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Applied Physics Letters

Study on the operation of a dual channel digital superconducting quantum interference device with direct-current-powered Josephson multiplexer readout

Eriko Takeda, Toshikazu Nishino, Kazumasa Takagi

Published Mar 20, 1995• 5 citations
Publisher

Abstract

Operation of a dual channel digital superconducting quantum interference device (SQUID) with a dc-powered Josephson multiplexer (MUX) readout has been observed successfully using a test circuit. In the circuit, output signals of two SQUIDs are digitized by Josephson comparators and read out by the MUX. The noise of the SQUIDs under the operation of the whole circuit is 0.54Φ0/√Hz at 1 kHz. Advantage of using a dc-powered circuit to realize a low noise SQUID measurement system is confirmed.

DOI
10.1063/1.113642

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Review of Scientific Instruments•Jan 26, 2004•4 citations
Operation of a dual channel digital superconducting quantum interference device (SQUID) with a dc-powered Josephson multiplexer (MUX) readout has been observed successfully using a test circuit. In the circuit, output signals of two SQUIDs are digitized by Josephson comparators and read out by the MUX. The noise of the SQUIDs under the operation of the whole circuit is 0.54Φ0/√Hz at 1 kHz. Advantage of using a dc-powered circuit to realize a low noise SQUID measurement system is confirmed.
We describe a superconducting quantum interference device (SQUID) multiplexer operated at microwave frequencies. The outputs of multiple SQUIDs are simultaneously modulated at different frequencies and summed into the input of one high electron mobility transistor (HEMT). The large bandwidth and dynamic range provided by HEMT amplifiers should make it possible to frequency-division multiplex a large number of SQUIDs in one output coaxial cable. We measure low SQUID noise (∼0.5μΦ0∕Hz at 4K) and demonstrate the multiplexed readout of two direct current (dc) SQUIDs at different resonant frequencies. In this work, dc SQUIDs are used, but this approach is equally applicable to radio-frequency SQUIDs.
Abstract Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22–48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300 mK in an adiabatic demagnetization refrigerator. The measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.3 μ Φ 0 / Hz at 10 kHz. The current noise equivalent to the input coil of input SQUID is about 2.4 pA / Hz . This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.
An improved read-out electronics without flux modulation for dc superconducting quantum interference devices (dc SQUIDs) is presented where the preamplifier is directly coupled to the SQUID. Compared to our previous designs, the 1/f voltage and current noise levels of the preamplifier were reduced by about a factor of 4 (rms) by using bipolar matched transistors instead of operational amplifiers at the input. Three types of flux-locked-loop electronics were developed and successfully tested: a low-power (120 mW) version for large multichannel arrays, a high-speed version with a 15 MHz bandwidth and a very fast (300 ns) reset mode, and a low-noise (0.44 nV/Hz) version with a fast and precise bias reversal circuit. The flux-locked-loop electronics are compatible with each other, so that only one type of low-power (180 mW) control unit is required to operate them. All essential specifications of practical SQUID systems (noise, dynamic behavior, and temperature stability) were determined by using liquid-helium and liquid-nitrogen cooled SQUIDs, respectively.
Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22-48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer (TDM) SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array (SSA) with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300300300 mKmKmK in an adiabatic demagnetisation refrigerator (ADR). The the measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.30.30.3 μΦ0/HzμΦ_{0}/\sqrt{Hz}μΦ0​/Hz​ at 101010 kHzkHzkHz. The current noise equivalent to the input coil of input SQUID is about 2.42.42.4 pA/HzpA/\sqrt{Hz}pA/Hz​. This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.
We have analyzed the biasing of the first-stage dc superconducting quantum interference devices (SQUIDs) of a time-domain dc-SQUID multiplexer (SQUID MUX) and find that the bias conditions of first-stage SQUIDs significantly affect the performance of the SQUID MUX in terms of total multiplexer noise and bandwidth. We present an experimental study of the operational parameters of a first-stage SQUID under varied bias conditions. Our measurements include a direct determination of the first-stage SQUID dynamic resistance RDYN1 and the flux noise of the first-stage SQUID biased over the range from voltage bias to current bias. Our measurements show that matching the bias resistors RS1 of the first-stage SQUIDs to RDYN1 improves the SQUID MUX noise performance as well as the first-stage bandwidth.