Special CPM Seminar

Testing Landauer's Principle in a Feedback Trap

John Bechhoefer

Department of Physics
Simon Fraser University

Landauer's principle, formulated in 1961, postulates that irreversible logical or computational operations such as memory erasure require work, no matter how slowly they are performed. For example, “resetting to one” a one-bit memory converts at least kT ln2 of work to heat. Bennett and Penrose later pointed out a link to Maxwell's demon: Were Landauer's principle to fail, it would be possible to repeatedly extract work from a heat bath and violate the second law of thermodynamics.

We report tests of Landauer's principle using a charged colloidal particle in water. Our setup consists of a time-dependent, “virtual” double-well potential created by a feedback loop that is much faster than the relaxation time of the particle. In a first set of experiments, at long cycle times, we observe that the average work is compatible with kT ln2 when one bit is erased. But in control experiments with comparable manipulations and no net information erasure, the work is zero. In a second set of experiments, we explore what happens when the different states occupy differing volumes in phase space. In this case, the average erasure cost can be below kT ln2 per bit. We also find, somewhat surprisingly, that not all slow protocols converge to the quasistatic limit.