J. Venkatraman

Spectroscopy of drive-induced unwanted state transitions in superconducting circuits

  1. W. Dai,
  2. S. Hazra,
  3. D. K. Weiss,
  4. P. D. Kurilovich,
  5. T. Connolly,
  6. H. K. Babla,
  7. S. Singh,
  8. V. R. Joshi,
  9. A. Z. Ding,
  10. P. D. Parakh,
  11. J. Venkatraman,
  12. X. Xiao,
  13. L. Frunzio,
  14. and M. H. Devoret
Microwave drives are essential for implementing control and readout operations in superconducting quantum circuits. However, increasing the drive strength eventually leads to unwanted
state transitions which limit the speed and fidelity of such operations. In this work, we systematically investigate such transitions in a fixed-frequency qubit subjected to microwave drives spanning a 9 GHz frequency range. We identify the physical origins of these transitions and classify them into three categories. (1) Resonant energy exchange with parasitic two-level systems, activated by drive-induced ac-Stark shifts, (2) multi-photon transitions to non-computational states, intrinsic to the circuit Hamiltonian, and (3) inelastic scattering processes in which the drive causes a state transition in the superconducting circuit, while transferring excess energy to a spurious electromagnetic mode or two-level system (TLS) material defect. We show that the Floquet steady-state simulation, complemented by an electromagnetic simulation of the physical device, accurately predicts the observed transitions that do not involve TLS. Our results provide a comprehensive classification of these transitions and offer mitigation strategies through informed choices of drive frequency as well as improved circuit design.
arxiv pdf

Experimental implementation of a Raman-assisted six-quanta process

  1. S. O. Mundhada,
  2. A. Grimm,
  3. J. Venkatraman,
  4. Z.K. Minev,
  5. S. Touzard,
  6. N. E. Frattini,
  7. V. V. Sivak,
  8. K. Sliwa,
  9. P. Reinhold,
  10. S. Shankar,
  11. M. Mirrahimi,
  12. and M.H. Devoret
Fault tolerant quantum information processing requires specific nonlinear interactions acting within the Hilbert space of the physical system that implements a logical qubit. The required
order of nonlinearity is often not directly available in the natural interactions of the system. Here, we experimentally demonstrate a route to obtain higher-order nonlinearities by combining more easily available lower-order nonlinear processes, using a generalization of the Raman transitions. In particular, we demonstrate a Raman-assisted transformation of four photons of a high-Q superconducting cavity into two excitations of a superconducting transmon mode and vice versa. The resulting six-quanta process is obtained by cascading two fourth-order nonlinear processes through a virtual state. This process is a key step towards hardware efficient quantum error correction using Schrödinger cat-states.
arxiv pdf