Phonon detection by double quantum dots

During the last few decades research has improved our knowledge and control over electrons and photons, enabling impressing advances for electronic and optoelectronic applications. The same degree of control is still lacking for phonons. The ability to manipulate phonons and phonon transport on a quantum level would lead to full control over heat flow in nanodevices. Beside improving thermoelectric devices, doing a part to solve the global energy crisis, and solving the thermal management bottlenecks affecting computer chips and data storage technologies, it could also lead to phonon transistors and the realization of phonon logic gates.
Technological advances come from the ability of controlled phonon manipulation. Developing and improving our ability to manipulate phonons requires controlled means of phonon generation and phonon detection. Towards the goal of a phonon spectrometer, this project investigated double quantum dots (DQD) for their feasibility as phonon detectors.
The DQDs were defined by an InAs/InP heterostructure, in situ grown into a wurzite (WZ) InAs nanowire (NW). The atomically sharp interface was shown to form ~350 meV high tunnel barriers providing excellent hard wall confinement. In a two barrier system, forming a single QD, very symmetric, electrically tunable tunnel rates from < 1ueV to >600 ueV were found.
The InAs/InP heterostructure was shown as a promising host material, with potentially high tunable energy resolution and a large detection range for acoustic phonons.
Overcoming the challenges posed by high precision required in fabricating a DQD device from a three barrier heterostructure NW, the proof of principle experiment using a DQD as a phonon detector was successfully provided in combination with a joule heater in close proximity, acting as an incoherent phonon source. Under a finite applied heating power, current due to inelastic tunnelling through the DQD was recorded. Tuning the thermal conductance between source and detector proves phonon absorption as the dominant process detected by the DQD in this configuration.
This successful proof of principle experiment is a major step towards the development of a phonon spectrometer, potentially opening the door to phonon computation and major improvements in our control over thermal transport.