Coherent Phonon Manipulation in Coupled Mechanical Resonators

Hajime Okamoto, Imran Mahboob, Koji Onomitsu*, and Hiroshi Yamaguchi
Physical Science Laboratory, *Materials Science Laboratory

 Semiconductor nanomechanical resonators enable the pursuit of new physical phenomenon than can only be observed through the tiny mechanical displacement as well as enabling the development of nanoscience and nanotechnology. Coupling such nanomechanical resonators has recently emerged as a subject of interest, because the sympathetic oscillation dynamics in the coupled system expand the potential applications of nanomechanical objects such as highly precise sensors, signal amplifier, and logic gates. However, an obstacle to the further development of this architecture arises from the usually weak coupling between the nanomechanical components. This limits the ability to coherently transfer the vibration energy between the resonators within the ring-down time.
 We have realized the strong coupling and coherent energy transfer between two GaAs doubly-clamped beam resonators (Fig. 1(a)) by the parametric mode mixing technique [1, 2]. The piezoelectric modulation of the spring constant of one beam at the frequency difference between the two beams leads to the dynamic coupling of the two beams, enabling the cyclic (Rabi) oscillations of phonons between the two vibrational states (Fig. 1(b), (c)). The Rabi cycle period, i.e., the coupling strength, is adjustable by changing the gate voltage (Fig. 1(d)). As a result, the vibration energy can be quickly transferred from one beam to the other enabling the vibration of the original beam to be switched off on a time-scale orders of magnitude shorter than its ring-down time [3]. This quick energy transfer opens up the prospect of high-speed repetitive operations for sensors and logics using nanomechanical systems.
 This work was supported by KAKENHI.

I. Mahboob, K. Nishiguchi, H. Okamoto, and H. Yamaguchi, Nature Phys. 8 (2012) 387.
H. Okamoto et al., Nature Phys. 9 (2013) 480.
H. Yamaguchi, H. Okamoto, and I. Mahboob, Appl. Phys. Express 5 (2012) 014001.
Fig. 1.
(a) Schematic drawing of the sample and the piezoelectric effect. The beams consist of 400-nm-thick i-GaAs, 100-nm-thick n-GaAs, 300-nm-thick AlGaAs, and 60-nm-thick Au electrodes. The piezoelectric effect enables harmonic driving, pumping and detection of the mechanical motion via gate voltage. (b) Schematic drawing of the mechanical resonance for beams L,R and the phonon reaction picture during the pumping. The frequency of beam R is higher than that of beam L (293.93 kHz) by 440 Hz. The coherent energy exchange between the two beams is achieved by applying the pump voltage to beam L with the frequency difference between the two beams. (c) Schematic of the pumping protocol in a mass and spring model. (d) Pump voltage dependence of the coherent oscillations measured via the time response of beam R at ωR.