We report the experimental realization of a 3D capacitively shunt superconducting flux qubit with long coherence times. At the optimal flux bias point, the qubit demonstrates energy relaxation times in the range of 60–90 μs and a Hahn-echo coherence time of about 80 μs, which can be further improved by dynamical decoupling. Qubit energy relaxation can be attributed to quasiparticle tunneling and unwanted two-level-system defects, while qubit dephasing is caused by flux noise away from the optimal point. Our results show that 3D c-shunt flux qubits demonstrate improved performance over other types of flux qubits, which is advantageous for applications such as quantum magnetometry and spin sensing.We report the experimental realization of a 3D capacitively shunt superconducting flux qubit with long coherence times. At the optimal flux bias point, the qubit demonstrates energy relaxation times in the range of 60–90 μs and a Hahn-echo coherence time of about 80 μs, which can be further improved by dynamical decoupling. Qubit energy relaxation can be attributed to quasiparticle tunneling and unwanted two-level-system defects, while qubit dephasing is caused by flux noise away from the optimal point. Our results show that 3D c-shunt flux qubits demonstrate improved performance over other types of flux qubits, which is advantageous for applications such as quantum magnetometry and spin sensing.

arXiv:1911.04635Applied Physics LettersDec 23, 201943 citations

Demonstration of High-Fidelity Gates in a Strongly Anharmonic with Long-Coherence C-Shunt Flux Qubit

Silu Zhao, Li Li, Weiping Yuan +13 more

We demonstrate high-fidelity single-qubit gates on a C-shunt flux qubit that simultaneously combines a large anharmonicity ( $\mathcal{A}/2π=848~\mathrm{MHz}$ ) with long relaxation time ( $T_1 = 23~μ\text{s}$ ). The large anharmonicity significantly suppresses leakage to higher energy levels, enabling fast and precise microwave control. Using DRAG pulses and randomized benchmarking, the qubit achieves gate fidelities exceeding 99.9\%, highlighting the capability of C-shunt flux qubits for robust and high-performance quantum operations. These results establish them as a promising platform for scalable quantum information processing.We demonstrate high-fidelity single-qubit gates on a C-shunt flux qubit that simultaneously combines a large anharmonicity ($\mathcal{A}/2π=848~\mathrm{MHz}$) with long relaxation time ($T_1 = 23~μ\text{s}$). The large anharmonicity significantly suppresses leakage to higher energy levels, enabling fast and precise microwave control. Using DRAG pulses and randomized benchmarking, the qubit achieves gate fidelities exceeding 99.9\%, highlighting the capability of C-shunt flux qubits for robust and high-performance quantum operations. These results establish them as a promising platform for scalable quantum information processing.

quant-pharXiv:2603.11692Mar 13, 20260 citations

A Long-lived Tunable Qubit for Bosonic Quantum Computing

Leonid Victorovich Abdurakhimov, Imran Mahboob, Hiraku Toida +2 more

This article reviews a recent experiment that demonstrated a new hybrid type of tunable superconducting qubit consisting of a two-dimensional (2D) superconducting capacitively shunted flux qubit coupled to a 3D microwave cavity.Such a 3D hybrid flux qubit has extremely long relaxation times, which are comparable to or exceed the best values reported for 2D flux qubits.This new design of frequency-tunable qubits is uniquely suited for applications in bosonic quantum computing, which exploits multiphoton states of 3D microwave cavities.This article reviews a recent experiment that demonstrated a new hybrid type of tunable superconducting qubit consisting of a two-dimensional (2D) superconducting capacitively shunted flux qubit coupled to a 3D microwave cavity.Such a 3D hybrid flux qubit has extremely long relaxation times, which are comparable to or exceed the best values reported for 2D flux qubits.This new design of frequency-tunable qubits is uniquely suited for applications in bosonic quantum computing, which exploits multiphoton states of 3D microwave cavities.

NTT technical reviewMay 1, 20212 citations

We demonstrate high-fidelity single-qubit gates on a C-shunt flux qubit that simultaneously combines a large anharmonicity (

\mathcal{A}/2π=848~\mathrm{MHz}

) with long relaxation time (

T_1 = 23~μ\text{s}

). The large anharmonicity significantly suppresses leakage to higher energy levels, enabling fast and precise microwave control. Using DRAG pulses and randomized benchmarking, the qubit achieves gate fidelities exceeding 99.9\%, highlighting the capability of C-shunt flux qubits for robust and high-performance quantum operations. These results establish them as a promising platform for scalable quantum information processing.