arXiv subjects

H. Magoon

Publications and source records attributed to H. Magoon.

4 recordsLinked to original sources

arXiv2026

Position- and Temperature-Dependent Responsivity in a KID-Based Phonon-Mediated Detector

We report on the position- and temperature-dependent response of a kinetic inductance phonon-mediated (KIPM) detector. To study position-dependence, we used a controllable mirror attached to a micro-electromechanical system (MEMS) to steer optical light with a 100 $μ$m spot size over the backside of the cryogenic detector. With both pulsed and continuous operation of the LED, we observe features of the detector housing and find that the signal is strongest when the LED is pointed directly at the KID. The "off-KID" response is measured to be 34% of the "on-KID" response and is largely independent of direction. We model phonon propagation and collection in the KIPM detector with G4CMP and assert that the isotropic angular dependence is unlikely to be due to discrete phonon absorption "sinks", such as the microwave feedline or the device mounting points, but can be explained instead by an isotropic energy loss in the crystal. We furthermore utilize the temperature flexibility of the MEMS and KIPM detector system to investigate temperature-dependent responsivity, both at the sensor level (i.e., frequency shifts in the KID) and at the detector level (i.e., position dependence). We fit the KID's response to a two-component heat capacity and present the model as an alternative way to understand the KID's response to absorbed energy. We show on- and off-KID data at a range of temperatures and show that the phonon dynamics are not temperature dependent. We comment on the resulting implication for KID dynamics and design improvements.

physics.ins-det↗

arXiv2026

A First Demonstration of the SQUAT Detector Architecture: Direct Measurement of Resonator-Free Charge-Sensitive Transmons

The Superconducting Quasiparticle-Amplifying Transmon (SQUAT) is a new sensor architecture for THz (meV) detection based on a weakly charge-sensitive transmon directly coupled to a transmission line. In such devices, energy depositions break Cooper pairs in the qubit capacitor islands, generating quasiparticles. Quasiparticles that tunnel across the Josephson junction change the transmon qubit parity, generating a measurable signal. In this paper, we present the design of first-generation SQUATs and demonstrate an architecture validation. We summarize initial characterization measurements made with prototype devices, comment on background sources that influence the observed parity-switching rate, and present experimental results showing simultaneous detection of charge and quasiparticle signals using aluminum-based SQUATs.

physics.ins-det↗

arXiv2024

First Measurement of Correlated Charge Noise in Superconducting Qubits at an Underground Facility

We measure space- and time-correlated charge jumps on a four-qubit device, operating 107 meters below the Earth's surface in a low-radiation, cryogenic facility designed for the characterization of low-threshold particle detectors. The rock overburden of this facility reduces the cosmic ray muon flux by over 99% compared to laboratories at sea level. Combined with 4$π$ coverage of a movable lead shield, this facility enables quantifiable control over the flux of ionizing radiation on the qubit device. Long-time-series charge tomography measurements on these weakly charge-sensitive qubits capture discontinuous jumps in the induced charge on the qubit islands, corresponding to the interaction of ionizing radiation with the qubit substrate. The rate of these charge jumps scales with the flux of ionizing radiation on the qubit package, as characterized by a series of independent measurements on another energy-resolving detector operating simultaneously in the same cryostat with the qubits. Using lead shielding, we achieve a minimum charge jump rate of 0.19$^{+0.04}_{-0.03}$ mHz, almost an order of magnitude lower than that measured in surface tests, but a factor of roughly eight higher than expected based on reduction of ambient gammas alone. We operate four qubits for over 22 consecutive hours with zero correlated charge jumps at length scales above three millimeters.

quant-ph↗

arXiv2024

Cryogenic optical beam steering for superconducting device calibration

We have developed a calibration system based on a micro-electromechanical systems (MEMS) mirror that is capable of delivering an optical beam over a wavelength range of 180 -- 2000 nm (0.62 -- 6.89 eV) in a sub-Kelvin environment. This portable, integrated system can steer the beam over a $\sim$3 cm $\times$ 3 cm area on the surface of any sensor with a precision of $\sim$100 $μ$m, enabling characterization of device response as a function of position. This fills a critical need in the landscape of calibration tools for sub-Kelvin devices, including those used for dark matter detection and quantum computing. These communities have a shared goal of understanding the impact of ionizing radiation on device performance, which can be pursued with our system. This paper describes the design of the first-generation calibration system and the results from successfully testing its performance at room temperature and 20 mK.

quant-ph↗