Ultrafast quantum photonics
The preeminent challenge of quantum technologies is the ability to accurately control the elementary quantum systems, while protecting them from unwanted interactions with their environment. On the one hand, single photons possess a natural advantage as carriers of quantum information because they are highly immune to external disturbances and travel at the speed of light. On the other hand, it is notoriously difficult to perform operations between single photons due to the relatively weak level of interaction between them that one can achieve in practice. The enhancement and flexible control of light-matter interaction on the nanoscale is the central purpose of nanophotonics.
This enhancement can be achieved by two complementary methods. In one approach, one aims at increasing the time for the interaction to take place by using high-quality resonators such as dielectric photonic cavities. This approach usually requires high level of coherence in matter and is therefore often associated with cryogenic temperatures and/or other methods to increase coherence.
An alternative approach consists in tightly concentrating the optical modes, thus intensifying the light-matter interaction. This type of mode concentration is offered by plasmonic nanoresonators, where light can be coupled to a free-electron plasma at optical frequencies. As a result of this coupling, hybrid particles termed plasmon-polaritons arise, having a much smaller wavelength than optical photons. The mode volumes can be made as small as a few cubic nanometers. The achieved interaction rates may exceed the decoherence rates in matter even at cryo-free temperatures. Quantum photonics in the ultrafast, sub-ps regime points a way towards cryo-free quantum photonics operating at THz rates . It promises practically usable quantum communication networks and distributed quantum computing architectures.
We have previously used plasmonic enhancement of light-matter interaction to demonstrate the world’s brightest room-temperature single-photon source based on a quantum emitter . We have recently also realized an integration-friendly version of such a source. We have also developed methods for the deterministic assembly of such sources from automatically preselected nanoscale constituents .
 S.I. Bogdanov, A. Boltasseva and V.M. Shalaev, Science, 364, 532 (2019)
 S.I. Bogdanov, M.Y. Shalaginov, A.S. Lagutchev, C.-C. Chiang, D. Shah, A.S. Baburin, I.A. Ryzhikov, I.A. Rodionov, A.V. Kildishev, A. Boltasseva, and V.M. Shalaev, Nano Letters, 18, 4837 (2018)
 C.-C. Chiang, S. I. Bogdanov, O. A. Makarova, X. Xu, S. Saha, D. Shah, D. Wang, A. S. Lagutchev, A. V. Kildishev, A. Boltasseva, and V. M. Shalaev, preprint available at https://arxiv.org/abs/1910.03005
 S.I. Bogdanov, O.A. Makarova, A.S. Lagutchev, D. Shah, C.-C. Chiang, S. Saha, A.S. Baburin, I.A. Ryzhikov, I.A. Rodionov, A.V. Kildishev, A. Boltasseva and V.M. Shalaev, preprint available on arXiv at http://arxiv.org/abs/1902.05996
Nanophotonics for spin-based quantum information and sensing
Electronic and nuclear solid-state spins constitute another material platform for quantum information and quantum sensing. In particular, optically active spins in diamond-based nitrogen-vacancy (NV) centers constitute a unique testbed for technologies such as quantum registers, quantum memories and nanoscale magnetometers. Single electron spins in NV centers can be coherently manipulated by microwave excitation at room temperature and allow an optical initialization and readout.
The optical readout is possible thanks to a spin-dependent fluorescence brightness produced by the NV centers. Its sensitivity is primarily limited by the gathered fluorescence intensity and the brightness contrast between the spin states (the spin contrast). Nanophotonics suggests promising methods to increase the fluorescence brightness of NV centers and improve the sensitivity of the spin readout for a variety of applications.
In the past, we have studied the influence of nanophotonic environment on the spin contrast in NV ensembles . We have observed spin-dependent fluorescence signal from plasmon-enhanced NV centers . We have also realized an interface for the optical collection and microwave signal delivery to NV centers based on a single multi-functional metallic layer . We now aim at designing and realizing on-chip nanophotonic and nanomagnetic interfaces that can increase spin readout sensitivity and harness the interaction between distant spins.
S. Bogdanov, M.Y. Shalaginov, P. Kapitanova, J. Liu, M. Ferrera, A. Lagutchev, P. Belov, J. Irudayaraj, A. Boltasseva and V. Shalaev, Physical Review B 96, 035146 (2017)
S.I. Bogdanov, O.A. Makarova, A.S. Lagutchev, D. Shah, C.-C. Chiang, S. Saha, A.S. Baburin, I.A. Ryzhikov, I.A. Rodionov, A.V. Kildishev, A. Boltasseva and V.M. Shalaev, preprint available on arXiv at http://arxiv.org/abs/1902.05996
M. Y. Shalaginov, S. I. Bogdanov, A. S. Lagutchev, A. V. Kildishev, A. Boltasseva, and V. M. Shalaev, preprint available on arXiv at https://arxiv.org/abs/1905.07057
Plasmonics and nanophotonics
S.K.H. Andersen, S. Bogdanov, Y. Xuan, O. Makarova, M.Y. Shalaginov, A. Boltasseva, V.M. Shalaev and S. Bozhevolnyi, ACS Photonics, 5, 692 (2018)
O.A. Makarova, M.Y. Shalaginov, S. Bogdanov, U. Guler, A. Boltasseva, A.V. Kildishev and V.M. Shalaev, Optics Letters 42, 3968 (2017)
S. Bogdanov, M.Y. Shalaginov, A. Boltasseva and V.M. Shalaev, Optical Materials Express 7, 111 (2017)
M. Razeghi, A. Haddadi, A.M. Hoang, E.K. Huang, G. Chen, S. Bogdanov, S.R. Darvish, F. Callewaert and R. McClintock, Infrared Physics and Technology, 59, 41 (2012).
S. Bogdanov, B.M. Nguyen, A.M. Hoang and M. Razeghi, Applied Physics Letters 98, 183501 (2011).
B.M. Nguyen, S. Bogdanov, S. Abdollahi Pour, and M. Razeghi, Applied Physics Letters 95, 183502 (2009).
B.M. Nguyen, D. Hoffman, E.K. Huang, S. Bogdanov, P.Y. Delaunay, M. Razeghi and M.Z. Tidrow, Applied Physics Letters 94, 223506 (2009).
Statistical and machine learning methods for quantum optics
There are usually several ways to measure a physical quantity. Sometimes, using advanced measurement protocols, one can achieve a great improvement, without changing the measurement hardware. In the field of quantum optics, some measurements are particularly time-consuming and could be improved with methods such as machine learning.
We have recently achieved accurate classification of “single” vs “non-single” quantum emitters using machine-learning , using the heuristic threshold of g(2)(0) = 0.5. The machine learning-based method greatly outperformed the conventional approach that uses exponential fitting. We are looking to extend these and other optimal data processing methods to various measurements in quantum optics and sensing for scalable construction and testing of quantum devices.
 Z.A. Kudyshev, S.I. Bogdanov, T. Isacsson, A.V. Kildishev, A. Boltasseva and V. M. Shalaev, preprint available on arXiv at https://arxiv.org/abs/1908.08577