aqora

Sub-micron Josephson junctions fabricated with cross-line process

Guofeng Zhang, Xue Zhang, Yongliang Wang +3 more

Physica C SuperconductivityMar 27, 20199 citations

Phase Diffusion in Low-EJ Josephson Junctions at Milli-Kelvin Temperatures

Wen-Sen Lu, K. V. Kalashnikov, Plamen Kamenov +2 more

Josephson junctions (JJs) with Josephson energy EJ≲1 K are widely employed as non-linear elements in superconducting circuits for quantum computing operating at milli-Kelvin temperatures. In the qubits with small charging energy EC ( EJ/EC≫1 ), such as the transmon, the incoherent phase slips (IPS) might become the dominant source of dissipation with decreasing EJ. In this work, a systematic study of the IPS in low-EJ JJs at milli-Kelvin temperatures is reported. Strong suppression of the critical (switching) current and a very rapid growth of the zero-bias resistance due to the IPS are observed with decreasing EJ below 1 K. With further improvement of coherence of superconducting qubits, the observed IPS-induced dissipation might limit the performance of qubits based on low-EJ junctions. These results point the way to future improvements of such qubits.Josephson junctions (JJs) with Josephson energy EJ≲1 K are widely employed as non-linear elements in superconducting circuits for quantum computing operating at milli-Kelvin temperatures. In the qubits with small charging energy EC ( EJ/EC≫1 ), such as the transmon, the incoherent phase slips (IPS) might become the dominant source of dissipation with decreasing EJ. In this work, a systematic study of the IPS in low-EJ JJs at milli-Kelvin temperatures is reported. Strong suppression of the critical (switching) current and a very rapid growth of the zero-bias resistance due to the IPS are observed with decreasing EJ below 1 K. With further improvement of coherence of superconducting qubits, the observed IPS-induced dissipation might limit the performance of qubits based on low-EJ junctions. These results point the way to future improvements of such qubits.

arXiv:2112.10870ElectronicsJan 13, 20238 citations

Energy efficient half-flux-quantum circuit aiming at milli-kelvin stage operation

Feng Li, Duong Pham, Yuto Takeshita +4 more

Abstract Half-flux-quantum (HFQ) circuits are based on 0–π superconducting quantum interference devices (SQUIDs) and is one of the energy-efficient superconductor digital circuits. The bit energy is determined by the critical current I cn of 0–π SQUID, which can be easily tuned with the loop inductance and junction critical current. In this work, an alternative π–π–π SQUID is adopted to demonstrate HFQ circuits to simplify the fabrication process and enhance circuit energy efficiency. The properties of superconductor/ferromagnet/insulator/superconductor Josephson junctions (π-JJs) are measured with temperature dependence from 4.2 K down to 10 mK. HFQ toggle flip-flops (TFFs) are successfully demonstrated at frequencies of up to 6.7 GHz and 44.5 GHz at temperatures of 4.2 K and 10 mK, respectively. Comparing the HFQ TFF with its rapid single-flux quantum counterpart under the same fabrication process, it is anticipated that the HFQ TFF will exhibit approximately 70% reduction in both static and dynamic energy dissipation. This research establishes the foundation for developing cryogenic interface control and readout circuits for large-scale quantum computing in the future.Abstract Half-flux-quantum (HFQ) circuits are based on 0–π superconducting quantum interference devices (SQUIDs) and is one of the energy-efficient superconductor digital circuits. The bit energy is determined by the critical current I cn of 0–π SQUID, which can be easily tuned with the loop inductance and junction critical current. In this work, an alternative π–π–π SQUID is adopted to demonstrate HFQ circuits to simplify the fabrication process and enhance circuit energy efficiency. The properties of superconductor/ferromagnet/insulator/superconductor Josephson junctions (π-JJs) are measured with temperature dependence from 4.2 K down to 10 mK. HFQ toggle flip-flops (TFFs) are successfully demonstrated at frequencies of up to 6.7 GHz and 44.5 GHz at temperatures of 4.2 K and 10 mK, respectively. Comparing the HFQ TFF with its rapid single-flux quantum counterpart under the same fabrication process, it is anticipated that the HFQ TFF will exhibit approximately 70% reduction in both static and dynamic energy dissipation. This research establishes the foundation for developing cryogenic interface control and readout circuits for large-scale quantum computing in the future.

Superconductor Science and TechnologyAug 16, 202312 citations

Development of integrated digital circuits with Josephson junctions

W. Jutzi

Apr 1, 19840 citations

Cooper-Pair Box as a Variable Capacitor

Hanhee Paik, Frederick W. Strauch, Roberto Ramos +8 more

We calculate the effective capacitance of a Cooper-pair box and demonstrate that the Cooper-pair box can be used as a variable capacitor. The gate voltage modulates the charge transfer through the small junction in the Cooper-pair box, leading to a gate-dependent capacitance. We describe ongoing experiments to use an Al/AlO/sub x//Al Cooper-pair box as a tunable circuit element at milli-Kelvin temperatures and discuss possible applications to quantum computing as a variable coupling element between two Josephson junction qubits.We calculate the effective capacitance of a Cooper-pair box and demonstrate that the Cooper-pair box can be used as a variable capacitor. The gate voltage modulates the charge transfer through the small junction in the Cooper-pair box, leading to a gate-dependent capacitance. We describe ongoing experiments to use an Al/AlO/sub x//Al Cooper-pair box as a tunable circuit element at milli-Kelvin temperatures and discuss possible applications to quantum computing as a variable coupling element between two Josephson junction qubits.

IEEE Transactions on Applied SuperconductivityJun 1, 20059 citations

High-T c Josephson junctions for electronic applications

S. Pagano, Sandro Barbanera, Vincenzo Boffa +6 more

Il Nuovo Cimento DDec 1, 19940 citations

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