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arXiv:2302.04053 · Chinese Physics Letters

Gatemon Qubit Based on a Thin InAs-Al Hybrid Nanowire

Jierong Huo, Zezhou Xia, Zonglin Li, Shan Zhang, Yuqing Wang, Dong Pan, Qichun Liu, Yulong Liu, Zhichuan Wang, Yichun Gao, Jianhua Zhao, Tiefu Li, Jianghua Ying, Runan Shang, Hao Zhang

Published Mar 1, 2023• 20 citations
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Abstract

We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T 1 ∼ 0.56 μs and the dephasing time T 2 * ∼ 0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.

DOI
10.1088/0256-307x/40/4/047302

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We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T 1 ∼ 0.56 μs and the dephasing time T 2 * ∼ 0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.
We introduce a hybrid qubit based on a semiconductor nanowire with an epitaxially grown superconductor layer. Josephson energy of the transmonlike device ("gatemon") is controlled by an electrostatic gate that depletes carriers in a semiconducting weak link region. Strong coupling to an on-chip microwave cavity and coherent qubit control via gate voltage pulses is demonstrated, yielding reasonably long relaxation times (~0.8 μs) and dephasing times (~1 μs), exceeding gate operation times by 2 orders of magnitude, in these first-generation devices. Because qubit control relies on voltages rather than fluxes, dissipation in resistive control lines is reduced, screening reduces cross talk, and the absence of flux control allows operation in a magnetic field, relevant for topological quantum information.
Coherent operation of gate-voltage-controlled hybrid transmon qubits (gatemons) based on semiconductor nanowires was recently demonstrated. Here we experimentally investigate the anharmonicity in epitaxial InAs-Al Josephson junctions, a key parameter for their use as a qubit. Anharmonicity is found to be reduced by roughly a factor of 2 compared to conventional metallic junctions and dependent on gate voltage. Experimental results are consistent with a theoretical model, indicating that Josephson coupling is mediated by a small number of highly transmitting modes in the semiconductor junction.
Recent experiments have demonstrated superconducting transmon qubits with semiconductor nanowire Josephson junctions. These hybrid gatemon qubits utilize field effect tunability characteristic of semiconductors to allow complete qubit control using gate voltages, potentially a technological advantage over conventional flux-controlled transmons. Here, we present experiments with a two-qubit gatemon circuit. We characterize qubit coherence and stability and use randomized benchmarking to demonstrate single-qubit gate errors below 0.7% for all gates, including voltage-controlled Z rotations. We show coherent capacitive coupling between two gatemons and coherent swap operations. Finally, we perform a two-qubit controlled-phase gate with an estimated fidelity of 91%, demonstrating the potential of gatemon qubits for building scalable quantum processors.
Abstract We demonstrate that superconducting gatemon qubits based on superconductor-semiconductor-superconductor Josephson junctions can be constructed on hole-type Ge/Si core/shell nanowires. The frequency of the qubit can be set firstly by controlling the diffusion of Al in the nanowire via thermal annealing, which yields a roughly suitable critical supercurrent for the junction, and then by fine tuning of a gate voltage, by which an accurate adjustment of the frequency can be realized. On the resulted qubit, Rabi oscillation with an energy relaxation time T1~180 ns was observed in the time domain, and the gate voltage dependence of both T1 and the dephasing time T2 was investigated. Such a hole-type superconducting gatemon qubit, based on materials with strong spin-orbit coupling and the absence of hyperfine interaction, could be used for exploring the quantum coherence phenomena of hole-gas and potentially also Majorana physics in Ge-based quantum devices.
Semiconductor-based superconducting qubits offer a versatile platform for studying hybrid quantum devices in circuit quantum electrodynamics (QED) architecture. Most of these circuit QED experiments utilize coplanar waveguides, where the incorporation of dc gate lines is straightforward. Here, we present a technique for probing gate-tunable hybrid devices using a three-dimensional (3D) microwave cavity. A recess is machined inside the cavity wall for the placement of devices and gate lines. We validate this design using a hybrid device based on an InAs-Al nanowire Josephson junction. The coupling between the device and the cavity is facilitated by a long superconducting strip, the antenna. The Josephson junction and the antenna together form a gatemon qubit. We further demonstrate the gate-tunable cavity shift and two-tone qubit spectroscopy. This technique could be used to probe various quantum devices and materials in a 3D circuit QED architecture that requires dc gate voltages.
We present a gate-voltage-tunable transmon qubit (gatemon) based on planar InAs\mathrm{In}\mathrm{As}InAs nanowires that are selectively grown on a high-resistivity silicon substrate using III-V buffer layers. We show that low-loss superconducting resonators with an internal quality of $2\ifmmode\times\else\texttimes\fi{}{10}^{5}$ can readily be realized using these substrates after the removal of buffer layers. We demonstrate coherent control and readout of a gatemon device with a relaxation time, ${T}_{1}\ensuremath{\approx}700\phantom{\rule{0.2em}{0ex}}\mathrm{ns}$, and dephasing times, ${T}_{2}^{\ensuremath{\ast}}\ensuremath{\approx}20\phantom{\rule{0.2em}{0ex}}\mathrm{ns}$ and ${T}_{2,\mathrm{echo}}\ensuremath{\approx}1.3\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$. Further, we infer a high junction transparency of 0.40.40.4--0.90.90.9 from an analysis of the qubit anharmonicity.