标题： 一种用于新物理测试的超冷机械量子传感器 显示英文标题

标题： An Ultra-Cold Mechanical Quantum Sensor for Tests of New Physics

摘要： 机械模式在量子基态中的初始化对于其在量子信息和量子传感协议中的应用至关重要。 在量子处理器中，模式初始状态的不纯会影响后续量子算法的保真度。 在量子传感器中，基态外的激发会增加检测器的噪声，它们的普遍存在对向机械模式注入能量的稀有事件设定了限制。 在本工作中，我们测量了高次谐波体声波谐振器（HBAR）中吉赫兹频率模式的激发态粒子数。 我们发现第一激发态的粒子数可以低至$P_p$=(1.2$\pm$5.5)$\times10^{-5}$，对应的有效温度为25.2毫开尔文，这些是受测量过程不完善限制的上限。 这些结果优于超导电路中测得的最低粒子数。 最后，我们利用测得的粒子数来限制高频引力波的振幅、超轻暗物质的动能混合强度以及描述波函数塌缩机制的薛定谔方程的非线性修正。 我们的工作确立了HBAR作为量子态初始化和基础物理研究的多功能资源。 显示英文摘要

摘要： Initialization of mechanical modes in the quantum ground state is crucial for their use in quantum information and quantum sensing protocols. In quantum processors, impurity of the modes' initial state affects the infidelity of subsequent quantum algorithms. In quantum sensors, excitations out of the ground state contribute to the noise of the detector, and their prevalence puts a bound on rare events that deposit energy into the mechanical modes. In this work, we measure the excited-state populations of GHz-frequency modes in a high-overtone bulk acoustic wave resonator (HBAR). We find that the population of the first excited state can be as low as $P_p$=(1.2$\pm$5.5)$\times10^{-5}$, corresponding to an effective temperature of 25.2 mK, which are upper bounds limited by imperfections in the measurement process. These results compare favorably to the lowest populations measured in superconducting circuits. Finally, we use the measured populations to constrain the amplitude of high-frequency gravitational waves, the kinetic mixing strength of ultra-light dark matter, and non-linear modifications of the Schr\"{o}dinger equation describing wavefunction collapse mechanisms. Our work establishes HBARs as a versatile resource for quantum state initialization and studies of fundamental physics.