Subject of study. Three-dimensional solitons of the theory of self-induced transparency of laser pulses with a converging cylindrical wavefront and different transverse spatial profiles of the pulse field in 87Rb vapor (resonant transition D2, wavelength 780.24 nm) are studied. Aim of study. The aim is the experimental study of threedimensional solitons of self-induced transparency of laser pulses for the development of new device prototypes for resonant quantum microwave photonics using laser signal processing methods in the microwave region of the spectrum. Method. In the caustic of a focused beam of a laser pump pulse with a cylindrical wavefront, a transverse spatial profile of the electric field strength of a special shape is created. The computer-generated holograms developed by us can be used to create an arbitrary profile. Main results. The properties of a three-dimensional self-induced transparency soliton are studied for various detuning frequencies of the input pulse field with respect to atomic resonance. The maximum laser pulse power is 8.5 mW, the pulse duration is 4-5 ns, and the time resolution of the recording system is 27 ps. It is shown that the all-optical control of the carrier frequency of the input pulse determines the properties of the output pulse: compression of the pulse duration (generation of a strobe pulse), the value of the soliton delay in time, and the time shift of the carrier frequency of the soliton. Practical significance. The results obtained in this study of the properties of three-dimensional self-induced transparency solitons will serve as the basis for the development of prototypes of signal processing devices using low-power laser diodes. (c) 2023 Optica Publishing Group

Subject of study. The self-diffraction process of a resonant pulse in a dense extended resonant medium was studied for the first time to our knowledge. This process leads to an angular deflection of the output radiation and sequen-tial emission of a large series of N pulses with a variable area in the range (-3n, ... , 0, ... , 3n). The pulses are emitted from a small focusing region (0.1-1 mm) of the pump pulse in a dense extended resonant medium. The pulse wavelength corresponds to the resonant transition Ii2 87Rb (wavelength 780.24 nm). Aim of study. The non-linear effect of the self-diffraction of a laser pulse with a cylindrical wavefront is studied in an extended resonant medium of rubidium vapor to develop new resonant microwave photonics devices using laser signal-processing methods in the microwave spectrum. Method. A transverse spatial profile of the electric field strength of a special shape f (x) is created in the caustic of a focused beam of a laser pump pulse with a cylindrical wavefront. The pump pulse must have a converging (for example, cylindrical) wavefront. Computer-synthesized holograms developed by us are used to create an arbitrary f(x) profile. Main results. The effect of the self-diffraction of a pump pulse is studied. This is accompanied by the emission of a series of N coherent resonant pulses with different areas in the range (-3n, ... , 0, ... , 3n) from a short focusing region (0.1-1 mm) of a resonant laser pump pulse. The self -diffraction of the pump pulse resulted in 16 emitted pulses with different areas. The distribution of series pulses over the diffraction angle was observed in the angle range from -5 degrees to +4 degrees. The nonlinear generation of 0n-pulses was observed at some angles. The results verify the nonlinear generation of 0n-pulses over a short interaction length between light and a resonant medium for the first time to our knowledge. Practical significance. The obtained results on the effect of the self-diffraction of a resonant pulse with a transverse spatial profile f(x) will serve as a basis for the development of prototype devices for signal-processing problems using low-power laser diodes. (c) 2023 Optica Publishing Group

