Research and CV

1. Quantum optics of ultracold quantum gases: Studying the ultimate quantum limit of the light-matter interaction

A toy model for merging quantum light with quantum many-body system: atoms trapped in an optical lattice inside a cavity

My current research is focused on theoretical quantum optics of ultracold degenerate gases, where the quantum natures of both light and matter play key roles. Joining the paradigms of two fields of modern physics, cavity QED and ultracold quantum gases, will enable conceptually new investigations of the light-matter interaction at the ultimate quantum level.

We have predicted several phenomena, which have been experimentally confirmed recently and will be further tested in the nearest future. (Nature Phys. 2007, Phys. Rev. Lett. 2007, 2009, 2011, 2015, 2020, Optica 2016, etc.)

This research includes the following areas

- quantum optics, e.g., cavity quantum electrodynamics (QED),
- Bose-Einstein condensation (BEC),
- ultracold gases in optical lattices,
- laser cooling,
- condensed matter physics of strongly correlated systems,
- nanophotonics,
- quantum information processing

Both quantum optics and many-body physics of the lowest achievable temperatures are very active fields of modern research. However, the interaction between them is far from being complete.

In the most theoretical and experimental works on ultracold atoms, the role of light is reduced to a classical tool for preparing intriguing atomic states. In contrast, the main goal of my research is to develop a theory of phenomena, where the quantum natures of both ultracold matter and light play equally important roles.

This research will close the gap between quantum optics and physics of ultracold quantum matter, considering the ultimate quantum regime of the light-matter interaction. The experiments on this regime became possible just several years ago, which makes the interaction between theory and experiment promising.

Open quantum systems beyond dissipation: feedback control

  • We have proposed a novel type of phase transitions beyond the dissipative ones: the feedback-induced phase transition (FPT).

  • We have shifted the paradigm of feedback control from the quantum states control to the control of quantum phase transitions, demonstrating the tuning of their universality class.

In Phys. Rev. Lett. (2020),
we have shown that applying feedback to a quantum system induces phase transitions beyond the dissipative ones: the feedback-induced phase transitions (FPT). Feedback enables controlling essentially quantum properties of the transition, i.e., tuning its universality class via the critical exponents. Feedback provides the non-Markovianity and nonlinearity to the hybrid quantum-classical system, and enables simulating effects similar to spin-bath problems and Floquet time crystals with tunable long-range (long-memory) interactions.

In Scientific Rep. (2020),
we show that the feedback phase transition leads to the self-organization of ultracold atoms even without a cavity.

In Phys. Rev. A (2021),

we present the feedback control of Dicke phase transition beyond the adiabatic limit.

Talk at the Quantum Information division of the Mexican Physical Society (2020)

Talk at the Harvard University, ITAMP (2017)

Talk at the University Paris-Saclay (2017)

Open quantum systems beyond dissipation: quantum measurements

Quantum nondemolition measurements

- We have formulated the quantum non-demolition (QND) measurement schemes to observe the properties of many-body atomic states detecting scattered light. Different many-body characteristics beyond the density-density correlations can be obtained by quantum optical methods. (Nature Physics (2007), Phys. Rev. Lett. (2007), Phys. Rev. A (2007), Laser Physics (2009))

- Those methods have been applied to ultracold polar molecules. (Phys. Rev. Lett. (2011), Phys. Rev. A (2011), Laser Physics (2013))

In Phys. Rev. A (2015), we proved that light is not only sensitive to the density correlations, but reflects the matter-field interference at its shortest possible distance in an optical lattice as well. We also showed, how to distinguish the Bose Glass, Mott insulator and superfluid phases.

- We suggested to use the entanglement between the light and motion of ultracold atoms to prepare the nonclassical many-body states exploiting the quantum nature of the measurement process (measurement back-action). The preparation of number squeezed and Schrödinger cat states was demonstrated. (Phys. Rev. Lett. (2009), Phys. Rev. A (2009), Laser Physics (2010), Laser Phys. (2011))

In Phys. Rev. Lett.-1 (2015), we have shown, how to generate multiple spatial modes of matter fields using the quantum measurement. The modes have nontrivial spatial overlap, display genuine multipartite entanglement, and can be used for measurement and detection of the entanglement in quantum gases.

