J. D. Whittaker

A frequency and sensitivity tunable microresonator array for high-speed quantum processor readout

  1. J. D. Whittaker,
  2. L. J. Swenson,
  3. M. H. Volkmann,
  4. P. Spear,
  5. F. Altomare,
  6. A.J. Berkley,
  7. B. Bumble,
  8. P. Bunyk,
  9. P. K. Day,
  10. B. H. Eom,
  11. R. Harris,
  12. J.P. Hilton,
  13. E. Hoskinson,
  14. M.W. Johnson,
  15. A. Kleinsasser,
  16. E. Ladizinsky,
  17. T. Lanting,
  18. T. Oh,
  19. I. Perminov,
  20. E. Tolkacheva,
  21. and J. Yao
Superconducting microresonators have been successfully utilized as detection elements for a wide variety of applications. With multiplexing factors exceeding 1,000 detectors per transmission
line, they are the most scalable low-temperature detector technology demonstrated to date. For high-throughput applications, fewer detectors can be coupled to a single wire but utilize a larger per-detector bandwidth. For all existing designs, fluctuations in fabrication tolerances result in a non-uniform shift in resonance frequency and sensitivity, which ultimately limits the efficiency of band-width utilization. Here we present the design, implementation, and initial characterization of a superconducting microresonator readout integrating two tunable inductances per detector. We demonstrate that these tuning elements provide independent control of both the detector frequency and sensitivity, allowing us to maximize the transmission line bandwidth utilization. Finally we discuss the integration of these detectors in a multilayer fabrication stack for high-speed readout of the D-Wave quantum processor, highlighting the use of control and routing circuitry composed of single flux-quantum loops to minimize the number of control wires at the lowest temperature stage.
arxiv pdf

Tunable-Cavity QED with Phase Qubits

  1. J. D. Whittaker,
  2. F. C. S. da Silva,
  3. M. S. Allman,
  4. F. Lecocq,
  5. K. Cicak,
  6. A. J. Sirois,
  7. J. D. Teufel,
  8. J. Aumentado,
  9. and R. W. Simmonds
We describe a tunable-cavity QED architecture with an rf SQUID phase qubit inductively coupled to a single-mode, resonant cavity with a tunable frequency that allows for both microwave
readout of tunneling and dispersive measurements of the qubit. Dispersive measurement is well characterized by a three-level model, strongly dependent on qubit anharmonicity, qubit-cavity coupling and detuning. A tunable cavity frequency provides a way to strongly vary both the qubit-cavity detuning and coupling strength, which can reduce Purcell losses, cavity-induced dephasing of the qubit, and residual bus coupling for a system with multiple qubits. With our qubit-cavity system, we show that dynamic control over the cavity frequency enables one to avoid Purcell losses during coherent qubit evolutions and optimize state readout during qubit measurements. The maximum qubit decay time T1 = 1.5 μs is found to be limited by surface dielectric losses from a design geometry similar to planar transmon qubits.
arxiv pdf