Y. J. Rosen

Noise-specific beats in the higher-level Ramsey curves of a transmon qubit

  1. L.A. Martinez,
  2. Z. Peng,
  3. D. Appelö,
  4. D. M. Tennant,
  5. N. Anders Petersson,
  6. J. L. DuBois,
  7. and Y. J. Rosen
In the higher levels of superconducting transmon devices, and more generally charge sensitive devices, T∗2 measurements made in the presence of low-frequency time-correlated 1/f charge
noise and quasiparticle-induced parity flips can give an underestimation of the total dephasing time. The charge variations manifest as beating patterns observed in the overlay of several Ramsey fringe curves, and are reproduced with a phenomenological Ramsey curve model which accounts for the charge variations. T∗2 dephasing times which more accurately represent the total dephasing time are obtained. The phenomenological model is compared with a Lindblad master equation model. Both models are found to be in agreement with one another and the experimental data. Finally, the phenomenological formulation enables a simple method in which the power spectral density (PSD) for the low-frequency noise can be inferred from the overlay of several Ramsey curves.
arxiv pdf

Cryogenic single-port calibration for superconducting microwave resonator measurements

  1. Haozhi Wang,
  2. S. Singh,
  3. C.R.H. McRae,
  4. J.C. Bardin,
  5. S.-X. Lin,
  6. N. Messaoudi,
  7. A.R. Castelli,
  8. Y. J. Rosen,
  9. E. T. Holland,
  10. D. P. Pappas,
  11. and J. Y. Mutus
Superconducting circuit testing and materials loss characterization requires robust and reliable methods for the extraction of internal and coupling quality factors of microwave resonators.
A common method, imposed by limitations on the device design or experimental configuration, is the single-port reflection geometry, i.e. reflection-mode. However, impedance mismatches in cryogenic systems must be accounted for through calibration of the measurement chain while it is at low temperatures. In this paper, we demonstrate a data-based, single-port calibration using commercial microwave standards and a vector network analyzer (VNA) with samples at millikelvin temperature in a dilution refrigerator, making this method useful for measurements of quantum phenomena. Finally, we cross reference our data-based, single-port calibration and reflection measurement with over-coupled 2D- and 3D-resonators against well established two-port techniques corroborating the validity of our method.
arxiv pdf

Anomalous Charge Noise in Superconducting Qubits

  1. B. G. Christensen,
  2. C. D. Wilen,
  3. A. Opremcak,
  4. J. Nelson,
  5. F. Schlenker,
  6. C. H. Zimonick,
  7. L. Faoro,
  8. L.B. Ioffe,
  9. Y. J. Rosen,
  10. J. L. DuBois,
  11. B. L. T. Plourde,
  12. and R. McDermott
We have used Ramsey tomography to characterize charge noise in a weakly charge-sensitive superconducting qubit. We find a charge noise that scales with frequency as 1/fα over 5 decades
with α=1.93 and a magnitude Sq(1Hz)=2.9×10−4 e2/Hz. The noise exponent and magnitude of the low-frequency noise are much larger than those seen in prior work on single electron transistors, yet are consistent with reports of frequency noise in other superconducting qubits. Moreover, we observe frequent large-amplitude jumps in offset charge exceeding 0.1e; these large discrete charge jumps are incompatible with a picture of localized dipole-like two-level fluctuators. The data reveal an unexpected dependence of charge noise on device scale and suggest models involving either charge drift or fluctuating patch potentials.
arxiv pdf