[Paper Review] Experimental nonequilibrium memory erasure beyond Landauer's bound

Mario A. Ciampini, Tobias G. Wenzl+5 more|arXiv (Cornell University)|Jul 9, 2021

Mechanical and Optical Resonators33 references4 citations

TL;DR

This experiment demonstrates that nonequilibrium memory states in an optomechanical two-state system enable information erasure with work and heat dissipation below Landauer's bound of $kT\ln 2$. By dynamically shaping nonlinear optical potentials via tailored laser beams and electric fields, the team achieved negative heat production and reduced energy consumption, validating a generalized nonequilibrium Landauer principle.

ABSTRACT

The clean world of digital information is based on noisy physical devices. Landauer's principle provides a deep connection between information processing and the underlying thermodynamics by setting a lower limit on the energy consumption and heat production of logically irreversible transformations. While Landauer's original formulation assumes equilibrium, real devices often do operate far from equilibrium. We show experimentally that the nonequilibrium character of a memory state enables full erasure with reduced power consumption as well as negative heat production. We implement the optimized erasure protocols in an optomechanical two-state memory. To this end, we introduce dynamical shaping of nonlinear potential landscapes as a powerful tool for levitodynamics as well as the investigation of far-from-equilibrium processes.

Motivation & Objective

• To investigate whether nonequilibrium initial states in a double-well potential can reduce the thermodynamic cost of information erasure below the equilibrium Landauer limit.
• To experimentally demonstrate that work and heat dissipation during erasure can be minimized or even become negative by harnessing the energy and entropy of nonequilibrium memory states.
• To develop and apply dynamically programmed optical micromanipulation for fast, nonlinear potential control in underdamped levitated systems.
• To extend the toolbox of levitated optomechanics beyond amplitude modulation to include full dynamical shaping of anharmonic potentials.
• To test the validity of a generalized nonequilibrium Landauer bound in a real experimental setup with precise trajectory and energy measurements.

Proposed method

• The experiment uses a single charged nanosphere optically levitated in a vacuum chamber, trapped in a double-well potential formed by orthogonal TEM₀₀ and TEM₁₀ laser modes.
• Laser powers and beam profiles are dynamically controlled via acousto-optic modulators and a spatial light modulator to shape the potential landscape in real time.
• An external electric field is applied via nearby electrodes to tilt the potential, enabling controlled reset of the system to a target state.
• Position and velocity of the nanoparticle are measured with split-detection of the transmitted TEM₀₀ beam at a time resolution of 0.16 μs.
• Work is calculated from discrete changes in potential energy along individual trajectories, and heat is derived from the first law of thermodynamics using energy and kinetic energy changes.
• The system is prepared in a nonequilibrium state by increasing the relative power of the TEM₁₀ mode, creating an asymmetric double-well potential with a defined nonequilibrium parameter $\epsilon$.

Experimental results

Research questions

• RQ1 Can information erasure in a nonequilibrium memory state consume less than $kT\ln 2$ of work and produce less than $kT\ln 2$ of heat?
• RQ2 Does the nonequilibrium character of the initial memory state allow for negative heat production during erasure?
• RQ3 To what extent can dynamically shaped nonlinear potentials reduce the thermodynamic cost of logical reset in a far-from-equilibrium system?
• RQ4 How does the generalized nonequilibrium Landauer bound compare to the equilibrium limit in a real experimental setup?
• RQ5 Can dynamical control of optical potentials in vacuum levitation systems enable precise, fast, and energy-efficient information processing?

Key findings

• The experiment achieved heat dissipation below $kT\ln 2$ during erasure, with values reaching negative heat production, indicating local cooling of the environment.
• Work consumption during erasure was reduced below the equilibrium Landauer bound of $kT\ln 2$, demonstrating a thermodynamic advantage from nonequilibrium initial states.
• For a nonequilibrium parameter $\epsilon = 4$, the system exhibited a significant reduction in both work and heat compared to the equilibrium case, with heat production dropping below the $kT\ln 2$ threshold.
• The results are in quantitative agreement with the generalized nonequilibrium Landauer bound proposed by Konopik *et al.* (2018), confirming theoretical predictions in a real system.
• The use of dynamically programmed optical micromanipulation enabled precise control of nonlinear potentials on sub-microsecond timescales, essential for achieving the optimized protocols.
• The study demonstrates that the thermodynamic cost of erasure can be shifted from the reset phase to the nonequilibrium preparation phase, offering new design principles for low-power computing architectures.