Integration of Single Quantum Dots in Suspended Phononic Waveguides

In fundamental research, surface acoustic waves (SAWs), nanoscale earthquakes on a chip are an extremely versatile tool to dynamically probe and manipulate charge and spin excitations condensed matter systems. When excited on piezoelectric materials both the oscillating mechanical stress of the SAW and its accompanying electric fields can be harnessed to establish strong interactions between single quantum emitters and sound on the nanoscale [1-4]. Here, we report on the integration of single quantum emitters in suspended phononic waveguides. Figure 1 (a) shows an electron micrograph of a 50 μm long and 2 μm wide suspended beam patterned on an approximately 150 nm thick (Al)GaAs heterostructure containing a single layer of GaAs quantum dots (QDs). In our experiment a Rayleigh SAW is excited by a multiharmonic frequency-chirped transducer [5] excited on the unpatterned region and coupled into the suspended beam where it propagates as a Lamb mode of identical frequency [6]. Figure 1 (b) and (c) compare the optomechanical response of a single QD in the unpatterend region and in the suspended beam, respectively. Clearly, the optomechanical of the quantum emitter inside the suspended phononic waveguide is enhanced by a factor of 3.5, compared to that of the emitter strained by the Rayleigh SAW. This finding may arise from an enhancement of the optomechanical coupling between the emitter and the elastic wave in the one-dimensional phononic waveguide. Employing phase resolved spectroscopy on an ensemble of quantum emitters we can unambiguously show, that the observed optomechanical response arises from the coupling between the low phase velocity, anti-symmetric (flexural) Lamb-Mode and the QD. Moreover, our fabricated phononic waveguides exhibit low propagation losses.