We present the result of the creation and investigation of the multi-element superconducting single photon detectors, which can recognize the number of photons (up to six) in a short pulse of the radiation at telecommunication wavelengths range. The best receivers coupled with single-mode fiber have the system quantum efficiency of ⁓85%. The receivers have a 100 ps time resolution and a few nanoseconds dead time that allows them to operate at megahertz counting rate. Implementation of the multi-element architecture for creation of the superconducting single photon detectors with increased sensitive area allows to create the high efficiency receivers coupled with multi-mode fibers and with preserving of the all advantages of superconducting photon counters.
Quantum cascade lasers (QCL) are widely adopted as prominent and easy-to-use solid-state sources of terahertz radiation. Yet some applications require generation and detection of very sharp and narrow terahertz-range pulses with a specific spectral composition. We have studied time-resolved light-current (L–I) characteristics of multimode THz QCL operated with a fast ramp of the injection current. Detection of THz pulses was carried out using an NbN superconducting hot-electron bolometer with the time constant of the order of 1 ns while the laser bias current was swept during a single driving pulse. A nonmonotonic behavior of the L–I characteristic with several visually separated subpeaks was found. This behavior is associated with the mode competition in THz QCL cavity, which we confirm by L–I measurements with use of an external Fabry–Perot interferometer for a discrete mode selection. We also have demonstrated the possibility to control the L–I shape with suppression of one of the subpeaks by simply adjusting the off-axis parabolic mirror for optimal optical alignment for one of the laser modes. The developed technique paves the way for rapid characterization of pulsed THz QCLs for further studies of the possibilities of using this approach in remote sensing.
We describe the performance of detector modules containing silicon single photon avalanche photodiodes (SPADs) and superconducting nanowire single photon detectors (SNSPDs) to be used for intensity interferometry. The SPADs are mounted in fiber-coupled and free-space coupled packages. The SNSPDs are mounted in a small liquid helium cryostat coupled to single mode fiber optic cables which pass through a hermetic feed-through. The detectors are read out with microwave amplifiers and FPGA-based coincidence electronics. We present progress on measurements of intensity correlations from incoherent sources including gas-discharge lamps and stars with these detectors. From the measured laboratory performance of the correlation system, we estimate the sensitivity to intensity correlations from stars using commercial telescopes and larger existing research telescopes.
This paper presents an ultrafast niobium nitride (NbN) superconducting single-photon detector (SSPD) with an active area of 3×3 μm2 that offers better timing performance metrics than the previous SSPD with an active area of 7×7 μm2. The improved SSPD demonstrates a record timing jitter (<25 ps), an ultrashort recovery time (<2 ns), an extremely low dark count rate, and a high detection efficiency in a wide spectral range from visible part to near infrared. The record parameters were obtained due to the development of a new technique providing effective optical coupling between a detector with a reduced active area and a standard single-mode telecommunication fiber. The advantages of the new approach are experimentally confirmed by taking electro-optical measurements.
KEYWORDS: Sensors, Superconductors, Ultrafast phenomena, Single photon detectors, Active sensors, Inductance, Picosecond phenomena, Active optics, Single mode fibers, Beam splitters
We present an ultrafast NbN Superconducting single-photon detector (SSPD) with active area of 3x3 μm2, which reveals better timing performances than a previously developed SSPD with active area of 10x10 μm2. The improved SSPD demonstrates the record timing jitter <25 ps, ultra short recovery time <2 ns, extremely low dark counts level, and high detection efficiency (DE) in a wide spectral range from visible to near-infrared. The record parameters were obtained thanks to the development of a new technique of an effective optical coupling between a detector with reduced-size active area and a standard single-mode telecommunication fiber. The advantages of a new approach are experimentally confirmed by performed electro-optical measurements of the device performances.
We discuss the possibility of polarization state reconstruction and measurement over 302 km by Superconducting Single- Photon Detectors (SSPDs). Because of the excellent characteristics and the possibility to be effectively coupled to singlemode optical fiber many applications of the SSPD have already been reported. The most impressive one is the quantum key distribution (QKD) over 250 km distance. This demonstration shows further possibilities for the improvement of the characteristics of quantum-cryptographic systems such as increasing the bit rate and the quantum channel length, and decreasing the quantum bit error rate (QBER). This improvement is possible because SSPDs have the best characteristics in comparison with other single-photon detectors. We have demonstrated the possibility of polarization state reconstruction and measurement over 302.5 km with superconducting single-photon detectors. The advantage of an autocompensating optical scheme, also known as "plugandplay" for quantum key distribution, is high stability in the presence of distortions along the line. To increase the distance of quantum key distribution with this optical scheme we implement the superconducting single photon detectors (SSPD). At the 5 MHz pulse repetition frequency and the average photon number equal to 0.4 we measured a 33 bit/s quantum key generation for a 101.7 km single mode ber quantum channel. The extremely low SSPD dark count rate allowed us to keep QBER at 1.6% level.
