Fabrication of single optical centres in diamond—a review
Introduction
Quantum information science (QIS) and quantum information processing (QIP) are two fields that are transforming our understanding of physics and information [1]. Although one of the flagship goals of QIS is the production of a practical and scalable quantum computer, the control of individual quantum systems has led to numerous other applications, some of which are already being commercialized. Along with an understanding of the fundamentals of QIS, there is an urgent need for platforms capable of maintaining and exploiting non-trivial quantum coherence.
One platform that has great potential for solid-state QIP is diamond. Additionally, the control of the quantum properties of diamond that is now possible has led to an explosion of activity in other fields. In particular, diamond colour centres are also being used as sensitive probes of magnetic fields [2], [3], [4], [5] and decohering environments [6], [7]. Strong, photostable room-temperature fluorescence from diamond colour centres coupled with the ability to functionalize diamond surfaces also leads to applications in biomarking and tracking [8], [9], [10]. Here we will discuss why diamond is so promising in the search for room-temperature QIS and recent progress in the optimal fabrication of these colour centres.
Diamond has been the subject of extensive research since antiquity. One of the most intriguing properties of diamond is the variation in colour seen across different stones. Perfect diamond is completely clear and has one of the widest bandgaps of any known material, being transparent from UV to far infra-red. Research carried out over the past few decades has revealed that diamond is host to more than 500 stable optical centres [11], [12], [13]. While these studies have yielded important information about the unique optical properties of diamond, they were initially often aimed at understanding the gemmological properties affected by the optical centres. Hence, there is a critical need to reappraise our understanding of diamond colour centres in light of the requirements of QIS, in particular focusing on centres in important optical bands beyond just the visible.
Diamond has many properties that set it apart from other materials. For quantum applications, we are more interested in diamond colour centres, rather than the diamond per se, although the low spin and possibility of isotopic pure samples giving zero spin bath is also critical, as is the biocompatibility. Diamond is unique as the only material that is host to a large number of room-temperature compatible, photostable colour centres with emission from the UV to the near infra-red. The imperatives for quantum information place new constraints on the properties required of engineered centres. In most cases these extend well beyond those attained or studied in natural diamonds. All colour centres are, by definition, imperfections in the otherwise perfect diamond lattice. These impurities result in new vibrational and electronic states, which give rise to the optical centres [13]. Although, ideally, centres of the same composition should be identical, nearby imperfections and inhomogeneities in the local charge environment causes significant centre-to-centre variability.
When considering optical applications involving diamond colour centres, there is some freedom and necessity to identify the best centre for a given application. In particular, for single-photon sources, we ideally want our source to be stable, bright (temporally narrow) and of narrow width (spectrally narrow), with the temporal and spectral linewidths connected by the transform limit. The requirement of narrow spectral width is important in quantum communication to ensure that the signal can be easily filtered from background signals, especially during daylight operation. For magnetometry, we require single-spin readout and efficient initialization of the centre. Biomarking usually only requires photostability, biocompatibility, high brightness and emission in a non-absorbing band for the biological system being observed. We should not expect that a ‘one size fits all’ approach is required or desirable. Different colour centres can be found for all these tasks, and in general optimization will need to be performed with regards to metrics appropriate to the tasks.
For the purposes of this review, we concentrate on the generation of single photons as our principal metric. This focus is not because all applications require the use of single photons, but because the ability to reliably engineer single indistinguishable photons is fundamental to many applications and typifies the levels of perfection required in all practical quantum applications. Our main focus here is to review the formation of nitrogen-vacancy (NV) colour centres in diamond as these are the best understood and most used diamond colour centres for all the applications mentioned above. Although other centres are already showing more desirable properties for certain applications, it is likely that NV will be the driver of quantum diamond research for some time to come. We discuss NV (ensembles and singles) in bulk single crystal and nanocrystal diamond formed via implantation and activation routes. We also discuss and compare some other centres that are promising for QIS applications.
Section snippets
The NV centre
The most widely studied optical centre in diamond is the nitrogen vacancy (NV) [14], [15], [16] centre, which consists of a substitutional N atom next to a vacancy in a diamond lattice as shown in Fig. 1 [17]. It occurs in two identified charge states, neutral (NV0) and singly negatively charged (NV−). Optically, the two charge states are identified by their zero phonon luminescence lines (ZPL) at 575 and 637 nm, respectively [18], [19]. Fig. 2 shows an indicative low temperature
NV production by ion implantation
NV centres are most efficiently created in type 1b synthetic diamond through electron irradiation and subsequent annealing at ∼900 °C in vacuum [14]. This approach relies, however, on N that is already present in the diamond matrix, which is of the order of 100 ppm in most type 1b diamonds. Such high N concentrations are excellent for creating large ensembles of NV but do not allow for control down to the single optical centre level. Further, since type Ib diamond contains other defects in
Optimization of NV production
To create the perfect single NV centre, several critical variables including ion energy, fluence, annealing temperature, annealing time, annealing environment and implantation temperature need to be optimized. Although some attempts [46] have been made at this optimization by varying the implanted species, the optimal recipe is still elusive and remains an important milestone in developing viable quantum diamond technologies. Significantly, the availability of reproducible synthetic diamonds
NV production by CVD techniques
Other areas of progress have included incorporation of NV centres during growth of CVD nanodiamonds. As mentioned earlier, nanodiamonds are especially suited to biological, sensing and magnetometry applications. Key advantages of nanodiamond over other competing platforms include biocompatibility [49] of diamond and the relative ease with which nanodiamond surfaces can be functionalized [50].