Quantum weak measurements

In Phys. Rev. A-1 (2016) we presented a general framework to describe the competition between global quantum measurement and standard local processes (tunneling and on-site interaction) in a strongly correlated many-body system. We demonstrated the following new phenomena: design of nonlocal spatially structured environment for otherwise closed many-body system, long-range correlated tunneling, nonlocal quantum Zeno effect, generation of multimode Schrödinger cat states, break-up and protection of strongly interacting fermion pairs.

In Atoms (2015) we have shown the measurement-induced entanglement between fermion spin components on a lattice, and showed that the homodyne detection can produce more robust states, than those produced by photon number measurements.

In Phys. Rev. A-3 (2016), we have extended the notion of quantum Zeno dynamics in the realm of non-Hermitian processes. Moreover, we presented an unconventional scenario for quantum Zeno dynamics: a system evolves within a Zeno subspace thanks to Raman-like transitions via virtual states outside that subspace. This corresponds to a rather strong, but not projective quantum measurement.

In Scientific Reports (2016), we demonstrated how the quantum backaction of weak continuous measurement can lead to the generation of antiferromagnetic order and density modulations in the system of ultracold fermions in optical lattices.

In Phys. Rev. A-4 (2016), we demonstrated that joining the ideas of quantum measurement and quantum optical lattices can broaden the field of quantum simulations, allowing simulating numerous models such as superexchange interactions, multispecies Dicke model, pair creation and annihilation, dynamical gauge fields, etc.

In arXiv:1601.02230 we demonstrated that the quantum feedback control can strongly influence the stability region of a BEC trapped inside a cavity. Moreover, it can be used to precisely position a BEC in space and tune the phase of the generated light.

In New J. Phys.-1 (2016), we predicted a nontrivial type of dynamics resulting from the novel competition between the quantum backaction of weak measurement and unitary many-body (or multimode) dynamics.

In Optica (OSA) (2016), we have described the quantum feedback control of novel many-body states, which appear as a result of the competition between the weak measurement backaction and many-body dynamics: multimode density waves and supersolids, antiferromagnetic and NOON states.

In Scientific Reports (2017), instead of coupling light to the atomic on-site density, we propose a method of coupling directly to the matter-phase-related variables. This constitutes a novel type of quantum measurements and projections, thus generalizing the standard measurement postulate for the case of competition between the weak measurement backaction and system's own dynamics.

Quantum optical lattices

- We developed a model to describe the ultracold atoms trapped in a fully quantum potential (“quantum optical lattices”), merging cavity QED and physics of ultracold gases. For example, the generalized Bose-Hubbard model taking into account the light quantization was formulated. (Eur. Phys. Journal D (2008), Phys. Rev. A (2007))

In Phys. Rev. Lett.-2 (2015), we demonstrated novel phase transitions solely due to the quantum light-matter correlations in a quantum optical lattice. Moreover, we showed the generation of nonclassical light (e.g. squeezed) in such systems (New J. Phys. (2015)).

In Phys. Rev. A-2 (2016), we proposed a new type of quantum simulators based on the collective enhancement of light-matter interactions.

In New J. Phys.-2 (2016), we showed that the emergent global bond order (i.e. the self-organization of matter-wave coherences, rather than densities) is linked to the valence bond solids (VBS). This opens a novel avenue for global quantum simulations, in particular, of high-Tc superconductors.

SELECTED PUBLICATIONS (cf. CV for the full list)

2. Optically dense media, polaritons, strong light-matter coupling, superradiance

I am interested in the study of optically dense resonant media. Especially, in the regime of strong light-matter coupling both in a cavity and free space. Such phenomena can be understood in terms of polaritons and collective superradiance.

I am interested in the realizations in both atomic and solid-state (semiconductor nanostructures with quantum wells and quantum dots) media.

