Balanced Comparator for RSFQ Qubit Readout

Author

Ohki, Tom ; Savin, Alexander ; Hassel, Juha ; Grönberg, Leif ; Karminskaya, Tatiana ; Kidiyarova-Shevchenko, Anna

Author_Institution

Chalmers Univ. of Technol., Gothenburg

Volume

17

Issue

2

fYear

2007

fDate

6/1/2007 12:00:00 AM

Firstpage

128

Lastpage

131

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.

Keywords

SQUIDs; comparators (circuits); error correction; superconducting logic circuits; RSFQ qubit readout; RSFQ-based readout; balanced comparator; cooling fins; effective noise temperature; electron overheating; error correction; reduced critical current density; shunt resistors; superconducting qubits; Cooling; Critical current; Current measurement; Density measurement; Electrons; Frequency measurement; Resistors; Sampling methods; Superconducting device noise; Temperature; Balanced comparator; RSFQ; qubit readout;

fLanguage

English

Journal_Title

Applied Superconductivity, IEEE Transactions on

Publisher

ieee

ISSN

1051-8223

Type

jour

DOI

10.1109/TASC.2007.897319

Filename

4277641