Acoustic waves are versatile on-chip information carriers that can be used in applications such as microwave filters and transducers. Nonreciprocal devices, in which the transmission of waves is non-symmetric between two ports, are desirable for the manipulation and routing of phonons, but building acoustic non-reciprocal devices is difficult because acoustic systems typically have a linear response. Here, we report non-reciprocal transmission of microwave surface acoustic waves using a nonlinear parity–time symmetric system based on two coupled acoustic resonators in a lithium niobate platform. Owing to the strong piezoelectricity of lithium niobate, we can tune the gain, loss and nonlinearity of the system using electric circuitry. Our approach can achieve 10 dB of non-reciprocal transmission for surface acoustic waves at a frequency of 200 MHz, and we use it to demonstrate a one-way circulation of acoustic waves in cascading non-reciprocal devices.

声波是通用的片上信息载体，可用于微波滤波器和换能器等应用中。对于声子的操纵和路由，其中​​波的传输在两个端口之间是非对称的不可逆设备是理想的，但是由于声学系统通常具有线性响应，因此构建声学不可逆设备是困难的。在这里，我们报告了使用基于铌酸锂平台中两个耦合声谐振器的非线性奇偶-时间对称系统的微波表面声波的非互易传输。由于铌酸锂的强压电性，我们可以使用电路来调节系统的增益，损耗和非线性。对于频率为200 MHz的表面声波，我们的方法可以实现10 dB的不可逆传输，