Nonadiabatic coupled-qubit Otto cycle with bidirectional operation and efficiency gains

Area of Science:

• Quantum thermodynamics
• Quantum information science
• Many-body physics

Background:

• Quantum Otto cycle is a fundamental thermodynamic model.
• Quantum systems exhibit non-adiabatic effects when processes occur too quickly.
• Hamiltonians that do not commute over time are common in multi-qubit systems.

Purpose of the Study:

• Investigate the impact of non-adiabaticity on a 2-qubit quantum Otto cycle.
• Analyze the resilience of unique quantum thermodynamic features under finite-duration strokes.
• Quantify the efficiency drop due to loss of quantum adiabaticity.

Main Methods:

• Utilized a 2-qubit working substance with a time-dependent, non-commuting Hamiltonian.
• Simulated unitary strokes of finite duration to induce non-adiabatic effects.
• Analyzed the quantum Otto cycle's performance metrics, including efficiency and operational characteristics.

Main Results:

• Qualitative features like counter-rotating cycles as heat engines remain robust.
• Cycle efficiency can paradoxically increase with reduced temperature differences.
• Efficiency significantly decreases with increasing non-adiabaticity but can exceed standard Otto values for slight deviations.

Conclusions:

• Quantum Otto cycles with non-commuting Hamiltonians show resilience in key behaviors.
• Non-adiabatic effects significantly impact but do not entirely destroy unique quantum thermodynamic phenomena.
• The study provides insights into the practical limitations and potential of quantum heat engines.