Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition (LPCVD) Si3N4 with a distributed bragg reflector (DBR) mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400,000 at room temperature. In addition these devices were used to form optical cavities with finesse up to 181,000 ± 1,000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators.In recent years there has been tremendous growth in the field of optomechanics [1, 2]. The interaction of light and mechanical motion has been used to demonstrate such phenomena as ground state cooling of a mechanical resonator [3][4][5], optomechanically induced transparency [6][7][8], and entanglement of a mechanical resonator with an electromagnetic field [9]. Another proposed application of optomechanics is testing the concept of quantum superpositions in large mass systems [10]. All of these experiments require low optical and mechanical loss rates. In this letter we will focus on our efforts to produce a large mass mechanical resonator with both high mechanical and optical quality factor, which can realistically be cooled to its ground state.There are several requirements for the devices to achieve this. The system must be sideband resolved for optical sideband cooling to the ground state [11,12]. A high mechanical quality factor is also necessary to generate a higher cooperativity and a lower mechanical mode temperature for the same cooling laser power. Furthermore, in the quantum regime, the quality factor sets the timescale of environmentally induced decoherence [13], which is crucial for proposed future experiments. Therefore, it is important to eliminate mechanical and optical loss sources.One major source of loss in mechanical systems is clamping loss, which is coupling to external mechanical modes [14][15][16]. As we will show, this is a critical source of loss for Si 3 N 4 trampoline resonators. Several methods of mechanically isolating a device from clamping loss have been demonstrated including phononic crystals [17,18] and low frequency mechanical resonators [19][20][21][22][23]. Due to the large size of phononic crystals at the frequency of our devices (about 250 kHz), we have selected to sur- * Electronic address: mweaver@physics.ucsb.edu † Now at: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA round our devices with a low frequency outer resonator. We significantly improve on the design of similar devices using silicon optomechanical resonators [24] by using...
For experimental investigations of macroscopic quantum superpositions and the possible role of gravitational effects on the reduction of the corresponding quantum wave function it is beneficial to consider large mass, low frequency optomechanical systems. We report optical side-band cooling from room temperature for a 1.5×10⁻¹⁰ kg (mode mass), low frequency side-band resolved optomechanical system based on a 5 cm long Fabry-Perot cavity. By using high-quality Bragg mirrors for both the stationary and the micromechanical mirror we are able to construct an optomechanical cavity with an optical linewidth of 23 kHz. This, together with a resonator frequency of 315 kHz, makes the system operate firmly in the side-band resolved regime. With the presented optomechanical system parameters cooling close to the ground state is possible. This brings us one step closer to creating and verifying macroscopic quantum superpositions.
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