Ground State Cooling of an Ultracoherent Electromechanical System

Abstract

Cavity electromechanics relies on parametric coupling between microwave and mechanical modes to manipulate the mechanical quantum state, and provide a coherent interface between different parts of hybrid quantum systems. High coherence of the mechanical mode is of key importance in such applications, in order to protect the quantum states it hosts from thermal decoherence. Here, we introduce an electromechanical system based around a soft-clamped mechanical resonator with an extremely high Q-factor (> 10 9 ) held at very low (30 mK) temperatures. This ultracoherent mechanical resonator is capacitively coupled to a microwave mode, strong enough to enable ground-state-cooling of the mechanics (nmin = 0.76 ± 0.16). This paves the way towards exploiting the extremely long coherence times (t coh > 100 ms) offered by such systems for quantum information processing and state conversion.

Soft-clamped silicon nitride string resonators at millikelvin temperatures

“…Further cooling to the base temperature of the refrigerator (T mc = 30 mK) leads to another steep increase of Q for the localized mode of device C reaching up to Q = 2 × 10 9 . The heating experiment has exclusively been conducted with device C. A similar increase has been reported for metal-coated silicon strings [26] and with silicon nitride membrane resonators [15][16][17][18], but its microscopic origin remains unclear. To confirm the validity of our result, we performed careful studies as a function of average optical power and mixing chamber temperature that we present in the following.…”

“…Low temperatures and high quality factors are also important for increasing the quantum coherence time of the resonator's oscillation states [18,47]. Dissipation imposes a limit to the coherence time, yielding in our case…”

“…Even though Si 3 N 4 resonators are expected to achieve their best performance at millikelvin temperatures, little is known about their actual properties (intrinsic Q, thermal conductivity, Young's modulus, ...) under such conditions [16,18], in particular in the presence of optical absorption [15,17]. This is in part owed to the technical difficulties added by working in a dry dilution refrigerator, whose vibrations can furthermore add force and frequency noise [19].…”

Quantum backaction evading measurements of a silicon nitride membrane resonator

“…( 14), sideband cooling allows in the limit of large effective damping γ eff , cooling the mechanical mode close to the ground state where n m = 0. This has been demonstrated in many different types of me-chanical oscillators, including SiN membranes [27,28].…”

“…In this work, we extend the scope of BAE measurements to a new class of systems with a high degree of coherence and therefore immediately adapted to force or metric sensing. As the mechanical oscillator, we use a silicon nitride membrane embedded in a microwave cavity [25][26][27][28]. High-stress silicon nitride (SiN) has emerged as the material to realize the highest mechanical quality factors for usage in quantum optomechanics [10,[29][30][31][32][33][34][35].…”