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.

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.