Radio-frequency optomechanical characterization of a silicon nitride drum

Abstract

On-chip actuation and readout of mechanical motion is key to characterize mechanical resonators and exploit them for new applications. We capacitively couple a silicon nitride membrane to an off resonant radio-frequency cavity formed by a lumped element circuit. Despite a low cavity quality factor (QE ≈ 7.4) and off resonant, room temperature operation, we are able to parametrize several mechanical modes and estimate their optomechanical coupling strengths. This enables a fast characterization of a device without requiring a superconducting cavity, thereby eliminating the need for cryogenic cooling. Finally, we observe optomechanically induced transparency and absorption, crucial for a number of applications including sensitive metrology, ground state cooling of mechanical motion and slowing of light.Cavity optomechanics boasts a number of tools for investigating the interaction between radiation and mechanical motion and enables the characterization and development of highly sensitive devices [1]. Silicon nitride membranes have been fabricated to exhibit very high tensile stress, resulting in high quality factors, and have been used for a number of applications including measurement of radiation pressure shot noise [2], optical squeezing [3], bidirectional conversion between microwave and optical light [4], optical detection of radio waves [5, 6], microkelvin cooling [7] and cooling to the quantum ground state of motion [8][9][10].Radio-frequency (rf) cavities allow for sensitive mechanical readout on-chip [5,11,12]. Here, we use an off-resonant rf cavity to actuate and characterize a silicon nitride membrane at room temperature. We detect several modes and extract the quality factor and cavity coupling strength for each of them. Furthermore, we observe optomechanically induced transparency (OMIT) and optomechanically induced absorption (OMIA) deep in the unresolved sideband regime. OMIT and OMIA are an unambiguous signature of the optomechanical interaction [13] and they can be used to slow or advance light [14]. OMIT has also been proposed as a means to achieve ground state cooling of mechanical motion in the unresolved sideband regime [15,16].Our device consists of a high-stress silicon nitride membrane which is 50 nm thick, has an area of 1.5 mm×1.5 mm and 90% of this area is metalized with 20 nm of Al. We suspend this membrane over two Cr/Au electrodes patterned on a silicon chip. For actuation, a dc voltage V dc = 15 V is applied to electrode 1, with electrode 2 grounded. Measurements were performed at room temperature and at approximately 10 −6 mbar. For optomechanical readout and control, electrode 1 is connected to an effective rf cavity. The cavity is realised using an on-chip inductor L and capacitors C D and C M mounted on the sample holder [17], in addition to the capacitance formed by the membrane C C . The cir-cuit behaves as an LC resonator with total capacitance C T = C C + C P , where C P accounts for the capacitance between the two sides of the antenna and other parasitic capacitances. This ca...

Measuring the Thermodynamic Cost of Timekeeping

“…2(c) as a function of f E . The mechanical response is evident as a strong increase in the sideband power at f P ± f E when f E matches the mechanical frequency f 0 ≈ 74.5 kHz [24].…”

“…As the membrane vibrates, the capacitance C C between the membrane and the electrodes changes. Driving the RF cavity with a resonant tone, we can probe the membrane's motion by monitoring the cavity's output signal [24]. The cavity is driven by injecting a RF signal via port 1 via a directional coupler.…”

“…The RF circuit is modelled and characterised in Ref. [24]. The entire setup forms a three-terminal circuit with input ports 1 and 3 and output port 2.…”

“…To excite quasi-Brownian motion, the membrane is driven by a white-noise electrical signal, which acts as an effective thermal bath that raises the mechanical mode temperature [18]. To monitor the membrane's displacement, it is capacitively coupled to a radio-frequency (RF) cavity operated in an optomechanical readout circuit [19][20][21][22][23][24]. The voltage output of this circuit is proportional to the instantaneous displacement.…”

Dual Optomechanical Cavities for All-Optical Actuation and Sensing of Mechanical Motion

“…Digital Object Identifier 10.1109/JPHOT.2022.3186408 consumption [7]. Cavity optomechanics has a wide range of potential applications, including tunable photonic filters [14] and wavelength routers [8], wavelength conversion [9] and switching [10], and radio-frequency optomechanical oscillators [11].…”