Coupling a Superconducting Quantum Circuit to a Phononic Crystal Defect Cavity

Abstract

Connecting nanoscale mechanical resonators to microwave quantum circuits opens new avenues for storing, processing, and transmitting quantum information. In this work, we couple a phononic crystal cavity to a tunable superconducting quantum circuit. By fabricating a one-dimensional periodic pattern in a thin film of lithium niobate and introducing a defect in this artificial lattice, we localize a 6-GHz acoustic resonance to a wavelength-scale volume of less than 1 cubic micron. The strong piezoelectricity of lithium niobate efficiently couples the localized vibrations to the electric field of a widely tunable high-impedance Josephson junction array resonator. We measure a direct phonon-photon coupling rate g=2π ≈ 1.6 MHz and a mechanical quality factor Q m ≈ 3 × 10 4 , leading to a cooperativity C ∼ 4 when the two modes are tuned into resonance. Our work has direct application to engineering hybrid quantum systems for microwave-to-optical conversion as well as emerging architectures for quantum information processing.

Efficient bidirectional piezo-optomechanical transduction between microwave and optical frequency

“…We demonstrated efficient acousto-optic modulation with V π = 24 mV, bidirectional conversion efficiency of 10 −5 with 3.3 µW red-detuned optical pump and 5.5% with 323 µW bluedetuned pump at room temperature. We expect our transducers to have reduced material loss and an increased efficiency at cryogenic temperature, opening up experiments in the quantum regime between optical photons, microwave photons and phonons, and superconducting qubits [30,31].…”

“…Optomechanical crystals (OMC) provide a natural way to achieve the former by implementing a simultaneous photonic-phononic crystal to confine both optical and mechanical waves [29]. However, efficient electrical coupling to the micron-scale mechanical resonances of a phononic crystal has only recently been achieved [30,31]. These demonstrations leverage the high piezoelectric coefficient of lithium niobate [32] and electrodes on or near the resonator to efficiently couple motion to high-impedance superconducting microwave circuits.…”

“…We demonstrate bidirectional conversion between microwave and optical photons with efficiency up to 10 −5 (5.5%) using the red-(blue-)detuned optical pump. The integrated piezo-optomechanical transducer is fabricated with Xcut thin-film lithium niobate on silicon (LNOS), a material platform demonstrated to be compatible with superconducting circuits and qubits [30,31] -opening a path for integration with quantum sensors and processors.…”

Real-Space Characterization of Cavity-Coupled Waveguide Systems in Hypersonic Phononic Crystals

“…The on-chip control of acoustic phonons at microwave frequencies, namely hypersound, has been essential for a wide range of applications such as sensing for bio-chemical detection [1], analog signal processing [2] and wireless communications [3]. Moreover, this has also realized an alternative way to drive another degree of freedom such as photons [4][5][6][7][8][9][10][11][12][13][14][15][16], electrons [17][18][19][20] and spins [21][22][23][24][25][26][27][28], thus giving rise to development of novel hybrid architectures. In the above systems, hypersonic vibrations can be exploited to efficiently actuate and modulate these energy particles, and to inter-connect information between different subsystems, which offers new opportunities in emerging fields such as quantum-acoustics [8][9][10][11][12][13][14][15] and spin-mechanics [21][22][23][24][25][26][27][28].…”

“…For instance, a local modulation in the periodic geometry creates a cavity [34] and a waveguide [35][36][37][38] sustained by the bandgap, which spatially traps and guides acoustic waves, respectively. This PnC concept has been introduced into various micromechanical systems at microwave frequencies, including surface acoustic wave (SAW) devices [39,40], suspended nanobeams [6,7,15,16,41] and membranes [37,38,42]. In terms of the scalability of device integration, a suspended PnC membrane is a suitable platform because it can realize both a high quality (Q) factor and a small mode volume (V m ), leading to a low loss and a small device footprint.…”