Synopsis: Quantum Pistons

Calculations reveal the relationship between work and free energy for a quantum particle contained in a box with a moving wall.
Synopsis figure
C. Jarzynski and H. T. Quan, Phys. Rev. E (2012)

In equilibrium, the change in free energy, ΔF, of a system as it transitions between two states sets a limit on the work, W, that can be realized in the process. Theorists have searched for similar exact relations between the work done on or by a system and its change in free energy in nonequilibrium processes, and some of these relations have been verified in experiments on small, effectively classical systems, such as macromolecules.

Showing the relations are also valid in nonequilibrium quantum systems is of fundamental importance. A case in point is the “Jarzynski equality” derived by Christopher Jarzynski at the University of Maryland, College Park, which states that, classically, the statistical average of exp[-W/KBT] is equivalent to exp[-ΔF/KBT]. Whether the equality applies to a quantum piston—a quantum particle in a one-dimensional box, with one of the walls moving at a fixed velocity—has remained an open question.

Writing in Physical Review E, Jarzynski and Haitao Quan, also at the University of Maryland, utilize a solution to the time-dependent Schrödinger equation for this quantum machine that shows the Jarzynski equality is in fact satisfied. Their result is not intuitively obvious, as there are important differences between the classical and quantum pistons; for example, the work performed on a classical particle is always negative in an expanding piston, but quantum fluctuations lead to the possibility of positive work in the quantum case. – Ronald Dickman


More Features »


More Announcements »

Subject Areas

Quantum PhysicsStatistical Physics

Previous Synopsis

Biological Physics

Fractal Teeth

Read More »

Next Synopsis

Nonlinear Dynamics

Lévy Flight of the Bumblebee

Read More »

Related Articles

Synopsis: Straying from the Norm in Pedestrian Movements
Complex Systems

Synopsis: Straying from the Norm in Pedestrian Movements

Experiments tracking people as they walk down a corridor reveal universal behaviors that, if incorporated into models, could ensure safe flow in large crowds. Read More »

Viewpoint: A New Twist on Relativistic Electron Vortices

Viewpoint: A New Twist on Relativistic Electron Vortices

Two studies explore the properties of vortices formed by electrons that travel at relativistic speeds. Read More »

Viewpoint: A New Angle on Quantum Impurities
Quantum Physics

Viewpoint: A New Angle on Quantum Impurities

Quasiparticles called angulons can simplify the theoretical description of a molecule immersed in a quantum solvent. Read More »

More Articles