Towards practical quantum computers: transmon qubit with a lifetime approaching 0.5 milliseconds

Wang, Chenlu; Li, Xuegang; Xu, Huikai; Li, Zhiyuan; Wang, Junhua; Yang, Zhen; Mi, Zhenyu; Liang, Xuehui; Su, Tianyun; Yang, Chuhong; Wang, Guangyue; Wang, Wenyan; Li, Yongchao; Chen, Mo; Li, Chengyao; Linghu, Kehuan; Han, Jie; Zhang, Yingshan; Feng, Yue; Yu, Shengquan; Ma, Teng; Zhang, Jingning; Wang, Ruixia; Zhao, Peng; Liu, Weiyang; Xue, Guangming; Jin, Yirong; Yu, Haifeng

doi:10.1038/s41534-021-00510-2

Cited by 161 publications

(59 citation statements)

References 28 publications

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“…The next step is experimental realization of this proposal, where relaxation and decoherence in transmons will degrade the performance. However, from its short gate time (16 ns) and recently reported long coherence times of transmons (over 300 µs) [54,55], the proposed coupler is expected to achieve high two-qubit gate fidelity.…”

Section: Discussionmentioning

confidence: 99%

Double-transmon coupler: Fast two-qubit gate with no residual coupling for highly detuned superconducting qubits

Goto¹

2022

Preprint

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Although two-qubit entangling gates are necessary for universal quantum computing, they are notoriously difficult to implement with high fidelity. Recently, tunable couplers have become a key component for realizing high-fidelity two-qubit gates in superconducting quantum computers. However, it is still difficult to achieve tunable coupling free of unwanted residual coupling for highly detuned qubits, which are desirable for mitigating qubit-frequency crowding or errors due to crosstalk between qubits. We thus propose a design for this kind of tunable coupler, which we call a doubletransmon coupler, because this is composed of two transmon qubits coupled through a common loop with an additional Josephson junction. Controlling the magnetic flux in the loop, we can achieve not only fast high-fidelity two-qubit gates, but also no residual coupling during idle time, where computational qubits are highly detuned fixed-frequency transmons. The proposed coupler is expected to offer an alternative approach to higher-performance superconducting quantum computers.

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Section: Discussionmentioning

confidence: 99%

Double-transmon coupler: Fast two-qubit gate with no residual coupling for highly detuned superconducting qubits

Goto¹

2022

Preprint

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“…The key limitation of transmon-based quantum computing is dielectric loss, which limits the qubit coherence time. Incremental progress in material science and fabrication technology over the years has enabled an increase in coherence times from few microseconds [5] to hundreds of microseconds [6,7]. Despite this remarkable progress, dielectric loss is still a major issue on the route to large scale quantum computing with superconducting qubits.…”

Section: Introductionmentioning

confidence: 99%

High fidelity two-qubit gates on fluxoniums using a tunable coupler

Moskalenko¹,

Simakov²,

Abramov³

et al. 2022

Preprint

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Superconducting fluxonium qubits provide a promising alternative to transmons on the path toward large-scale superconductor-based quantum computing due to their better coherence and larger anharmonicity. A major challenge for multi-qubit fluxonium devices is the experimental demonstration of a scalable crosstalk-free multi-qubit architecture with high fidelity single-qubit and two-qubit gates, single-shot readout and state initialization. Here, we present a two-qubit fluxonium-based quantum processor with a tunable coupler element following our theoretical proposal [1]. We experimentally demonstrate fSim-type and controlled-Z gates with 99.55% and 99.23% fidelities, respectively. The residual ZZ interaction is suppressed down to the few kHz level. Using a galvanically coupled flux control line, we implement high fidelity single-qubit gates and ground state initialization with a single arbitrary waveform generator channel per qubit.

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“…Currently, most of the superconducting multi-qubit processors utilize transmon qubits 7,24,28,29 that can be reproducibly fabricated 28 and have coherence times up to several hundred microseconds 30,31 , leading to record average gate fidelities of 99.98% for single-qubit gates 32 and 99.8%-99.9% for two-qubit gates 33 . The transmon was derived from the charge qubit 34 by adding a shunt capacitor in parallel with a Josephson junction, with the result of exponentially suppressing the susceptibility of its transition frequency to charge noise.…”

Section: Introductionmentioning

confidence: 99%

Unimon qubit

Hyyppä¹,

Kundu²,

Chan³

et al. 2022

Preprint

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Superconducting qubits 1, 2 are one of the most promising candidates to implement quantum computers, with projected applications in physics simulations 3 , optimization 4 , machine learning 5 , and chemistry 6 . The superiority of superconducting quantum computers over any classical device in simulating random but well-determined quantum circuits has already been shown in two independent experiments 7, 8 and important steps have been taken in quantum error correction 9-11 . However, the currently wide-spread qubit designs [12][13][14][15][16] do not yet provide high enough performance to enable practical applications or efficient scaling of logical qubits owing to one or several following issues: sensitivity to charge or flux noise leading to decoherence, too weak non-linearity preventing fast operations, undesirably dense excitation spectrum, or complicated design vulnerable to parasitic capacitance. Here, we introduce and demonstrate a superconducting-qubit type, the unimon, which combines the desired properties of high non-linearity, full insensitivity to dc charge noise, insensitivity to flux noise, and a simple structure consisting only of a single Josephson junction in a resonator. We measure the qubit frequency, ω 01 /(2π), and anharmonicity α over the full dc-flux range and observe, in agreement with our quantum models, that the qubit anharmonicity is greatly enhanced at the optimal operation point, yielding, for example, 99.9% and 99.8% fidelity for 13-ns single-qubit gates on two qubits with (ω 01 , α) = (4.49 GHz, 434 MHz) × 2π and (3.55 GHz, 744 MHz) × 2π, respectively. The energy relaxation time T 1 10 µs is stable for hours and seems to be limited by dielectric losses. Thus, future improvements of the design, materials, and gate time may promote the unimon to break the 99.99% fidelity target for efficient quantum error correction and possible quantum advantage with noisy systems.

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Towards practical quantum computers: transmon qubit with a lifetime approaching 0.5 milliseconds

Cited by 161 publications

References 28 publications

Double-transmon coupler: Fast two-qubit gate with no residual coupling for highly detuned superconducting qubits

Double-transmon coupler: Fast two-qubit gate with no residual coupling for highly detuned superconducting qubits

High fidelity two-qubit gates on fluxoniums using a tunable coupler

Unimon qubit

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