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Quantum Computing Progress and Prospects (2019) / Chapter Skim
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Appendix C: Superconducting Quantum Computers
Pages 205-211

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From page 205...
... Josephson junctions on either silicon or sapphire substrates. While superconducting qubits can be fabricated using the same design tools and fabrication equipment used to build silicon chips, the premium placed on high coherence necessitates that the specific fabrication steps be modified to eliminate defects that create losses.
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From page 206...
... . However, due to the fabrication complexity, additional processing steps, and the need for an interwiring layer of dielectric materials like silicon dioxide or silicon nitride that cause loss, qubits made in multilayer niobium processes generally have low coherence times, typically in the 10-100 nanosecond range [3]
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From page 207...
... In addition to the qubits, the circuits include a simple mechanism to couple the qubit to its 5 GHz microwave control signal and to a superconducting resonator, typically designed to operate at around 7-8 GHz, which reads out the qubit state using the circuit quantum electrodynamics architecture [12]
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From page 208...
... C.4 CONTROL AND MEASUREMENT PLANE The control and measurement plane for a superconducting quantum computer needs to generate the bias voltages/currents used to tune the qubits, create the microwave control signals, and reliably detect qubit measurements, while dealing with the large temperature differences that exist between the circuits that generate the control signals and the quantum plane that consumes them. C.4.1 Control Wiring and Packaging The delivery of electromagnetic control signals from the room-temperature region where they are generated to the qubits inside the refrigerator at mK temperatures requires careful thermal and electrical engineering.
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From page 209...
... For the high isolation needed for quantum circuits, coaxial connectors, coaxial wiring harnesses, miniature multipin connectors, and so on are types of connectors being used to bring signals into the package. The higher isolation that these connectors provide make them larger than the simple pin or ball connection used in packages for conventional silicon devices, and thus the number of signals per unit area is much smaller.
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From page 210...
... For contemporary superconducting qubit applications, the AWGs and ADCs typically operate with 1-2 GS/s and 10-14 bits of resolution. Commercially available precision-grade local oscillators typically have a 1-12 GHz frequency range with a single-sideband phase noise of –120 dB at 10 kHz offset; this level of phase is generally sufficient to achieve gate error rates at the 10–8 level [17]
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From page 211...
... Johnson, et al., 2011, Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architecture, Physical Review Letters 107:240501.
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Key Terms

  • quantum computing
  • physical review
  • base temperature
  • control signals
  • superconducting qubit

  • dilution refrigerators
  • control signal
  • review letters
  • tunable qubits
  • thermal noise

  • quantum data
  • trapped ion
  • microwave control
  • heat loads
  • qubit state

  • typically designed
  • measurement plane
  • coherence times
  • fabrication process
  • quantum circuits

  • conventional silicon
  • npj quantum
  • quantum information
  • qubits require
  • josephson junction

  • data plane
  • lower temperatures
  • versus tunable
  • digital quantum
  • logic operations


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