N. Earnest

Atomic layer deposition of titanium nitride for quantum circuits

  1. A. Shearrow,
  2. G. Koolstra,
  3. S. J. Whiteley,
  4. N. Earnest,
  5. P. S. Barry,
  6. F. J. Heremans,
  7. D. D. Awschalom,
  8. E. Shirokoff,
  9. and D.I. Schuster
Superconducting thin films with high intrinsic kinetic inductance are of great importance for photon detectors, achieving strong coupling in hybrid systems, and protected qubits. We
report on the performance of titanium nitride resonators, patterned on thin films (9-110 nm) grown by atomic layer deposition, with sheet inductances of up to 234 pH/square. For films thicker than 14 nm, quality factors measured in the quantum regime range from 0.4 to 1.0 million and are likely limited by dielectric two-level systems. Additionally, we show characteristic impedances up to 28 kOhm, with no significant degradation of the internal quality factor as the impedance increases. These high impedances correspond to an increased single photon coupling strength of 24 times compared to a 50 Ohm resonator, transformative for hybrid quantum systems and quantum sensing.
arxiv pdf

Random access quantum information processors

  1. R. K. Naik,
  2. N. Leung,
  3. S. Chakram,
  4. P. Groszkowski,
  5. Y. Lu,
  6. N. Earnest,
  7. D. C. McKay,
  8. Jens Koch,
  9. and D.I. Schuster
Qubit connectivity is an important property of a quantum processor, with an ideal processor having random access — the ability of arbitrary qubit pairs to interact directly. Here,
we implement a random access superconducting quantum information processor, demonstrating universal operations on a nine-bit quantum memory, with a single transmon serving as the central processor. The quantum memory uses the eigenmodes of a linear array of coupled superconducting resonators. The memory bits are superpositions of vacuum and single-photon states, controlled by a single superconducting transmon coupled to the edge of the array. We selectively stimulate single-photon vacuum Rabi oscillations between the transmon and individual eigenmodes through parametric flux modulation of the transmon frequency, producing sidebands resonant with the modes. Utilizing these oscillations for state transfer, we perform a universal set of single- and two-qubit gates between arbitrary pairs of modes, using only the charge and flux bias of the transmon. Further, we prepare multimode entangled Bell and GHZ states of arbitrary modes. The fast and flexible control, achieved with efficient use of cryogenic resources and control electronics, in a scalable architecture compatible with state-of-the-art quantum memories is promising for quantum computation and simulation.
arxiv pdf