Maria Nowicki

Unified scaling of transmon sub-resonant parametric drive strength limits

  1. Jacob Repicky,
  2. Girish Kumbhar,
  3. Mingkang Xia,
  4. Roman Baskov,
  5. Param Patel,
  6. Maria Nowicki,
  7. Luigi Frunzio,
  8. Steven M. Girvin,
  9. and Michael Hatridge
Achieving fast gates and high-fidelity readout in superconducting quantum circuits often benefits from the use of large amplitude microwave drives. As the strength increases, unwanted
effects such as excitation out of the logical states also become more prevalent. In transmon qubits, coherent controls relying on sub-resonant drives are fundamentally limited by the eventual appearance of strong hybridization in the spectrum. Understanding how this threshold depends on intrinsic device parameters is vital for the design and operation of circuits utilizing the transmon as a source of nonlinearity. In this work, we present an experimental study of 14 transmons with a wide range of anharmonicities, and use comparison with Floquet branch analysis and semiclassical simulations to establish a straightforward relationship between the critical value of the effective drive amplitude ηmax and the ratio γ=ωq/α, where ωq is the transmon frequency and −α is the anharmonicity. For the case where the transmon is used as a parametrically driven coupler, these results further allow us to estimate maximum parametric interaction rates, which informs the circuit design process for optimizing gate rates and fidelities.
arxiv pdf

Simple, High Saturation Power, Quantum-limited, RF SQUID Array-based Josephson Parametric Amplifiers

  1. Ryan Kaufman,
  2. Chenxu Liu,
  3. Katarina Cicak,
  4. Boris Mesits,
  5. Mingkang Xia,
  6. Chao Zhou,
  7. Maria Nowicki,
  8. José Aumentado,
  9. David Pekker,
  10. and Michael Hatridge
High-fidelity quantum non-demolition qubit measurement is critical to error correction and rapid qubit feedback in large-scale quantum computing. High-fidelity readout requires passing
a short and strong pulse through the qubit’s readout resonator, which is then processed by a sufficiently high bandwidth, high saturation power, and quantum-limited amplifier. We have developed a design pipeline that combines time-domain simulation of the un-truncated device Hamiltonian, fabrication constraints, and maximization of saturation power. We have realized an amplifier based on a modified NIST tri-layer Nb fabrication suite which utilizes an array of 25 radio frequency Superconducting QUantum Interference Devices (rf SQUIDs) embedded within a low-Q resonator powered by a high-power voltage pump delivered via a diplexer on the signal port. We show that, despite the intensity of the pump, the device is quantum-efficient and capable of high-fidelity measurement limited by state transitions in the transmon. We present experimental data demonstrating up to -91.2 dBm input saturation power with 20 dB gain, up to 28 MHz instantaneous bandwidth, and phase-preserving qubit measurements with 62% quantum efficiency.
arxiv pdf