Alexander Korneev, Alexander Divochiy, Yury Vachtomin, Yulia Korneeva, Irina Florya, Michael Elezov, Nadezhda Manova, Michael Tarkhov, Pavel An, Anna Kardakova, Anastasiya Isupova, Galina Chulkova, Konstantin Smirnov, Natalya Kaurova, Vitaliy Seleznev, Boris Voronov, Gregory Goltsman
Superconducting single-photon detector (SSPD) is a planar nanostructure patterned from 4-nm-thick NbN film
deposited on sapphire substrate. The sensitive element of the SSPD is 100-nm-wide NbN strip. The device is
operated at liquid helium temperature. Absorption of a photon leads to a local suppression of superconductivity
producing subnanosecond-long voltage pulse. In infrared (at 1550 nm and longer wavelengths) SSPD outperforms
avalanche photodiodes in terms of detection efficiency (DE), dark counts rate, maximum counting rate and
timing jitter. Efficient single-mode fibre coupling of the SSPD enabled its usage in many applications ranging
from single-photon sources research to quantum cryptography. Recently we managed to improve the SSPD
performance and measured 25% detection efficiency at 1550 nm wavelength and dark counts rate of 10 s-1. We
also improved photon-number resolving SSPD (PNR-SSPD) which realizes a spatial multiplexing of incident
photons enabling resolving of up to 4 simultaneously absorbed photons. Another improvement is the increase of
the photon absorption using a λ/4 microcavity integrated with the SSPD. And finally in our strive to increase the
DE at longer wavelengths we fabricated SSPD with the strip almost twice narrower compared to the standard
100 nm and demonstrated that in middle infrared (about 3 μm wavelength) these devices have DE several times
higher compared to the traditional SSPDs.
At present superconducting detectors become increasingly attractive for various practical applications. In this paper we
present results on the depelopment of fiber coupled receiver systems for the registration of IR single photons, optimized
for telecommunication and quantum-cryptography. These receiver systems were developed on the basis of
superconducting single photon detectors (SSPD) of VIS and IR wavelength ranges. The core of the SSPD is a narrow
(~100 nm) and long (~0,5 mm) strip in the form of a meander which is patterned from a 4-nm-thick NbN film
(TC=10-11 K, jC=~5-7•106
A/cm2); the sensitive area dimensions are
10×10 μm2. The main problem to be solved while the
receiver system development was optical coupling of a single-mode fiber (9 microns in diameter) with the SSPD
sensitive area. Characteristics of the developed system at the optical input are as follows: quantum efficiency >10 % (at
1.3 μm), >4 % (at 1.55 μm); dark counts rate ≤1 s-1; duration of voltage pulse ≤5 ns; jitter ≤40 ps. The receiver systems
have either one or two identical channels (for the case of carrying out correlation measurements) and are made as an
insert in a helium storage Dewar.
We present the results of our studies of NbN phonon-cooled HEB mixers at terahertz frequencies. The mixers were fabricated from NbN film deposited on a high-resistivity Si substrate with an MgO buffer layer. The mixer element was integrated with a log-periodic spiral antenna. The noise temperature measurements were performed at 2.5 THz and at 3.8 THz local oscillator frequencies for the 3 x 0.2 μm2 active area devices. The best uncorrected receiver noise temperatures found for these frequencies are 1300 K and 3100 K, respectively. A water vapour discharge laser was used as the LO source. The largest gain bandwidth of 5.2 GHz was achieved for a mixer based on 2 nm thick NbN film deposited on MgO layer over Si substrate. The gain bandwidth of the mixer based on 3.5 nm NbN film deposited on Si with MgO is 4.2 GHz and the noise bandwidth for the same device amounts to 5 GHz. We also present the results of our research into decrease of the direct detection contribution to the measured Y-factor and a possible error of noise temperature calculation. The use of a square nickel cell mesh as an IR-filter enabled us to avoid the effect of direct detection and measure apparent value of the noise temperature which was 16% less than that obtained using conventional black polyethylene IR-filter.
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