Quantum Optics in Diamonds

Scientific results:

1. We have researched various coloring centers in diamonds and oxide (nitride or fluoride) nanomaterials that are promising for fluorescence thermometry of biological objects, as well as for registering magnetic and electric fields at the nanometer scale.
2. A methodology has been proposed and tested for doping diamonds with impurities of silicon and phosphorus. It was demonstrated the value of the deviation of NV^-/NV⁰ in a sample that is strongly doped with phosphorus, in comparison to a sample without phosphorus impurities, rises by a factor of over 25. This has a high importance for a whole range of practical applications, for instance, to increase optically detected magnetic resonance (ODMR) signal and (or) to excite negative NV^-centers with optical radiation having a higher wavelength.
3. Using plasma immersion ion implantation into an Ib diamond, we have produced a dense shallow layer of NV centers (laying at a depth not exceeding 3.6 nm) that is optimal for use for measuring magnetic fields at the nanoscale.
4. We have determined temperature dependencies of the parameters of the spectra of photoluminescence of such coloring centers in a diamond as: SiV-, GeV- and SnV-centers that can be excited in a window of biological transparency. It was demonstrated that they can be used for high-precision measurement of temperature.
5. Our researchers have measured the autocorrelation function of the radiation field of individual coloring centers in a diamond and registered the fluorescence of individual centers using narrowed fibers. We have conducted a numerical modeling that demonstrated the possibility of realizing strong coupling between an individual coloring center and a mode of narrowed am optical fiber.
6. We have created a quantum temperature sensor with a resolution of 20 mK/Hz to register two-dimensional thermal images with a spectral resolution of 25 µm. It does not require microwave excitation and preserves its precision and resolution in the temperature range that is significant for obtaining thermal images in vivo.
7. A new reusable luminescence temperature sensor with a sensitivity of 5.4 ms × K^-1 for attenuation time of luminescence in the range form 270 to 370 К. Experiments demonstrated that it is stable against the negative impact of oxygen and UV radiation. The strong luminescence of the sensor is excited by radiation in the range of wavelengths  from 280 to 425 nm.
8. We have implemented the effect of coherent population trapping in ensembles of NV-centers in a diamond under conditions of anti-crossing of levels of the main state when a strong magnetic field is applied.
9. The Laboratory has proposed and tested a method for controlling the angle between the axes of a diamond crystal with NV centers and an external magnetic field on the basis of cross-relaxation resonances. We have developed a modified protocol for measuring magnetic fields without the use of microwave radiation.
10. Using gel technologies, we synthesized YVO₄ upconversion nanoparticles: Yb, Er. The potential of the use of nanoparticles as upconversion probes in problems of optogenetics and bioimaging has been demonstrated in experiments involving Burgundy snails, in which we studied the distribution of nanoparticles across different organs of an animal after an injection.
11. For the first time we have obtained data that characterize the rate of natural removal of injected YVO₄: Yb, Er upconversion particles from the organism of a Burgundy snail. The obtained results indicate the low toxicity of nanoparticles and opens wide possibilities of their application as minimally invasive nano-sized probes in the fluorescence spectroscopy of biological objects in vivo.
12. We have synthesized YLiF₄: Er, Yb nanoparticles, whose upconversion luminescence reacts to an electric field. It was demonstrated that these biocompatible nanoparticles can be used for probing electric fields in various biocompatible systems.
13. YLiF₄: Er-Yb upconversion nanoparticles have been successfully attached to the RNA sequence of the COVID-19 coronavirus and model complementary RNA through an intermediate protein, biotin. These experiments provide wide possibilities for the creation of various biological test systems
14. In samples of diamonds with a germanium impurity after excitation of samples with a pulse of a femtosecond laser at a wavelength of 257 nm we found visible (with a naked eye) phosphorescence in the 480–530 nm spectral region. It has been established that the characteristic time in the dynamics of the drop of phosphorescence in diamonds with implanted germanium exceeds minutes. We implemented the effect of electromagnetically-induced transparency in ensembles of GeV centers in a diamond.
15. Boron-doped nanodiamonds have been used to locally heat the environment. These experiments are interesting for the development of hyperthermia methods and thermal ablation therapy. Moreover, we demonstrated the possibility of changing the temperature in the biological range with a sensitivity of 250 mK/√Hz. Thus we created promising dual-use bioprobes that can also be used in quantum probing, including magnetic probing.
16. We have found the temperature memory  effect in a thin material based on β-diketonate europium(III) complexes. The essence of the effect is the capability of a film to be in various states at the same temperature. The obtained results open wide prospects for the creation of luminescent photonic materials of a new type with a memory function. 

Implementation of research results:

• The Laboratory has created an experimental bench based on a confocal microscope and a spectrometer that allows to register the luminescence spectrum from a specific region of a research object (diamonds, oxides, fluorides etc.) with submicron resolution in a broad temperature range (from 4 to 400 K) when excited by a diode laser (525 nm, 532 nm, 635 nm and 980 nm). Using this bench, it is possible to measure the correlation characteristics of the radiation of samples with submicron precision with the use of detectors of single photons and beam splitters.
• As part of the customer problem of producing nano-sized diamonds with  various coloring centers, we manufactured a diamond anvil with the working cell made of a material called Inconel. It allows to create pressure of more than 60 GPa and withstand temperatures of 500 ^оС and higher.
• We are currently conducting negotiations with industrial partners: «Research and Manufacturing Association «QuantTech» Ltd (Moscow, Zelenograd) and «Metrika–B» Ltd (Kazan) on collaborative development and implementation of the results of the research. The industrial partners became interested the possibility of using nanosensors designed by our Laboratory in their products. In particular, our developments could be used in terminals providing technological vision and image recognition.

Education and retraining of personnel:

Employees of the Laboratory have developed two new lecture courses for Kazan Federal University (KFU) and two blocks of laboratory classes for Innopolis University (Republic of Tatarstan). One textbook has been published. Two scientific schools for young researchers have been conducted, as well as an internship of one postgraduate student from Turkey. Under the supervision of employees of the Laboratory 4 master’s degree theses have been defended. Three employees of the Laboratory have defended Candidate of Sciences in Physics and Mathematics dissertations. 

Organizational and structural changes: 

The Laboratory of Quantum Optics in Diamonds has become the basis of the Center of Quantum Optical and Spin Technologies of the Kazan Scientific Center of the Russian Academy of Sconces.

Collaborations:

• Texas A&M University (USA): joint research and publications.
• King Abdulaziz City for Science and Technology (Saudi Arabia): joint experiments and research, internships of young researchers, joint publications.
• Gebze Technical University (Turkey): joint research, internships of young researchers and postgraduates, grants and publications.
• Scientific and Practical Materials Research Center of the National Academy of Sciences of Belarus (Belarus): joint research, grants and publications.
• Institute for Nuclear Problems of Belarusian State University (Belarus): joint research, grants and publications.
• Institute of Applied Physics of the Russian Academy of Sconces (Russia): joint experiments and research, grants and publications.
• Moscow State University (Russia): joint research and scientific events.