Single and double quantum dot (QD) transistors have been used to investigate entropy transitions
in the single particle limit. Precisely controlled QD electron states allow a few-particle thermodynamic system to be defined. Charge stability diagrams are calculated to find the Gibbs entropy S
vs. bias voltage, providing a framework to define single-particle entropy diagrams. The calculation
method is applied to experimental dopant atom QD transistor characteristics. As multiple states
become occupied, S increases in a stepwise manner towards S = k ln Ω, where Ω is the total number
of microstates, retaining the Boltzmann interpretation of entropy. The temperature T-S diagram
vs. gate voltage reflects underlying single-particle state transitions and enables the definition of
heat cycles. These diagrams approximate the behaviour of macroscopic phase changes in magnetic,
liquid-vapour, and superconducting systems.