Wideband Josephson Parametric Amplifier with Integrated Transmission Line Transformer

  1. Leonardo Ranzani,
  2. Guilhem Ribeill,
  3. Brian Hassick,
  4. and Kin Chung Fong
We describe a wide-band Josephson Parametric Amplifier (JPA) that is impedance-matched using an integrated compact superconducting transmission line transformer. The impedance transformer
consists of two broadside coupled transmission lines configured in a Ruthroff topology which enables a wide matching bandwidth from 2 to 18 GHz, reducing the input line impedance and the device resonance quality factor by a factor of 4. This enables gain flatness and flexibility in the choice of the amplifier’s tuning range. The amplifier has up to 20dB gain, with less than 1 dB of ripple, 2-3 GHz gain-bandwidth product and -126 dBm input 1-dB compression point. Moreover, the device active area fits into a 1mm x 1mm space, thus easing integration into large quantum systems.

Miniaturizing transmon qubits using van der Waals materials

  1. Abhinandan Antony,
  2. Martin V. Gustafsson,
  3. Guilhem J. Ribeill,
  4. Matthew Ware,
  5. Anjaly Rajendran,
  6. Luke C.G. Govia,
  7. Thomas A. Ohki,
  8. Takashi Taniguchi,
  9. Kenji Watanabe,
  10. James Hone,
  11. and Kin Chung Fong
Quantum computers can potentially achieve an exponential speedup versus classical computers on certain computational tasks, as was recently demonstrated in systems of superconductingqubits. However, these qubits have large footprints due to the need of ultra low-loss capacitors. The large electric field volume of \textit{quantum compatible} capacitors stems from their distributed nature. This hinders scaling by increasing parasitic coupling in circuit designs, degrading individual qubit addressability, and limiting the minimum achievable circuit area. Here, we report the use of van der Waals (vdW) materials to reduce the qubit area by a factor of >1000. These qubit structures combine parallel-plate capacitors comprising crystalline layers of superconducting niobium diselenide (NbSe2) and insulating hexagonal-boron nitride (hBN) with conventional aluminum-based Josephson junctions. We measure a vdW transmon T1 relaxation time of 1.06 μs, demonstrating that a highly-compact capacitor can reach a loss-tangent of <2.83×10−5. Our results demonstrate a promising path towards breaking the paradigm of requiring large geometric capacitors for long quantum coherence in superconducting qubits, and illustrate the broad utility of layered heterostructures in low-loss, high-coherence quantum devices.[/expand]

Kinetic Inductance Traveling Wave Amplifiers For Multiplexed Qubit Readout

  1. Leonardo Ranzani,
  2. Mustafa Bal,
  3. Kin Chung Fong,
  4. Guilhem Ribeill,
  5. Xian Wu,
  6. Junling Long,
  7. Hsiang-Sheng Ku,
  8. Robert P. Erickson,
  9. David Pappas,
  10. and Thomas A. Ohki
We describe a kinetic inductance traveling-wave (KIT) amplifier suitable for superconducting quantum information measurements and characterize its wideband scattering and noise properties.
We use mechanical microwave switches to calibrate the four amplifier scattering parameters up to the device input and output connectors at the dilution refrigerator base temperature and a tunable temperature load to characterize the amplifier noise. Finally, we demonstrate the high fidelity simultaneous dispersive readout of two superconducting transmon qubits. The KIT amplifier provides low-noise amplification of both readout tones with readout fidelities in excess of 89% and negligible effect on qubit lifetime and coherence.