Modulating Surface Acoustic Wave Generation through Superconductivity

TL;DR

This paper demonstrates the use of superconducting niobium nitride interdigitated transducers to modulate surface acoustic wave transmission, enabling improved integration with quantum devices and fine control over device states.

Contribution

It introduces a novel superconducting NbN-based SAW device with tunable transmission states controlled by superconductivity, advancing quantum device integration.

Findings

Achieved a 16x difference in SAW transmission between superconducting and normal states.

Demonstrated fabrication of NbN SAW devices using photolithography and reactive ion etching.

Observed transmission changes correlate with NbN resistance at its critical temperature.

Abstract

Surface acoustic waves (SAWs), with their five orders-of-magnitude slower propagation velocity, allow for considerably shorter wavelengths at the same frequency compared to electromagnetic waves. The short wavelengths allow for device miniaturization and on-chip integration. The generic design of these devices involve piezoelectric substrates with comblike arrays of Al or Au electrodes known as interdigitated transducers deposited on the surface. However, Al and Au both have shortcomings at the cryogenic temperatures required for quantum applications, namely the formation of two-level systems and the lack of superconductivity perpetuating Ohmic losses, respectively. In this work, SAWs are generated in the high-MHz to low-GHz range using niobium nitride (NbN) interdigitated transducers (IDTs) and Bragg reflectors. We demonstrate the fabrication of acoustic devices through photolithography and reactive ion etching (RIE). The sharp transition between superconducting and normal states and the corresponding change in SAW transmission allows for fine control of the 'on' (superconducting) and 'off' (normal) states of NbN, with a \Delta_T = K separating the transmission minimum and maximum. We demonstrate a 16x difference in transmission between the 'on' and 'off' states of the device. The SAW transmission behavior mirrors the change in resistance of NbN at its Tc. These findings open up new possibilities for the integration of NbN SAW resonators into existing quantum architectures based on NbN and a method for adjusting transmission properties independent of applied voltage.