Single-photon Emission From Colour Centres In Diamond: Study Of Nickel-related Defects And Applications

In the foundation and development of quantum physics, single-photon sources play an important role and always attract researchers' interest. As a non-classical light source, single-photon sources are used to demonstrate the principle of quantum mechanics, illustrating the quantum strangeness, such as wave-particle duality of light. On the other hand, techniques of quantum information based on the principle of quantum mechanics need single-photon sources to realize quantum cryptography and quantum computation. Especially, in quantum cryptography it encodes the secret key information on a sequence of single photons. Any measurement will unavoidably modify the eigenstate of the single quantum system, hence an eavesdropper cannot gather information about the secret key without being revealed, provided that the pulses used in transmission do not contain two or more photons.Up to now, many single-photon sources have been developed such as single atoms and ions in a trap, single molecules, single quantum dots, and single colour centres in diamond. However, these single-photon sources either require a complex experimental setup, or are not photostable at room temperature. Nitrogen-vacancy (N-V) colour centres in diamond appear to be perfectly photostable emitters even at room temperature. But the N-V center emits a broad spectrum (FWHM～100nm) at room temperature, partly superimposed to the one of daylight, which is a strong limitation for practical quantum cryptography in the open air. In this thesis, a new kind of diamond-based single-photon source is developed. It is based on the photoluminescence from single nickel-nitrogen related NE8 colour centres in diamond. The photoluminescence from a single NE8 centre has several striking features compared to N-V centres. It has a narrow emission band about 2 nm in the near infrared regime (around 790 nm), which enables an efficient narrow bandpass filter to pick up the useful single-photon while removing the stray light. It has a short emission lifetime of 2 ns, which will support high-repetition-rate quantum key generation. The photons emitted are linearly polarized, which makes polarization encoding in quantum cryptography much easier. The stable photoluminescence at room temperature ensures the reliability of the single-photon source in the applications. And the NE8 colour centres can be fabricated by chemical vapor deposition (CVD) method, which opens many possibilities for the development of highly efficient diamond-based single-photon sources. With the CVD-grown diamond nanocrystal, the collection efficiency of the single-photon source based on NE8 colour centres is evidently improved. The photoluminescence excitation spectroscopy of NE8 colour centres is studied for the first time at single emitter level. The optimal excitation wavelength for the NE8 centres is found to be at 765 nm. With a pulsed excitation at 765 nm, a triggered single-photon source based on the NE8 colour centres in CVD-grown diamond nanocrystal is built. This single-photon source delivers 30 kcts/s single-photon pulses at an excitation repetition rate of 20 MHz. The whole system is compact, efficient, and applicable to the quantum cryptography in the real condition.In this thesis, the application of single-photon sources in demonstration of fundamentals of quantum physics is also studied. With a triggered single-photon source based on N-V colour centres is used to illustrate the quantum feature of the light. Single-photon wave-front splitting interference with Fresnel's biprism shows the wave-particle duality of light. On one hand, the gradual build-up of the interference pattern is recorded by a charge coupled device (CCD) camera to show the wave-like behavior of the single photons. On the other hand, an antibunching effect is clearly observed for single-photon pulses to illustrate the particle-like behaviour of the single photons. Based on the same N-V single-photon source, Wheeler's delayed-choice gedanken experiment is demonstrated with single photons. The experiment results confirm that the behaviour of the photons in the interferometer depends on the choice of the observable that is measured, even when that choice is made at a position and a time such that it is separated from the entrance of the photons into the interferometer by a space-like interval. It is for the first time that Wheeler's thought experiment is faithfully realized. With the true single-photon source, it is shown that the quantum mechanics triumphs common sense yet again.