# Quantum Hamiltonian daemons: unitary analogs of combustion engines

## TL;DR

This paper explores a quantum analog of classical Hamiltonian daemons, demonstrating how quantum systems can emulate engine-like energy transfer through quantum jumps and entanglement, revealing new quantum operational regimes.

## Contribution

It introduces a quantum mechanical model of a daemon, showing how quantum effects alter energy transfer mechanisms compared to classical systems.

## Key findings

- Quantum daemons operate via quantum jumps and entanglement.
- Efficiency limits in the quantum regime resemble classical counterparts.
- Quantum daemons can cease operation through Landau-Zener transitions.

## Abstract

Hamiltonian daemons have recently been defined classically as small, closed Hamiltonian systems which can exhibit secular energy transfer from high-frequency to low-frequency degrees of freedom (steady downconversion), analogous to the steady transfer of energy in a combustion engine from the high Terahertz frequencies of molecular excitations to the low kilohertz frequencies of piston motion. Classical daemons achieve downconversion within a small, closed system by exploiting nonlinear resonances; the adiabatic theorem permits their operation but imposes non-trivial limitations on their efficiency. Here we investigate a simple example of a quantum mechanical daemon. In the correspondence regime it obeys similar efficiency limits to its classical counterparts, but in the strongly quantum mechanical regime the daemon operates in an entirely different manner. It maintains an engine-like behavior in a distinctly quantum mechanical form: a weight is lifted at a steady average speed through a long sequence of quantum jumps in momentum, at each of which a quantum of fuel is consumed. The quantum daemon can cease downconversion at any time through non-adiabatic Landau-Zener transitions, and continuing operation of the quantum daemon is associated with steadily growing entanglement between fast and slow degrees of freedom.