Devin L. Underwood

Using Cryogenic CMOS Control Electronics To Enable A Two-Qubit Cross-Resonance Gate

  1. Devin L. Underwood,
  2. Joseph A. Glick,
  3. Ken Inoue,
  4. David J. Frank,
  5. John Timmerwilke,
  6. Emily Pritchett,
  7. Sudipto Chakraborty,
  8. Kevin Tien,
  9. Mark Yeck,
  10. John F. Bulzacchelli,
  11. Chris Baks,
  12. Pat Rosno,
  13. Raphael Robertazzi,
  14. Matthew Beck,
  15. Rajiv V. Joshi,
  16. Dorothy Wisnieff,
  17. Daniel Ramirez,
  18. Jeff Ruedinger,
  19. Scott Lekuch,
  20. Brian P. Gaucher,
  21. and Daniel J. Friedman
Qubit control electronics composed of CMOS circuits are of critical interest for next generation quantum computing systems. A CMOS-based application specific integrated circuit (ASIC)
fabricated in 14nm FinFET technology was used to generate and sequence qubit control waveforms and demonstrate a two-qubit cross resonance gate between fixed frequency transmons. The controller was thermally anchored to the T = 4K stage of a dilution refrigerator and the measured power was 23 mW per qubit under active control. The chip generated single–side banded output frequencies between 4.5 and 5.5 GHz with a maximum power output of -18 dBm. Randomized benchmarking (RB) experiments revealed an average number of 1.71 instructions per Clifford (IPC) for single-qubit gates, and 17.51 IPC for two-qubit gates. A single-qubit error per gate of ϵ1Q=8e-4 and two-qubit error per gate of ϵ2Q=1.4e-2 is shown. A drive-induced Z-rotation is observed by way of a rotary echo experiment; this observation is consistent with expected qubit behavior given measured excess local oscillator (LO) leakage from the CMOS chip. The effect of spurious drive induced Z-errors is numerically evaluated with a two-qubit model Hamiltonian, and shown to be in good agreement with measured RB data. The modeling results suggest the Z-error varies linearly with pulse amplitude.
arxiv pdf

Beyond Strong Coupling in a Massively Multimode Cavity

  1. Neereja M. Sundaresan,
  2. Yanbing Liu,
  3. Darius Sadri,
  4. Laszlo J. Szocs,
  5. Devin L. Underwood,
  6. Moein Malekakhlagh,
  7. Hakan E. Tureci,
  8. and Andrew A. Houck
The study of light-matter interaction has seen a resurgence in recent years, stimulated by highly controllable, precise, and modular experiments in cavity quantum electrodynamics (QED).
The achievement of strong coupling, where the coupling between a single atom and fundamental cavity mode exceeds the decay rates, was a major milestone that opened the doors to a multitude of new investigations. Here we introduce multimode strong coupling (MMSC), where the coupling is comparable to the free spectral range (FSR) of the cavity, i.e. the rate at which a qubit can absorb a photon from the cavity is comparable to the round trip transit rate of a photon in the cavity. We realize, via the circuit QED architecture, the first experiment accessing the MMSC regime, and report remarkably widespread and structured resonance fluorescence, whose origin extends beyond cavity enhancement of sidebands. Our results capture complex multimode, multiphoton processes, and the emergence of ultranarrow linewidths. Beyond the novel phenomena presented here, MMSC opens a major new direction in the exploration of light-matter interactions.
arxiv pdf

A scanning transmon qubit for strong coupling circuit quantum electrodynamics

  1. William E. Shanks,
  2. Devin L. Underwood,
  3. and Andrew A. Houck
Like a quantum computer designed for a particular class of problems, a quantum simulator enables quantitative modeling of quantum systems that is computationally intractable with a
classical computer. Quantum simulations of quantum many-body systems have been performed using ultracold atoms and trapped ions among other systems. Superconducting circuits have recently been investigated as an alternative system in which microwave photons confined to a lattice of coupled resonators act as the particles under study with qubits coupled to the resonators producing effective photon-photon interactions. Such a system promises insight into the nonequilibrium physics of interacting bosons but new tools are needed to understand this complex behavior. Here we demonstrate the operation of a scanning transmon qubit and propose its use as a local probe of photon number within a superconducting resonator lattice. We map the coupling strength of the qubit to a resonator on a separate chip and show that the system reaches the strong coupling regime over a wide scanning area.
arxiv pdf

Low-Disorder Microwave Cavity Lattices for Quantum Simulation with Photons

  1. Devin L. Underwood,
  2. Will E. Shanks,
  3. Jens Koch,
  4. and Andrew A. Houck
We assess experimentally the suitability of coupled transmission line resonators for studies of quantum phase transitions of light. We have measured devices with low photon hopping
rates t/2pi = 0.8MHz to quantify disorder in individual cavity frequencies. The observed disorder is consistent with small imperfections in fabrication. We studied the dependence of the disorder on transmission line geometry and used our results to fabricate devices with disorder less than two parts in 10^4. The normal mode spectrum of devices with a high photon hopping rate t/2pi = 31MHz shows little effect of disorder, rendering resonator arrays a good backbone for the study of condensed matter physics with photons.
arxiv pdf