Touch the back of a laptop and it often feels warm. This is because part of the energy used for computation and communication escapes to the outside as heat. Yet even this "waste heat" still contains a great deal of usable energy. Technologies that convert such waste heat into electricity for reuse are known as energy harvesting.
Conventional energy-harvesting technologies have been developed within the framework of classical thermodynamics. In classical thermodynamics, a heat source is typically assumed to be in thermal equilibrium—a stable state in which temperature becomes uniform and heat flow is minimal.
However, as waste heat approaches thermal equilibrium, the amount of energy that can be reused decreases, and consequently the amount that can be extracted as electricity also diminishes.
For this reason, researchers have focused on non-thermal states, special quantum states that do not settle into thermal equilibrium. Non-thermal states have been realized in various ways—for example, in atoms whose temperature distribution is controlled by lasers, or in coherent atomic ensembles (special states in which many atoms behave in synchrony, following the same rhythm).
In many cases, however, creating these non-thermal states requires highly precise control, making practical applications to energy recovery challenging.
In recent years, a promising candidate has attracted increasing attention: the Tomonaga–Luttinger (TL) liquid. A TL liquid refers to a special state in which electrons are confined to a narrow channel and move collectively while strongly influencing one another. Rather than behaving independently, the electrons flow in a coordinated manner reminiscent of a liquid—hence the name.
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