Alexander Madden

Transmon Architecture for Emission and Detection of Single Microwave Photons

  1. Daniel L. Campbell,
  2. Stephen McCoy,
  3. Melinda Andrews,
  4. Alexander Madden,
  5. Viva R. Horowitz,
  6. Bakir Husremović,
  7. Samuel Marash,
  8. Christopher Nadeau,
  9. Man Nguyen,
  10. Michael Senatore,
  11. Samuel Schwab,
  12. Erin Sheridan,
  13. and Matthew D. LaHaye
We showcase the recently developed double transmon coupler (DTC) circuit as a compact, drop-in, tunable and transition-selective link between an otherwise coherent transmon and the
continuum of modes in a waveguide. We use these transmon-DTC devices as transmon emitter/dectectors (TEDs) for microwave photons. We highlight the flexibility of these devices by sending photons from a source TED to a measurement TED using a meter of coaxial cable and a circulator, each TED with nominally identical circuit parameters. We detect 60% of the photons using this setup where we infer that 95% of the photons at the input of the measurement TED are detected. Reset and photon emission/detection each require about 2μs, for a minimum protocol duration of 4μs, for our choice of TED parameters. Transmon-waveguide links like the DTC serve an important role in quantum information processors: they provide a mechanism for unconditional fast reset, metrology, and as nascent quantum communication interfaces for quantum networking.
arxiv pdf

Ta-based Josephson junctions using insulating ALD TaN tunnel barriers

  1. Ekta Bhatia,
  2. Jack Lombardi,
  3. Tuan Vo,
  4. Michael Senatore,
  5. Alexander Madden,
  6. Soumen Kar,
  7. Hunter Frost,
  8. Stephen Olson,
  9. Jakub Nalaskowski,
  10. John Mucci,
  11. Brian Martinick,
  12. Ilyssa Wells,
  13. Thomas Murray,
  14. Kevin Musick,
  15. Corbet S. Johnson,
  16. Stephen McCoy,
  17. Daniel L. Campbell,
  18. Matthew D. LaHaye,
  19. and Satyavolu S. Papa Rao
Josephson junctions form the core circuit element in superconducting quantum computing circuits, single flux quantum digital logic circuits, and sensing devices such as SQUIDs. Aluminum
oxide has typically been used as the tunnel barrier. Its formation by exposure to low oxygen pressures at room temperature for short periods of time makes it susceptible to aging and limits the thermal budget of downstream processes. In this paper, we report the first demonstration of {\alpha}-Ta/insulating TaN/a-Ta superconductor/insulator/superconductor Josephson junctions fabricated on 300 mm wafers using CMOS-compatible processes. The junctions were fabricated on high-resistivity silicon substrates using standard processes available at 300 mm scale, including 193 nm optical lithography, ALD of TaN in a cluster tool, and chemical mechanical planarization to enable highly planar interfaces. Junction areas ranging from 0.03 um2 to 9 um2 with ALD TaN thickness between 2 nm and 7 nm were characterized. A critical current density of 76 uA/um2 was observed in junctions using 4 nm ALD TaN in the tunnel barrier. The dependence of Jc on ALD TaN layer thickness is analyzed, and the influence of junction geometry, packaging, and temperature on I-V characteristics is discussed. Junctions were retested after a period of 4 months to quantify junction aging. The potential of this novel material system and a 300 mm superconducting junction process flow to fabricate thermally and environmentally stable junctions is discussed. The vision of a Superconducting Quantum Process Design Kit for a Multi-Project Wafer program to enable rapid development and proliferation of superconducting quantum and digital digital logic systems is presented. This work represents the first step towards establishing such a Quantum Foundry, providing access to high quality qubits and single-flux quantum logic circuits at 300 mm wafer scale.
arxiv pdf