Quantum computing experiments are moving into a new realm of increasing size and complexity, with the short-term goal of demonstrating an advantage over classical computers. Boson sampling is a promising platform for such a goal, however, the number of involved single photons was up to five so far, limiting these small-scale implementations to a proof-of-principle stage. Here, we develop solidstate sources of highly efficient, pure and indistinguishable single photons, and 3D integration of ultra-low-loss optical circuits. We perform an experiment with 20 single photons fed into a 60-mode interferometer, and, in its output, sample over Hilbert spaces with a size of 10 14 -over ten orders of magnitude larger than all previous experiments. The results are validated against distinguishable samplers and uniform samplers with a confidence level of 99.9%.

Boson sampling is a problem strongly believed to be intractable for classical computers, but can be naturally solved on a specialized photonic quantum simulator. Here, we implement the first time-bin-encoded boson sampling using a highly indistinguishable (∼94%) single-photon source based on a single quantum-dot-micropillar device. The protocol requires only one single-photon source, two detectors, and a loop-based interferometer for an arbitrary number of photons. The single-photon pulse train is time-bin encoded and deterministically injected into an electrically programmable multimode network. The observed three- and four-photon boson sampling rates are 18.8 and 0.2 Hz, respectively, which are more than 100 times faster than previous experiments based on parametric down-conversion.

The rapid development of superconducting nanowire single-photon detectors (SNSPDs) over the past decade has led to numerous advances in quantum information technology. The record for the best system detection efficiency (SDE) at an incident photon wavelength of 1550 nm is 93%. This performance was attained from an SNSPD made of amorphous WSi; such SNSPDs are usually operated at sub-Kelvin temperatures. In this study, we fabricated an SNSPD using polycrystalline NbN. Its SDE is 90.2% at 2.1 K for incident photons with a 1550-nm wavelength, and this temperature is accessible with a compact cryocooler. The SDE saturated at 92.1% when the temperature was lowered to 1.8 K. We expect the results lighten the practical and high performance SNSPD to quantum information and other high-end applications. Main textA single-photon detector with high detection efficiency is the key enabling technology for quantum information and various applications, including the test of loophole-free Bell inequality violation 1 , quantum teleportation 2 , measurement-device-independent quantum key distribution 3 , and linear optical quantum computation 4 . Superconducting single-photon detectors outperform their semiconducting counterparts in terms of not only detection efficiency but also dark count rate, timing jitter, and counting rate 5 . In the case of the telecommunication wavelength (1550 nm), the highest system detection efficiency (SDE) greater than 90% has been reported for two types of detectors. One is a transition edge sensor (TES) made of tungsten (W), with an SDE of 95% 6 ; the other is a superconducting nanowire single-photon detector (SNSPD) made of amorphous WSi, with an SDE of 93% 7 . However, because of the low superconducting transition temperature of W and WSi, the requirement of sub-Kelvin cryogenics represents a burden for practical applications. Many studies focused on SNSPDs fabricated using different materials and aiming to obtain a high SDE at higher operating temperatures have been reported [8][9][10][11] ; however, none of these attempts has been successful. Regarding another important parameter, timing jitter, a WSi SNSPD and a W TES have values of approximately 150 ps and 50-100 ns, respectively, which limits their use in