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Register a new userDevelopment of an Array of Kinetic Inductance Magnetometers (KIMs)
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We describe optimization of a cryogenic magnetometer that uses nonlinear kinetic inductance in superconducting nanowires as the sensitive element instead of a superconducting quantum interference device (SQUID). The circuit design consists of a loop geometry with two nanowires in parallel, serving as the inductive section of a lumped LC resonator similar to a kinetic inductance detector (KID). This device takes advantage of the multiplexing capability of the KID, allowing for a natural frequency multiplexed readout. The Kinetic Inductance Magnetometer (KIM) is biased with a DC magnetic flux through the inductive loop. A perturbing signal will cause a flux change through the loop, and thus a change in the induced current, which alters the kinetic inductance of the nanowires, causing the resonant frequency of the KIM to shift. This technology has applications in astrophysics, material science, and the medical field for readout of Metallic Magnetic Calorimeters (MMCs), axion detection, and magnetoencephalography (MEG).
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Inductance is a key parameter when optimizing the performance of superconducting quantum interference device (SQUID) magnetometers made from the high temperature superconductor YBa$_2$Cu$_3$O$_{7-x}$ (YBCO) because lower SQUID inductance $L$ leads to lower flux noise, but also weaker coupling to the pickup loop. In order to optimize the SQUID design, we combine inductance simulations and measurements to extract the different inductance contributions, and measure the dependence of the transfer function $V_{Phi}$ and flux noise $S_Phi^{1/2}$ on $L$. A comparison between two samples shows that the kinetic inductance contribution varies strongly with film quality, hence making inductance measurements a crucial part of the SQUID characterization. Thanks to the improved estimation of the kinetic inductance contribution, previously found discrepancies between theoretical estimates and measured values of $V_{Phi}$ and $S_Phi^{1/2}$ could to a large extent be avoided. We then use the measurements and improved theoretical estimations to optimize the SQUID geometry and reach a noise level of $S_B^{1/2}$ = 44 fT/$sqrt{textrm{Hz}}$ for the best SQUID magnetometer with a 8.6 mm $times$ 9.2 mm directly coupled pickup loop. Lastly, we demonstrate a method for reliable one-time sensor calibration that is constant in a temperature range of several kelvin despite the presence of temperature dependent coupling contributions, such as the kinetic inductance. The found variability of the kinetic inductance contribution has implications not only for the design of YBCO SQUID magnetometers, but for all narrow linewidth SQUID-based devices operated close to their critical temperature.
We report on a 2x2 array of radio-frequency atomic magnetometers in magnetic induction tomography configuration. Active detection, localization, and real-time tracking of conductive, non-magnetic targets are demonstrated in air and saline water. Penetration in different media and detection are achieved thanks to the sensitivity and tunability of the sensors, and to the active nature of magnetic induction probing. We obtained a 100% success rate for automatic detection and 93% success rate for automatic localization in air and water, up to 190 mm away from the sensors plane (100 mm underwater). We anticipate magnetic induction tomography with arrays of atomic magnetometers finding applications in civil engineering and maintenance, oil&gas industry, geological surveys, marine science, archeology, search and rescue, and security and surveillance.
We describe the fabrication of homogeneous sub-stoichiometric titanium nitride films for microwave kinetic inductance detector (mKID) arrays. Using a 6 inch sputtering target and a homogeneous nitrogen inlet, the variation of the critical temperature over a 2 inch wafer was reduced to <25 %. Measurements of a 132-pixel mKID array from these films reveal a sensitivity of 16 kHz/pW in the 100 GHz band, comparable to the best aluminium mKIDs. We measured a noise equivalent power of NEP = 3.6e-15 W/Hz^(1/2). Finally, we describe possible routes to further improve the performance of these TiN mKID arrays.
Searches for new physics push experiments to look for increasingly rare interactions. As a result, detectors require increasing sensitivity and specificity, and materials must be screened for naturally occurring, background-producing radioactivity. Furthermore the detectors used for screening must approach the sensitivities of the physics-search detectors themselves, thus motivating iterative development of detectors capable of both physics searches and background screening. We report on the design, installation, and performance of a novel, low-background, fourteen-element high-purity germanium detector named the CAGe (CUP Array of Germanium), installed at the Yangyang underground laboratory in Korea.
Thermal Kinetic Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. In this paper, we first discuss the expected noise sources in TKIDs and derive the limits where the phonon noise contribution dominates over the other detector noise terms: generation-recombination, amplifier, and two-level system (TLS) noise. Second, we characterize aluminum TKIDs in a dark environment. We present measurements of TKID resonators with quality factors of about $10^5$ at 80 mK. We also discuss the bolometer thermal conductance, heat capacity, and time constants. These were measured by the use of a resistor on the thermal island to excite the bolometers. These dark aluminum TKIDs demonstrate a noise equivalent power NEP = $2 times 10^{-17} mathrm{W}/mathrm{sqrt{Hz}} $, with a $1/f$ knee at 0.1 Hz, which provides background noise limited performance for ground-based telescopes observing at 150 GHz.
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