Grigoriy S. Mazhorin

High-fidelity transmon coupler activated CCZ gate on fluxonium qubits

  1. Ilya A. Simakov,
  2. Grigoriy S. Mazhorin,
  3. Ilya N. Moskalenko,
  4. Seidali S. Seidov,
  5. and Ilya S. Besedin
The Toffoli gate takes a special place in the quantum information theory. It opens up a path for efficient implementation of complex quantum algorithms. Despite tremendous progress
of the quantum processors based on the superconducting qubits, realization of a high-fidelity three-qubit operation is still a challenging problem. Here, we propose a novel way to perform a high-fidelity CCZ gate on fluxoniums capacitively connected via a transmon qubit, activated by a microwave pulse on the coupler. The main advantages of the approach are relative quickness, simplicity of calibration and significant suppression of the unwanted longitudinal ZZ interaction. We provide numerical simulation of 95-ns long gate of higher than 99.99% fidelity with realistic circuit parameters in the noiseless model and estimate an error of about 0.25% under the conventional decoherence rates.
arxiv pdf

Coupler microwave-activated controlled phase gate on fluxonium qubits

  1. Ilya A. Simakov,
  2. Grigoriy S. Mazhorin,
  3. Ilya N. Moskalenko,
  4. Nikolay N. Abramov,
  5. Alexander A. Grigorev,
  6. Dmitry O. Moskalev,
  7. Anastasiya A. Pishchimova,
  8. Nikita S. Smirnov,
  9. Evgeniy V. Zikiy,
  10. Ilya A. Rodionov,
  11. and Ilya S. Besedin
Tunable couplers have recently become one of the most powerful tools for implementing two-qubit gates between superconducting qubits. A tunable coupler typically includes a nonlinear
element, such as a SQUID, which is used to tune the resonance frequency of an LC circuit connecting two qubits. Here we propose a complimentary approach where instead of tuning the resonance frequency of the tunable coupler by applying a quasistatic control signal, we excite by microwave the degree of freedom associated with the coupler itself. Due to strong effective longitudinal coupling between the coupler and the qubits, the frequency of this transition strongly depends on the computational state, leading to different phase accumulations in different states. Using this method, we experimentally demonstrate a CZ gate of 44 ns duration on a fluxonium-based quantum processor, obtaining a fidelity of 97.6±0.4% characterized by cross-entropy benchmarking.
arxiv pdf