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Applied Physics Letters

Real time quasiparticle tunneling measurements on an illuminated quantum capacitance detector

Kristjan Stone, Koko G. Megerian, Peter K. Day, P. M. Echternach, Juan Bueno, Nuria Llombart

Published Jun 25, 2012• 21 citations
Publisher

Abstract

Quasiparticle tunneling events are measured in real time using a quantum capacitance detector (QCD), allowing for the extraction of tunneling rates as a function of temperature and optical loading of radiation coming from a black body source filtered to 200 m. The measurements are used to corroborate the basic operating principles of the QCD. An estimate of the residual quasiparticle density is made, and the noise equivalent power (NEP) is assessed to be 7.2×10−20W/Hz1/2 at the lowest signal power of 9.2×10−20W. This NEP was higher than the photon noise by only a factor of 7 over a wide signal power range.

DOI
10.1063/1.4731880

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Quasiparticle tunneling events are measured in real time using a quantum capacitance detector (QCD), allowing for the extraction of tunneling rates as a function of temperature and optical loading of radiation coming from a black body source filtered to 200 m. The measurements are used to corroborate the basic operating principles of the QCD. An estimate of the residual quasiparticle density is made, and the noise equivalent power (NEP) is assessed to be 7.2×10−20W/Hz1/2 at the lowest signal power of 9.2×10−20W. This NEP was higher than the photon noise by only a factor of 7 over a wide signal power range.
We fabricated and tested a proof-of-concept quantum capacitance detector, a superconducting radiation detector described in a recent publication [Shaw et al., Phys. Rev. B 79, 144511 (2009)]. In this concept, quasiparticle tunneling in a single Cooper-pair box is used to measure the density of quasiparticles in a superconducting absorber. We measured and characterized the response of the device to electrical quasiparticle injection obtaining its sensitivity. Moreover, we have converted the sensitivity to electrical noise-equivalent power, which is in the 10−18 W/Hz1/2 range at loading powers between 10−15–10−16 W.
We present the optical characterization at 200 μm wavelength of an antenna coupled quantum capacitance detector (QCD), a cryogenic detector based on a single Cooper pair box (SCB). The response of the device to a cryogenic blackbody source and the device noise have been measured giving an optical noise-equivalent power (NEP) at a readout frequency of 10 kHz of 2 × 10−17 W/Hz1/2 at an optical loading of 17 fW. For optical loadings of a few pW, the optical NEP was on the order of 10−16 W/Hz1/2, demonstrating that QCDs could already work as detectors for far-infrared and submillimeter wave radiation in a ground based telescope.
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We propose a sensitive new detector based on Cooper pair breaking in a superconductor. The quantum capacitor detector (QCD) exploits the extraordinary sensitivity of superconducting single-electron devices to the presence of quasiparticles generated by pair-breaking photons. This concept would enable single-photon detection at far-IR and sub-millimeter frequencies with detector sensitivities that exceed that of transition-edge-sensor bolometers (TES), kinetic inductance detectors (KID), and superconducting tunnel junction detectors (STJ). The detectors we propose are based on the single Cooper pair box (SCB), a mesoscopic superconducting device that has been successfully developed at JPL for applications in quantum computing. This concept allows for frequency multiplexing of a large number of pixels using a single RF line, and does not require individual bias of each pixel. The QCD is ideal for the sensitive spectrographs considered for upcoming cold space telescopes, such as BLISS for SPICA in the coming decade, and for the more ambitious instruments for the SAFIR / CALISTO and SPIRIT / SPECS missions envisioned for the 2020 decade. These missions require large detector arrays (> 10,000 elements) which are limited by astrophysical background noise, corresponding to a noise-equivalent power (NEP) as low as 2x10-20 W / Hz1/2. Given its intrinsic response time, the QCD could also be used for energy-resolved visible photon detection, with estimated energy resolution > 100, enabling imaging low-resolution spectroscopy with an array of detectors.
We have directly measured non-equilibrium quasiparticle tunneling in the time domain as a function of temperature and RF carrier power for a pair of charge qubits based on the single Cooper-pair box, where the readout is performed with a multiplexed quantum capacitance technique. We have extracted an effective electron temperature for each applied RF power, using the data taken at the lowest power as a reference curve. This data has been fit to a standard T 5 electron heating model, with a qualitative correspondence with established material parameters.
We have directly measured non-equilibrium quasiparticle tunnelling in the time domain as a function of temperature and RF carrier power for a pair of charge qubits based on the single Cooper-pair box, where the readout is performed with a multiplexed quantum capacitance technique. We have extracted an effective electron temperature for each applied RF power, using the data taken at the lowest power as a reference curve. This data has been fit to a standard T? electron heating model, with a reasonable correspondence with established material parameters.