Exceptional-point-based accelerometers with enhanced signal-to-noise ratio.

Exceptional points (EP) are non-Hermitian degeneracies where eigenvalues and their corresponding eigenvectors coalesce1-4. Recently, EPs have attracted attention as a means to enhance the responsivity of sensors, through the abrupt resonant detuning occurring in their proximity5-20. In many cases, however, the EP implementation is accompanied by noise enhancement, leading to the degradation of the sensor's performance15-20. The excess noise can be of fundamental nature (owing to the eigenbasis collapse) or of technical nature associated with the amplification mechanisms utilized for the realization of EPs. Here we show, using an EP-based parity-time symmetric21,22 electromechanical accelerometer, that the enhanced technical noise can be surpassed by the enhanced responsivity to applied accelerations. The noise owing to eigenbasis collapse is mitigated by exploiting the detuning from a transmission peak degeneracy (TPD) - which forms when the sensor is weakly coupled to transmission lines - as a measure of the sensitivity. These TPDs occur at a frequency and control parameters for which the biorthogonal eigenbasis is still complete and are distinct from the EPs of the parity-time symmetric sensor. Our device shows a threefold signal-to-noise-ratio enhancement compared with configurations for which the system operates away from the TPD.

Robust Scattered Fields from Adiabatically Driven Targets around Exceptional Points.

Scattering processes are typically sensitive to the incident wave properties and to interference effects generated via wave-matter interactions with the target. We challenge this general belief in the case of targets that undergo time-periodic modulations encircling quasiadiabatically an exceptional point in a given parameter space. When the scattering dwell time is above a critical value τ_{c}, the scattered field is surprisingly insensitive to the properties of the incoming wave and local operational details of the driving. Instead, it reaches a fixed point attractor that can be controlled by the direction of the driving cycle. For dwell times below τ_{c}, the unusual robustness is abruptly suppressed. Such protocols may become useful tools in control engineering, including the management of thermal and quantum fluctuations.

Adiabatic Thermal Radiation Pumps for Thermal Photonics.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

Heat transport in active harmonic chains.

We show that a harmonic lattice model with amplifying and attenuating elements, when coupled to two thermal baths, exhibits unique heat transport properties. Some of these novel features include anomalous nonequilibrium steady-state heat currents, negative differential thermal conductance, as well as nonreciprocal heat transport. We find that when these elements are arranged in a PT-symmetric manner, the domain of existence of the nonequilibrium steady state is maximized. We propose an electronic experimental setup based on resistive-inductive-capacitive (RLC) transmission lines, where our predictions can be tested.