The National Institute of Standards and Technology (NIST) researchers have substituted the superconducting material utilized in a single-photon detector with a new tungsten-silicon alloy, which increased the efficacy of the detector as well as its light sensitivity to longer wavelengths.
With the new tungsten-silicon alloy, the ultrafast detectors can be used in experiments studying the nature of reality, systems and quantum communications and upcoming applications such as remote sensing.
Colorized micrograph of an ultrafast single-photon detector made of superconducting nanowires
The superconducting nanowire detector is one among the numerous sensors designed or utilized at NIST to record single photons. The nanowire detector originally developed in Russia utilizes niobium nitride wires and its quantum efficiency-capability or detection to produce an electrical signal for every incoming photon below 10%.
The tungsten-silicon alloy model, developed by NIST, has demonstrated an efficacy of 19%-40% across a wide range of wavelengths between 1280 and 1650 nm, which includes spectrums utilized in telecommunications. The restrictions of the detector are primarily due to absorption of imperfect photon and its efficacy could reach 100% by further design enhancements.
Superconducting nanowire detectors are ultra fast and can count roughly one billion photons per sec. They demonstrate minimum dark or false counts, function with a broad range of wavelengths, and generate strong signals, particularly at telecom wavelengths.
Producing long, narrow, high sensitivity nanowires from niobium nitride is difficult. The higher energy sensitivity of tungsten-silicon alloy which produces more reliable signals is the main reason for its selection by NIST. The tungsten-silicon alloy allows a photon to break more electron pairs than niobium nitride. The internal structure of the tungsten alloy is less granular and more uniform, producing the nanowires with high sensitivity.
With higher energy sensitivity, the nanowires made of tungsten-silicon alloy can have larger sizes of up to 150 nm width when compared to 100 nm or less for niobium nitride, expanding the functional areas of the detector to trap all the photons.
The NIST researchers are now trying to increase the efficacy of tungsten alloy detectors by integrating them in optical cavities that capture light for ultra high absorption. High-efficient nanowire detectors can be used in challenging applications, including linear optical quantum computing that encodes data in single photons.