Quantum counterpart of equipartition theorem in quadratic systems

The equipartition theorem is a fundamental law of classical statistical physics, which states that every degree of freedom contributes <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>k</a:mi><a:mi mathvariant="normal">B</a:mi></a:msub><a:mi>T</a:mi><a:mo>/</a:mo><a:mn>2</a:mn></a:mrow></a:math> to the energy, where <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>T</c:mi></c:math> is the temperature and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>k</d:mi><d:mi mathvariant="normal">B</d:mi></d:msub></d:math> is the Boltzmann constant. Recent studies have revealed the existence of a quantum version of the equipartition theorem. In the present work, we focus on how to obtain the quantum counterpart of the generalized equipartition theorem for arbitrary quadratic systems in which the multimode Brownian oscillators interact with multiple reservoirs at the same temperature. An alternative method of deriving the energy of the system is also discussed and compared with the result of the quantum version of the equipartition theorem, after which we conclude that the latter is more reasonable. Our results can be viewed as an indispensable generalization of recent works on a quantum version of the equipartition theorem. Published by the American Physical Society 2024