Ultrasensitive Photoresponse of Graphene Quantum Dot in the Coulomb Blockade Regime to THz Radiation

Graphene quantum dots (GQDs) have recently attracted considerable attention, with appealing properties for terahertz (THz) technology. This includes the demonstration of large thermal bolometric effects in GQDs when illuminated by THz radiation. However, the interaction of THz photons with GQDs in the Coulomb blockade regime - single electron transport regime - remains unexplored. Here, we demonstrate the ultrasensitive photoresponse to THz radiation (from <0.1 to 10 THz) of a hBN-encapsulated GQD in the Coulomb blockade regime at low temperature (170 mK). We show that THz radiation of $\sim$10 pW provides a photocurrent response in the nanoampere range, resulting from a renormalization of the chemical potential of the GQD of $\sim$0.15 meV. We attribute this photoresponse to an interfacial photogating effect. Furthermore, our analysis reveals the absence of thermal effects, opening new directions in the study of coherent quantum effects at THz frequencies in GQDs

Ultra-long carrier lifetime in neutral graphene-hBN van der Waals heterostructures under mid-infrared illumination

International audienceGraphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN het-erostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors of 30 ps for photoexcited carriers at low density and energy, using mid-infrared photo-conductivity measurements. We further demonstrate the switching of carrier lifetime from 30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of HPhP relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics

Vacuum-field-induced THz transport gap in a carbon nanotube quantum dot

International audienceAbstract The control of light-matter interaction at the most elementary level has become an important resource for quantum technologies. Implementing such interfaces in the THz range remains an outstanding problem. Here, we couple a single electron trapped in a carbon nanotube quantum dot to a THz resonator. The resulting light-matter interaction reaches the deep strong coupling regime that induces a THz energy gap in the carbon nanotube solely by the vacuum fluctuations of the THz resonator. This is directly confirmed by transport measurements. Such a phenomenon which is the exact counterpart of inhibition of spontaneous emission in atomic physics opens the path to the readout of non-classical states of light using electrical current. This would be a particularly useful resource and perspective for THz quantum optics