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Register a new userCryogenic LED pixel-to-frequency mapper for kinetic inductance detector arrays
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We present a cryogenic wafer mapper based on light emitting diodes (LEDs) for spatial mapping of a large microwave kinetic inductance detector (MKID) array. In this scheme, an array of LEDs, addressed by DC wires and collimated through horns onto the detectors, is mounted in front of the detector wafer. By illuminating each LED individually and sweeping the frequency response of all the resonators, we can unambiguously correspond a detector pixel to its measured resonance frequency. We have demonstrated mapping a 76.2 mm 90-pixel MKID array using a mapper containing 126 LEDs with 16 DC bias wires. With the frequency to pixel-position correspondence data obtained by the LED mapper, we have found a radially position-dependent frequency non-uniformity < 1.6% over the 76.2 mm wafer. Our LED wafer mapper has no moving parts and is easy to implement. It may find broad applications in superconducting detector and quantum computing/information experiments.
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We have fabricated an array of subgap kinetic inductance detectors (SKIDs) made of granular aluminum ($T_csim$2~K) sensitive in the 80-90 GHz frequency band and operating at 300~mK. We measure a noise equivalent power of $1.3times10^{-16}$~W/Hz$^{0.5}$ on average and $2.6times10^{-17}$~W/Hz$^{0.5}$ at best, for an illuminating power of 50~fW per pixel. Even though the circuit design of SKIDs is identical to that of the kinetic inductance detectors (KIDs), the SKIDs operating principle is based on their sensitivity to subgap excitations. This detection scheme is advantageous because it avoids having to lower the operating temperature proportionally to the lowest detectable frequency. The SKIDs presented here are intrinsically selecting the 80-90 GHz frequency band, well below the superconducting spectral gap of the film, at approximately 180 GHz.
The concept of the radio-frequency superconducting nanowire single-photon detector (RF-SNSPD) allows frequency-division multiplexing (FDM) of the bias and readout lines of several SNSPDs. Using this method, a multi-pixel array can be operated by only one feed line. Consequently, the system complexity as well as the heat load is significantly reduced. To allocate many pixels into a small bandwidth the quality factor of each device is crucial. In this paper, we present an improved RF-SNSPD design. This new design enables a simple tuning of the quality factor as well as the resonant frequency. With a two-pixel device we have demonstrated the operation without crosstalk between the detectors and showed the time, spatial and photon number resolution. Thereby a single pixel requires only a bandwidth of 14 MHz.
We present a compact current sensor based on a superconducting microwave lumped-element resonator with a nanowire kinetic inductor, operating at 4.2 K. The sensor is suitable for multiplexed readout in GHz range of large-format arrays of cryogenic detectors. The device consists of a lumped-element resonant circuit, fabricated from a single 4-nm-thick superconducting layer of niobium nitride. Thus, the fabrication and operation is significantly simplified in comparison to state-of-the-art approaches. Because the resonant circuit is inductively coupled to the feed line the current to be measured can directly be injected without having the need of an impedance matching circuit, reducing the system complexity. With the proof-of-concept device we measured a current noise floor {delta}Imin of 10 pA/Hz1/2 at 10 kHz. Furthermore, we demonstrate the ability of our sensor to amplify a pulsed response of a superconducting nanowire single-photon detector using a GHz-range carrier for effective frequency-division multiplexing.
Microwave kinetic inductance detector (MKID) provides a way to build large ground based sub-mm instruments such as NIKA and A-MKID. For such instruments, therefore, it is important to understand and characterize the response to ensure good linearity and calibration over wide dynamic range. We propose to use the MKID readout frequency response to determine the MKID responsivity to an input optical source power. A signal can be measured in a KID as a change in the phase of the readout signal with respect to the KID resonant circle. Fundamentally, this phase change is due to a shift in the KID resonance frequency, in turn due to a radiation induced change in the quasiparticle number in the superconducting resonator. We show that shift in resonant frequency can be determined from the phase shift by using KID phase versus frequency dependence using a previously measured resonant frequency. Working in this calculated resonant frequency, we gain near linearity and constant calibration to a constant optical signal applied in a wide range of operating points on the resonance and readout powers. This calibration method has three particular advantages: first, it is fast enough to be used to calibrate large arrays, with pixel counts in the thousand of pixels; second, it is based on data that are already necessary to determine KID positions; third, it can be done without applying any optical source in front of the array.
We demonstrate photon counting at 1550 nm wavelength using microwave kinetic inductance detectors (MKIDs) made from TiN/Ti/TiN trilayer films with superconducting transition temperature Tc ~ 1.4 K. The detectors have a lumped-element design with a large interdigitated capacitor (IDC) covered by aluminum and inductive photon absorbers whose volume ranges from 0.4 um^3 to 20 um^3. We find that the energy resolution improves as the absorber volume is reduced. We have achieved an energy resolution of 0.22 eV and resolved up to 7 photons per pulse, both greatly improved from previously reported results at 1550 nm wavelength using MKIDs. Further improvements are possible by optimizing the optical coupling to maximize photon absorption into the inductive absorber.
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