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Electro-Acoustic Modulation of Surface Acoustic Waves on Thin-Film Lithium Niobate Substrate

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2020-03

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Weninger, Nicolas. 2020. Electro-Acoustic Modulation of Surface Acoustic Waves on Thin-Film Lithium Niobate Substrate. Bachelor's thesis, Harvard John A. Paulson School of Engineering and Applied Science.

Abstract

Surface Acoustic Waves (SAWs) are an important physical phenomenon that could allow for universal coupling between solid state systems such as two-level quantum systems, and for applications in modern high-data rate signal processing. Their slow propagation speed, inability to disperse to vacuum and ability to be used on-chip with piezoelectric materials results in SAWs being an attractive alternative to photons and photon-coupling of such systems. Lithium Niobate (LN) is an appropriate material for this use. The high piezoelectric coupling coefficient, demonstrated non-linear effects, and well-established fabrication techniques make Lithium Niobate (LN) an ideal material for use with SAWs. Current passive SAW devices still present challenges. It is currently not possible to couple and drive different isolated two-level quantum systems without active SAW modulation, and current passive SAW filters do not allow for as versatile signal processing as active SAW modulation would. This project demonstrates active electro-acoustic modulation on an LN platform with a fabricated prototype device. More specifically, I design, simulate and fabricate structures on an LN substrate that demonstrate SAW amplitude modulation with a dynamic range of 4 dB, and 180° phase modulation, which can be controlled to give a frequency shift. I also design a benchtop control mechanism for the device.

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Surface Acoustic Waves (SAWs) are longitudinal waves that travel across the surface of a material. Their unique generation and propagation properties have resulted in SAW-enabled devices finding use in many current applications, like mobile phone radios. They have also found recent use in coupling two-level quantum systems in quantum computing. These devices are passive and thus still present challenges to their broader application. The physical features of a device define the use case for the design, which cannot change dynamically. This means that existing SAW devices are unable to meet the demands of evolving telecommunication standards and to drive the states of isolated two-level quantum systems. Active devices with the ability to change the properties of SAWs in transit overcome these challenges. This project demonstrates electrically-controlled in-transit SAW amplitude modulation with a dynamic range of 4 dB, and phase modulation of 180° through simulations and fabricated prototype devices. This achievement paves the way for enabling smaller, higher bandwidth and higher bitrate communication systems, ushering in multi-gigabit-class wireless protocols. It also brings us one step closer to realising commercial quantum computing, by being able to leverage the benefits of different quantum systems for quantum error correction schemes and larger qubit architectures.

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http://nrs.harvard.edu/urn-3:HUL.InstRepos:42665426

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