Quantum circuits

Universal control of flux-tunable bosonic mode

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Dr. Axel Eriksson

Dr. Axel Eriksson

Chalmers University of Technology, Sweden

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Summary

Challenge: Achieving universal control of a flux-tunable bosonic mode requires driving both charge and flux ports simultaneously at frequency multiples. This demands absolute phase coherence across channels and extremely rigorous timing requirements to maintain the state.

Solution: Presto uses Direct Digital Synthesis to enable full phase control over all pulses generated across multiple channels. This architecture allows for inter-channel pulse timing with 100 ps precision, enabling the generation of high-quality cubic phase states.
Figure 1

Pulse sequence used to create a cubic phase state (experimentally measured Wigner function on the right).

Universal control of flux-tunable bosonic mode

Q: Can you tell us about your research focus at Chalmers University of Technology?
A: My research focuses on superconducting circuits. Recently, we focused on demonstrating universal control of a bosonic mode by utilizing its intrinsic nonlinearity. Specifically, we succeeded by driving a resonator with a SNAIL nonlinear element using pulses at frequencies that are multiples of the resonance frequency.

Q: What results were you able to achieve with this setup?
A: The results were significant. This circuit produced a Cubic phase state in just 60 ns, which is two orders of magnitude faster than previous demonstrations. We used the Presto platform to perform these experiments.

Q: How did using Presto change your hardware workflow compared to previous setups?
A: The "rack-in-a-box" design makes the lab setup and device programming incredibly convenient. But the biggest change is that Presto performs direct digital synthesis. This allows us to quickly calibrate flux-tunable systems without the struggle of analog mixer calibrations.

Q: You mentioned a need for extreme precision. How did the IMP team handle that requirement?
A: The user support is amazing. We realized our use cases required timing pulses arriving at the quantum chip with extreme precision. We reached out to IMP support, and the timeline was impressive:

  • Within an hour, we concluded on a solution.
  • Within a day, they updated their API to allow pulse timing down to 100 ps.
  • Within a week, we had integrated the functionality.

Q: What was the final outcome of that collaboration?
A: Once we calibrated the system, we produced—to our knowledge—the highest quality cubic phase state ever produced on any quantum platform.

Q: Based on this experience, what is your verdict on Presto?
A: I highly recommend Presto and IMP. Presto is an amazing tool for measuring quantum circuits, and IMP consistently enhances its capabilities with valuable features.

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