Single-atom demonstration of quantum Landauer principle (1803.10424v1)

Abstract: One of the outstanding challenges to information processing is the eloquent suppression of energy consumption in execution of logic operations. Landauer principle sets an energy constraint in deletion of a classical bit of information. Although some attempts have been paid to experimentally approach the fundamental limit restricted by this principle, exploring Landauer principle in a purely quantum mechanical fashion is still an open question. Employing a trapped ultracold ion, we experimentally demonstrate a quantum version of Landauer principle, i.e., an equality associated with energy cost of information erasure in conjunction with entropy change of the associated quantized environment. Our experimental investigation substantiates an intimate link between information thermodynamics and quantum candidate systems for information processing.

Single-Atom Demonstration of Quantum Landauer Principle

The paper "Single-atom demonstration of quantum Landauer principle" presents an experimental exploration of the quantum Landauer principle, conducted by manipulating a single trapped ion. This paper aims to probe the energy cost associated with information erasure and its corresponding entropy change in a quantized environment, thereby investigating the thermodynamic implications within quantum mechanical systems.

The Landauer principle traditionally posits that the erasure of a classical bit of information dissipates a minimum amount of heat, quantified as $k_B T \ln 2$, where $k_B$ is the Boltzmann constant and $T$ is the temperature of the environment. However, this paper focuses on extending the principle to quantum systems where both the system and the environment are treated quantum mechanically. The researchers employ a single $^{40}\text{Ca}^+$ ion confined in a linear Paul trap, which serves as an ideal platform given its precise controllability and the coherent dynamics it can sustain.

The central contribution of this work lies in the experimental verification of an "improved" or quantum Landauer principle. This version extends beyond the classical inequality, presenting an equality that links the heat dissipated ($\Delta Q$), the change in entropy ($\Delta S$), mutual information related to system-reservoir correlations ($I(S':R')$), and the relative entropy of the reservoir ($D(\rho'_{R} \| \rho_{R})$). The equality is expressed as:

$$\Delta Q/k_B T = \Delta S + I(S':R') + D(\rho'_R \| \rho_R).$$

In the experimental setup, the internal states of the ion represent the system qubit, while its vibrational modes in the trap act as the thermal reservoir. The researchers prepared the qubit in a maximally mixed state before erasure and initialized the reservoir at a finite temperature. The procedure for information erasure involved manipulating the ion via a red-sideband transition, which induced a unitary evolution leading to a net decrease in the system's entropy while increasing the reservoir's energy.

Experimental results demonstrated that the quantum correlation between the system and its finite-sized reservoir significantly influences the energy cost of information erasure. Notably, the mutual information and the relative entropy terms contribute predominantly at different temperature regimes, substantiating the theoretical arguments underpinning the quantum Landauer principle.

The findings hold significant implications for quantum information processing. Understanding the quantum limits of energy dissipation is essential as it affects both the initialization processes and the error-correction protocols in quantum computing environments. The paper suggests that the heat produced in erasing quantum information could potentially exceed classical expectations due to system-reservoir entanglement.

Future investigations could explore the influence of different quantum state preparations on the principle and extend these experiments to multi-qubit systems. Moreover, the experimental demonstration now opens the door to further exploration of correlated system-reservoir dynamics and other quantum thermodynamic processes. This work, therefore, represents a pivotal advancement in applying thermodynamic principles to quantum domains, ensuring theoretically sound energy optimization in the burgeoning field of quantum technologies.