Expanding the Capability of Microwave Multiplexed Readout for Fast Signals in Microcalorimeters

Area of Science:

• Physics
• Astrophysics
• Cryogenic Instrumentation

Background:

• Microwave SQUID multiplexing is crucial for large microcalorimeter arrays in X-ray and gamma-ray detection.
• High photon counting rates necessitate high sensor current slew rates, posing challenges for traditional readout methods.
• Current readout schemes often require high sampling rates (e.g., 1 MHz) to capture fast events.

Purpose of the Study:

• To develop a practical algorithm for reconstructing X-ray pulses exceeding the nominal slew rate limit in microwave multiplexed readout.
• To improve the effective slew rate limit of SQUID-based detectors without compromising energy resolution.
• To enable faster data acquisition and potentially extend the measurable energy range of photons.

Main Methods:

• Implemented a microwave multiplexed readout scheme utilizing flux-ramp modulation to linearize SQUID response.
• Developed an algorithm to identify and reconstruct pulses where phase shifts between samples exceed the nominal limit (π).
• Tested the algorithm using X-ray transition-edge sensor pulses to evaluate its impact on energy resolution.

Main Results:

• The developed algorithm successfully reconstructs pulses exceeding the nominal slew rate limit.
• Pulse reconstruction shows a negligible impact on energy resolution, with arrival time effects from under-sampling being more significant.
• The effective slew rate limit is increased by more than a factor of two.

Conclusions:

• The novel pulse reconstruction algorithm effectively overcomes slew rate limitations in microwave SQUID multiplexing.
• This advancement allows for reduced resonator bandwidth requirements or extended energy range for microcalorimeter detectors.
• The technique offers additional benefits such as improved crosstalk and reduced readout noise.