Superconducting nanowire single-photon detectors (SNSPDs) have made a tremendous impact in recent years on a diverse array of research fields, by enabling researchers to access near unity system detection efficiency, fast count rates, and precise timing through commercial availability. Originally focused on discrete devices operating between the Near IR to Telecom wavelength regimes, the industry is expanding to the visible and mid-infrared domains while incorporating multi-detector structures and photon number resolving techniques. This talk will discuss developments at Quantum Opus in these areas as well as emerging applications in new fields for SNSPDs.
Confocal fluorescence microscopy is a common imaging technique for biomedical applications such as tumor characterization, precision resections, etc... However, the imaging process is limited by photo bleaching of samples and optical scattering limits imposed by wavelength limitations of traditionally used detection technologies. Here we show that by leveraging the high detection efficiency and large spectral range of superconducting nanowire single-photon detectors, it is possible to image deeper into tissue with a significant reduction in laser excitation power compared to the same technique using silicon photo-multipliers.
Many quantum applications will benefit significantly from photon number resolving detection. However, photon number resolving detectors have been largely experimental devices implemented in laboratory settings. Recent advances in superconducting nanowire device fabrication and readout techniques have enabled the implementation of photon number resolution in widely deployable commercial single-photon detection systems. We will discuss progress in implementing photon number resolved detection with commercially produced superconducting nanowire single photon detectors via spatial multiplexing of independently instrumented detector elements and photon number dependent rise-time changes in single-element nanowire devices.
We present a single-flux-quantum (SFQ) based digital correlator to trace independent signals from two superconducting single-photon detectors (SSPDs) triggering its inputs. In our design two SSPDs are magnetically coupled to inputs of a readout system where direct current (DC)-to-SFQ converters are used to convert transient SSPD output pulses, triggered by detection of single-photon events, to SFQ pulses. The coincidence verification of SFQ pulses, generated by the two DC-to-SFQ converters, is performed with a modified SFQ coincidence buffer. The coincidence buffer is designed to generate an SFQ output pulse only when its both inputs are triggered simultaneously, or within a preset margin time. The output of the coincidence buffer is connected via, this time, an SFQ-to-DC converter, to a pulse counter operated at room temperature. We performed extensive simulations of both the SSPD equivalent circuit and correlator redout elements for the proposed coincidence scheme, using a WRSpice and PSCAN2 simulation platforms that are specifically designated to model Josephson junctions and widely used to simulate operation of the SFQ circuitry. In particular, we investigated our coincidence correlator scheme for measurements of the second-order correlation function, used to demonstrate the antibunching effect in the single-photon detection of non-classical light.
High count rates (10’s to 100’s to 1000’s of MHz) and very precise timing (10’s of ps FWHM jitter or less) are two of the features which make superconducting nanowire single-photon detectors a revolutionary experimental and engineering tool. Both of these performance metrics also depend on the device bias current level. The maximum count rate is determined by how soon after detection the bias current recharges to the level required for maximum efficiency, while the timing jitter decreases with increased bias current even beyond level which yields maximum efficiency. For a device with a strong detection efficiency plateau, the bias current recharge can push the device into the regime of maximum efficiency at a fractional level of the current required to achieve the desired jitter. Here, we present an experimental analysis of this effect. These results should enable users to consider the trade-off between count rate and timing jitter for various experiments.
An optical correlation receiver is described that provides ultra-precise distance and/or time/pulsewidth measurements even for weak (single photons) and short (femtosecond) optical signals. A new type of optical correlation receiver uses a fourth-order (intensity) interferometer to provide micron distance measurements even for weak (single photons) and short (femtosecond) optical signals. The optical correlator uses a low-noise-integrating detector that can resolve photon number. The correlation (range as a function of path delay) is calculated from the variance of the photon number of the difference of the optical signals on the two detectors. Our preliminary proof-of principle data (using a short-pulse diode laser transmitter) demonstrates tens of microns precision.
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