Clark T J, Vadakkumbatt V, Souris F, Ramp H, Davis J P
Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
Rev Sci Instrum. 2018 Nov;89(11):114704. doi: 10.1063/1.5051042.
A wide variety of applications of microwave cavities, such as measurement and control of superconducting qubits, magnonic resonators, and phase noise filters, would be well served by having a highly tunable microwave resonance. Often this tunability is desired at low temperatures, where one can take advantage of superconducting cavities. To date, such cryogenic tuning while maintaining a high quality factor has been limited to ∼500 MHz. Here we demonstrate a three-dimensional superconducting microwave cavity that shares one wall with a pressurized volume of helium. Upon pressurization of the helium chamber, the microwave cavity is deformed, which results in tuning of its resonant frequency by more than 5 GHz, greater than 60% of the original 8 GHz resonant frequency. The quality factor of the cavity remains approximately constant at ≈7 × 10 over the entire range of tuning. As a demonstration of its usefulness, we implement a tunable cryogenic phase noise filter, which reduces the phase noise of our source by approximately 10 dB above 400 kHz.
微波腔的多种应用，如超导量子比特、磁振子谐振器和相位噪声滤波器的测量与控制，都将受益于具有高度可调谐的微波共振。通常这种可调谐性在低温下是很有用的，因为在低温下可以利用超导腔。到目前为止，在保持高品质因数的同时进行这种低温调谐一直局限于约500兆赫兹。在此，我们展示了一种三维超导微波腔，它与一个充有压力氦气的腔体共用一面壁。对氦气腔进行加压时，微波腔会发生变形，这导致其谐振频率调谐超过5吉赫兹，大于原始8吉赫兹谐振频率的60%。在整个调谐范围内，腔体的品质因数在约7×10处大致保持恒定。作为其有用性的一个证明，我们实现了一个可调谐低温相位噪声滤波器，该滤波器在400千赫兹以上将我们源的相位噪声降低了约10分贝。
