RQC Seminar

247th RQC Seminar

• Speaker

  Dr. Jeroen Verjauw
  ( IQM Quantum Computers )

• Date

  15:15~16:00, November 20, 2025 (Thursday)

• Venue

  Onsite( Wako Coop. Center 4F W426, 研究交流棟 W426）

• Title

  Introduction to the Superconducting IQM Star Quantum Processing Unit

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
We introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon qubits [1]. This architecture can be used as a testbed for algorithms that benefit from high connectivity [2]. In contrast to other quantum processors where the qubits have a fix coupling to a central resonator, we employ flux-tunable transmon qubits as active coupling elements. These tunable couplers enable tuning the interaction between any qubit and the central resonator while simultaneously suppressing the residual interaction to the spectator qubits, which is crucial both during gate operation and idling.

To operate the quantum processing unit (QPU), we develop the qubit-resonator conditional Z (CZ) gate, and the qubit-resonator MOVE operation. The latter allows for transferring a quantum state between one of the peripheral qubits and the computational resonator in the single excitation manifold, ensuring that the resonator encodes a qubit for quantum computing. We calibrate and benchmark the considered native set of qubit-resonator operations which enable entangling two arbitrary qubits with constant circuit depth, independent of their physical distance. In addition, we explore the higher photon population dynamics in the resonator, which further enables quantum simulation of bosonic systems [3].

To provide a global benchmark for the quantum computing capability of our QPU, we entangle all qubits in a Greenberger-Horne-Zeilinger (GHZ) state. Furthermore, we investigate the GHZ fidelity versus an increasing number of entangled qubits, going beyond six qubits by using a scaled up QPU design

REFERENCES:
1. Renger, M., J. Verjauw, N. Wurz, et al., "A superconducting qubit-resonator quantum processor with effective all-to-all connectivity," arXiv:2503.10903, 2025.
2. Vigneau, F., et al., "Quantum error detection in qubit-resonator star architecture," arXiv:2503.12869, 2025.
3. LeppAakangas, J., et al., "Quantum algorithms for simulating systems coupled to bosonic modes using a hybrid resonator-qubit quantum computer," arXiv:2503.11507, 2025.