Much of the previous work on NV in nanodiamonds has been performed with detonation samples, but it
Other optical centres in diamond
A drawback for using the NV− is that, at room temperature, its intensity is dominated by a large phonon side band that extends from 600 to 800 nm. With a small Debye–Waller factor of 5% [55], the zero phonon line constitutes only a small fraction of the total luminescence and is not bright enough on its own for many practical applications. As a consequence, many applications involving the NV− need to use the entire emission spectrum. The research focus has thus widened in search of more
Summary of candidate systems
The discussion above has identified the NE8, NV, SiV and Cr-related centres as the main optical centres in diamond that have been considered for applications in QIP and QIS. Because of the choice available in finding the correct centre for the correct application, in this section we summarise some of the imperatives for important applications, and how the candidate centres match up. As shown in Table 1, the four applications we consider are biomarking, quantum computing, magnetometry and
Conclusion
From fundamental and gemological properties, diamond colour centres have been proposed as candidates for quantum information processing (QIP), and from there are rapidly finding applications in other emerging areas of technology such as magnetometry and cellular biomarking. Until recently, the nitrogen-vacancy (NV) has been the only colour centre available for quantum applications: with the realization of controlled fabrication of more desirable centres, this is no longer the case. The recent
Acknowledgements
J.O.O, I.A and A.S. would like to acknowledge financial support from the ARC Nanotechnology Network and Australian Research Network for Advanced Materials. J.O.O. would also like to thank Department of Innovation, Industry, Science and Research (DIISR) for funding (CG090191). A.D.G. is the recipient of an Australian Research Council Queen Elizabeth II Fellowship (DP0880466). A.D.G, A.S. and S.P. acknowledge ARC linkage grant (LP0775022).
References (80)
- et al.
Diamond Relat. Mater.
(2006) - et al.
Biophys. J.
(2007) - et al.
J. Lumin.
(1987) - et al.
Mater. Today
(2008) - et al.
Diamond Relat. Mater.
(2003) - et al.
Diamond Relat. Mater.
(2007) - et al.
Diamond Relat. Mater.
(2009) - et al.
Science
(2003) - et al.
Quantum Computation and Quantum Information
(2000) - et al.
Nature
(2008)
Nature
Nature Materials
Phys. Rev. B
Nanotechnology
Phys. Rev. Lett.
Proc. Natl. Acad. Sci. USA
The Properties of Diamond
Optical Properties of Diamond
Proc. R. Soc. London Ser. A
J. Phys. C: Solid State Phys.
Phys. Rev. B
Opt. Exp.
Phys. Rev. B
Appl. Phys. B
J. Phys. C
Science
New J. Phys.
Phys. J. D
J. Phys. C
Nature Photonics
Science
Science
Science
Science
Phys. Rev. B
Appl. Phys. A
J. Vac. Sci. Technol. B
Appl. Phys. Lett.
Phys. Rev. A
Cited by (69)
Diamond nitrogen-vacancy center charge state ratio determination at a given sample point
2022, Journal of LuminescenceCitation Excerpt :In recent years, research on the excellent optical properties [1] of diamond and its applications in optics, photonics, and quantum technology [2–4] has grown extremely rapidly.
High-pressure synthesis and characterization of diamond from europium containing systems
2021, CarbonCitation Excerpt :The search involves the main methods of diamond synthesis using high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) technologies. In the past decade, considerable attention has been paid to the manufacturing of diamonds with color centers, which are proving to be a promising system for the emerging quantum applications, such as solid-state single photon sources [1,2], nanoscale electromagnetic field sensing [3,4], biolabelling [5,6], quantum optics [7], and quantum information processing [8,9]. Impressive progress has been achieved recently in the fabrication and utilization of color centers in diamond based on various impurities, including nitrogen [10,11], silicon [12,13], chromium [14] germanium [15,16], tin [17,18] and lead [19].
The effect of step-wise surface nitrogen doping in MPECVD grown polycrystalline diamonds
2020, Materials Science and Engineering: BCitation Excerpt :The NV0 centres at 575 nm is observed in sample P2–P6, while the 637 nm peak which may have originated from the NV− centres was only observed in sample P6. The broad nature of the peaks at 575 nm and 637 nm might have resulted from the presence of other defects in the material [23]. For magnetometry applications, the FWHM of the peaks are irrelevant, because emissions in the red spectra range are only desired.
Increased nitrogen-vacancy centre creation yield in diamond through electron beam irradiation at high temperature
2019, CarbonCitation Excerpt :The temperature of 740 °C is the highest that can be reliably maintained in our custom built high-temperature irradiation chamber. This temperature is below the optimum temperatures to create NV centres with conventional annealing [23,28,29], which is between 800 °C and 900 °C. Nonetheless, it is sufficient to cause significant vacancy diffusion during the annealing time used here [20,23].
Quantum-optical characterization of single-photon emitters created by MeV proton irradiation of HPHT diamond nanocrystals
2018, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsNitrogen Substitutions Aggregation and Clustering in Diamonds as Revealed by High-Field Electron Paramagnetic Resonance
2024, Journal of the American Chemical Society