Quantum Dot based Optomechanical Transducer – QDOT

During the last decade, progress in nanofabrication has triggered a rapid growth of the field of nanomechanics. Nanotechnologies have enabled the realization of ultrasmall mechanical oscillators, which are used in ultra-sensitive position, force or mass measurement devices. This has led to the tremendous development of microelectromechanical systems (MEMS) that are now present in everyday objects such as smartphones or cars to serve as accelerometers, magnetometers, pressure or gas sensor, and in scientific equipments such as atomic force microscopes. On a more fundamental side, one of the landmark results has been the observation of the cooling of a mechanical oscillator to its quantum ground state (zero phonon) about 5 years ago. This has brought nanomechanics well into the quantum domain, opening the way for quantum enhanced nanosensors.

The outstanding success of MEMS resonators is prominently related to their reduced mass, enabling both very low power consumption and increased sensitivity. To further increase the sensing potential towards the next generation of integrated transducers, mechanical systems have been scaled down. Two major bottlenecks have subsequently appeared: Firstly, due to their extremely reduced dimensions, these Nano-electromechanical systems (NEMS) are extremely difficult to detect. Secondly, their ultra-low mass makes them extremely sensitive to external perturbations, including those induced by the measurement scheme itself.

The project QDOT proposes to tackle these technological limitations and to develop and optimize a novel, quantum-limited integrated sensor. Our approach relies on a hybrid nanomechanical system consisting of a quantum dot (QD) embedded in a vibrating photonic nanowire. Both system components are in reciprocal interaction via strain: When vibrating, the nanowire experiences deformations yielding to strain changes at the QD location. These strain changes result in frequency shifts of the excitonic resonance, whose detection can therefore be used for monitoring the nanomechanical motion in an extremely sensitive manner with the additional benefit of ultra-low probe power (picowatt). Conversely, each photon emitted by the QD comes along recoil which may drive the nanomechanical motion. Detecting the nanomechanical motion can therefore be utilized for monitoring the QD state in a non-demolition way.

Our concept holds several important advantages for sensing applications. Firstly, on the technical side, the nanomechanical resonator incorporates an ultra-sensitive (non-contact) optical motion detector which is robust against misalignments and does not require any recalibration procedure. Secondly, the system combines ultra-high extraction efficiency, ultra-low dissipative losses and ultra-high strain coupling rate, which secures an almost perfectly preserved quantum potential, and represents close to ideal conditions towards reaching the Heisenberg limit, corresponding to minimal measurement induced perturbation of the sensor. Thirdly, the extremely reduced size of the “quantum detector” enables the decrease of the nanomechanical resonator size down to scales where conventional nanomechanical detection schemes become inefficient, while preserving the above mentioned advantages.

Such unique set of properties are as many assets for the objective of QDOT to develop the next generation of effective nanomechanical force sensors combining quantum-limited efficiency, ultra-low power consumption and ultr-stable operation.

To reach this ambitious goal, QDOT will deploy disruptive methods, representing a very high potential for further industrial implementation and international impact.