10 August 2023 Thu 4 pm

Continuous technological advances in the control and measurement of quantum systems and recent research interest in quantum devices, make it crucial for us to understand the thermodynamics of quantum systems. The study of quantum thermodynamics [1,2] aims to develop a novel thermodynamic framework, that goes beyond conventional thermodynamics, to account for finite-size effects and to explore the possible advantages of non-classical features, namely entanglement and quantum coherence, of the system. In this direction, quantum thermal machines (heat engines and refrigerators) [3,4,5] essentially provide a platform to study thermodynamic principles at the quantum level, e.g., the study of non-equilibrium thermodynamics and quantum fluctuation, strong coupling, non-Markovianity etc. We study quantum thermal machines (QTM), particularly quantum Otto engines (QOE), with coupled spin working systems. We explore QOE under two scenarios, one with a local spin working system and another with non-selective measurements to fuel the engine [6]. We investigate how anisotropic spin interaction affects QOEs performance. We show that the local work extraction is more robust than the global one in a two-spin QOE, and the local spin QOE efficiency can break the standard quantum Otto limit with a non-zero anisotropy parameter. If the unitary strokes of the cycle are performed in a finite time, an oscillatory behaviour of the efficiency for both the local spin and measurement-based QOE is observed. These oscillations can be interpreted in terms of interference between the relevant transition amplitudes in the unitary strokes of the cycle [6]. Therefore, with a suitable choice of timing of the unitary processes in the short time regime, these QOEs can outperform the same QOEs operating at the quasistatic limit. 

[1] Sai Vinjanampathy, and Janet Anders. "Quantum thermodynamics." Contemporary Physics 57.4 (2016): 545-579.

[2] Felix Binder, et al. "Thermodynamics in the quantum regime." Fundamental Theories of Physics 195 (2018): 1-2.

[3] Sourav Bhattacharjee, and Amit Dutta. "Quantum thermal machines and batteries." The European Physical Journal B 94 (2021): 1-42.

[4] Loris Maria Cangemi, Chitrak Bhadra, and Amikam Levy. "Quantum Engines and Refrigerators." arXiv preprint arXiv:2302.00726 (2023).

[5] Nathan M. Myers, Obinna Abah, and Sebastian Deffner. "Quantum thermodynamic devices: From theoretical proposals to experimental reality." AVS quantum science 4.2 (2022).

[6] Chayan Purkait, and Asoka Biswas. "Measurement-based quantum Otto engine with a two-spin system coupled by anisotropic interaction: Enhanced efficiency at finite times." Physical Review E 107.5 (2023): 054110.  

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