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May 1, 2021
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Russian technologies of the future

Scientists from the Center for Quantum Technologies of the Faculty of Physics of Moscow State University are working on the creation of single-photon emitters.

At the moment, the research phase of the work is being completed, and by the end of the year, prototypes of the devices will be released. In the future, such emitters will help make optical circuits used in quantum computers and quantum cryptography systems more compact and more economical to manufacture. In addition, the emitter solves the important problem of equipment import substitution.

Single-photon light sources (single-photon emitters) are sources that emit light in the form of individual photons. They are one of the key elements in many problems in the field of quantum informatics, including quantum computing and quantum cryptography. Such devices are nanodiamonds with color centers deposited on the surface of a photonic crystal that supports the propagation of surface electromagnetic waves called Bloch surface waves (BSWs). Nanodiamonds are coated with a polymer layer, and then waveguide structures are created in the region of nanodiamonds with a single color center using the method of two-photon laser lithography.

Thus, the method of integrating single-photon sources into a waveguide is implemented by combining two technologies within one experimental setup: the technology of scanning the luminescence signal and searching for nanodiamonds emitting in a single-photon mode, followed by laser lithography technology to create waveguides over the found nanodiamonds.

“The key difference of this development from other single-photon emitters is the use of Bloch surface waves. This is a type of electromagnetic waves that propagate along the surface of a photonic crystal – a structure consisting of periodically alternating layers of dielectric materials, ”said Andrey Fedyanin, head of the nanophotonics sector of the Center for Quantum Technologies of Moscow State University, Doctor of Physical and Mathematical Sciences, Professor of the Russian Academy of Sciences, Vice-Rector of Moscow State University.

At the moment, BPWs are being actively investigated for use in integrated optical circuits due to their unique characteristics. For example, the dispersion law of the BPW is determined by the parameters of the photonic crystal (materials and layer thicknesses) and it is possible to achieve the existence of the BPW in any given region of the spectrum. In addition, the use of exclusively dielectric materials leads to a long propagation length of the BPW in the visible range of radiation, which is especially important for the integration of single-photon sources emitting in this range.

“The main advantage of solid-state single-photon sources based on nanodiamonds being developed at the Moscow State University’s CCT is their integration with waveguide structures. Thus, single photons emitted by a source can immediately enter integrated-optical circuits for quantum computing without the need for bulk optical elements. This significantly improves the convenience of working with single-photon sources, ”notes Kirill Safronov, a researcher at the Moscow State University’s CCT. – It is also important to note the more convenient and cost-effective manufacture of such devices, which provides the use of inexpensive technology of two-photon laser lithography. Thanks to it, it is possible to create complex compact integrated-optical structures in a single lithography cycle without increasing the cost of the final device. In addition, potentially single-photon sources based on nanodiamonds can be replaced by any other nanoscale solid-state sources without significantly changing the procedure for their integration into waveguides. “

The task of creating a single-photon source integrated on a chip is part of a larger-scale project to control Bloch surface waves using dielectric structures on the surface of a one-dimensional photonic crystal, which is being implemented by a group of scientists from the nanophotonics sector of the Center for Quantum Technologies under the leadership of Professor A.A. Fedyanin.

This project is aimed at solving the fundamental problem of developing new methods for controlling the generation and propagation of Bloch surface electromagnetic waves at the one-dimensional photonic crystal – dielectric interface. The solution of this problem is necessary for the development of the fundamental foundations of a new all-dielectric integrated optics platform based on Bloch surface waves.

In addition to solid-state single-photon sources, which are being developed at the Center for Quantum Technologies, there are other options. In particular, the development of sources based on colloidal crystals, from a superconducting qubit, based on semiconductor nanostructures is underway.

Dmitry Stepnov

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