Phys. Rev. A **97**, 012312 (2018)

**DOI:** 10.1103/PhysRevA.97.012312

An ensemble of nitrogen-vacancy (NV) centers coupled to a circuit QED device is shown to enable an efficient, high-fidelity generation of high-N00N states. Instead of first creating entanglement and then increasing the number of entangled particles N, our source of high-N00N states first prepares a high-N Fock state in one of the NV ensembles and then entangles it to the rest of the system. With such a strategy, high-N N00N states can be generated in just a few operational steps with an extraordinary fidelity. Once prepared, such a state can be stored over a longer period of time due to the remarkably long coherence time of NV centers.

J. Biophotonics, 11: e201600203 (2018)

Optical coupling between a single, individually addressable neuron and a properly designed optical fiber is demonstrated. Two‐photon imaging is shown to enable a quantitative in situ analysis of such fiber–single‐neuron coupling in the live brain of transgenic mice. Fiber‐optic interrogation of single pyramidal neurons in mouse brain cortex is performed with the positioning of the fiber probe relative to the neuron accurately mapped by means of two‐photon imaging. These results pave the way for fiber‐optic interfaces to single neurons for a stimulation and interrogation of individually addressable brain cells in chronic in vivo studies on freely behaving transgenic animal models, as well as the integration of fiber‐optic single‐neuron stimulation into the optical imaging framework.

M. S. Pochechuev, I. V. Fedotov, O. I. Ivashkina, M. A. Roshchina, D.V. Meshchankin, D. A. Sidorov‐Biryukov, A. B. Fedotov, K. V. Anokhin, A. M. Zheltikov

J. Biophotonics. 2018; e201700106.

Reconnectable bundles consisting of thousands of optical fibers are shown to enable high‐quality image transmission, offering a platform for the creation of implantable fiberscopes for minimally invasive in vivo brain imaging. Experiments on various lines of transgenic mice verify the performance of this fiberscope as a powerful tool for chronic in vivo neuroimaging using genetically encoded calcium indicators, neuronal activity markers as well as axon growth regulators and brain‐specific protein drivers in deep regions of live brain.

P. A. Zhokhov & A. M. Zheltikov

*Scientific Reports *V.* ***8**, Article number: 1824 (2018)

**DOI:** 10.1038/s41598-017-18624-z

We show that a broadly accepted criterion of laser-induced breakdown in solids, defining the laserbreakdown threshold in terms of the laser fluence or laser intensity needed to generate a certain fraction of the critical electron density rc within the laser pulse, fails in the case of high-intensity fewcycle laser pulses. Such laser pulses can give rise to subcycle oscillations of electron density ρ with peak ρ values well above ρc even when the total energy of the laser pulse is too low to induce a laser damage of material. The central idea of our approach is that, instead of the ρ = ρc ratio, the laser-breakdown threshold connects to the total laser energy coupled to the electron subsystem and subsequently transferred to the crystal lattice. With this approach, as we show in this work, predictions of the physical model start to converge to the available experimental data.

S. A. Moiseev, K. I. Gerasimov, R. R. Latypov, N. S. Perminov, K. V. Petrovnin & O. N. Sherstyukov

*Scientific Reports *V.* ***8**, Article number: 3982 (2018)

**DOI:** 10.1038/s41598-018-21941-6

In this paper we experimentally demonstrated a broadband scheme of the multiresonator quantum memory-interface. The microwave photonic scheme consists of the system of mini-resonators strongly interacting with a common broadband resonator coupled with the external waveguide. We have implemented the impedance matched quantum storage in this scheme via controllable tuning of the mini-resonator frequencies and coupling of the common resonator with the external waveguide. Proof-of-principal experiment has been demonstrated for broadband microwave pulses when the quantum efficiency of 16.3% was achieved at room temperature. By using the obtained experimental spectroscopic data, the dynamics of the signal retrieval has been simulated and promising results were found for high-Q mini-resonators in microwave and optical frequency ranges. The results pave the way for the experimental implementation of broadband quantum memory-interface with quite high efficiency *η* > 0.99 on the basis of modern technologies, including optical quantum memory at room temperature.

Maksim A. Smirnov, Nikolay S. Perminov, Raoul R. Nigmatullin, Anvar A. Talipov, and Sergey A. Moiseev

Applied Optics Vol. 57, Issue 1, pp. 57-61 (2018)

**DOI:** 10.1364/AO.57.000057

Single-photon detectors based on avalanche photodiodes (SPADs) are key elements of many modern highly sensitive optical systems. One of the bottlenecks of such detectors is an afterpulsing effect, which limits detection rate and requires an optimal hold-off time. In this paper, we propose a novel approach for statistical analysis of SPAD dark counts, and we demonstrate its usefulness for the search of the experimental condition where the afterpulsing effect can be strongly eliminated. This approach exploits a sequence of ranked time intervals between the dark counts and does not contain a complex mathematical analysis of the experimental data. We show that the approach can be efficiently applied for a small number of the dark counts, and it seems to be very beneficial for practical fast characterization of SPAD devices.

