Ping Xu

The Quantum Zeno effect inhibits the evolution of quantum states through repeated yet weak measurements, thereby significantly enhancing the detection probability of interaction-free measurement (IFM). This fundamental mechanism facilitates high-efficiency counterfactual quantum communication that information delivery without particle transmission through the channel. Regrettably, the original protocol left the weak trace of particles in the channel; fortunately, an upgraded counterfactual communication protocol eliminates this issue by modifying the structure unit according to two-state vector formalism~(TSVF). However, no study has realized the application of the quantum Zeno effect in weak-trace-free counterfactual communication to achieve efficient information transmission. In this paper, we experimentally demonstrate weak-trace-free counterfactual communication via the quantum Zeno effect on a nanophotonic chip, achieving a transmission probability of 74.2 ± 1.6% for bit 0 and 85.1 ± 1.3% for bit 1. Furthermore, we successfully transmit our Quanta group's logo through counterfactual communication implemented on the chip.

Quantum key distribution (QKD) has been proved to be information-theoretically secure in theory. In practice, the self-differencing avalanche photodiode detectors (SD-APDs) are commonly used in high-speed QKD systems. However, we experimentally show that the SD- APD under test can be successfully hacked by the pulse-illumination attack. This attack might compromise the security of a high-speed QKD system with SD-APDs. This study also indicates that the best-practice criteria for practical security of SD-APDs might take the threat of pulse-illumination attack into account.