Balanced comparator for RSFQ qubit readout

T. Ohki, A. Savin, Juha Hassel, Leif Grönberg, T. Karminskaya, A. Kidiyarova-Shevchenko

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    9 Citations (Scopus)


    The balanced comparator is an essential part of RSFQ-based readout for superconducting qubits. In this paper we report measurements of the sensitivity of the balanced comparator fabricated in a specialized 30 A/cm2 process with 3.6 ìm critical currents and measured at 30-500 mK. At sampling frequency of 3.5 GHz the measured gray zone is ÄI = 104 nA. Due to electron overheating in the shunt resistors the effective noise temperature is 140 mK. The gray zone has a strong dependence on sampling frequency above 5 GHz due to over-clocking. Related measurements have been reported where cooling fins and reduced critical current density of 10 A/cm2 were used, and a quantum limited gray zone of 40 nA was achieved. This makes single shot readout possible for the phase, RF-SQUID and persistent current qubits. The readout speed is 30-50 ps, which is quite favorable for error correction schemes.
    Original languageEnglish
    Pages (from-to)128-131
    JournalIEEE Transactions on Applied Superconductivity
    Issue number2
    Publication statusPublished - 2007
    MoE publication typeA1 Journal article-refereed


    • Balanced comparator
    • Qubit readout
    • RSFQ


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