Quantum optics and ultracold gases are established fields, but they almost do not overlap: the quantum nature of light is typically neglected in works on ultracold atoms. In our work the quantumness of both light and ultracold matter plays a key role. First, we show that light is a quantum nondemolition (QND) probe of many-body phases: they can be distinguished by correlations and full distribution functions (we consider bosons, fermions, and dipolar molecules). Light is not only sensitive to densities, but also to the matter-field interference. Second, we prove that the measurement backaction constitutes a novel source of competitions in many-body systems, especially, for non-QND cases. This leads to a plethora of new phenomena: oscillations of multipartite entangled modes, protection and break-up of fermion pairs, antiferromagnetic orders, long-range pair tunnelling and entanglement beyond Hubbard models. We prove that feedback control induces phase transitions and tunes their universality class. Third, the quantization of trapping potential (quantum optical lattices) leads to novel phases, including both density orders (supersolids, density waves) and bond orders of matter fields (superfluid and supersolid dimers, trimers). Results beyond ultracold atoms include: We extend the paradigm of feedback control from the state control to control of phase transitions. We present the measurement backaction as a novel source of competitions in many-body physics. We merge quantum Zeno dynamics and non-Hermitian physics and show a novel type of Zeno phenomena with Raman transitions beyond Zeno dynamics. We propose quantum simulators based on collective light-matter interaction. Our models can be applied to arrays of other systems (qubits). In general, quantum measurements and feedback produce new phenomena untypical to both closed unitary systems and open dissipative ones in many-body physics.

We shift the paradigm of feedback control from the control of quantum states to the control of phase transitions in quantum systems. We show that feedback allows tuning the universality class of phase transitions via modifying its critical exponent. We expand our previous treatment [D. A. Ivanov, T. Yu. Ivanova, S. F. Caballero-Benitez, and I. B. Mekhov, Phys. Rev. Lett. 124, 010603 (2020)] of Dicke model and go beyond the approximation of adiabatically eliminated light field. Both linearized and nonlinear models of spin ensembles are considered. The tunability of quantum fluctuations near the critical point by the feedbacks of nontrivial shapes is explained by considering the fluctuation spectra and the system behavior at single quantum trajectories.

We have experimentally studied for the first time a new operation principle of the coherent diffractional pulse shaper (Rabi shaper). In the experiment, we observed an effect of tunable pulse shaping of nanosecond semiconductor laser pulse during the resonant pumping of the D 2 line (780.24 nm) of 87 Rb vapor in the range of self-diffraction angles φ = ± 4 ° . We observed the synthesis of nanosecond 0π-pulses at the small length of the nonlinear interaction 0.1…1 mm. We propose to use the Rabi shaper as an energy efficient tunable shaper of classical and single-photon wave packets. We analyze a possibility of the Rabi shaper operation in quantum systems with feedback.

We show that applying feedback and weak measurements to a quantum system induces phase transitions beyond the dissipative ones. Feedback enables controlling essentially quantum properties of the transition, i.e., its critical exponent, as it is driven by the fundamental quantum fluctuations due to measurement. 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.

We have experimentally studied for the first time a new operation principle of the all-optical coherent streak-camera (Rabi deflector). In the experiment, we observed an effect of significant dynamical angular deflection of a pulse of semiconductor laser during the resonant pumping of the D2 line (780.24 nm) of 87Rb vapor in the range of diffraction angles ϕ = ± 5.45°. We propose to use the Rabi deflector as an energy efficient shaper of classical and single-photon wave packets. We analyze a possibility of the Rabi deflector operation in quantum systems with feedback.

Feedback is a general idea of modifying system behavior depending on the measurement outcomes. It spreads from natural sciences, engineering, and artificial intelligence to contemporary classical and rock music. Recently, feedback has been suggested as a tool to induce phase transitions beyond the dissipative ones and tune their universality class. Here, we propose and theoretically investigate a system possessing such a feedback-induced phase transition. The system contains a Bose-Einstein condensate placed in an optical potential with the depth that is feedback-controlled according to the intensity of the Bragg-reflected probe light. We show that there is a critical value of the feedback gain where the uniform gas distribution loses its stability and the ordered periodic density distribution emerges. Due to the external feedback, the presence of a cavity is not necessary for this type of atomic self-organization. We analyze the dynamics after a sudden change of the feedback control parameter. The feedback time constant is shown to determine the relaxation above the critical point. We show as well that the control algorithm with the derivative of the measured signal dramatically decreases the transient time.

