The Nitrogen-Vacancy (NV) center in diamond is a defect in the diamond lattice where a nitrogen atom replaces a carbon atom and a nearby carbon atom is missing, creating a vacancy. This defect exhibits unique optical and spin properties, including bright and stable fluorescence and long-lived spin coherence, making it a promising candidate for various applications in quantum information science, sensing, and biophysics. The NV center can be optically initialized and read out, and its spin can be manipulated using microwave and radiofrequency fields. Its exceptional sensitivity to magnetic and electric fields, temperature, and strain makes it a valuable tool for nanoscale sensing and imaging.

1. Defect in diamond- NV centers
Defect in diamond- NV centers
Defects in diamond- NV centers
Pankaj Kumar
PEP 680 - Quantum Optics
Final Project

2. Content
● Structure of NV Center
● Energy Level Diagram
● Discuss ODMR
● Properties of NV Center
● Applications of NV Center in physics and biology
● Summary

3. NV Center Structure
Diamond as excellent host
● Bandgap of 5.4eV
● Naturally abundant diamond
has magnetic impurities with
low concentration
Color centers in diamond-
● There are number of possible
defect centers in diamond
● Nitrogen Vacancy center is one of
them
● Nearest-neighbour pair of
substitutional Nitrogen and lattice
vacancy form an NV center

4. How NV centers are prepared ?
● Plasma is generated by applying
high energy to a gas containing
carbon atoms, typically methane, in
a reactor chamber.
● The plasma creates a high-
temperature environment where
the carbon atoms bond together
and begin to form diamond
crystals.
● Nitrogen atoms are introduced into
the plasma to create NV centers in
the growing diamond crystals.
● To create vacancies, a focused electron beam is used to knock
out carbon atoms from specific locations in the diamond crystal
lattice.
● The diamond crystal is then annealed at high temperature and
pressure to remove any defects and stabilize the NV centers in
the crystal lattice. Millimeter-sized single-crystal diamond
grown by chemical vapor deposition

5. Energy-level diagram of NV⁻
● Two triplet states split into three spin sublevels.
Because of the axial symmetry of the NV center, the
two mS = ±1 states are degenerate, and the mS = 0
state is energetically lower
● The energy difference between spin sublevels is D =
2.87 GHz for the ground state and D = 1.42 GHz for the
excited state, where D is the so-called zero-field
splitting (due to the interaction of the unpaired electron spins
with the crystal lattice.)
● The transition rate between mS = 0 and mS = ± 1
sublevels is given by the spin-lattice relaxation time T1
and is a few milliseconds at room temperature
D
D
optical contrast
is only
temporary and
disappears for
long laser
illumination,

6. Energy-level diagram of NV⁻
Degeneracy between mS = 0 and mS =±1
can be lifted by magnetic fields, causing the
mS =±1 levels to shift in opposite direction
due to Zeeman Splitting

7. Optically detected magnetic resonance (ODMR)
Effect of magnetic field on EPR (Electron Paramagnetic Resonance)
● EPR spectrum of the NV center is taken by slowly
sweeping an auxiliary microwave field over the EPR
resonance
● As the microwave frequency is resonant with the EPR
transition, excitation from mS = 0 to mS = ± 1 occurs,
resulting in a reduction of fluorescence intensity.

8. Properties and applications of NV center

9. NV center as Single Photon Emitter
The g^(2) correlation function is a measure of
photon bunching, or the probability that two
photons will be emitted at the same time.

