Dynamical back‐action effects in low loss optomechanical oscillators

Abstract

The problem of the stability of a cavity optomechanical system based on an oscillator having at the same time low optical and mechanical losses is addressed. As it is the aim to extend the use of optical squeezing as a tool for improving quantum limited displacement sensing at low frequency, a family of opto-mechanical devices designed to work at frequencies of about 100 kHz was developed . The devices actually meet the initial design goals, but new requirements have emerged from the analysis of their behavior in optical cavities, due to the interaction between the cavity locking system and the low order normal modes of the devices.The optomechanics field of research has been gathering a lot of momentum during the last couple of years, driven by the achievement of long-awaited experimental results. For example, micro-and nano-oscillators can now be cooled down to an occupation number below unity, or very close to it, opening up the possibility to observe quantum phenomena [1][2][3][4][5][6].We are particularly interested in optical squeezing as a tool for improving quantum limited displacement sensing [7] in the audio-band, in particular for improving the sensitivity of gravitational wave interferometers [8]. Experiments have recently achieved squeezing around the mechanical resonance in the MHz range, using a silicon nanomechanical resonator [9], and a thin semi-transparent membrane within a Fabry-Pérot cavity [10]. At lower frequencies however, various sources of technical noise, such as thermal noise, phase/frequency noise associated with the input field and/or the slow cavity fluctuations, have detrimental effects on the manifestation of quantum phenomena, making lowfrequency ponderomotive squeezing much more difficult to achieve. As a first step, we are addressing these problems by developing a family of opto-mechanical devices specifically designed to ease the detection of pondero-motive squeezing (or, more generally, to produce a cavity quantum optomechanical system) at frequencies of about 100 kHz.Our approach is focused on relatively thick silicon oscillators with high reflectivity coating [11]. The relatively high mass (about 100 μg) of our devices is compensated by the capability to manage high power at low temperatures (down to 1 K), owing to a favorable geometric factor (thick connectors) and the excellent thermal conductivity of silicon crystals at cryogenic temperature. We point out that most of the schemes designed to detect quantum properties of light cannot take advantage from laser cooling of the mechanical oscillator involved in the measurement. Therefore, a low thermal noise background is required (i.e., low temperature), together with a weak interaction between the oscillator and its thermal bath (i.e., high mechanical quality factors Q).In such devices, the mirror coatings must provide high reflectivity and low losses, as radiation-pressure

Low-Loss Optomechanical Oscillator for Quantum-Optics Experiments

“…In this respect, we mention another class of silicon microresonators, where requirements on losses are satisfied thanks to the use high-order torsional modes [48,49]. However, the presence of lower-order modes makes these systems unsuitable for the use in high-finesse optical cavities, due to the onset of complex dynamical instabilities [50]. A thorough discussion of the dynamics of a multimodal optomechanical system goes beyond the scope of this paper, and we only note that the introduction of on-chip seismic isolation forces us to consider the effect of some fixed and reproducible isolation mode, with the advantage of isolating the system from poorly reproducible modes of the wafer and of the sample holder.…”

“…Figure 7 also highlights a further important feature of the device, namely that in the low-frequency range (up to the main oscillator mode) only the filters' vibration modes are present. Given that these modes are about 100 times heavier than the main oscillator mode, they do not affect significantly the cavity stability region [50] and allow one to reach the sensitivity floor at the oscillator frequency. The possibility to operate in a high-finesse cavity with relevant input power is demonstrated by the spectra in Fig.…”

Тепловое Излучение Абсолютно Черного Тела, Движущегося В Равновесном Газе Фотонов

“…В случае движущихся тел оно имеет свои особенности. В настоящее время интерес к этому вопросу стимулируется развитием микроэлектромеханических (МЭМС) и микрооптомеханических (МОМС) систем [1][2][3], исследованиями быстро вращающихся частиц в атомных ловушках [4,5] и астрофизическими приложениями [6][7][8][9][10].…”

Quantum nondemolition measurement of optical field fluctuations by optomechanical interaction

“…The PDH signal is also bandpass filtered around 22 kHz, and added to the signal driving the intensity modulator of the noise eater acting on the main beam. We so implement a feedback cooling [38] on the wheel oscillator, with two purposes: firstly, we improve its dynamic stability, that is otherwise critical due to the combined effect of optomechanical interaction and frequency locking servo loop [39]. Secondly, we depress the fluctuations of the wheel oscillator, that would otherwise provide a major contribution to the overall cavity phase noise.…”