We study the thermodynamics of a Brownian particle under the influence of a time multiplexed harmonic potential of finite width. The memory storage mechanism and the erasure protocol realized by time multiplexed potentials are utilized to experimentally realize erasure with work close to the Landauer's bound. We quantify the work done on the system with respect to the duty-ratio of time multiplexing, which also provides a handle to approach reversible erasures. A Langevin dynamics based simulation model is developed for the proposed memory bit and the erasure protocol, which guides the experimental realization. The study also provides insights into transport at the micro scale. PACS numbers: 05.40.-a, 05.70.LnThe Landauer's principle, pioneered by Rolf Landauer in 1961, provides a critical link between information theory and thermodynamics of physical systems [1]. It states that there is no process where the work done to erase one bit of information is less than k b T ln 2 (Landauer's bound), when the prior probability of the bit being in any of the two states is equal [2]. Here, k b is the Boltzmann constant and T is the temperature of the heat bath.Numerous analyses have established the Landauer's bound through different approaches [3][4][5][6][7]. The experimental study of Landauer's bound has only recently be- In this article, we study the stochastic energetics of transport realized by time multiplexing of a finite width harmonic potential to effectively realize a bi-stable potential. Here a single laser in an optical tweezer setup, is multiplexed at two locations with varying dwell times to create a series of potentials (symmetric as well as asymmetric bi-stable potentials), that effectuates the erasure process. Moreover, experimental variables to realize reversible erasure are identified and utilized for approaching the Landauer's bound. A Langevin framework for a Brownian particle under the influence of a time multiplexed laser is developed and is shown to obey quantitative trends observed in experiments. We use our method of shaping the potential, by changing the dwell time of multiplexing of the laser, to erase one bit of information. The ease of implementation and the high-resolution accounting of energetics enabled by photodiode based measurements are other advantages of the method reported. We resort to Sekimoto's stochastic energetics [12][13][14][15] framework to quantify the work done on the system in the erasure process. The underlying principles developed in this article are applicable toward the study of transport achieved by time multiplexing of a single potential, and are not restricted to realizations based on optical traps.Experiment and Simulation Model for one-bit Memory: A Brownian particle in a double well potential is used to model a one-bit memory. The memory is designated the state 'zero' if the particle is in the left well, and the state 'one' if it is in the right well. We realize a Brownian particle in a harmonic potential of finite width experimentally, by using a custom built op...

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Intracellular transport is an essential function in eucaryotic cells, facilitated by motor proteins—proteins converting chemical energy into kinetic energy. It is understood that motor proteins work in teams enabling unidirectional and bidirectional transport of intracellular cargo over long distances. Disruptions of the underlying transport mechanisms, often caused by mutations that alter single motor characteristics, are known to cause neurodegenerative diseases. For example, phosphorylation of kinesin motor domain at the serine residue is implicated in Huntington’s disease, with a recent study of phosphorylated and phosphomimetic serine residues indicating lowered single motor stalling forces. In this article we report the effects of mutations of this nature on transport properties of cargo carried by multiple wild-type and mutant motors. Results indicate that mutants with altered stall forces might determine the average velocity and run-length even when they are outnumbered by wild type motors in the ensemble. It is shown that mutants gain a competitive advantage and lead to an increase in the expected run-length when the load on the cargo is in the vicinity of the mutant’s stalling force or a multiple of its stalling force. A separate contribution of this article is the development of a semi-analytic method to analyze transport of cargo by multiple motors of multiple types. The technique determines transition rates between various relative configurations of motors carrying the cargo using the transition rates between various absolute configurations. This enables a computation of biologically relevant quantities like average velocity and run-length without resorting to Monte Carlo simulations. It can also be used to introduce alterations of various single motor parameters to model a mutation and to deduce effects of such alterations on the transport of a common cargo by multiple motors. Our method is easily implementable and we provide a software package for general use.

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