10. ● Brightness: NV centers can emit single photons with high
efficiency, making them bright and suitable for various
applications.
● Narrow linewidth: The emitted photons have a narrow
linewidth, making them useful in spectroscopy and quantum
information processing.
● Long coherence time: The NV center's electronic spin state
has a long coherence time, allowing for the creation of long-
lived quantum states.
● Photostability: NV centers are photostable and can emit
photons for long periods, making them suitable for long-term
experiments.
● Room temperature operation: The NV center's optical
properties are stable at room temperature, allowing for
convenient and cost-effective operation.
Properties of NV center as single photon emitter

11. Scanning NV magnetometer
● Scanning NV magnetometer records the interaction of the NV center with the local magnetic
field
● Reduction of the optical fluorescence when microwaves are applied at the spin resonance
frequency.
● Local magnetic field B can be directly deduced from the frequency difference between the two
resonance peaks, given by 2γB, where γ = 28 MHz/mT is the transduction factor or
gyromagnetic ratio.

12. Virus RNA Sensor Based on Single NV Centers
SARS-CoV-2 Quantum Sensor Based on Nitrogen-Vacancy Centers in Diamond
● Diamond surface was functionalized
with SARS-CoV-2 spike protein
antibodies.
● Functionalized diamond surface
was exposed to SARS-CoV-2 virus
particles & antibodies on the
diamond surface selectively
captured the virus particles.
● Confocal microscope equipped with
a magnetic field coil and microwave
source to measure the magnetic
field signature of the captured virus
particles
● microwave source was used to
manipulate the NV center's
electronic spin state and measure
the resulting changes in
fluorescence intensity, which were
indicative of the magnetic field
signature of the virus particles

13. Virus detection using NV center
● Tiny diamonds are
functionalized by attaching
them to a particular virus
molecule.
● When these functionalized
diamonds are introduced into a
biological sample, the
microwaves used to
stimulate the NV centers
within the diamonds, causing
them to emit light.
● By measuring the emitted light, researchers can detect the
presence of the functionalized diamond and therefore the virus
it is attached to, allowing for the diagnosis of disease.

14. Determine the location based on the magnetic field measurement using NV Center
● The NV center is used as a sensitive
compass to measure the natural magnetic
field where you are located. The magnetic
field can be measured by applying
microwaves to the NV center and
measuring the fluorescence emitted.
● The measured magnetic field is then
cross-referenced with a detailed map of
the Earth's magnetic field,.
● By comparing the measured magnetic field with the map, you can
determine your location on the Earth's surface. This method does
not rely on GPS satellites and can be used in locations where GPS
signals are weak or unavailable.

15. ● Diamond color centers are fluorescent impurities in
diamond.
● The NV center is a color center consisting of a substitutional
nitrogen and a lattice vacancy. The luminescence of the NV
center is extremely robust, with no bleaching or blinking
under normal conditions.
● NV centers can be embedded in nanocrystals down to 4–5
nm in size. Diamond nanocrystals are chemically very robust,
nontoxic, and easily functionalized for biological targeting.
● The unique features of the NV center are its magnetic (spin
triplet) ground state and the dependence of its fluorescence
intensity on the spin orientation. This feature is utilized to add
(magnetic) sensing capabilities.
Summary and Conclusion

16. ● EPR spectra of single NV centers can be detected by
measuring the fluorescence intensity in response to
microwave irradiation (ODMR technique).
● Sensing is performed by monitoring shifts of the EPR
spectra due to external perturbations. Perturbations can
be generated by many means, including magnetic and
electric fields, temperature, spatial orientation, strain,
pressure, and other physical parameters.
● NV centers can be embedded in nanocrystals, sensor
arrays, and scanning probe heads, giving rise to an
extraordinary variety of possible applications.
Summary

17. References
● Nitrogen-Vacancy Centers in Diamond: Nanoscale Sensors for Physics and Biology
https://www.annualreviews.org/doi/pdf/10.1146/annurev-physchem-040513-103659
● SARS-CoV-2 Quantum Sensor Based on Nitrogen-Vacancy Centers in Diamond
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8691455/
● https://qzabre.com/background/
● https://www.youtube.com/watch?v=zAuOurbjHbA
● https://www.youtube.com/watch?v=NsdiFurewZY
● https://www.youtube.com/watch?v=VCT0wDLyvSs
Thank You !

19. Spin States in NV center