Jian Ma

Multiplexed readout of ultrasensitive bolometers

  1. Priyank Singh,
  2. András Gunyhó,
  3. Heikki Suominen,
  4. Giacomo Catto,
  5. Florian Blanchet,
  6. Qi-Ming Chen,
  7. Arman Alizadeh,
  8. Aarne Keränen,
  9. Jian Ma,
  10. Timm Mörstedt,
  11. Wei Liu,
  12. and Mikko Möttonen
Recently, ultrasensitive calorimeters have been proposed as a resource-efficient solution for multiplexed qubit readout in superconducting large-scale quantum processors. However, experiments
demonstrating frequency multiplexing of these superconductor-normal conductor-superconductor (SNS) sensors are coarse. To this end, we present the design, fabrication, and operation of three SNS sensors with frequency-multiplexed input and probe circuits, all on a single chip. These devices have their probe frequencies in the range \SI{150}{\mega\hertz} — \SI{200}{\mega\hertz}, which is well detuned from the heater frequencies of \SI{4.4}{\giga\hertz} — \SI{7.6}{\giga\hertz} compatible with typical readout frequencies of superconducting qubits. Importantly, we show on-demand triggering of both individual and multiple low-noise SNS bolometers with very low cross talk. These experiments pave the way for multiplexed bolometric characterization and calorimetric readout of multiple qubits, a promising step in minimizing related resources such as the number of readout lines and microwave isolators in large-scale superconducting quantum computers.
arxiv pdf

Single-Shot Readout of a Superconducting Qubit Using a Thermal Detector

  1. András M. Gunyhó,
  2. Suman Kundu,
  3. Jian Ma,
  4. Wei Liu,
  5. Sakari Niemelä,
  6. Giacomo Catto,
  7. Vasilii Vadimov,
  8. Visa Vesterinen,
  9. Priyank Singh,
  10. Qiming Chen,
  11. and Mikko Möttönen
Measuring the state of qubits is one of the fundamental operations of a quantum computer. Currently, state-of-the-art high-fidelity single-shot readout of superconducting qubits relies
on parametric amplifiers at the millikelvin stage. However, parametric amplifiers are challenging to scale beyond hundreds of qubits owing to practical size and power limitations. Nanobolometers have properties that are advantageous for scalability and have recently shown sensitivity and speed promising for qubit readout, but such thermal detectors have not been demonstrated for this purpose. In this work, we utilize an ultrasensitive bolometer in place of a parametric amplifier to experimentally demonstrate single-shot qubit readout. With a modest readout duration of 13.9 μs, we achieve a single-shot fidelity of 0.618 which is mainly limited by the energy relaxation time of the qubit, T1=28 μs. Without the T1 errors, we find the fidelity to be 0.927. In the future, high-fidelity single-shot readout may be achieved by straightforward improvements to the chip design and experimental setup, and perhaps most interestingly by the change of the bolometer absorber material to reduce the readout time to the hundred-nanosecond level.
arxiv pdf