Entropy Measurement in a Mesoscopic Double Quantum Dot

Entropy is one of the most fundamental physical quantities in physics, playing a pivotal role in understanding a wide range of phenomena, from classical heat engines to quantum information theory. However, applying conventional heat-capacity-based entropy measurement has been challenging in quantum devices due to the difficulty of defining the amount of heat on such a small scale. Recently, a measurement of a single electron’s entropy in a quantum dot was demonstrated using the Maxwell relation. This method revealed statistical behaviors of the available degrees of freedom in the quantum dot. Here, we extend the system to double quantum dots to investigate how entropy changes depending on the coupling strength between the dots. When double quantum dots are capacitively coupled, the entropy of each dot is consistent with that of a single quantum dot. In contrast, in the case of strongly coupled double quantum dots, the entropy reflects electron entanglement, such as singlet and triplet states. These entropy measurements offer a novel approach to exploring exotic quantum states and understanding entangled quantum states.