Bipolar Thermoelectric Superconducting Quantum Devices

Abstract

Quantum technologies increasingly require accurate modeling of their hardware components and of the non-equilibrium regimes in which they operate, where managing heat and energy flow becomes a central challenge. Thermoelectric effects, the direct conversion of a thermal gradient into electrical signals, offer one such route to this control. In this review, we present an overview of the bipolar thermoelectric effect, a recent development for thermoelectric conversion in reciprocal systems, where linear effects are forbidden by symmetry. This symmetry yields a bipolar thermoelectric signal, in which the generated voltage can exhibit both polarities at a fixed temperature gradient. This represents a non-trivial novelty relative to conventional thermoelectric effects, in which carrier dominance determines the sign of the thermoelectric signal. We summarize the underlying physical principles, showing how thermoelectricity emerges as a strong violation of detailed balance. Concrete physical conditions for obtaining bipolar thermoelectricity are then outlined, of which a tunnel junction between two superconductors with unequal energy gaps and suppressed Josephson coupling is the paradigmatic example. Afterward, we discuss the experimental observation of the effect to date and related proposals for different applications, including volatile memories and radiation detection. Finally, we briefly survey recent developments and outlooks, ranging from extensions to new platforms to a proposal for a novel quantum thermoelectric effect.