Two-stage Superconducting Quantum Interference Device Research Articles

Design and Fabrication of Two-stage SQUID for Transition Edge Sensor

The X-ray transition edge sensor (TES) modeled by calorimeter is extremely sensitive to temperature changes when operating at a voltage bias in the temperature region, and is widely used for the detection of particles and photons from submicron frequency to gamma rays. Superconducting quantum interference device (SQUID) is the key to TES current signal readout, we have designed a two-stage SQUID amplifier circuit. First-stage sensor SQUID uses first-grade gradiometer with high input mutual inductance about 176.2 , it increases the coupling sensitivity with the TES detector and has stronger resistance to external interference. Second-stage SQUID array(SSA) adopts 32 single SQUIDs in series, which has low magnetic flux noise and high magnification. We have verified the characteristics of this two-stage circuit and demonstrated that it has a lower magnetic flux noise.

A Practical Two-Stage SQUID Readout Circuit Improved With Proportional Feedback Schemes

Nonlinearity with multiple working points limits the practical applications of a two-stage superconducting quantum interference device (SQUID) readout circuit, which is promising for low-noise performance. To solve this problem, we proposed a simple two-stage SQUID readout circuit with two conventional dc SQUIDs improved with proportional feedback schemes, where transfer coefficient of the first-stage SQUID circuit is enhanced by additional positive feedback circuit; transfer characteristics of the second-stage SQUID circuit are linearized by an additional negative feedback circuit. Two proportional feedback schemes are cooperated together based on matching conditions to achieve both noise suppression and working point matching. Working principles were verified in experiment results. The overall transfer characteristics achieved have only one working point and are simply adjusted according to the voltage swing of an amplifier. Transfer coefficient of the first-stage SQUID circuit was raised up to 10 (20 dB), and the total flux noise of two-stage SQUID readout circuit was reduced below 1 μΦ 0 /√Hz, where Φ 0 = 2.07×10 -15 Wb. Our two-stage SQUID readout circuit is easy-to-operate and suited for high-performance practical SQUID systems.

Two-Stage Directly-Coupled Superconducting Quantum Interference Device Array Magnetometer

The characteristics of the voltage-biased superconducting quantum interference device (SQUID) were investigated. Under the proper bias conditions, the flux-to-current transfer coefficient in a voltage-bias mode is the same as that in a current bias mode. To enhance the flux-to-current transfer coefficient, we proposed the parallel SQUID array connected by wire bonding. The enhancement in current modulation amplitude with the parallel array is verified experimentally. The probabilities of finding successful SQUIDs to form the array are also calculated. According to the theoretical analysis, the field noise of the two-stage directly-coupled SQUID magnetometer is less than that of the conventional directly-coupled SQUID magnetometer. The proposed design can be implemented by using the high-Tc junction technologies.

10 ℏ superconducting quantum interference device amplifier for acoustic gravitational wave detectors

From measurements of additive and back action noise, we estimate the noise temperature of a two-stage superconducting quantum interference device (SQUID) amplifier developed for the acoustic wide-band gravitational wave detectors of the next generation. The minimum noise temperature evaluated at 8.9 kHz and T≤0.3 K is about 4 μK and corresponds to 10 times the quantum-limited noise temperature. As the high-Q electrical resonator used for the back action noise measurements behaves in many respects like the input load constituted by an acoustic gravitational wave detector, this SQUID amplifier is expected to keep the same noise performance once installed on the detector.

27ℏ SQUID amplifier operating with high-Q resonant input load

We have extended to ultracryogenic temperatures the complete noise characterization of a low-noise two-stage superconducting quantum interference device (SQUID) amplifier developed for resonant gravitational wave detectors. The additive current noise is evaluated from open input measurements. To evaluate the back action voltage noise, the SQUID is strongly coupled to a high-Q macroscopic electrical resonator operating at 11.7 kHz. From these measurements, we estimate a minimum noise temperature of 15μK, corresponding to 27 times the quantum-limited noise temperature. Implications of this result for the sensitivity of resonant gravitational wave detectors are briefly discussed.

Noise sources and dissipation mechanisms of a 120 ℏ SQUID amplifier

A two-stage superconducting quantum interference device (SQUID), based on a commercial sensor, is strongly coupled to an electrical resonator at 11 kHz with a quality factor Q=600 000 and operated in the temperature range 1.33–4.17 K. From the analysis of the noise generated by this system, the back action noise of the SQUID amplifier is estimated. The minimum noise temperature, calculated from back action and additive noise measurements, is 63 μK at 1.33 K, and corresponds to 120 times the quantum-limited noise temperature. We discuss and experimentally verify a mechanism, which can limit the noise temperature and add losses to the system.

