Kinetic Inductance Detectors (KID), proposed in 2003 by the Caltech-JPL group, are now reaching maturity. In Grenoble, a collaboration coordinated and driven by the Institut Néel has developed the NIKA (New IRAM KID Arrays) instrument, showing state-of-the art performances at the 30-meters telescope at Pico Veleta. NIKA has been the first example of instrument based on this new technology open to the international astronomical community via competitive semestral calls. We are now developing NIKA2, a 1-ton scale instrument with base temperature of 100mK and containing very large arrays of KID. NIKA2 will map large portions of the sky simultaneously at 150 and 250 GHz, and be able to measure the linear polarization of the incoming radiation. I will present the technological details of the NIKA2 instrument, and a sample of the scientific results obtained by NIKA, i.e. clusters of galaxies mapped with unprecedented sensitivity/resolution, primordial galaxies, Pluto observations etc. I will spend a few minutes to explain our innovative readout scheme, allowing a real-time self calibration of the resonators response. I will conclude giving a quick overview of the activities ongoing in our collaborations, including superconducting resonators for superfluid helium hydrodynamics studies, the use of KID for x, gamma and cosmic rays imaging, new materials and configurations allowing to produce KID sensitive down to 50GHz photons, fundamental superconductivity studies based on our detectors etc.

I represent here larger collaborations. For example, the NIKA2 collaboration includes a large number of scientists and engineers.

Superconducting nanowire single-photon detectors (SSPDs) have been applied for various fields, e.g., quantum information, due to their various advantages such as high system detection efficiency (SDE). In the field of life science, fluorescence correlation spectroscopy (FCS) is an important tool for investigating a molecular motion of fluorescent materials in living cells. FCS can determine the size and the number of molecules by an autocorrelation of fluorescence from fluorescently-labeled molecules. In the conventional FCS systems, silicon avalanche photodiodes (APDs) with high detection efficiency of 60 – 70% have been used as a single-photon detector. However, there is a problem of the noise, called “after-pulse” in APDs, which is undesired error pulses after one detection event. Due to the after-pulse, it was impossible to determine autocorrelation functions in a sub-microsecond regime by APDs. In contrast, SSPD is free from after-pulse and provides a great advantage to determine autocorrelation functions at a sub-microsecond level. In this work, we developed visible-wavelength SSPDs (VW-SSPDs) and applied VW-SSPDs to the FCS system. We fabricated a meandering NbN nanowire with the thickness of 10.5 nm and the line width of 150 nm. The active area was a circular shape with a diameter of 35 µm, which is large enough to couple well with the light from a multimode fiber. The SiO₂ layer located on the substrate worked as an optical cavity, and the thickness was chosen to enhance the optical absorptance for the wavelength of 600 nm. The multimode-fiber-coupled VW-SSPD showed the high SDE of 70% for 635-nm-wavelength photons. We installed the VW-SSPD in the FCS system and measured an autocorrelation of the fluorescent molecules. Obtained results show that the developed VW-SSPD can produce reliable measurements of autocorrelation even in a sub-microsecond regime [1].
[1] T. Yamashita et al., Optics Express, vol. 22, no. 23, pp. 28783 – 28789 (2014).

This work was supported by a grant from the Japan Science and Technology Agency (to YH and HT).

The ALPS II experiment, Any Light Particle Search II at DESY in Hamburg, will look for light (m < 10⁻⁴ eV) new fundamental bosons (e.g., axion-like particles, hidden photons and other WISPs) in the next years by the means of a light-shining-through the wall setup.
A few years ago, its predecessor had constrained the coupling to photons of axion-like particles (ALPS) to g_aγ ≤ 7 · 10⁻⁸ GeV ^{− 1}, m ≤ 10⁻⁴ eV. Several improvements are foreseen to reach much better sensitivities (g_aγ ≤ 7 · 10⁻¹¹ GeV⁻¹). One of the main modifications which have been done is the substitution of the CCD camera by two microcalorimetric W-TESs (Transition Edge Sensors with tungsten chips). These TESs, operated at 80 mK have already allowed single infrared photon detections as well as non-dispersive spectroscopy with very low background rates.
The detection efficiency for such TES is > 95 % and the dark count rate < 10^-2 s^-1. At this wavelength, the intrinsic dark count rate is of 10^-4 s^-1. The relative energy resolution for 1064 nm signals is < 8%. In order to bias accurately the device and for reading purposes, TESs are inductively coupled to a SQUID (Superconducting Quantum Interference Device).
In the near future, complete characterization, calibration and optimization (e.g., background suppression) need to be finalized. The latest progress in this task will be presented as well as next steps planned for future developments.

