High-resolution gamma-ray spectroscopy with a microwave-multiplexed transition-edge sensor array

Abstract

We demonstrate very high resolution photon spectroscopy with a microwave-multiplexed two-pixel transitionedge sensor (TES) array. We measured a 153 Gd photon source and achieved an energy resolution of 63 eV full-width-at-half-maximum at 97 keV and an equivalent readout system noise of 86 pA/ √ Hz at the TES. The readout circuit consists of superconducting microwave resonators coupled to radio-frequency superconductingquantum-interference-devices (SQUID) and transduces changes in input current to changes in phase of a microwave signal. We use flux-ramp modulation to linearize the response and evade low-frequency noise. This demonstration establishes one path for the readout of cryogenic X-ray and gamma-ray sensor arrays with more than 10 3 elements and spectral resolving powers R = λ/∆λ > 10 3 .Multiplexed readout of sub-Kelvin cryogenic detectors is an essential requirement for large focal plane arrays. Next-generation instruments for the detection of electromagnetic radiation from gamma-ray to far-infrared wavelengths will have pixel counts in the 10 3 -10 6 range and require readout techniques that do not compromise their sensitivity. To date, many instruments have used time-, frequency-, or code-domain SQUID multiplexing schemes 1-3 . One such instrument, the TES bolometer camera SCUBA2, has achieved background-limited sensitivity in 10 4 pixels using time-domain multiplexing (TDM) 4 . Similarly, calorimetric gamma-ray/X-ray spectrometers that use TDM have reached excellent energy resolutions of δE ≈ 50 eV at 100 keV in a 256-pixel array 5 . However, the scalability of these readout approaches is limited by the finite measurement bandwidth (∼ 10 MHz) achievable in a flux-locked loop.Kinetic Inductance Detectors (KIDs) 6,7 , on the other hand, provide a possible path to higher multiplexing factors. These devices are naturally frequency-multiplexed and the ultimate limit on the available bandwidth is many gigahertz, which is set by the readout cryogenic amplifier. Present limits in room-temperature electronics impose a 550 MHz bandwidth limit 8 , but this figure will improve steadily. However, the sensing element is part of a thin-film superconducting resonator, so readout and signal generation can be difficult to simultaneously optimize. This challenge is particularly severe for spectroscopic X-ray and gamma-ray detectors, which must stop high-energy photons and where spatial variation in the device response must be smaller than 0.1%. X-ray and gamma-ray spectroscopy results achieved to date with KIDs are not yet compellingly better than conventional semiconducting detectors 9,10 . a) Electronic mail: omid.noroozian@nist.govMicrowave SQUID multiplexing 11,12 (µMux) is a readout technique that potentially combines the proven sensitivity of TESs and the scalable multiplexing power found in KIDs. Microwave SQUID multiplexing uses radiofrequency (rf) SQUIDs coupled to high quality-factor (Q) microwave resonators and has sufficiently low noise to read out the most sensitive cryogenic detectors. Additionally, it al...

High sensitivity phonon-mediated kinetic inductance detector with combined amplitude and phase read-out

“…9 Thanks to the high sensitivity and to the multiplexed read-out, KIDs have been proposed in several physics sectors, such as photon detection, astronomy, [9][10][11] search for dark matter interactions, 12,13 and for the read-out of transition-edge sensors arrays. 14,15 KIDs show all the desirable features for an innovative light detector with the exception of a wide active surface: macro-bolometers used by experiments such as CUORE 16 and CUPID-0 17,18 are characterized by surfaces of several cm 2 , while typical KIDs sizes barely reach few mm 2 . This limit can be overcome by following the phonon mediated approach: 13,19 photons are coupled to the KIDs through a large insulating substrate, which converts them into phonons.…”

Direct neutrino mass measurement by the HOLMES experiment

“…The HOLMES arrays are read-out with the microwave multiplexing (μMUX) developed by NIST, which is based on rf-SQUIDs as input devices [17]. The μMUX read-out leverages the Software Defined Radio (SDR) implemented in the firmware of a ROACH-2 board by NIST [18].…”

BFORE: The B-mode Foreground Experiment

“…4. We plan to use microwave readout for the KIDs [31] and microwave SQUID multiplexing [e.g., 32,33] for the TES arrays to achieve large multiplexing factors and maintain compatibility while minimizing cabling complexity.…”