High-current resolution broad-band SQUID amplifier suitable for TES calorimeter

A superconducting quantum interference device (SQUID) amplifier has been developed as a current detector with both high-current resolution and broad bandwidth for a transition edge sensor calorimeter. The amplifier is a two stage SQUID (TSS) that consists of an input-SQUID with a 38-turn input coil and a 100-serial SQUID array (100-SSA) output, and has been integrated on a 3 /spl times/ 3 mm Si chip using Nb thin film fabrication technology. It is designed to increase the amplifier gain and maintain matching with the parameters of the calorimeter. To avoid flux trapping in the SSA, the washer coil of the dc-SQUIDs in the SSA was made with a narrow line width of 17.5 /spl mu/m. We experimentally confirmed that the designed output voltage was achieved using a one-layer p-metal magnetic shield tube in the earth's magnetic field. The performance of the shielded TSS amplifier was evaluated in liquid helium. The TSS amplifier had a gain of 10 kV/A and an impedance of 0.07 /spl Omega/ at 100 kHz. When a flux locked loop circuit was used to drive the amplifier, a current resolution of 1 pA//spl radic/Hz and a rise time of 1 /spl mu/s were achieved.

Low-noise SQUIDs with large transfer: two-stage SQUIDs based on DROSs

We have realized a two-stage integrated superconducting quantum interference device (SQUID) system with a closed loop bandwidth of 2.5 MHz, operated in a direct voltage readout mode. The corresponding flux slew rate was 1.3×10 5 Φ 0/s and the measured white flux noise was 1.3 μ Φ 0/√Hz at 4.2 K. The system is based on a conventional dc SQUID with a double relaxation oscillation SQUID (DROS) as the second stage. Because of the large flux-to-voltage transfer, the sensitivity of the system is completely determined by the sensor SQUID and not by the DROS or the room-temperature preamplifier. Decreasing the Josephson junction area enables a further improvement of the sensitivity of the two-stage SQUID systems.

Sensitivity enhancement of Quantum Design dc superconducting quantum interference devices in two-stage configuration

The energy sensitivity of a direct current (dc) superconducting quantum interference device (SQUID) can be improved if it is operated in a two-stage configuration. Employing this technique, a commercial dc SQUID system was modified and made competitive with other sensors especially designed for very low noise applications. We report the noise measurements performed in the temperature range 4.2 K–25 mK. At 4.2 K, the coupled energy sensitivity obtained with the two-stage dc SQUID was approximately ten times better than with a conventional readout electronics. The noise energy decreases linearly until approximately 300 mK, in good agreement with theoretical previsions. At lower temperature the hot-electron effect produces a saturation and the best energy sensitivity measured with open input coil is 35 ℏ.

Two-stage superconducting-quantum-interference-device amplifier in a high-Q gravitational wave transducer

We report on the total noise from an inductive motion transducer for a gravitational-wave antenna. The transducer uses a two-stage superconducting quantum interference device (SQUID) amplifier and has a noise temperature of 1.1 mK, of which 0.70 mK is due to back action noise from the SQUID chip. The total noise includes thermal noise from the transducer mass, which has a measured Q of 2.60×106. The noise temperature exceeds the expected value of 3.5 μK by a factor of 200, primarily due to voltage noise at the input of the SQUID. Noise from flux trapped on the chip is found to be the most likely cause.

Two-stage amplifier based on a double relaxation oscillation superconducting quantum interference device

A low-noise single-chip two-stage superconducting quantum interference device (SQUID) system with a double relaxation oscillation SQUID as the second stage has been realized. The system was operated in a direct voltage readout mode, with a closed loop bandwidth up to 1 MHz. Operated at 4.2 K, the white flux noise measured in flux locked loop was 1.3 μΦ0/√Hz, corresponding to an energy sensitivity of ε≈27h. Owing to the large flux-to-voltage transfer of up to 3.6 mV/Φ0, the room-temperature preamplifier noise did not dominate the overall flux noise.

Continuous feedback operation of a two-stage dc SQUID system

We report on the continuous feedback operation of a two-stage dc Superconducting Quantum Interference Device (SQUID) system in which one SQUID works as a low-noise preamplifier to read out a second low-noise sensor SQUID. We first flux-locked the readout SQUID and measured the characteristics of the sensor SQUID, including its current-voltage characteristics, current-flux characteristics, and noise spectrum. We then investigated how the two SQUIDs could work together by simultaneously flux-locking both the sensor and the readout SQUIDs. With this two-SQUID flux-locking scheme, we recovered the noise spectrum of the sensor SQUID to within 4%. We discuss how to understand and optimize the two-stage SQUID feedback system.

A low-noise, two-stage DC SQUID amplifier with high bandwidth and dynamic range

We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.