In collaboration with the researcher from Shanghai Jiaotong University, Professor Mang Feng’s group for Bound-System Quantum Information Processing at Wuhan Institute of Physics and Mathematics (WIPM), Chinese Academy of Sciences has just published their latest research exploring the quantized Landauer principle in Physical Review Letters, which is selected as Editor’s Suggestion and Featured in Physics due to its importance. Professor Massimiliano Esposito at University of Luxembourg writes a commentary on this work in Physics (an electronic journal of American Physics Society) with the title “Landauer Principle Stands up to Quantum Test”.

In the information processing, a minimum amount of energy is required to be consumed against deleting a bit of information. This is known as the famous Landauer principle, which implies an irreversibility of logic operations and is associated with the elucidation of “Maxwell demon” – a paradox in thermodynamics for hundreds of years. Contrary to its classical version the quantum Landauer principle is based on a fully quantized system and quantized reservoir as well. So the deletion of information in a quantum bit (qubit) strongly depends on the reservoir temperature as well as the quantum correlation between the system and reservoir. Based on the entropy conservation, the quantized Landauer principle presents a strict equality among the entropy change of the system, the energy variation of the reservoir and the quantum correlation between the system and reservoir, which is more complicated than the original Landauer principle where no system-reservoir correlation is taken into account. However, this new principle has never been verified experimentally since its discovery in 2014, due to the difficulties incorporated in designing a quantized reservoir and measuring the system-reservoir correlation. Besides, eliminating information from a qubit takes energy of 10-28 joules. As such, observation of such a small energy variation requires an ultracold ion and great precision in measurements.

Professor Feng’s group has recently accomplished an elaborate experimental implementation for testing this quantized Landauer principle based on the experimental techniques consisting of arbitrary quantum-state preparation, precise laser-control of the carrier and sideband transitions as well as precision measurement of quantum states. By modeling both the quantized system and reservoir in a single 40Ca+ ion, the group members outlined the implementation steps based on the real experimental parameters stringently considering the detrimental influence of decoherence. In the experiment, the detection error for the system (the ion’s spin) is less than 3% and for the reservoir (the ion’s vibration) is smaller than 0.02 quanta. So the experimental observations are in strong agreement with the theoretical prediction. This is the first experimental demonstration of a fully quantized Landauer principle and a sophisticated approach to witness the minimum energy cost in quantum logic operations for the first time. In particular, the experimental observations have exposed an unprecedented thermodynamic effect which had never been reported before. Under the condition of quantum correlation, the energy cost of the system could be related to information generation instead of deletion.

This work will be helpful for understanding the fundamental physical limitations of irreversible logical operations at the quantum level. It indicates that like in our macroscopic world, no perpetual motion machine exists in quantum world, and even more energy consumption is needed in quantum world than in macroscopic world in processing information.

Assistant Professor Leilei Yan and PhD students Taiping Xiong and Kamren Rehen contributed equally to this work. Associate Professors Fei Zhou and Wanli Yang and Professor Mang Feng are corresponding authors of this work. The study was supported by National Key Research and Development Program of China, the Strategic Research Program of the Chinese Academy of Sciences and National Natural Science Foundation of China.

Experimental schematic of the quantized Landauer principle

Experimental observation for the quantized Landauer principle in a single ultracold 40Ca+ ion