Jongsoo Yoon

Single superconducting quantum interference device multiplexer for arrays of low-temperature sensors

We present the design and experimental evaluation of a superconducting quantum interference device (SQUID) multiplexer for an array of low-temperature sensors. Each sensor is inductively coupled to a superconducting summing loop which, in turn, is inductively coupled to the readout SQUID. The flux-locked loop of the SQUID is used to null the current in the summing loop and thus cancel crosstalk. The sensors are biased with an alternating current, each with a separate frequency, and the individual sensor signals are separated by lock-in detection at the SQUID output. We have fabricated a prototype 8 channel multiplexer and discuss the application to a larger array.

High-resolution operation of frequency-multiplexed transition-edge photon sensors

We present the multiplexed readout of two gamma-ray microcalorimeters made from transition-edge sensors. We use a frequency-domain multiplexing scheme in which each sensor is biased at an identifying frequency. We show that the energy resolution of the sensors is unaffected by multiplexing, and that crosstalk between the sensors is negligible. Our results indicate the feasibility of multiplexing 30 sensors or more to one readout line.

A frequency-domain read-out technique for large microcalorimeter arrays demonstrated using high-resolution /spl gamma/-ray sensors

Cryogenic sensors composed of transition-biased superconducting films have demonstrated remarkable sensitivity at /spl gamma/-ray, x-ray, optical, and far-infrared to millimeter wavelengths. However, for these sensors to find widespread application in astronomy and materials analysis, technologies for building and reading out large arrays are required. We are currently developing a frequency-domain multiplexing scheme for the read-out of large numbers of microcalorimeters using a much smaller number of amplifiers. In this scheme, each sensor is biased at an identifying frequency and operated in a series LC circuit to suppress out-of-band noise. Here, we present results demonstrating the undegraded operation of two /spl gamma/-ray sensors multiplexed using this technique. In addition, we provide a series of design rules which relate the minimum bias frequency and the values of the reactive elements in the system to a small number of sensor properties. Finally, we discuss the ultimate limits on the number of sensors that can be measured with a single amplifier.

Low-noise electrometer and its low-noise cryogenic probe with completely guarded sample chamber

We describe a low-noise cryogenic probing system capable of measuring currents at the femtoAmpere (fA) level with integration time ⩽1 s and current noise spectra at the 1 fA/√Hz level with the sample cooled to cryogenic temperatures. The system consists of a low-noise electrometer and a low-noise cryogenic probe with completely guarded sample chamber. The low-noise electrometer has amplification of 0.1 V/1 pA with f3 dB=70 Hz, 1.1 V/pA with f3 dB=20 Hz, and/or 10.1 V/pA with f3 dB=1.4 Hz, and input current noise power density of 0.4 fA/√Hz rms and input voltage noise power density of ≈0.3 μV/√Hz rms at 1 Hz frequency. With the cryogenic probe, the entire measurement system has input current noise of 0.8 fA/√Hz rms at 1 Hz. The completely guarded sample chamber reduces parasitic conductance to <10−16 S and parasitic capacitance to ⩽15 fF between pairs of pins for current–voltage measurements. With this instrumentation, we are able to characterize the current and current noise of quantum well infrared photo...

AC voltage-biased superconducting bolometer for a frequency-domain SQUID multiplexer

We demonstrate that a voltage-biased superconducting bolometer (VSB), read out with superconducting quantum interference device (SQUID), can be biased with a sinusoidal voltage. We show that the load curves taken with AC- and DC-bias are nearly identical indicating that there is no identifiable degradation in the performance of the bolometer due to the AC bias. We discuss the use of a frequency-domain SQUID multiplexer with an array of VSBs that are AC-biased.