Exploring the role of asymmetric-pulse modulation in quantum thermal machines and quantum thermometry

Floquet quantum thermal transistor

We apply periodic control to realize a quantum thermal transistor, which we term as the Floquet quantum thermal transistor. Periodic modulation allows us to control the heat flows and achieve large amplification factors even for fixed bath temperatures. Importantly, this transistor effect persists in the cutoff region, where traditional quantum thermal transistors operating in the absence of periodic modulation, fail to act as viable heat modulation devices.

Controlling thermodynamics of a quantum heat engine with modulated amplitude drivings

External driving of bath temperatures with a phase difference of a nonequilibrium quantum engine leads to the emergence of geometric effects on the thermodynamics. In this work we modulate the amplitude of the external driving protocols by introducing envelope functions and study the role of geometric effects on the flux, noise, and efficiency of a four-level driven quantum heat engine coupled with two thermal baths and a unimodal cavity. We observe that having a finite width of the modulation envelope introduces an additional control knob for studying the thermodynamics in the adiabatic limit. The optimization of the flux as well as the noise with respect to thermally induced quantum coherences becomes possible in the presence of geometric effects, which hitherto has not been possible with sinusoidal driving without an envelope. We also report the deviation of the slope and generation of an intercept in the standard expression for efficiency at maximum power as a function of Carnot efficiency in the presence of geometric effects under the amplitude modulation. Further, a recently developed universal bound on the efficiency obtained from the thermodynamic uncertainty relation is shown not to hold when a small width of the modulation envelope along with a large value of cavity temperature is maintained.

Analog of a Quantum Heat Engine Using a Single-Spin Qubit

A quantum two-level system with periodically modulated energy splitting could provide a minimal universal quantum heat machine. We present the experimental realization and the theoretical description of such a two-level system as an impurity electron spin in a silicon tunnel field-effect transistor. In the incoherent regime, the system can behave analogously to either an Otto heat engine or a refrigerator. The coherent regime could be described as a superposition of those two regimes, producing specific interference fringes in the observed source-drain current.