Double-Transmon Coupler I: Elimination of Residual ZZ Coupling for Highly Detuned Transmon Qubits

Tunable couplers have attracted much attention as a key device to achieve high performance in superconducting quantum computers. Recently, we have proposed a new kind of tunable coupler composed of two fixed-frequency transmons coupled through a loop with an additional Josephson junction, which we call a double-transmon coupler (DTC) [1]. By tuning the flux in the loop, we can completely eliminate residual ZZ coupling between highly detuned qubits. This is a remarkable feature of the DTC, because conventional tunable couplers with a single frequency-tunable transmon (single-transmon couplers) can eliminate the ZZ coupling only if the detuning is smaller than the qubit anharmonicity [2] and therefore they have finite residual ZZ coupling for highly detuned qubits [3,4]. The DTC also allows us to perform fast, high-fidelity two-qubit gates [1], as explained in the next talk.

[1] H. Goto, Phys. Rev. Appl. 18, 034038 (2022) (Editors’ Suggestion)

[2] J. Stehlik et al., Phys. Rev. Lett. 127, 080505 (2021)

[3] M. C. Collodo et al., Phys. Rev. Lett. 125, 240502 (2020)

[4] Y. Xu et al., Phys. Rev. Lett. 125, 240503 (2020)