We have proposed a novel type of collective parametric processes, which cannot be explained by any single-atom model:

- We demonstrated the light amplification in the strong coupling regime in a cavity. (Quantum Information Processing (2006), Laser Physics (2005))

- Moreover, the parametric amplification of polaritons and solitons in free space without use of any cavity has been proved. (Phys. Rev. A (2004), Phys. Rev. A (2003), Laser Physics (2005), Quantum Information Processing (2006))

SELECTED PUBLICATIONS (cf. CV for the full list)

  • “Coherent tunable diffractional pulse shaping and generation of the 0π-pulse in Rb vapor,” S.N. Bagayev, V.A. Averchenko, I.A. Chekhonin, M.A. Chekhonin, I.M. Balmaev, I.B. Mekhov, Journ. Phys.: Conf. Ser. 2086, 012133 (2021);

  • “Experimental new ultra-high-speed all-optical coherent streak-camera,” S.N. Bagayev, V.A. Averchenko, I.A. Chekhonin, M.A. Chekhonin, I.M. Balmaev, I.B. Mekhov, Journ. Phys.: Conf. Ser. 1695, 012129 (2020) ;

  • “Ultra high-speed all-optical coherent memory cells,” S. N. Bagayev, I. B. Mekhov, V. G. Nikolaev, I. A. Chekhonin, M. A. Chekhonin, Journ. Phys.: Conf. Ser. 1410, 012161 (2019);

  • “New ultra high-speed all-optical coherent D-trigger,” S. N. Bagayev, V. S. Egorov, V. G. Nikolaev, I. B. Mekhov, I. A. Chekhonin, M. A. Chekhonin, Journ. Phys.: Conf. Ser. 1124, 051018 (2018);

  • “Interaction of Phase-Modulated Femtosecond Pulses with an Optically Dense Quasi-Resonant Medium of Rubidium Vapors,” S. N. Bagaev, A. A. Preobrazhenskaya, N. A. Timofeev, A. A. Pastor, I. B. Mekhov, I. A. Chekhonin, P. Yu. Serdobintsev, V. S. Egorov, M. A. Chekhonin, and A. M. Mashko, Opt. Spectrosc. 125, 667 (2018);

  • "Strong light-matter coupling: coherent parametric interactions in a cavity and free-space", V.S. Egorov, V.N. Lebedev, I.B. Mekhov, P.V. Moroshkin, I.A. Chekhonin, and S.N. Bagayev, "Quantum Information Processing – From Theory to Experiment", v. 199, p. 341, IOS Press (Amsterdam, Netherlands, 2006);

  • "Coherent light sources under strong field–matter coupling in an optically dense resonant medium without population inversion", S.N. Bagayev, V.V. Vasil’ev, V.S. Egorov, V.N. Lebedev, I. B. Mekhov, P. V. Moroshkin, A. N. Fedorov, and I. A. Chekhonin, Laser Physics, 15, 975 (2005);

  • "Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling", V.S. Egorov, V.N. Lebedev, I.B. Mekhov, P.V. Moroshkin, I.A. Chekhonin, and S.N. Bagayev, Phys. Rev. A 69, 033804 (2004);

  • "Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms", S.N. Bagayev, V.S. Egorov, I.B. Mekhov, P.V. Moroshkin, I.A. Chekhonin, E.M. Davliatchine, and E. Kindel, Phys. Rev. A 68, 043812 (2003);

  • "Nonstationary parametric amplification of polychromatic radiation propagating in an extended absorbing resonant medium", S.N. Bagaev, V.S. Egorov, I.B. Mekhov, P.V. Moroshkin, I.A. Chekhonin, E. M. Davliatchine, and E. Kindel, Opt. Spectrosc. 94, 92 (2003);

  • "Parametric collective phenomena during the propagation of polychromatic laser pulses in an optically dense resonant medium without population inversion", S.N. Bagaev, V.S. Egorov, I.B. Mekhov, P.V. Moroshkin, I.A. Chekhonin, Opt. Spectrosc. 93, 955 (2002);

3. Other interests

In addition, I have studied different aspects of nonlinear dynamics and statistical physics:

- solitons,

- parametric interactions,

- light squeezing,

- semiconductor lasers with quantum wells (VCSELs),

- plasma physics (kinetics of particles at ultralow (Phys. Rev. E (1999)) and extremely high (ISPC-14 (1999), Hakone VII (2000)) pressures).


For general presentations see 1, 2