The spectral and statistical properties are explored for surface plasmon (SP) emission in resonance fluorescence from a driven two level emitter in the proximity of 2D single graphene sheet. We derive an exact closed form analytic expression for the emitted SP field valid in the near and far regions. The SP field profile and spectrum function depend on the graphene conductivity and take into account the dynamic control parameters, namely Fermi energy. We present analysis for the spectrum and second order coherence functions and discuss the possibility of their control using graphene system parameters to manipulate the spectral linewidth and second order coherence function.

In this work, an approach based on the use of yttrium iron garnet (YIG) to increase the efficiency of quantum frequency conversion has been theoretically studied. YIG, which is a ferrimagnetic insulator transparent to both microwave and optical frequencies, has a very low damping parameter. Therefore, the coupling of YIG to microwave resonator modes is very strong. It has been demonstrated that it is possible to use the spin-wave oscillations of YIG to increase essentially the coupling of microwave photons to $\text{Er}^{3+}$ spin-flip transitions. The basic parameters of 2 -stage microwave-to-optic transduction in the proposed Erbium-YIG-based Hybrid Quantum System have been theoretically analyzed. The conditions needed for efficient coupling between magnetic resonance levels of $\text{Er}^{3+}$ ions and spin wave modes have been also considered.

We propose a 2D graphene structure containing atomic ensemble as a platform for implementing nanoscale enhanced coherent interactions of plasmonic fields with resonant atomic systems. We determine the graphene surface plasmon modes, and the properties of its electromagnetic fields, and emphasize the role of graphene sheet separation on the interaction with atomic systems for various dipole orientations and positions between the graphene sheets. We analyze the conditions for implementation of coherent interaction of SP mode with resonant atomic ensembles. By solving the Maxwell-Bloch equations that govern the resonant interaction of surface plasmons with atoms, we derive the modified area theorem, which makes it possible to identify the most common nonlinear patterns in the behavior of plasmons under the studied conditions. We obtain analytical and numerical solutions of the area theorem, and find the possibility of stable propagation of isolated SP pulses of graphene surface plasmon modes at "fractional" pulse area values relative to π. We show that the coherent dynamics of SP fields can be realized in nanoscale design and we highlight the possibilities of using this scheme of coherent dynamics for implementing compact multimode nanoscale quantum memory and its integration with other quantum devices on the proposed platform.

We propose a multiresonator quantum memory consisting of four mini-resonators coupled with a common resonator, which is connected with an external waveguide via a switch. Using the optimization methods, it is possible to effectively transmit a signal from the waveguide to the memory and its long-term multi-cycle storage when the switch is turned off. The advantages of the proposed memory and its potential and implementation range are discussed.

We presented numerical estimates of the degree of quantum entanglement based on Schmidt mode analysis for ultra-broadband biphotonic states generated in a photonic crystal fiber. We show that these states have a high degree of quantum entanglement even when the source is pumped broadband by femtosecond laser pulses.

Pulse area approach has been established as a versatile analytical tool for studying the resonant interaction between the light and the resonant atomic ensemble. In recent years photon and spin echoes in cavity assisted schemes become increasingly interesting. In this article we develop the photon echo pulse area approach to describe primary and multi-pulse echo generation in the atomic ensemble placed in the ring cavity. We show that the pulse area approach predicts relative echo magnitudes and whether the system is operating in a single- or a multi-pulse generation regime. We also analyze the conditions needed for the realization of these generation regimes. This work develops the pulse area theorem approach for analytical study of photon/spin echoes in optical and microwave cavities and echo based protocols of quantum memory.

The results of laser site selective and Zeeman spectroscopy studies of ZnWO4 single crystal doped with Er3+ ions are reported. Three types of Er3+ sites have been discovered. The energies of the levels of the (4)I(15/)2 and I-4(13/2) multiplets and the g-factors of several states were determined for three orientations of the crystal relative to the magnetic field. The possible structure of three types of sites and further research techniques are discussed.

We report a theoretical analysis of a photonic quantum interface, which makes it possible to deterministically convert photonic qubits from subcarrier wave to polarization encoding. The interface provides unambiguous conversion of an arbitrary phase of the input signal into the corresponding polarization of the converted radiation. Possibilities of implementing this interface in an integrated optical design and its use in constructing a hybrid quantum network are discussed.

The operation of a fast quantum memory protocol on a single three-level atom in cavity is theoretically modeled. The influence of losses, such as cavity loss and atomic relaxation on the efficiency of photon loading on long-lived atomic states, is considered. By choosing the optimal experimentally achieved parameters of the system and control pulse, we show the possibility of increasing efficiency up to 56.9

The generation of interband photon pairs with wavelengths near 0.5 and 1.6 μm in a photonic-crystal fiber under low-power cw optical pumping by a diode laser with a central wavelength of 0.8 μm has been experimentally demonstrated. It has been found that the generation rate of entangled photons under cw pumping is comparable with values obtained with pulsed pumping by a femtosecond Ti:sapphire laser if the average cw pump power is an order of magnitude higher than the average pulsed pump power. The reached rates of photon generation are ensured by the used photonic-crystal fiber with a small effective mode area and a special dispersion profile. The reached low noise in the output signal is ensured by the separation of carrier frequencies of generated photons into different spectral bands.

