Efficient Bell state analyzer for time-bin qubits with fast-recovery WSi superconducting single photon detectors
Raju Valivarthi, I. Lucio-Martinez, Allison Rubenok, P. Chan, Francesco Marsili, Varun Boehm Verma, Matthew D. Shaw, J. A. Stern, Joshua A. Slater, Daniel Oblak, S. W. Nam, Wolfgang Tittel
We experimentally demonstrate a high-efficiency Bell state measurement for time-bin qubits that employs two superconducting nanowire single-photon detectors with short dead-times, allowing projections onto two Bell states, |ψ⁻〉 and |ψ⁺〉. Compared to previous implementations for time-bin qubits, this yields an increase in the efficiency of Bell state analysis by a factor of thirty.
We experimentally demonstrate a high-efficiency Bell state measurement for time-bin qubits that employs two superconducting nanowire single-photon detectors with short dead-times, allowing projections onto two Bell states, |ψ⁻〉 and |ψ⁺〉. Compared to previous implementations for time-bin qubits, this yields an increase in the efficiency of Bell state analysis by a factor of thirty.
One of the key properties of single-photon detectors is their recovery time, i.e. the time required for the detector to recover its nominal efficiency. In the case of superconducting nanowire single-photon detectors (SNSPDs), which can feature extremely short recovery times in free-running mode, a precise characterization of this recovery time and its time dynamics is essential for many quantum optics or quantum communication experiments. We introduce a fast and simple method to characterize precisely the recovery time of SNSPDs. It provides full information about the recovery of the efficiency in time for a single or several consecutive detections. We also show how the method can be used to gain insight into the behavior of the bias current inside the nanowire after a detection, which allows predicting the behavior of the detector and its efficiency in any practical experiment using these detectors.
One of the key properties of single-photon detectors is their recovery time, i.e., the time required for the detector to recover its nominal efficiency. In the case of superconducting nanowire single-photon detectors (SNSPDs), which can feature extremely short recovery times in free-running mode, a precise characterization of this recovery time and its time dynamics is essential for many quantum optics or quantum communication experiments. We introduce a fast and simple method to characterize precisely the recovery time of SNSPDs. It provides full information about the recovery of the efficiency in time for a single or several consecutive detections. We also show how the method can be used to gain insight into the behavior of the bias current inside the nanowire after a detection, which allows predicting the behavior of the detector and its efficiency in any practical experiment using these detectors.
Superconducting nanowire single-photon detectors (SNSPDs) are an attractive technology for applications which benefit from high-count rate photon detection such as quantum communication protocols, photon-starved classical communications, metrology of single-emitters, and photonic quantum computing. However, at high-count rates, a significant portion of photons may be incident during recovery intervals following prior detection events. After detection, the device efficiency recovers over nanoseconds to tens of nanoseconds before reaching a steadystate value. Therefore, for a given SNSPD bias current setpoint, a single efficiency and recovery time specification may not be sufficient to characterize the performance of a device at high count rates. Here we present and experimentally validate a model of the recovery time as a function of bias current for any given system efficiency. These results may be used to improve analysis of measurements performed using SNSPDs operating in the high count rate regime.
With recent advances in quantum technologies for applications such as communication, cryptography, computing, metrology and sensing, the performance and scalability of single-photon detection as a vital key component is becoming increasingly important. At the same time, ongoing efforts in the development of high-performance photonic integrated circuits (PIC) benefit the miniaturization and scalability of these quantum technologies. Waveguide-integrated superconducting nanowire single-photon detectors (WI-SNSPDs) allow to combine excellent performance metrics, such as high detection efficiency, low dark-count rates and low timing jitter below 20 ps with the scalability and functionality that PIC platforms such as Si3N4 provide. We have previously demonstrated broadband efficient single-photon detection with a single device over a range from visible to mid-infrared wavelengths and ultra-fast detector recovery times allowing for up to GHz count rates. Here, we present the utilization of WI-SNSPDs for discrete-variable quantum cryptography receivers with the complete photonic circuitry embedded together with the single-photon detectors on a single silicon chip, where the secret-key rates greatly benefit from the short recovery times of the detectors especially for metropolitan distances. We further realize a fully packaged 64 channel WI-SNSPD matrix for use in a wavelengthdivision multiplexed QKD setup.
Superconducting nanowires enable the operation of outstanding single-photon detectors, which are required particularly for quantum information and weak-light measurement applications. However, the trade-off between detection speed and efficiency, which is related to the filling factors of superconducting nanowires, is still a challenge. Here, we propose a fast, efficient single-photon detector fabricated by integrating ultralow-filling-factor meandered superconducting nanowires atop a photonic crystal (PhC) resonator. This unique structure enables a fast photon response due to the low kinetic inductance of the short nanowires and ensures efficient photon absorption due to the resonant effect of the PhC structure. The proposed detector has a filling factor of only ∼12% while maintaining a high maximum absorption in our simulation of 90%. The fabricated device exhibits a maximum system detection efficiency of 60%, a maximum count rate of ∼80 MHz, and a recovery time of only ∼12 ns, which is three times faster than that of the conventional meandered structure at the same sensing diameter (18 μm). This work helps advance the movement toward high-efficiency, high-speed single-photon detectors and promotes their future application in quantum communication and imaging.
Superconducting Nanowire Single-Photon Detectors (SNSPDs) are well known for their single-photon sensitivity, low jitter, and high efficiency. Their dynamic range is generally limited either to zero or one (no photon, or a photon absorbed), and if single-photon sensitivity is needed in the vicinity of a strong light pulse, a counteraction like gating needs to be deployed. In such a scheme, we aim at the fastest possible transition time which is helpful to increase sensitivity, to temporally filter any strong laser excitation, and further suppress dark counts. Here, we present our work of time-gated SNSPDs where the detection current can be switched on- and off to allow the detector not to be saturated. We start our discussion by introducing the simplest gating scheme based on a square wave resulting in switch-off-switching transition times of ≈50ns. Then we present a new method to improve this relatively slow transition time to the sub-nanosecond range. Latest measurements of efficiency recovery and jitter are presented, and we show that a 1550nm light pulse with 100’000 photons within 500ns, applied right before the on-transition of the SNSPD, does not yet affect the performance in the on-state.