Avalanche amplification of a single exciton in a semiconductor nanowire

Interfacing single photons and electrons is a crucial element in sharing quantum information between remote solid-state qubits(1-8). Semiconductor nanowires offer the unique possibility of combining optical quantum dots with avalanche photodiodes, thus enabling the conversion of an incoming single photon into a macroscopic current for efficient electrical detection. Currently, millions of excitation events are required to perform electrical readout of an exciton qubit state(1,6). Here, we demonstrate multiplication of carriers from only a single exciton generated in a quantum dot after tunnelling into a nanowire avalanche photodiode. Owing to the large amplification of both electrons and holes (>10(4)), we reduce by four orders of magnitude the number of excitation events required to electrically detect a single exciton generated in a quantum dot. This work represents a significant step towards achieving single-shot electrical readout and offers a new functionality for on-chip quantum information circuits.