Superconducting metamaterials for waveguide quantum electrodynamics

  1. Mohammad Mirhosseini,
  2. Eunjong Kim,
  3. Vinicius S. Ferreira,
  4. Mahmoud Kalaee,
  5. Alp Sipahigil,
  6. Andrew J. Keller,
  7. and Oskar Painter
The embedding of tunable quantum emitters in a photonic bandgap structure enables the control of dissipative and dispersive interactions between emitters and their photonic bath. Operation
in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite range emitter-emitter interactions via bound photonic states. Here we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant (λ/60). The metamaterial is formed by periodically loading a transmission line with compact, low loss, low disorder lumped element microwave resonators. We probe the coherent and dissipative dynamics of the system by measuring the Lamb shift and the change in the lifetime of the transmon qubit. Tuning the qubit frequency in the vicinity of a band-edge with a group index of ng=450, we observe an anomalous Lamb shift of 10 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to long-lived metastable qubit states and states strongly coupled to propagating waveguide modes.

Superconducting qubits on silicon substrates for quantum device integration

  1. Andrew J. Keller,
  2. Paul B. Dieterle,
  3. Michael Fang,
  4. Brett Berger,
  5. Johannes M. Fink,
  6. and Oskar Painter
We present the fabrication and characterization of transmon qubits formed from aluminum Josephson junctions on two different silicon-based substrates: (i) high-resistivity silicon (Si)
and (ii) silicon-on-insulator (SOI). Key to the qubit fabrication process is the use of an anhydrous hydrofluoric vapor process which removes silicon surface oxides without attacking aluminum, and in the case of SOI substrates, selectively removes the lossy buried oxide underneath the qubit region. For qubits with a transition frequency of approximately 5GHz we find qubit lifetimes and coherence times comparable to those attainable on sapphire substrates (T1,Si=27μs, T2,Si=6.6μs; T1,SOI=3.5μs, T2,SOI=2.2μs). This qubit fabrication process in principle permits co-fabrication of silicon photonic and mechanical elements, providing a route towards chip-scale integration of electro-opto-mechanical transducers for quantum networking of superconducting microwave quantum circuits.