Application of NV Centres – Diamond Photonics

    One of the classical application of diamond NV centre is the  diamond Raman lasers [229-234] for generating intense  yellow light (573 nm) which corresponds to the peak  absorption of oxyhaemoglobin for treatment of skin diseases.  The NV-  centre [235] inside diamond lattice consists of  substitutional nitrogen atom with a vacancy present at the  adjacent lattice site. The luminescence from NV-  centre is  very strong and stable. Moreover it can be optically detected  with external magnetic field perturbations. This particular  optically detected magnetic resonance (ODMR) property  made this defect color centre of diamond a very important  candidate for future quantum computers. EPR spectra of  single NV-  centres has been detected by measuring the  fluorescence intensity or ODMR [236-238] in response to  microwave irradiation and, shift in EPR spectra can be  caused by external perturbations of magnetic [239] and  electric fields [240, 241], temperature [242], spatial  orientation, strain [243], pressure, nuclear spin [244] and  other physical parameters. Continuous wave (difference in  frequency is measured at zero field), pulsed probe  experiments (difference in frequency is measured with  Ramsay Fringe) and spin relaxometry (in absence of  microwave the relaxation time is measured under pump  probe excitation) enable different sensing applications of NVcentre in magnetometry. For example spin relaxometry can  be utilised to measure paramagnetic ion concentrations in  solutions. Shallow (<10nm) NV-  centres can be created on  SCD plates by ion bombardment or thin film growth, for  making sensor arrays for microfluidics or wide-field  microscopy. Absolute orientation of nanodiamond spherical  particles can be optically trapped and controlled by  adjustment of light polarisation, using the vector dependence  of the NV center on magnetic field. Cell membranes have  different electric potential across them and that difference in  electric field potential can be detected by single nanodiamond  embedded with NV centre. Nanoscale thermometry can  measure temperatures in living cells by nanodiamond, with  10mK/ Hz sensitivity even at zero Kelvin and upto 200o C,  using the temperature dependence of zero field splitting. NVcentre can also react to change in strain or pressure which  can further be used in high pressure anvil experiments or  M/NEMS. Putting NV-  centre at the tip of a scanning probe  over surfaces can produce images of the surface with  separation as low as 2 nm . Either single  nanodiamond [245] has been attached to AFM cantilever tip  or single crystal diamond has been etched out to fabricate a  tip. Another emerging application of diamond NV-  centre is  nanoscale NMR [246, 247]. 13C isotope naturally embedded  (1.1%) in the diamond lattice has been placed in a higher  magnetic field of hundreds of mT with detection of MHz  Larmour precession of the nuclear spin. 

    Quantum computation [248] has now been realised at room  temperature with long coherence time of diamond NVcentres. At liquid helium temperatures NV-  can also act as  optically addressable solid state spin qubits for quantum  computation [249]. A fiber-based open Fabry-Perot  microcavity incorporating a thick (>10
m) diamond  membrane with NV-  emitters has been developed for cavityquantum electro-dynamics application. Modified microcavity  spectra has been observed in the presence of the membrane  with Purcell enhancement [250] of approximately 20 for  emitters within the diamond in such device [251]. Strong  enhancement was achieved for the zero-phonon line of  nitrogen–vacancy centers of a diamond micro-ring (4.5μm in  diameter and 500 nm wide) coupled to a ridge waveguide  (300 nm wide with spacing between the ring and the  waveguide of about 100 nm). The zero-phonon line is  efficiently coupled from the ring into the waveguide and then  scattered out of plane by the grating outcouplers[252].