MEMS Calibration

Our group utilizes quantum information science (QIS) technology for its sensitivity to detect individual particle interactions with a target substrate. The primary devices used in the search for dark matter are high-voltage eV-resolution (HVeV) detectors, microwave kinetic inductance detectors (MKIDs), and eventually, superconducting quasiparticle amplifying transmons (SQUATs). These detectors can achieve sub-eV energy scale resolution in the search for dark matter. However, a key uncertainty in using these for a dark matter analysis is understanding position dependence in their response to phonon-producing events. The best way to measure this is to simulate phonon production at known locations in the substrate and measure relative device response.

In the DMQIS group, we have developed a system centered around a micro-electro-mechanical system (MEMS) mirror-based, steerable mirror which can be used to redirect broadband light onto a cm-scale target at mK temperatures. The MEMS mirror is electronically controlled to scan over a 3cm X 3cm area, enabling characterization as a function of position. This is based on an earlier device developed at Stanford [1, 2] to measure spatial variations in charge transport in Si and Ge crystals. The commercial vendor Mirrorcle Technologies [3] modified the MEMS mirror to add superconducting Al control lines on the mirror to ensure it operates at sub-Kelvin temperatures. That initial device projected a beam from a higher temperature and was open to 4K blackbody radiation, which would prevent a superconducting device from operating at such low energy scales. In addition, it used monochromatic, refractive optics for beam focusing, requiring a change to cryogenic optics to use different wavelengths of light, as was done for a photoelectric cross-section measurement [4].

Our new system, based on the original Stanford device, is called the Cryogenic Calibration System (CCS), which we colloquially refer to as ‘MEMS in a can’. The CCS is designed to be fully enclosed at the base stage of the cryostat, operates with broad-band reflective optics, and integrates customizable filter slots to allow for integration with IR-sensitive payloads. The current CCS system (v2) has been significantly miniaturized to allow it to fit into a 5” diameter cryo-perm magnetic shield, such that it can be used on a wide range of field-sensitive superconducting devices. Independent of the device, calibration is necessary to distinguish between background events and potential particle events. The CCS can provide such calibration by depositing controlled amounts of energy onto the surface of a detector, allowing for the response to be determined as a function of area, and can achieve a beam diameter of ~100 μm for precise characterization. This integrated system can be implemented in many different cryogenic-based experiments to calibrate devices in both the quantum sensing and quantum computing fields.

References: 
[1] Moffat 2016. Two-Dimensional Spatial Imaging of Charge Transport in Germanium Crystals at Cryogenic Temperatures. 10.2172/1350526
[2] Moffat, Robert J. (2006). Temperature and Flow Transducers. 10.1002/0471777455.ch5
[3] https://www.mirrorcletech.com/wp/products/mems-mirrors/ 
[4] Kurinsky 2018. The Low-Mass Limit: Dark Matter Detectors with eV-Scale Energy Resolution. 10.2172/1472104