1. Balanced comparator for RSFQ qubit readout
- Author
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Thomas A. Ohki, Juha Hassel, Leif Grönberg, Alexander Savin, Anna Kidiyarova-Shevchenko, and T. Karminskaya
- Subjects
Physics ,Flux qubit ,Noise temperature ,Comparator ,business.industry ,Qubit readout ,Balanced comparator ,Condensed Matter Physics ,Temperature measurement ,RSFQ ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Qubit ,Rapid single flux quantum ,Optoelectronics ,Electrical and Electronic Engineering ,Quantum information ,Resistor ,business - Abstract
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 muA critical currents and measured at 30-500 mK. At sampling frequency of 3.5 GHz the measured gray zone is DeltaI = 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.
- Published
- 2007
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