Recently, the research team of Feng Mang, Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences, cooperated with Guangzhou Industrial Technology Research Institute, Hunan Normal University, Pennsylvania State University, etc., using the ultra-cold 40Ca+ ion experimental platform (Figure 1), and experimentally realized the world's first topological quantum heat engine based on Liuville's singularity and demonstrated its dynamic behavior. The working substance of this heat engine is an open (non-Ermi) single-bit quantum system. In such a system, there is a degenerate point of intrinsic energy (that is, the eigenstate and intrinsic energy collapse to one point), which is called the "Leviel singularity" (LEP). By changing the frequency conversion range of the work stroke of the quantum heat engine and comparing the two types of heat engine cycles that surround and do not surround the LEP, the experiment witnesses that "the topological properties caused by the Liu Weill singularity can enhance the output work and efficiency of the quantum heat engine", which provides important experimental evidence for exploring the novel characteristics and application potential of quantum heat engine. On March 17, the relevant research results were published online in Physical Review Letters.
A heat engine is a type of machinery that uses working substances to absorb heat from the heat reservoir and output usable work. The earliest heat engines appeared in the mid-18th century. Subsequently, the British engineer Watt's improvement of the steam type heat engine led to the emergence of the first industrial revolution, and mankind entered the industrial age. In the 21st century, thanks to the rapid development of micro-nano processing technology and experimental technology, the size of the heat engine has also been reduced from the centimeter order to the micro-nano level, especially the introduction of quantum properties may make the efficiency of the heat engine exceed the highest efficiency of the traditional heat engine. Therefore, the search for micro-nano quantum systems with higher heat engine efficiency is a frontier scientific issue and a technical challenge. Since the endothermic and exothermic strokes in the quantum heat engine cycle process are completed by the interaction between the working substance and the external environment, how to accurately and skillfully manipulate the non-Ermi quantum properties of the working material is particularly important.
In this experiment, the researchers used ion trap quantum manipulation technology to realize two types of quantum heat engine cycles that surround and do not surround LEP. The ion trap system is recognized in the world as a system that comprehensively exceeds the quantum fault tolerance calculation threshold in key parameters such as coherence time, quantum state preparation, quantum state operation (single and two-bit) quantum state operation, and quantum state measurement, and is currently one of the most promising physical systems to demonstrate the superiority of quantum technology applications. The Feng Mang team has long been committed to developing the key technology of precision manipulation based on 40Ca+ ions, which not only realizes the precise manipulation of the spin quantum state, but also can accurately open and close the dissipation channel of the quantum system and adjust the size of the dissipation, so as to controllably display all the novel characteristics of the non-Ermi quantum system. The team has reported the possibility of using LEP to regulate quantum heat engines, showing that quantum coherence in different strokes has an important impact on the power output and efficiency of heat engines [Nature Communications 13, 6625 (2022)]. The existence of LEP leads to a topological phase transition from the broken phase to the exact phase, but whether the topological phase transition itself has thermodynamic effects is an open question.
In this work, the experimental parameters of LEP and its precise phase and broken phase were accurately determined with the help of the three-level structure of a single ultracold 40Ca+ ion. By adjusting the frequency detuning of the applied light field, two types of quantum heat engine cycles are realized with and without surrounding LEP. The quantum heat engine demonstrated in the experiment consists of four strokes: equal dissipative compression, equal detuned heating, equal dissipative expansion and equal detuning cooling, in which equal dissipative compression is in the broken phase and equal dissipative expansion is in the exact phase (Figure 2). The results of multiple experiments show that the quantum heat engine cycle that does not surround LEP may do negative work; The quantum heat engine cycle around LEP always does positive work (Figure 3). Based on strict data analysis and numerical simulation, the topological properties of LEP are finally confirmed to have thermodynamic properties, which can be applied to effectively enhance the output work and efficiency of quantum heat engines.
This study accurately demonstrates the world's first quantum heat engine based on the topological properties of Liuville's singularity in non-Ermi quantum systems at the atomic level, witnessing the thermodynamic effects brought about by topological properties. The conclusions of this research and the technology presented are expected to be applied to the development of micro-intelligent devices such as molecular motors and nanorobots. This study reveals for the first time the special relationship between the Landau-Zener-Stückelberg process, topological phase transitions, and quantum heat engine efficiency, but its deeper physical significance needs to be further explored.
The research work is supported by the key projects of the National Natural Science Foundation of China, the major special projects of Guangdong Provincial Key Field R&D Program, and the Guangzhou Key Laboratory Project.
Ultra-cold 40Ca+ ion experimental platform, the ion trap that traps the ions is protected by a magnetic shielding device (that is, a silver-white metal box behind the photo). The rest of the optical equipment is used to assist the laser system in manipulating ions to complete the various strokes required for the quantum heat engine.
Experimental data and their corresponding output net work changes. (a, b) Change of excited state distribution number corresponding to equal dissipative strokes around the singularity over time. (c, d) Change of excited state distribution over time for equal dissipative strokes that do not surround the singularity. (e, f) The change in net work corresponding to the equal dissipative stroke around the singularity. (g, h) The change in net work corresponding to the equal dissipative stroke that does not surround the singularity. In the figure, the green lines and shaded areas represent equal dissipative compression in the broken phase, while the red lines and shaded areas represent equal dissipative expansion in the strict phase
Surround and do not surround the net work output of the LEP. (a) The heat engine cycle surrounding the LEP not only ensures that the heat engine cycle always outputs positive work, but also enhances the net work output. (b) The output work of the heat engine cycle that does not surround the LEP has positive or negative output.
Source: Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences
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