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Implementations of quantum information require single-photon detectors (SPDs) with high detection efficiency (DE) at a wavelength of 940 nm, which is a challenge for the available semiconducting SPDs. Superconducting nanowire SPDs (SNSPDs) are capable of detecting visible and near-infrared single photons with high DE. However, these detection capabilities place stringent design requirements on the cavity and nanowire geometry structures. We design, fabricate, and measure SNSPDs with high DE optimized for the 940-nm wavelength. The NbN SNSPDs were fabricated on 1-D photonic crystals for high optical absorptance. By tuning the filling factor of the nanowire through numerical simulations and experiments, we were able to obtain an SNSPD (7 nm thick, 125 nm width, and 0.57 filling factor, as well as active area of 18 * 18 μm) with a saturated system DE of 83.6 ± 3.7%, at a dark count rate of 10 Hz, and a low polarization dependence of 1.17 ± 0.02. To our best knowledge, this is the highest value reported for NbN SNSPDs at 940-nm wavelength. The availability of an SNSPD with high system DE at 940 nm may have a profound impact in the field of photonic quantum technologies, such as multiphoton entanglement.

High-quality (001)-oriented perovskite [(SrIrO3)m/(SrTiO3)] superlattices (m=1/2, 1, 2, 3 and ∞) films have been grown on SrTiO3(001) epitaxially using reactive molecular beam epitaxy. Compared to previously reported superlattices synthesized by pulsed laser deposition, our superlattices exhibit superior crystalline, interface and surface structure, which have been confirmed by high-resolution X-ray diffraction, scanning transmission electron microscopy and atomic force microscopy, respectively. The transport measurements confirm a novel insulator-metal transition with the change of dimensionality in these superlattices, and our first systematic in situ photoemission spectroscopy study indicates that the increasing strength of effective correlations induced by reducing dimensionality would be the dominating origin of this transition.

We develop single-photon detectors comprising single-mode fiber-coupled superconducting nanowires, with high system detection efficiencies at a wavelength of 940 nm. The detector comprises a 6.5-nm-thick, 110-nm-wide NbN nanowire meander fabricated onto a Si substrate with a distributed Bragg reflector for enhancing the optical absorptance. We demonstrate that, via the design of a low filling factor (1/3) and active area (Φ = 10 μm), the system reaches a detection efficiency of ∼60% with a dark count rate of 10 Hz, a recovery time

Ultra-thin pieces of Bi2Sr2CaCu2O8+?single crystals (d<100 nm) can be isolated by cleaving pre-etched mesas off the main crystal using a flip-chip technique. Further thinning of the pieces by Ar-ion milling down to a few nanometres reveals the superconductor-insulator transition in the samples. In a refined technique, a precise control of the etching depth from both sides of the crystal makes it possible to form stacks of intrinsic Josephson junctions (IJJs) inside these ultra-thin single crystals. The stacks can be tailor-made to any small height (0-9 nm) thus assuring any low number of IJJs in the stacks (N= 0-6). Several features can be seen in the current-voltage (I-V) characteristics of these stacks, and therefore dI/dV(V) curves contain several peaks that behave differently with N. While the high-bias peaks shift in the normalized voltage V/N, the low-lying peaks at V/N32.4 ± 0.8 mV are N-independent. These peaks are reproducibly found in stacks of various lateral dimensions (0.5-11 µm2, N= 1...5) in a wide temperature range (T<0.8Tc). We briefly discuss possible reasons for the small values of the peak voltage. [ABSTRACT FROM AUTHOR]

Superconducting nanowire single-photon detectors (SNSPDs) with both high system detection efficiency (SDE) and low dark count rate (DCR) play significant roles in quantum information processes and various applications. The background dark counts of SNSPDs originate from the room temperature blackbody radiation coupled to the device via a fiber. Therefore, a bandpass filter (BPF) operated at low temperature with minimal insert loss is necessary to suppress the background DCR. Herein, a low-loss BPF integrated on a single-mode fiber end-face was designed, fabricated and verified for the low temperature implement. The fiber end-face BPF was featured with a typical passband width about 40 nm in the 1550 nm telecom band and a peak transmittance of over 0.98. SNSPD with high SDE fabricated on a distributed Bragg reflector was coupled to the BPF. The device with such a BPF showed an SDE of 80% at a DCR of 0.5 Hz, measured at 2.1 K. Compared the same device without a BPF, the DCR was reduced by over 13 dB with an SDE decrease of <3%. [ABSTRACT FROM AUTHOR]

We demonstrate a large active area superconducting single-nanowire photon detector with a diameter of Φ100 μm. The detector was fabricated on a Si substrate with distributed Bragg reflector acting as an optical cavity and coupled with a 105 μm multi-mode optical fiber. Owing to the extensive kinetic inductor caused by the large sensitive area of the detector, the response waveform exhibited a large overshoot, causing the device to latch with the increasing bias current. By adding a resistor in series with the device, the overshoot was suppressed, and the maximal bias current increased from 25 to 31 μA. A well-saturated detection efficiency with a maximal value of 65% was achieved at the wavelength of 532 nm. Moreover, the maximal counting rate improved from 1 to 10 MHz. [ABSTRACT FROM AUTHOR]

Superconducting nanowire single-photon detectors (SNSPDs) are widely used for the detection of visible and near-infrared single photons. Due to the nature of the polarization sensitive absorption of the nanowire, the detection efficiency (DE) of the meander SNSPD is polarization sensitive. In order to obtain a polarization-insensitive device with high DE, we fabricated NbN SNSPDs with spiral structure, which were embedded into an optical cavity. No meaningful current crowding effect was observed in the spiral SNSPDs. The spiral SNSPD showed a maximal system detection efficiency of 52.5% at 1550 nm with a dark count rate of 100 Hz and a polarization extinction ratio of 1.04, due to the combination of a spiral geometry and an optical cavity. [ABSTRACT FROM AUTHOR]

The performance of superconducting nanowire single-photon detectors (SNSPDs) relies on substrate materials. Magnesium fluoride (MgF2) exhibits outstanding optical properties, such as large optical transmission range and low refractive index (n = 1.38), making it an attractive substrate. We present the fabrication and the performance of SNSPDs made of a 4.5 nm thick NbN thin film deposited on MgF2 substrate for the wavelength of 1550 nm. The front-side illuminated SNSPDs without an optical cavity showed a maximal detection efficiency of 12.8% at a system dark count rate (DCR) of 100 Hz, while the backside illuminated SNSPDs with a SiO2/Au optical cavity atop displayed a maximal detection efficiency of 33% at a DCR of 100 Hz. [ABSTRACT FROM AUTHOR]