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Applied Physics Letters

Demonstration of a multiplexer of dissipationless superconducting quantum interference devices

John A. B. Mates, Gene C Hilton, K. D. Irwin, Leila R. Vale, Konrad W. Lehnert

Published Jan 14, 2008• 154 citations
Publisher

Abstract

We report on the development of a microwave superconducting quantum interference device (SQUID) multiplexer to read out arrays of low-temperature detectors. In this frequency-division multiplexer, superconducting resonators with different frequencies couple to a common transmission line and each resonator couples to a different dissipationless SQUID. We demonstrate multiple designs, with high-Q values (4100–18 000), noise as low as 0.17μΦ0∕Hz, and a naturally linear readout scheme based on flux modulation. This multiplexing approach is compatible with superconducting transition-edge sensors and magnetic calorimeters and is capable of multiplexing more than a thousand detectors in a single transmission line.

DOI
10.1063/1.2803852

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We report on the development of a microwave superconducting quantum interference device (SQUID) multiplexer to read out arrays of low-temperature detectors. In this frequency-division multiplexer, superconducting resonators with different frequencies couple to a common transmission line and each resonator couples to a different dissipationless SQUID. We demonstrate multiple designs, with high-Q values (4100–18 000), noise as low as 0.17μΦ0∕Hz, and a naturally linear readout scheme based on flux modulation. This multiplexing approach is compatible with superconducting transition-edge sensors and magnetic calorimeters and is capable of multiplexing more than a thousand detectors in a single transmission line.
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We are developing a microwave readout multiplexer for arrays of superconducting quantum interference devices (SQUIDs). A series of microwave resonators with frequencies ∼10 GHz are each loaded by a dc SQUID to a degree that depends on the flux state of the SQUID. By using resonators with high quality factors and slightly different resonance frequencies, many of these resonator‐coupled SQUIDs may be read out with a single excitation line and cryogenic amplifier. Our multiplexer is similar to the one demonstrated by Irwin and Lehnert except for the use of higher‐frequency, fully‐lithographed transmission line resonators. We discuss a technique for modulating the SQUID array in series that alleviates the need to individually flux‐bias the SQUIDs. The multiplexer has applications to the readout of detector arrays for astronomy as well as medical magnetic imaging.
We present a hybrid microwave superconducting quantum interference device (SQUID) multiplexer that combines two frequency-division multiplexing techniques to allow multiplexing a given number of cryogenic detectors with only a fraction of frequency encoding resonators. Similar to conventional microwave SQUID multiplexing, our multiplexer relies on inductively coupling non-hysteretic, unshunted rf-SQUIDs to superconducting microwave resonators as well as applying flux ramp modulation for output signal linearization. However, instead of utilizing one resonator per SQUID, we couple multiple SQUIDs to a common readout resonator and encode the SQUID input signals in sidebands of the microwave carrier by varying the flux ramp modulation frequency for each SQUID. We prove the suitability of our approach using a prototype device and argue by means of fundamental information theory that our approach is particularly suited for reading out large cryogenic bolometer arrays.
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.
Dissipationless microwave radio frequency superconducting interference device (RF-SQUID) multiplexers are attractive for readouts of large format arrays of transition edge sensors (TES). This multiplexer has the potential for readout bandwidth of several GHz and power consumption of ≈0.1 pW per pixel, which are ≈103 and ≈10-4 times as large as those of DC-SQUID-based conventional multiplexers. To evaluate their readout performance for TES photon counters ranging from near infrared to gamma ray, white noise of this multiplexer was experimentally studied at 4 K. The reason for this was, firstly, to avoid the low-frequency fluctuation obvious at around 0.1 K but trivial for the energy resolution of photon counters, and secondly for a feasibility study of readout operation at 4 K for extended applications. To increase resonant Q at 4 K and maintain low-noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1×104≤QI≤2×104 and the square root of spectral density of current noise referred to the SQUID input √SI =31 pA/√Hz, where QI is the internal Q of resonators. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Systematic noise measurement with various microwave readout power PMR and two-directional readout on the complex plane of transmission component of scattering matrix S21 makes the contribution of each noise source obvious. By decreasing these noises to the degree achievable by current technology, we predicted the microwave RF-SQUID multiplexer would exhibit √SI ≤5 pA/√Hz; i.e., close to √SI of state-of-the-art DC-SQUID-based multiplexers.
Abstract The readout system with a high multiplexing ratio has become a bottleneck limiting the application of large-scale Transition Edge Sensor (TES) detector arrays. In recent years, the microwave superconducting quantum interference device (SQUID) multiplexer has emerged as a key technology for effectively reading large-scale cryogenic detector arrays. Currently, the microwave SQUID multiplexer is being adopted by an increasing number of experiments due to its capability of achieving a multiplexing ratio of 2000:1 within the readout bandwidth. In this study, we developed a 32-channel microwave SQUID multiplexer prototype. And we measured 8 channels of the prototype. The measured equivalent noise current of the prototype reached 154 pA/√ Hz.