum power.
(October 27, 2015) In
a recent study published in Nature Physics, ICFO researchers Ignacio Martínez,
Édgar Roldán, the late Dmitri Petrov and Raúl Rica, in collaboration with the
Universidad Complutense de Madrid, have reported on the development of a
microscopic motor operating between two thermal baths, that is, a micro Carnot
engine.
At the macroscopic level, a thermal engine is what makes car
engines work, where a substance such as gas is compressed and expanded at
different temperatures, converting thermal energy into mechanical energy, and
thus, making the car move. Almost two centuries ago, the theoretical studies by
Carnot set an upper bound to any thermal engine. Unfortunately, the so-called
Carnot engine is a theoretical construction never tested experimentally. In
their study, the researchers focused their efforts in creating a “microscopic
engine” with the same properties as the Carnot engine, allowing the
experimental validation of one of the milestones of Thermodynamics.
They created microscopic motors that work using a
temperature difference, exactly as the engines in cars work, using the
temperature difference between the hot gas inside the piston and the air
outside. Instead of using a gas, they used a single particle and lasers and
electrical fields in replacement of the cylinders, pistons and crankshafts,
although the functioning process is essentially the same. They developed the
microscopic heat engine by trapping a microparticle with a laser trap and tune
the effective temperature of the particle via noisy electric fields, which
increase the Brownian fluctuations of the trapped particle. Moreover, by
modifying the laser power they were able to control the confinement of the
particle in the trap, a sort of effective volume analogous to that of the gas
inside the cylinder of a car engine. The simultaneous control over these two parameters
following specific protocols established the cyclic operation that any kind of
engine has, in particular those that define the Carnot cycle.