How quantum Otto engine monitoring affects its performance – sciencedaily


Heat engines are devices that use waste heat to perform mechanical work and generate energy. The invention of heat engines ushered in the era of the industrial revolution two hundred and fifty years ago. Among them, the Otto engine, which uses separate heatstroke and work, is used in almost all automobiles and has been an industry standard due to its relatively high power and efficiency. In an Otto engine, an active substance is usually a gas confined in a piston, which undergoes four successive strokes: it is first compressed, then heated, relaxed and finally cooled to its initial temperature.

Today, with significant advances in nano-manufacturing, the quantum revolution is upon us, putting quantum heat engines in the limelight. Like their classical counterparts, quantum heat engines could operate in various protocols which could be continuous or cyclic. Unlike the classical motor which uses a macroscopic amount of the active substance, the active substance of a quantum motor exhibits pronounced quantum characteristics. The most important of them is the discretion of the possible energies that it can take. Even stranger from a classical point of view is the fact that a quantum system can stay in two or more of its authorized energies at the same time. This property, which has no classical analogue, is known as “consistency”. Otherwise, a quantum Otto engine is also characterized by four strokes like its classic counterpart.

Determining Otto Quantum Engine performance metrics, such as power output or efficiency, is key to improving design and customizing better working substances. Direct diagnosis of such metrics requires measuring motor energies at the start and end of each stroke. While a classical motor is only negligibly affected by measurements, in quantum motors the act of measuring itself causes a bizarre measuring effect in which the quantum state of the motor is severely affected by quantum mechanics. . Above all, any coherence of the system at the end of the cycle would be completely eliminated by the measurement effect.

These strange measurement-induced effects have long been thought to be irrelevant to understanding quantum motors and have therefore been overlooked in traditional quantum thermodynamics. In addition, little thought has been given to designing monitoring protocols that allow reliable diagnosis of engine performance while minimizing modification.

However, groundbreaking new research conducted at the Center for Theoretical Physics of Complex Systems at the South Korea Institute of Basic Sciences could change this rigid perspective. Researchers studied the impact of different measurement-based diagnostic schemes on the performance of a quantum Otto engine. In addition, they discovered a minimally invasive measurement method that preserves consistency across cycles.

The researchers used the “repeating ladder pattern,” where they record engine states using an auxiliary probe, and probe measurements are only taken at the end of the engine’s duty cycles. This avoids the need to measure the engine multiple times after each stroke and avoids unwanted quantum effects induced by the measurement, such as removing any consistency that has built up during the cycle.

Maintaining consistency throughout the life of the engine has improved critical performance metrics such as maximum power output and reliability, making the engine perform better and more reliable. According to Professor Thingna, “this is the first example in which the influence of an experimenter, who wants to know if the motor is doing what it is designed for, has been correctly taken into account”.

Covering a wide range of different modes of engine operation with an active substance having only two quantum states, the researchers found that the monitoring scheme applied only matters for idealized cycles that run infinitely slowly. But all motors which run in a finite time and are therefore of practical interest perform considerably better for their power output and reliability when monitored according to the repeated contact pattern.

Overall, the researchers concluded that the nature of the measurement techniques may bring theory closer to experimental data. Therefore, it is essential to take these factors into account when monitoring and testing quantum heat engines. This research was published in the journal Physical Review X Quantum.

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