Raman spectroscopy is a versatile and well-established analytical tool in life science application. Due to its high molecular specificity, it enables the identification of a large number of molecules by their spectral fingerprint. In order to detect the inelastically scattered Raman light, usually a spectrometer is used where the signal is spectrally dispersed by a grating.
We demonstrate an alternative method, using an optical fiber as dispersive element. As the group velocity within the fiber is wavelength-dependent, different Raman bands arrive at different times at the detector. In combination with time-correlated single-photon counting, Raman spectra can be measured in the time domain.
In order to achieve the best possible temporal resolution, we implemented a Superconducting Nanowire Single-Photon Detector (SNSPD), which possesses a timing accuracy of about 20 ps. In doing so, we have been able to measure Raman spectra of various substances in the time domain. Using gradient index fibers of varying length, influences on the spectral resolution have been studied.
In view of future applications, we discuss the requirements on the detector.

We have successfully demonstrated multi-pixel operations of serially-connected superconducting stripline detectors (SSLDs) integrated with superconducting readout circuits as single monolithic chips toward 1 mega pixel (1000 x 1000) superconducting image sensors like CMOS ones. The SSLDs with widths of a few micron were made by patterning additional niobium-molybdenum bi-layers formed on the conventional Nb/AlOx/Nb integrated circuits. In case of neutron image sensors, we deposit conversion layers of boron 10 on the bi-layers.

Serial connection of 2, 6, 16, and 500 SSLDs with individual detector lengths of about 2 cm is driven by a single DC current source to reduce the number of cables from room temperature electronics. When a particle such as a photon, neutron, comes to a certain SSLD, a voltage pulse is generated across the SSLD in response to a change of kinetic inductance or resistance [1]. Numerical analysis shows that the pulse has no influence on the operation of the other SSLDs by insertion of low pass filters with cut-off frequency of 100 MHz between adjacent SSLDs and by mutual coupling with low-impedance readout circuit.

We designed quasi-one-junction-SQUID-based (QOS-based) readout circuits connected to RSFQ encoders. The binary address data corresponding to the fired SSLD is sent to room-temperature electronics. Thus, only 9 cables are needed for outputting 500 SSLDs. The short relaxation time about a few ns is achieved by using the bi-layer and by inserting a resistor between SSLDs and connecting readout circuits.

We applied a laser with wavelength of 1550 nm to the serially-connected SSLDs and moved the laser spot from a certain SSLD to the others. We observed the voltage only at the QOS connected to the fired SSLD. No voltage was observed at the other QOSs. This means that the individual readout, that is, multi-pixel operation is confirmed experimentally even in the serially-connected SSLDs.
[1] Y. Narukami, et al., IEEE. Trans. Appl. Supercond. 25, 2400904 (2015).

This work was partially supported by KAKENHI (23226019) and TUBITAK grant (111E191). The circuits were designed under the support of VDEC of the University of Tokyo, in collaboration with Cadence Design Systems, Inc., and fabricated in the clean room for analog-digital superconductivity (CRAVITY) of AIST.

The superconductivity of magnesium diboride (MgB­₂) was first discovered in 2001. The remarkably high transition temperature of 39 K is attractive for detector applications. MgB₂ detectors have a sensitivity for single photons and neutrons. In this paper, we have demonstrated that MgB2 can be applied to biomolecule ion detection in time-of-flight mass spectrometry (TOF MS). TOF MS requires detectors with fast response time and mass-independent detection efficiency. Superconducting strip ion detectors (SSIDs) are characterized by their ultrafast response times in the nanosecond range and mass-independend high sensitivity to ion impact in the keV range. Therefore, SSIDs are promising for TOF MS applications.
The cryostat was connected to a linear TOF MS (Applied Biosystems Voyager DE-STR, South San Francisco, CA), which uses matrix-assisted laser desorption/ionization (MALDI) to ionize biomolecules. The biomolecule sample used in this study was Angiotensin I (molecular weight of 1,296) with the matrix of a-cyano-4-hydroxycinnamic acid or Lysozyme (molecular weight of about 14,300) with the matrix of sinapic acid. After ionization, the ions were accelerated by a high voltage of Va = 20 kV and flew in the flight tube until they strike the SSID surface in the cryostat.
The TOF MS spectra for Angiotensin I and Lysozyme were successfully obtained at a base temperature of up to 13 K without any thermal blocking filters, which is promising to realize a practical ion detection system with a small-sized cryocooler. The circuit simulations and the time-dependent Ginzburg-Landau simulations revealed the detecting mechanism of the MgB₂-SSID for tens of keV ions: (1) the massive power deposition induces no oscillation of the superfluid density, which means that no vortex-antivortex pair unbiding occurs, (2) the normal region expansion is completed within 16 ps, which corresponds to the maximum length of 1010 nm, and (3) the normal region lasts for 390 ps. Since the current design of MgB₂ SSIDs is a simple meander structure, the sensitive area is impractically smaller than an ion beam size of ~cm in TOF MS. In future, the sensitive area should be increased by using the parallel configuration used for Nb SSIDs.

This work was financially supported by Grants-in-Aid for Scientific Research (A) and (C) from the Japan Society for the Promotion of Science (No. 22246056 and No. 25420350, respectively). The autors thank to M. Ukibe, S. Shiki, G. Fujii, M. Koike for frutiful discussion.