Superconducting Tunnel Junction Detectors We are developing superconducting tunnel junctions (STJs) for the detection of single UV/visible photons. When a photon is absorbed in the left electrode of the aluminum/aluminum oxide/aluminum STJ, it breaks Cooper pairs and creates excess quasiparticles. The quasiparticles tunnel across the voltage-biased junction as electrons, and the created current pulse has a charge proportional to the incoming photon's energy. If the outdiffusion of the quasiparticles from the right electrode is slowed by a long narrow wire, they will backtunnel across the junction as holes. We are investigating this internal mechanism for charge multiplication as a way to improve the signal-to-noise ratio of our detectors. For more information, see the paper "Enhancing the Energy Resolution of a Single-Photon STJ Spectrometer using Diffusion Engineering," V. Savu, L. Frunzio and D.E. Prober, IEEE Trans. Appl. Supercond. 17(2), 324 (2007). We are also developing STJs for terahertz detection. Terahertz photons break Cooper pairs and create excess quasiparticles in the STJ. The quasiparticle density is read out by measuring the STJ subgap current via microwave reflectometry. To characterize these devices, we have developed an on-chip variable-temperature blackbody source. The source consists of a voltage-biased gold nanowire that is coupled to the detector via a coplanar stripline. This work is in collaboration with the group of Prof. R. Schoelkopf (Yale) and NASA-GSFC. For more information, see the paper "Ultrasensitive Quantum-Limited Far-Infrared STJ Detectors," D.E. Prober, J.D. Teufel, C.M. Wilson, L. Frunzio, M. Shen, R.J. Schoelkopf, T.R. Stevenson, and E.J. Wollack, IEEE Trans. Appl. Supercond. 17(2), 241 (2007). Earlier work in our lab explored the performance and fundamental sensitivity limits of STJ detectors for detection frequencies from microwaves to x-rays. For more information, please refer to the publications page.