Fiber-cavity-based optomechanical device

Abstract

We describe an optomechanical device consisting of a fiber-based optical cavity containing a silicon nitiride membrane. In comparison with typical free-space cavities, the fiber-cavity's small mode size (10 µm waist, 80 µm length) allows the use of smaller, lighter membranes and increases the cavity-membrane linear coupling to 3 GHz/nm and the quadratic coupling to 20 GHz/nm 2 . This device is also intrinsically fiber-coupled and uses glass ferrules for passive alignment. These improvements will greatly simplify the use of optomechanical systems, particularly in cryogenic settings. At room temperature, we expect these devices to be able to detect the shot noise of radiation pressure.In quantum mechanics, a measurement of one variable is accompanied by back-action on the conjugate variable. In the particular case of an optical displacement measurement, the quantum back-action is radiation pressure shot noise (RPSN) 1,2 , the Poissonian noise in the momentum transferred by reflecting photons.When a high-finesse cavity is used to increase the sensitivity of the displacement measurement, the RPSN is also increased. The connection between increased cavity finesse, increased measurement sensitivity, and increased RPSN can be understood qualitatively by noting that the number of times each photon interacts with a mechanical element inside a cavity is approximately equal to the cavity finesse.In the field of optomechanics, floppy mechanical elements are integrated into high-finesse optical cavities in order to observe various quantum effects, including RPSN 3,4 . The goal of observing RPSN is motivated by basic questions about quantum measurements, as well as by the fact that RPSN is expected to limit the performance of next-generation gravitational-wave observatories (though squeezed light can be used to mitigate the effect) 5,6 . To date, RPSN has not been observed in solid-state optomechanical devices, largely because it has been obscured by the thermal Langevin force that produces Brownian motion 7 . While it has been proposed that correlation measurements can be used to distinguish RPSN in the presence of a much larger Langevin force 7,8 , such a measurement would be simplified by increasing the RPSN relative to the thermal Langevin force. There is an additional motivation for increasing the RPSN: the optomechanical generation of squeezed light (e.g. for improving the performance of gravitational-wave observatories) requires a setup in which the RPSN dominates over the Langevin force 9,10 . Increasing the effect of RPSN in comparison to thermal motion involves optimizing both the mechanical system a) Electronic mail: nathan.flowers-jacobs@yale.edu = 82 A 2n /κ when the laser is resonant with the cavity and the mechanical resonance frequency ω m is much less than the cavity FWHM linewidth κ (the "bad cavity" limit). Thus, the RPSN force is increased by increasing the optomechanical coupling A = dω cav /dx, increasing the average number of photons stored in the cavityn, and decreasing κ.In this paper, we present a n...

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“…Such systems can be realised in tunable optomechanical systems like membrane in the middle set-up [29] and atom-chip based systems [32]. Recent experimental progress has witnessed the presence of both LOC and QOC in various optomechanical systems [33,49,50]. In addition, the sign of quadratic coupling present in the system determines the quadrature in which squeezing occurs.…”

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“…[65]. We choose the cavity decay as κ ≃ 10 2 GHz, and the driving pulses with duration τ p = 0.1 ns.…”

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“…atomic systems 9 . Another example is the significantly larger optomechanical coupling strength compared to macroscopic resonators 10 . Furthermore fiber cavities are well-suited for use in sub-Kelvin cryogenic environments 11 , since they don't require open apertures to couple light into the cryostat, which minimizes undesired heating effects.…”