Feng Mang's team at the Institute of Precision Measurement, Chinese Academy of Sciences, successfully realized the first international non-Ermy quantum heat engine experiment

Recently, Feng Mang's research team at the Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences, in collaboration with scientists from the Guangzhou Institute of Industrial Technology, Zhengzhou University and the University of Michigan, has developed a quantum heat engine: using a single atom as a motor, it is expected to be applied in the fields of energy, biology, medicine and engineering for the development of molecular motors, nanorobots and miniature smart molecular motors, nano-robots, and miniature smart devices. By using lasers to precisely manipulate the state of quantum ions, the team overcame the hurdle of operating dynamical systems at the microscopic scale.

The research was published in October in the journal Nature Communications under the title "Dynamic control of quantum heat engines using singularities" [1].

01New quantum heat engine: driven by laser beams of different frequencies and intensities

Quantum systems are particularly sensitive to external disturbances, but energy exchange with the outside world is inevitable. The paper says that breakthroughs in laser technology have led to a quantum heat engine that can resist external interference. A steam engine goes through four thermodynamic modes in a complete working cycle: namely, adiabatic compression, isothermal heating, adiabatic expansion and isothermal cooling.

In Feng's team's quantum heat machine, a single calcium ion (Ca+) acts as a steam-like working medium, and the compression or heating process of the cycle is driven by laser beams of different frequencies and intensities. This quantum heat machine generates power in the form of light: the varying intensities of the light make changes in the pattern of the ions observable.

A single-spin quantum heat machine in 40Ca+ ions exhibits a Liouvillian singularity (LEP), as shown in the D-figure.

Specifically, the experimental team reports the experimental realization of a single-ion heat machine and demonstrates the effect of the Liouvillian singularity on the dynamics, and performance of the quantum heat machine. It is shown that during the isothermal heating and cooling strokes of the Otto cycle, the engine operates in the exact phase and the broken phase, respectively, which are separated by a Liouvillian singularity; more work and output power are produced and higher efficiency is achieved compared to performing the Otto cycle entirely in the exact phase: because the system has oscillatory dynamics and higher coherence of the system. This result offers more possibilities for the control of quantum heat engines.

Schematic diagram of the Otto cycle with the isothermal heating process in the exact phase and the isothermal cooling process in the fracture phase.

02Overturning the mainstream idea

The experimental results have overturned the mainstream notion that the efficiency of a quantum heat engine can be improved by increasing the quantum coherence. It was previously believed that the stronger the quantum characteristics of an ion, the higher the efficiency of the heat engine, and that the efficiency of a quantum heat engine is only related to the start-up power of the heat engine. However, with the help of a controllable laser, Feng's team found that the quantum characteristics of ions can reach the maximum efficiency under different heat engine modes.

The theory was not only an exploration of cutting-edge science, but also a challenge to the prevailing view and divided opinion among some scientists: the paper's submission process took more than a year, and peer experts raised many questions.

"But the truth speaks for itself. We finally presented and published the work; despite the controversy surrounding it." Von Mann said [2], "We were also cautious about it. We have been working in this field for more than 10 years, and we have been focusing on energy and information conversion in quantum systems. We have submitted these papers after repeatedly verifying the theory and experiments."

03Two major developments remain before practical applications ......

There is still more work to be done before the technology can be used.

The researchers say there is still much work to be done before a usable molecular motor is available.

Our research mainly provides a demonstration," said Fengmang. In order to actually make usable molecular motors or power nanorobots: we need to find a suitable working medium, like water vapor in a steam engine."

The team has two subsequent lines of research: finding the exact point at which the laser helps the engine produce the highest output power; and also, creating a cold machine by changing the direction of the engine cycle, using the same principle as a refrigerator compressor.

Reference links：

[1]https://www.nature.com/articles/s41467-022-33667-1

[2]https://www.scmp.com/news/china/science/article/3199714/chinese-scientists-build-atom-sized-4-stroke-quantum-engine