Using the Nyquist approach, temperature fluctuations of an object, in thermal contact with a reservoir, are studied. We argue that, upon decreasing the size of the object, one necessarily reaches the quantum regime. The crossover temperature between the classical and quantum regimes is given by T* ∼ ℏ/kBτ, where τ is the thermal relaxation time of the system. For a nano-scale metallic particle in a good thermal contact with a reservoir, T* can be on a scale of a few Kelvin. © 2003 Elsevier Science B.V. All rights reserved.
Balatsky, A. V., & Zhu, J. X. (2003). Quantum Nyquist temperature fluctuations. In Physica E: Low-Dimensional Systems and Nanostructures (Vol. 18, pp. 341–342). https://doi.org/10.1016/S1386-9477(02)01080-9