Flux coupled tunable superconducting resonator

  1. Juliang Li,
  2. Pete Barry,
  3. Tom Cecil,
  4. Marharyta Lisovenko,
  5. Volodymyr Yefremenko,
  6. Gensheng Wang,
  7. Serhii Kruhlov,
  8. Goran Karapetrov,
  9. and Clarence Chang
We present a design and implementation of frequency-tunable superconducting resonator. The resonance frequency tunability is achieved by flux-coupling a superconducting LC-loop to a
current-biased feedline; the resulting screening current leads to a change of the kinetic inductance and shift in the resonance frequency. The thin film aluminum resonator consists of an interdigitated capacitor and thin line inductors forming a closed superconducting loop. The magnetic flux from the nearby current feedline induces Meissner shielding currents in the resonator loop leading to change in the kinetic part of the total inductance of the resonator. We demonstarte continuous frequency tuning within 160 MHz around the resonant frequency of 2.7 GHz. We show that: (1) frequency upconversion is achieved when kHz AC modulation signal is superimposed onto the DC bias resulting in sidebands to the resonator tone; (2) three-wave mixing is attained by parametrically pumping the nonlinear kinetic inductance using a strong RF pump signal in the feedline. The simple architecture is amenable to large array multiplexing and on-chip integration with other circuit components. The concept could be applied in flux magnetometers, upconverters, and parametric amplifiers operating above 4 Kelvin cryogenic temperatures when alternative high critical temperature material with high kinetic inductance is used.

A Nonlinear Charge and Flux Tunable Cavity Derived from an Embedded Cooper Pair Transistor

  1. B. L. Brock,
  2. Juliang Li,
  3. S. Kanhirathingal,
  4. B. Thyagarajan,
  5. William F. Braasch Jr.,
  6. M. P. Blencowe,
  7. and A. J. Rimberg
We introduce the cavity-embedded Cooper pair transistor (cCPT), a device which behaves as a highly nonlinear microwave cavity whose resonant frequency can be tuned both by charging
a gate capacitor and by threading flux through a SQUID loop. We characterize this device and find excellent agreement between theory and experiment. A key difficulty in this characterization is the presence of frequency fluctuations comparable in scale to the cavity linewidth, which deform our measured resonance circles in accordance with recent theoretical predictions [B. L. Brock et al., Phys. Rev. Applied (to be published), arXiv:1906.11989]. By measuring the power spectral density of these frequency fluctuations at carefully chosen points in parameter space, we find that they are primarily a result of the 1/f charge and flux noise common in solid state devices. Notably, we also observe key signatures of frequency fluctuations induced by quantum fluctuations in the cavity field via the Kerr nonlinearity.