Cryogenic microwave filter cavity with a tunability greater than 5 GHz

Abstract

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 in situ 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 in situ 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 3 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.Three dimensional (3D) microwave cavities have proven to be an indispensable part of many quantum systems. They have recently been used in conjunction with superconducting qubits 1 to make spectacular progress in the field of cavity QED, where they are integral components in the implementation of universal gate sets, 2 nondestructive measurement of single microwave photons, 3 and implementation of programmable interference between quantum memories. 4 When paired with ferromagnetic spheroids, 5 they readily exhibit strong coupling to spin resonances, 6,7 which has allowed for the field of cavity magnonics to flourish with applications such as bidirectional microwave-optical conversion 8 and resolving magnon number states. 9 When coupled to a mechanical element, such as a membrane 10 or superfluid helium, 11 they form an optomechanical system with the potential for exceedingly high cooperativities and quality factors, allowing for the rich toolbox of optomechanics to be employed.In all of these applications, cryogenic tunability of the microwave cavity -without sacrificing the quality factor (Q)would allow for the use of superconducting materials, desirable for the high quality factors they confer. For instance, one can imagine a superconducting qubit encapsulated inside a superconducting resonator. Normally, such a qubit is tuned by the application of a magnetic field, 12 but this is prohibited inside a superconducting cavity due to field exclusion from the Meissner effect. With a highly-tunable cavity, one could enjoy all the advantages of a superconducting cavity while still being able to control its detuning with respect to a qubit. Similarly for cavity magnonics, a highly-tunable cavity could allow control of the phonon-magnon hybridization without the need for a tunable magnetic field.In addition to their uses outlined above, microwave cavities are useful in both classical and quantum systems as phase noise filters. [13][14][15] Classically, phase noise...

Cavity magnomechanical storage and retrieval of quantum states

“…The photon frequency can be modulated by using a tunable 3D microwave cavity as realized in the Refs. [38,39,40,41], which will modulate the cavity detuning, δ a . In the following section we will show that, using these time-dependent modulations, a STIRAPlike protocol can be designed to effectively transfer the microwave cavity state to the mechanical mode and then retrieve it back to the microwave cavity mode.…”

Frequency Fluctuations in Tunable and Nonlinear Microwave Cavities

“…In the field of quantum information, they have been used as parametric oscillators to achieve single-shot readout of a superconducting qubit [1,2] and as quantum buses for selective qubit coupling [3]. As standalone cryogenic microwave devices, they have been used as filters [4] and as parametric amplifiers operating near the quantum limit of added noise [5]. In the study of fundamental physics, they have been used to investigate the dynamical Casimir effect [6,7].…”

Strong magnon–photon coupling within a tunable cryogenic microwave cavity

“…1a). 26 Increasing the pressure causes the membrane to deform, reducing the distance between the membrane and the two circular posts. The tunability of this cavity can be understood by noticing that the electric field is primarily confined within this gap.…”

“…If critical coupling was required one could use loop-couplers, as demonstrated by Clark et al in Ref. 26. Characterization of the cavity tunability was performed by measuring the resonance frequency and quality fac-tor as a function of reservoir pressure, shown in Fig.…”