We study the interaction of two counterpropagating unipolar video pulses of electromagnetic radiation in a dense resonant two-level medium. The pulse durations are less than one oscillation period of an atomic transition. We show that a polariton cluster (i.e. the compact long-living strongly coupled state of electromagnetic field and matter polarization) is created, when two unipolar pulses collide in a resonant medium of the frequency ω0 (the pulses correspond to self-induced transparency solitons of the same amplitudes and opposite polarities). We have studied for the first time the conditions of maximal excitation of a resonant polarization in the polariton cluster volume. We show that there exist optimal durations and amplitudes of the recording pulses. We studied the processes of double and multiple recording and erasing of an optical memory cell in a thin layer of a resonant medium (quantum dots). We demonstrated that the pulse rate of the recording-erasing pulses can reach 60 000 GHz and higher, which happens under the coherent regime of the interaction between the electromagnetic field and polarization of the medium.

Впервые показано, что при изменении временных параметров возбуждающего импульса лазера (величина чирпа, длительность импульса и его амплитуда) можно управлять величиной и знаком эффекта " конденсации спектра" импульса на частоте резонансного перехода плотной резонансной среды.Важно отметить, что

We study the interaction of two counterpropagating unipolar video pulses of electromagnetic radiation in a dense resonant two-level medium. The pulse durations are less than one oscillation period of an atomic transition. We show that a polariton cluster (i.e. the compact long-living strongly coupled state of electromagnetic field and matter polarisation) is created, when two unipolar video pulses collide in a resonant medium of the frequency ωo (the pulses correspond to self-induced transparency solitons of the same amplitudes and opposite polarities).

For the first time, it is demonstrated that the magnitude and sign of the effect of spectral condensation of a laser pulse at the resonant-transition frequency of a dense medium can be controlled by changing the driving-pulse parameters (chirp, pulse width, and pulse amplitude). In the process of this, importantly, the driving-pulse energy and spectrum remain unchanged. Direct time-resolved measurements revealed an oscillatory character of the induced superradiance of rubidium vapors representing a long train of decaying short pulses. The width and repetition rate of the pulses in the train are determined by atomic density N-0 of the medium, while the width of an entire superradiance pulse (10 ps) is considerably larger than that of the driving laser pulse (50 fs).

A many-body atomic system coupled to quantized light is subject to weak measurement. Instead of coupling light to the on-site density, we consider the quantum backaction due to the measurement of matter-phase-related variables such as global phase coherence. We show how this unconventional approach opens up new opportunities to affect system evolution. We demonstrate how this can lead to a new class of final states different from those possible with dissipative state preparation or conventional projective measurements. These states are characterised by a combination of Hamiltonian and measurement properties thus extending the measurement postulate for the case of strong competition with the system’s own evolution.

We show that weak measurement leads to unconventional quantum Zeno dynamics with Raman-like transitions via virtual states outside the Zeno subspace. We extend this concept into the realm of non-Hermitian dynamics by showing that the stochastic competition between measurement and a system's own dynamics can be described by a non-Hermitian Hamiltonian. We obtain a solution for ultracold bosons in a lattice and show that a dark state of tunneling is achieved as a steady state in which the observable's fluctuations are zero and tunneling is suppressed by destructive matter-wave interference.

We show that coupling ultracold atoms in optical lattices to quantized modes of an optical cavity leads to quantum phases of matter, which at the same time possess properties of systems with both short- and long-range interactions. This opens perspectives for novel quantum simulators of finite-range interacting systems, even though the light-induced interaction is global (i.e., infinitely long range). This is achieved by spatial structuring of the global light-matter coupling at a microscopic scale. Such simulators can directly benefit from the collective enhancement of the global light-matter interaction and constitute an alternative to standard approaches using Rydberg atoms or polar molecules. The system in the steady state of light induces effective many-body interactions that change the landscape of the phase diagram of the typical Bose-Hubbard model. Therefore, the system can support nontrivial superfluid states, bosonic dimer, trimer, etc., states, and supersolid phases depending on the choice of the wavelength and pattern of the light with respect to the classical optical lattice potential. We find that by carefully choosing the system parameters one can investigate diverse strongly correlated physics with the same setup, i.e., modifying the geometry of light beams. In particular, we present the interplay between the density and bond (or matter-wave coherence) interactions. We show how to tune the effective interaction length in such a hybrid system with both short- range and global interactions.

Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most fundamental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.

In contrast to the fully projective limit of strong quantum measurement, where the evolution is locked to a small subspace (quantum Zeno dynamics), or even frozen completely (quantum Zeno effect), the weak non-projective measurement can effectively compete with standard unitary dynamics leading to nontrivial effects. Here we consider global weak measurement addressing collective variables, thus preserving quantum superpositions due to the lack of which path information. While for certainty we focus on ultracold atoms, the idea can be generalized to other multimode quantum systems, including various quantum emitters, optomechanical arrays, and purely photonic systems with multiple-path interferometers (photonic circuits). We show that light scattering from ultracold bosons in optical lattices can be used for defining macroscopically occupied spatial modes that exhibit long-range coherent dynamics. Even if the measurement strength remains constant, the quantum measurement backaction acts on the atomic ensemble quasi-periodically and induces collective oscillatory dynamics of all the atoms. We introduce an effective model for the evolution of the spatial modes and present an analytic solution showing that the quantum jumps drive the system away from its stable point. We confirm our finding describing the atomic observables in terms of stochastic differential equations.

Interactions between many-body atomic systems in optical lattices and light in cavities induce long-range and correlated atomic dynamics beyond the standard Bose-Hubbard model, due to the global nature of the light modes. We characterize these processes, and show that uniting such phenomena with dynamical constraints enforced by the backaction resultant from strong light measurement leads to a synergy that enables the atomic dynamics to be tailored, based on the particular optical geometry, exploiting the additional structure imparted by the quantum light field. This leads to a range of tunable effects such as long-range density-density interactions, perfectly correlated atomic tunneling, superexchange, and effective pair processes. We further show that this provides a framework for enhancing quantum simulations to include such long-range and correlated processes, including reservoir models and dynamical global gauge fields.

It is well known that in the presence of a ring cavity the light scattering from a uniform atomic ensemble can become unstable resulting in the collective atomic recoil lasing. This is the result of a positive feedback due to the cavity. We propose to add an additional electronic feedback loop based on the photodetection of the scattered light. The advantage is a great flexibility in choosing the feedback algorithm, since manipulations with electric signals are very well developed. In this paper we address the application of such a feedback to atoms in the Bose-Einstein condensed state and explore the quantum noise due to the incoherent feedback action. We show that although the feedback based on the photodetection does not change the local stability of the initial uniform distribution with respect to small disturbances, it reduces the region of attraction of the uniform equilibrium. The feedback-induced nonlinearity enables quantum fluctuations to bring the system out of the stability region and cause an exponential growth even if the uniform state is globally stable without the feedback. Using numerical solution of the feedback master equation we show that there is no feedback-induced noise in the quadratures of the excited atomic and light modes. The feedback loop, however, introduces additional noise into the number of quanta of these modes. Importantly, the feedback opens an opportunity to position the modulated BEC inside a cavity as well as tune the phase of scattered light. This can find applications in precision measurements and quantum simulations.

Light enables manipulating many-body states of matter, and atoms trapped in optical lattices is a prominent example.However, quantum properties of light are completely neglected in all quantum gas experiments.Extending methods of quantum optics to many-body physics will enable phenomena unobtainable in classical optical setups.We show how using the quantum optical feedback creates strong correlations in bosonic and fermionic systems.It balances two competing processes, originating from different fields: quantum backaction of weak optical measurement and many-body dynamics, resulting in stabilized density waves, antiferromagnetic and NOON states.Our approach is extendable to other systems promising for quantum technologies.