Mid-infrared Nb4N3-based superconducting nanowire single photon detectors for wavelengths up to 10 µm

Micromachined Joule-Thomson cooling for long-time and precise thermal management

Efficient thermal management is essential for low-temperature optoelectronic devices. Traditional liquid nitrogen (LN2) cooling presents challenges such as frequent replenishment needs and limited operational duration. This study introduces micromachined Joule-Thomson (MJT) cooling as a superior alternative for temperature regulation in optoelectronic devices. We evaluated the thermal and optical performance of MJT cooling for a CdSe/ZnS quantum dot (QD) sample within a temperature range of 120-300 K. Thermal analysis showed that with a single 50 l nitrogen refill, the MJT system can operate continuously for over one week, surpassing the LN2 system by 11 times. The temperature stability was affected little by laser irradiation, with a <0.2 K rise at 5 mW of laser power. In addition, the MJT cooling led to an average blueshift of 1-3 meV in the emission peak of QDs and 0.3-2.3 meV reduced spectral broadening compared to LN2, attributed to a smaller sample-to-cold-stage temperature gap of about 8-9 K in the MJT setup. The standard deviations of peak energy and FWHM are in the order of E - 1 meV magnitude, demonstrating a comparable thermal uniformity compared to LN2. The vibration spectra obtained for both vertical and horizontal directions reveal the superior low-vibration characteristics of MJT cooling. These findings validate MJT cooling as a superior and reliable strategy for the thermal management of optoelectronics, ensuring prolonged operational durations, reliable temperature stability, enhanced temperature precision, high thermal homogeneity, and low vibrations.

Niobium Nitride Preparation for Superconducting Single-Photon Detectors

Niobium nitride (NbN) is widely used in the production of superconducting nanowire single-photon detectors (SNSPDs) due to its high superconducting transition temperature and suitable energy gap. The processing parameters used for the preparation of NbN films and the subsequent processing of nanowires have a significant effect on the performance of the SNSPD. In this review, we will present various thin film growth methods, including magnetron sputtering, atomic layer deposition (ALD), and chemical vapor deposition (CVD). The relationships between the superconducting performance of each thin film and the corresponding deposition process will be discussed. Subsequently, NbN nanowire fabrication methods and microstructures based on thin film etching will be summarized, and their impact on the qualities of the finished SNSPDs will be systematically analyzed. Finally, we will provide an outlook for the future development of preparation for SNSPD.

Highly efficient NbTiN nanostrip single-photon detectors using dielectric multilayer cavities for a 2-µm wavelength band

We report superconducting nanostrip single-photon detectors (SNSPDs) with dielectric multilayer cavities (DMCs) for a 2-µm wavelength. We designed a DMC composed of periodic SiO₂/Si bilayers. Simulation results of finite element analysis showed that the optical absorptance of the NbTiN nanostrips on the DMC exceeded 95% at 2 µm. We fabricated SNSPDs with an active area of 30 µm × 30 µm, which was sufficiently large to couple with a single-mode fiber of 2 µm. The fabricated SNSPDs were evaluated using a sorption-based cryocooler at a controlled temperature. We carefully verified the sensitivity of the power meter and calibrated the optical attenuators to accurately measure the system detection efficiency (SDE) at 2 µm. When the SNSPD was connected to an optical system via a spliced optical fiber, a high SDE of 84.1% was observed at 0.76 K. We also estimated the measurement uncertainty of the SDE as ±5.08% by considering all possible uncertainties in the SDE measurements.

Millimeter-scale active area superconducting microstrip single-photon detector fabricated by ultraviolet photolithography

The effective and convenient detection of single photons via advanced detectors with a large active area is becoming significant for quantum and classical applications. This work demonstrates the fabrication of a superconducting microstrip single-photon detector (SMSPD) with a millimeter-scale active area via the use of ultraviolet (UV) photolithography. The performances of NbN SMSPDs with different active areas and strip widths are characterized. SMSPDs fabricated by UV photolithography and electron beam lithography with small active areas are also compared from the aspects of the switching current density and line edge roughness. Furthermore, an SMSPD with an active area of 1 mm × 1 mm is obtained via UV photolithography, and during operation at 0.85 K, it exhibits near-saturated internal detection efficiency at wavelengths up to 800 nm. At a wavelength of 1550 nm, the detector exhibits a system detection efficiency of ∼5% (7%) and a timing jitter of 102 (144) ps, when illuminated with a light spot of ∼18 (600) µm in diameter, respectively.