High-Precision Test of Landauer's Principle in a Feedback Trap

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, to ``reset to one'' a one-bit memory requires at least kT ln2 of work, which is dissipated as heat. Bennett and, independently, 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. We report tests of Landauer's principle in an experimental system consisting of a charged colloidal particle in water. To test stochastic thermodynamic ideas, we create a time-dependent, ``virtual'' double-well potential via a feedback loop that is much faster than the relaxation time of the particle in the virtual potential. In a first experiment, the probability of ``erasure'' (resetting to one) is unity, and at long cycle times, we observe that the average work is compatible with $kT$ ln2. In a second, the probability of erasure is zero; the system may end up in two states; and, at long cycle times, the average measured work tends to zero. In individual cycles, the work to erase can be below the Landauer limit, consistent with the Jarzynski equality.