Benjamin A. Mazin

Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators

We present measurements of the temperature and power dependence of the resonance frequency and frequency noise of superconducting niobium thin-film coplanar waveguide resonators carried out at temperatures well below the superconducting transition (Tc=9.2 K). The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system (TLS) model for amorphous dielectrics. These results support the hypothesis that TLSs are responsible for the noise in superconducting microresonators and have important implications for resonator applications such as qubits and photon detectors.

A microwave kinetic inductance camera for sub/millimeter astrophysics

The MKID Camera is a millimeter/submillimeter instrument being built for astronomical observations from the Caltech Submillimeter Observatory. It utilizes microwave kinetic inductance detectors, which are rapidly achieving near-BLIP sensitivity for ground-based observations, and a software-defined radio readout technique for elegant multiplexing of a large number of detectors. The Camera will have 592 pixels distributed over 16 tiles in the focal plane, with four colors per pixel matched to the 750 μm, 850 μm, and 1.0 - 1.5 mm (split in two) atmospheric transmission windows. As a precursor to building the full-up camera and to enable ongoing detector testing, we have built a DemoCam comprised of a 16-pixel MKID array with which we have made preliminary astronomical observations. These observations demonstrate the viability of MKIDs for submillimeter astronomy, provide insight into systematic design issues that must be considered for MKID-based instruments, and they are the first astronomical observations with antenna-coupled superconducting detectors. In this paper, we describe the basic systems and specifications of the MKID Camera, we describe our DemoCam observations, and we comment on the status of submillimeter MKID sensitivities.

Power dependence of phase noise in microwave kinetic inductance detectors

Excess phase noise has been observed in microwave kinetic inductance detectors (MKIDs) which prevents the noise-equivalent power (NEP) of current detectors from reaching theoretical limits. One characteristic of this excess noise is its dependence on the power of the readout signal: the phase noise decreases as the readout power increases. We investigated this power dependence in a variety of devices, varying the substrate (silicon and sapphire), superconductor (aluminum and niobium) and resonator parameters (resonant frequency, quality factor and resonator geometry). We find that the phase noise has a power law dependence on the readout power, and that the exponent is -1/2 in all our devices. We suggest that this phase noise is caused by coupling between the high-Q microwave resonator that forms the sensitive element of the MKID and two-level systems associated with disorder in the dielectric material of the resonator. The physical situation is analogous to the resonance fluorescence in quantum optics, and we are investigating the application of resonance fluorescence theory to MKID phase noise.

Microwave kinetic inductance detectors for visible to near infrared astronomy (Conference Presentation)

Mazin Lab at UCSB is developing MKID instrument for astronomy at near infrared, optical and ultraviolet wavelength. We use MIKDs as single photon detectors by measuring the arrival time of incoming photons with an accuracy of a few microseconds and with a relatively high energy resolution (R~10 at 1um). We fabricate kilopixels array of MKIDs and we incorporate them in our own instruments for UVOIR astronomy with the main application being exoplanets direct imaging.nWe present the work being made in our lab in the development and fabrication of 10 to 20k pixels arrays for the DARKNESS (Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer) and MEC (MKID Exoplanet Camera) instruments, respectively. The 6-step fabrication process has been upgraded over the last months in order to improve the sensitivity of the arrays. The detectors are made of platinum silicide (PtSi) since MKIDs with very high internal quality factor have been successfully fabricated from this material. Furthermore, PtSi with very uniform superconducting properties over 4inch substrate are much more easier to deposit than the regular TiN used in most existing MKIDs technology. Among various upgrades, we coated the PtSi sensitive area with a SiO2/Ta2O5 bi-layer in order to reduce the reflection of optical photons hitting the detectors. The light absorption is increased by a factor of 2 in the instruments bandwidth. The DARKNESS instrument has been successfully commissioned last summer and MEC, the world largest superconducting camera, is installed at the Subaru telescope since the beginning of the year. Our effort leads to the fabrication of arrays of detectors with a median internal quality factor of 100 000 with an energy resolution of 10 at 1um and a pixel yield approaching 95%.n In addition, we will present new MKID design in which the conventional meander inductor and interdigitated capacitor are replaced by a square inductor and a large parallel plate capacitor made of two metal plates separated by a ~10-nm thick dielectric layer. This parallel plate design allows us to drive the MKIDs at a higher power, which in turns should increase the sensitivity of the detectors. Following promising results from our first design, second generation of parallel plate MKID devices have been made from Hf/HfO2/Nb tri-layers deposited in-sit. We obtained high quality factor from the parallel plate MKIDs and we were able to detect photons with this new MKIDs design. Another way to improve the sensitivity of MKIDs is to use a low Tc material, compared to Tc ~ 1K usually used. We fabricated MKIDs arrays with superconducting Hafnium, Tc = 450mK, and we demonstrated that resonators with very high internal quality factors Qi~300 000 and an energy resolution of 9 at 808nm can be achieved.