Phononic bandgap nano-acoustic cavity with ultralong phonon lifetime

Abstract

We present measurements at millikelvin temperatures of the microwave-frequency acoustic properties of a crystalline silicon nanobeam cavity incorporating a phononic bandgap clamping structure for acoustic confinement. Utilizing pulsed laser light to excite a co-localized optical mode of the nanobeam cavity, we measure the dynamics of cavity acoustic modes with single-phonon sensitivity. Energy ringdown measurements for the fundamental 5 GHz acoustic mode of the cavity shows an exponential increase in phonon lifetime versus number of periods in the phononic bandgap shield, increasing up to τ ph,0 ≈ 1.5 seconds. This ultralong lifetime, corresponding to an effective phonon propagation length of several kilometers, is found to be consistent with damping from non-resonant two-level system defects on the surface of the silicon device. Potential applications of these ultracoherent nanoscale mechanical resonators range from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits.

Acoustic and Optical Properties of a Fast Spinning Dielectric Nanoparticle

“…Accounting for anharmonic corrections to the atom-atom interaction beyond the linear elastic approximation could unveil tunable phonon-phonon interactions and provide richer phonon dynamics [55]. Further research directions (some of which we currently investigate) include: (i) Using whispering gallery modes or evanescent coupling to photonic structures to measure changes in the nanoparticle geometry [32,35,56]; (ii) Studying Brillouin scattering off a levitated rotating nanoparticle [51]; (iii) Studying the complex coupled dynamics between rotation, translation, and vibrations caused by the rotation-dependent polarizability and birefringence which modify the optical potential; (iv) Studying more complex internal degrees of freedom such as spin waves (magnons) or electrons [21]; (v) Understanding the origin of the linewidths of such excitations [22] as well as their dependence on rotationinduced strain. We hope that this work will stimulate experiments exploring the internal mesoscopic quantum physics of levitated nanoparticles.…”

“…More recently, attention has been focused on the solid-state quantum excitations of nanoparticles [19][20][21]. The latter is motivated by the fact that well-isolated nanoparticles can be used to study solids at the mesoscopic scale, where their quantum excitations can be highly discretized and long lived [22], and their dynamics may consequently be radically different from bulk solids and non-isolated mesoscopic systems. Internal solid-state quantum excitations (e.g., acoustic phonons, magnons, or plasmons) should not be confused with the internal degrees of freedom of nanoparticles embedded with quantum emitters [15,[23][24][25][26][27].…”

Microwave generation and frequency comb in a silicon optomechanical cavity with a full phononic bandgap

“…In order to reduce phonon leakage, the cavity can be surrounded by a two-dimensional (2D) acoustic shield, which is basically a 2D structure exhibiting a complete phononic bandgap at the required frequency [17]. This hybrid 1D/2D approach has been successfully applied in a number of experiments, such as the cooling down to the quantum ground state [3,19], or phonon guidance through waveguides [20],and, more recently, to demonstrate mechanical quality factors Q m ≈ 10 10 in cryogenic environments [21].…”

Room-temperature Mechanical Resonator with a Single Added or Subtracted Phonon

“…Cryogenically cooled oscillators are used more widely due to sig-nificantly reduced dissipation and reduction of thermal noise from the environment, which usually masks quantum features. Motivated by the long intrinsic relaxation times possible in cryogenically cooled mechanical oscillators [21], and success in strongly coupling them to superconducting qubits [22][23][24][25], proposals for realizing quantum machines that leverage their coherence and small size [26][27][28] have emerged recently. Separately, cavity-optomechanical approaches for quantum sensing and transduction are being pursued by groups around the world.…”