Ultrabright and efficient single-photon generation based on nitrogen-vacancy centres in nanodiamonds on a solid immersion lens

Single photons are fundamental elements for quantum information technologies such as quantum cryptography, quantum information storage and optical quantum computing. Colour centres in diamond have proven to be stable single-photon sources and thus essential components for reliable and integrated quantum information technology. A key requirement for such applications is a large photon flux and a high efficiency. Paying tribute to various attempts to maximize the single-photon flux, we show that collection efficiencies of photons from colour centres can be increased with a rather simple experimental setup. To do so, we spin-coated nanodiamonds containing single nitrogen-vacancy (N-V) colour centres on the flat surface of a ZrO₂ solid immersion lens. We found stable single-photon count rates of up to 853 kcts s^{− 1} at saturation under continuous wave excitation while having access to more than 100 defect centres with count rates from 400 to 500 kcts s^{− 1}. For a blinking defect centre, we found count rates up to 2.4 Mcts s^{− 1} for time intervals of several tens of seconds. It seems to be a general feature that very high rates are accompanied by blinking behaviour. The overall collection efficiency of our setup of up to 4.2% is the highest yet reported for N-V defect centres in diamond. Under pulsed excitation of a stable emitter of 10 MHz, 2.2% of all pulses caused a click on the detector adding to 221 kcts s^{− 1} thus, opening the way towards diamond-based on-demand single-photon sources for quantum applications.