The superconducting nanowire single photon detector (SNSPD) is constituted by a thin film of superconducting material shaped into a meandering nanowire through nanofabrication processes. This pattern enables to cover a wide surface area, collecting the whole output of an optical fiber, while constituting a single path for the current. The detectors are operated at 2.5 Kelvin and a constant current below the critical current of the superconductor is applied to the device. The nanoscale cross section gives our photon detectors extremely high sensitivity upon absorption of just a single photon.
Once a single photon is absorbed in the meandering nanowire, superconductivity is locally broken. As a result, the current is directed towards the amplification electronics and creates a voltage pulse. The detection process takes only about 10 ps. After the photon is absorbed, superconductivity recovers in the nanowire within a short time and the SNSPD is ready to detect the next photon.
In applications such as lifetime measurement of photoluminescence and photon correlation measurement, high time resolution of photon detectors is of great importance. The time resolution of single photon detectors is characterized by the full width at half maximum (FWHM) of the variation in the temporal delay from the absorption of a photon to the generation of an output electrical pulse, which is defined as the timing jitter.
For example, in antibunching experiment, the antibunching dip of the correlation function reveals whether there is a single photon emitter. Low timing jitter of the single photon detector will be crucial to achieve a distinct antibunching dip and low g2(0) value.
Single Quantum SNSPDs have demonstrated the lowest timing jitter on the market. This is realized by cryogenic amplification. Cryogenic amplifier enclosed in a housing and mounted to the 40K stage of the cryostat enables the SNSPDs to reach the highest single-to-noise ratio and thus the optimal timing jitter. A typical Single Quantum SNSPD with cryogenic amplifier reaches <15 ps timing jitter.