In this Letter, we report a first, to the best of our knoqledge, experimental realization of a bright ultra-broadband (180 THz) fiber-based biphoton source with widely spectrally separated signal and idler photons. Such a two-photon source is realized due to the joint use of a broadband two-loop phase-matching of interacting light waves and high optical nonlinearity of a silica-core photonic crystal fiber. The high performance of the developed fiber source identifies it as an important and useful tool for a wide range of optical quantum applications.

We show how the area theorem is applicable to the analytical description of the nonlinear interaction of surface plasmon modes with resonant two-level atoms. A closed analytical solution is obtained and analyzed for a dielectric-negative index metamaterial interface, which shows that surface plasmons can form long-propagating 27r pulses when interacting with an optically dense two-level atomic ensemble. The possible applications of the surface pulse area theorem and the conditions for the detection of 27r surface plasmon pulses are discussed.

We present the optical and magneto-optical spectroscopy and electron paramagnetic resonance (EPR) investigations of CaMoO4 single crystals doped with the erbium ions. Telecom-wavelength resonance transition inhomogeneous line width of Er3+ is relatively narrow for oxide crystals which makes this material promising for quantum technologies applications. The hyperfine structure in optical spectra of 167Er3+ isotope is well resolved. Energies and symmetries of wavefunctions of 39 energy levels of Er3+ ions in the crystal-field (CF) of S4 symmetry and g-factors of some CF Kramers doublets were measured and successfully simulated on the basis of CF calculations. The obtained set of CF parameters was used for modeling the hyperfine structure profiles observed in the optical absorption spectra.

Microwave quantum memory promises advanced capabilities for noisy intermediate-scale superconducting quantum computers. Existing approaches to microwave quantum memory lack complete combination of high efficiency, long storage time, noiselessness and multi-qubit capacity. Here we report an efficient microwave broadband multimode quantum memory. The memory stores two spectral modes of single photon level microwave radiation in on-chip system of eight coplanar superconducting resonators. Single mode storage shows a power efficiency of up to $60\pm 3\%$ at single photon energy and more than $73\pm 3\%$ at higher intensity. The demonstrated efficiency is an order of magnitude larger than the previously reported multimode microwave quantum memory. The noiseless character of the storage is confirmed by coherent state quantum process tomography. The demonstrated results pave the way to further increase in efficiency and hence building a practical multimode microwave memory for superconducting quantum circuits.

An actual task of quantum communications over long distances is the creation of a bright source of photon pairs operating at standard wavelengths of fiber optic communication lines. In this work, we experimentally investigated the spectral and correlation characteristics of photon pairs generated on the phenomenon of spontaneous four-wave mixing in a highly nonlinear photonic-crystal fiber with a wavelength of one of the photons near 1.5 μm. The demonstrated source can be used as an efficient single photon generator at a telecommunications wavelength with prediction and tuning over a wide spectral range.

We present a scheme of quantum repeater that uses entangled multimode coherent states which are obtained by electro-optic modulation of symmetric and antisymmetric Schrödinger cat states. In this method subcarrier modes of the phase modulated states generated by the remote parties are sent to a symmetric beam splitter at the central node. The entangled coherent states are heraldedly prepared by photon counting measurements at the output channels of the beam splitter. We study how the effects of decoherence in the quantum channel affect statistics of photocounts and corresponding fidelity. We show how the proposed scheme can be useful for extending range of quantum key distribution with sub carrier wave encoding by exploiting quantum teleportation with the generated entanglement.

We derive the area theorem for light pulses interacting with inhomogeneously broadened ensemble of two-level atoms in a single-mode optical waveguide and present its analytical solution for Gaussian-type modes, which demonstrates the significant difference from the formation of $2π$ pulses by plane waves. We generalize this theorem to the description of photon echo and apply it to the two-pulse (primary) echo and the revival of silenced echo (ROSE) protocol of photon echo quantum memory. For the first time, we implemented ROSE protocol in a single-mode laser-written waveguide made of an optically thin crystal $Tm^{3+}:Y_3Al_5O_{12}$. The experimental data obtained are satisfactorily explained by the developed theory. Finally, we discuss the obtained experimental results and possible applications of the derived pulse area approach.

The results of investigations of Er3+ ions at an optical transition with a telecommunication wavelength (λ~1530 nm) in a YPO4 crystal by using photon echo and high-resolution laser spectroscopy in magnetic fields up to 4 T are presented. The maximum coherence time (T2) was 113 μs in a magnetic field of 4 T when it is oriented along the optical axis c of the crystal. The main sources of decoherence are discussed.