Instabilities in nanodiamond nitrogen-vacancy centre single photon sources under prolonged pulsed excitation

Jack Aspinall,Jason M Smith,Imogen Brown,Sanmi O Adekanye,Amit R Dhawan

doi:10.1364/ome.10.000332

Abstract

Colour centres in nanodiamonds provide robust sources of fluorescence and can be used as triggered sources of single photons at room temperature. However, practical devices require stability over thousands of hours of operation, and the use of strong pulsed optical excitation, placing significant burden on the robustness of the emitters that requires bespoke testing. In this work we report the response of single NV centres in nanodiamonds of 50 nm and 100 nm diameter to accelerated lifetime testing, exciting the defects close to saturation around 1013 times to simulate the minimum operational lifetime of a practical device. For nanodiamonds 50 nm in diameter, observed changes in the fluorescence intensity and lifetime suggest a progressive size reduction as a result of the pulsed laser excitation, combined with the introduction of non-radiative centres on or near the nanodiamond surface which affect the quantum efficiency of the NV centre and ultimately lead to photobleaching of the emission. We find examples of NV centres in 100 nm nanodiamonds for which triggered single photon emission remains stable for over these accelerated lifetime tests, demonstrating their suitability for use in practical devices.

Highlights

Colour centres in diamond show promise for use in a range of quantum photonic devices including single photon sources
Likewise we did not observe a significant increase in g2(0) which would indicate the generation of additional nitrogen vacancy (NV) centres within the nanodiamond [21]
Prior to prolonged pulsed excitation this NV centre had a very long measured lifetime of 90.1 ns suggesting that the NV centre is situated in a small nanodiamond and that the relaxation is primarily radiative

Summary

Introduction

Colour centres in diamond show promise for use in a range of quantum photonic devices including single photon sources. The nitrogen vacancy (NV) centre has received particular interest [5,6] owing to its near-unity quantum efficiency in bulk diamond, high photostability and easy optical pumping. Coupling the emission to an optical microcavity mode [7] can significantly increase the spectral density of the source, but brings with it substantial challenges in the reproducible engineering of robust devices. An NV centre within a nanodiamond experiences a lower photonic density of states than in the bulk [8], leading to a longer radiative lifetime [9,10,11,12] and reduced quantum efficiency [12,13,14]. In the smallest nanodiamonds reduced photostability is observed as a result of additional non-radiative relaxation pathways [15]

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Results

Discussion

Conclusion