Two-level system damping in a quasi-one-dimensional optomechanical resonator

Abstract

Nanomechanical resonators have demonstrated great potential for use as versatile tools in a number of emerging quantum technologies. For such applications, the performance of these systems is restricted by the decoherence of their fragile quantum states, necessitating a thorough understanding of their dissipative coupling to the surrounding environment. In bulk amorphous solids, these dissipation channels are dominated at low temperatures by parasitic coupling to intrinsic two-level system (TLS) defects, however, there remains a disconnect between theory and experiment on how this damping manifests in dimensionally-reduced nanomechanical resonators. Here, we present an optomechanically-mediated thermal ringdown technique, which we use to perform simultaneous measurements of the dissipation in four mechanical modes of a cryogenically-cooled silicon nanoresonator, with resonant frequencies ranging from 3 -19 MHz. Analyzing the device's mechanical damping rate at fridge temperatures between 10 mK -10 K, we demonstrate quantitative agreement with the standard tunneling model for TLS ensembles confined to one dimension. From these fits, we extract the defect density of states (P 0 ∼ 1 -4 × 10 44 J −1 m −3 ) and deformation potentials (γ ∼ 1 -2 eV), showing that each mechanical mode couples on average to less than a single thermally-active defect at 10 mK.

Coherent Magneto-optomechanical Signal Transduction and Long-Distance Phase-Shift Keying

“…To test the coherent response of the wavelength conversion, we first use a homodyne optical detection system sensitive to shifts in the phase of the optical field within the silicon microdisk. The microdisk lies in one arm of the homodyne system [35], such that as the mechanical resonator moves in the evanescent field of the microdisk it shifts the optical phase in the cavity and hence the phase of the detected optical signal. This optical signal is demodulated using a digital lockin amplifier -referenced to the same 10 MHz Rb source as the signal generators -at the mechanical resonance frequency to attain the amplitude and, more importantly, phase of the signal modulated at f m .…”

“…Such low-mode volume superconducting resonators may also be vital for extending this technique to wavelength transduction in the quantum regime. For quantum-level transduction, one would also need to eliminate thermomechanical noise, which is difficult in MHz-frequency devices [20,35]. To facilitate this, it may be possible to construct optomechanical crystal torque sensors [36] with higher mechanical frequencies that would more easily allow for ground-state preparation [4,5], or to use carefully timed dynamical backaction cooling as has been performed for microwave drum resonators [37].…”

Emerging unitary evolutions in dissipatively coupled systems

“…These quadratures X ϕn do not have to be orthogonal, but crucial is their relative phase ϕ 1 −ϕ 2 , which determines the phase in the resulting nonlocal jumpoperator L. To have H SB generate the dissipative process D [L] (ρ), we couple mode a to a Markovian bath with rate γ a . In the case of strong damping, i.e., for γ a → ∞, the auxiliary mode can be adiabatically eliminated [31,32] and one is left with the dissipative process described by the Lindblad operator…”

Spectral Characterization of Couplings in a Mixed Optomechanical Model*

“…Recently, much attention has been paid to the studies on the mixed optomechanical model with both linear and quadratic optomechanical couplings [42][43][44][45][46][47]. In this model, the linear and quadratic optomechanical couplings provide the physical mechanisms for conditional displacement and squeezing of the mechanical resonator, respectively.…”

“…In this model, the linear and quadratic optomechanical couplings provide the physical mechanisms for conditional displacement and squeezing of the mechanical resonator, respectively. These mechanisms will create interesting physical effects such as the squeezing and cooling the mechanical mode [42], the harmonic generation of selfsustained oscillations [43], the phonon quantum nondemolition measurements [44], the unconditional preparation of nonclassical states [45], and the optomechanically induced transparency [46]. Such a system has also been experimentally demonstrated where the mechanical resonator is prepared and detected near its ground-state motion [47].…”