Structure of Quantum Theory

We address a foundational question in energy harvesting: Can energy be extracted from a partly random source without transferring randomness or incurring thermodynamical costs? We answer affirmatively by presenting protocols that extract energy while avoiding both entropy transfer and energy dissipation. These protocols outperform, in terms of fundamental limits, existing rectification methods that dissipate power and feedback control protocols that transfer randomness to the control system. The key idea is to exploit the harvesting system taking multiple pathways to reach the same final energy eigenstate. A central example involves Rabi oscillations in a two-level quantum system (such as an atom or qubit) interacting with an electromagnetic field. The system is deterministically excited to its highest energy level after a fixed interaction time, regardless of the field's random initial phase. This phase-insensitive energy transfer occurs because different phase values lead the system through different trajectories that converge to the same excited state. A general argument involving Noether symmetries provides a way to find numerous examples. The approach does not work on thermal source states, consistent with the second law of thermodynamics.

References:

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