We identify and experimentally demonstrate a physical scenario whereby high-peak-power mid-infrared (mid-IR) pulses can be compressed as a part of their free-beam spatiotemporal evolution within the regions of anomalous dispersion in air to yield few-cycle subterawatt field waveforms. Unlike filamentation-assisted pulse compression, the pulse-compression scenario identified in this work does not involve any noticeable ionization of air, enabling a whole-beam self-compression of mid-IR laser pulses without ionization-induced loss. Ultrashort high-peak-power 3.9 μm laser pulses are shown to exhibit such self-compression dynamics when exposed to the dispersion anomaly of air induced by the asymmetric-stretch rovibrational band of carbon dioxide. Even though the group-velocity dispersion cannot be even defined as a single constant for the entire bandwidth of mid-IR laser pulses used in experiments, with all soliton transients shattered by high-order dispersion, 100–200 GW, 100 fs, 3.9 μm laser pulses can be compressed in this regime to 35 fs subterawatt field waveforms.

Sergey N. Andrianov, Sergey A. Moiseev

Eur. Phys. J. B (2017) 90: 165.

**DOI:** 10.1140/epjb/e2017-80328-8

We have shown the possibility of non-Dicke superradiance for non-ideal magnon Bose-Einstein condensate (BEC) in a broadband frequency bath. Here, it is found that all the stored energy in the system of Bose-condensed magnons can be irradiated into a short pulse with a time delay caused by the strong frequency modulation of magnons due to direct inter-particle interactions in the Bose-condensed state. The last mechanism radically distinguishes this effect from the well-known Dicke superradiance of two-level atomic ensemble where the delay is connected with enhancement of the inter-atomic correlations due to exchange by virtual photons. In our case, the superradiance is the consequence of Bose-condensation in the coherent state where the particles are coupled by direct interaction. We have discussed the conditions for observation of this effect for Bose-condensed magnons in a solid-state sample with a spatial size smaller comparing with the wavelength of the emitted field. In general, we had shown that this kind of superradiance can proceed in samples with ferromagnetic type interaction. As for the antiferromagnetic ones, the effect of magnon superradiance takes place without delay.

Fanchao Meng, Bowen Liu, Sijia Wang, Junku Liu, Yanfeng Li, Chingyue Wang, A. M. Zheltikov, and Minglie Hu

**Optics Express **Vol. 25, Issue 26, pp. 32972-32984 (2017)

**DOI:** 10.1364/OE.25.032972

We demonstrate two-color dispersive wave emission in the ultraviolet and near-infrared regions in an argon filled hypocycloid-core kagome fiber pumped by a femtosecond laser around 1 μm. These two dispersive waves show drastically distinct features in terms of bandwidth and tunability. The dispersive wave in the ultraviolet region has a bandwidth of tens of nanometers and can be widely tuned from at least 267 nm to 460 nm by changing the gas pressure, input pulse energy, and pump wavelength. In contrast, the dispersive wave in the near-infrared region has a narrower bandwidth of ~5 nm and is quite stably positioned near the edge of the fundamental transmission band even if the gas pressure or input pulse energy is significantly changed. An antiresonant tube model is applied to explain the experimental results and a good agreement is found between them. The dynamics show that the narrow-band dispersive wave in the near-infrared region originates from the steep slope of the dispersion near the edge of the transmission band.

N.M. Arslanov and S.A. Moiseev

*Quantum Electron.* **47** 783 (2017)

**DOI:** 10.1070/QEL16467

The possibility of enhancing the quantum efficiency of photon echo broadband quantum memory in rare-earth-ion-doped crystals with a frequency comb structure of optical transition inhomogeneous broadening is studied. We have found the optimal parameters of the frequency combs for implementing the pre-assigned quantum efficiency in the chosen spectral range of the optical transitions of rare-earth ions with real parameters. The obtained results allow the conditions to be formulated for increasing the efficiency of broadband quantum memory. The possibilities of experimental implementation of such memory are also discussed.

M.M. Minnegaliev, E.I. Baibekov, K.I. Gerasimov, S.A. Moiseev, M.A. Smirnov and R.V. Urmancheev

*Quantum Electron.* **47** 778 (2017)

**DOI**: 10.1070/QEL16470

The longitudinal and transverse relaxation times for a transition between hyperfine sublevels of the lower electronic states of the ^{4}I_{15/2} and ^{4}I_{9/2} multiplets of ^{167}Er^{3+} ions in ^{7}LiYF_{4} crystals have been determined for the first time using two-pulse and stimulated photon echo measurements in zero magnetic field at a temperature of 4 K. The decay of the photon echo signal has been shown to be modulated, which is tentatively attributed to the superhyperfine interaction of the ^{167}Er^{3+} ions with their ^{19}F^{−} nearest neighbours. The contributions of various types of interaction to the ultranarrow linewidth (~24 MHz) of the transition in question are discussed. Our results demonstrate that this optical transition of the ^{167}Er^{3+} ion in ^{7}LiYF_{4} crystals is potentially attractive for use in Raman quantum memory schemes.

A. V. Mitrofanov, A. A. Voronin, D. A. Sidorov-Biryukov, M. V. Rozhko, E. A. Stepanov, A. B. Fedotov, V. Shumakova, S. Ališauskas, A. Pugžlys, A. Baltuška & A. M. Zheltikov

*Scientific Reports *V.* ***7**, Article number: 2103 (2017)

**DOI:** 10.1038/s41598-017-01598-3

We present experimental studies of long-distance transmission of ultrashort mid-infrared laser pulses through atmospheric air, probing air dispersion in the 3.6–4.2-μm wavelength range. Atmospheric air is still highly transparent to electromagnetic radiation in this spectral region, making it interesting for long-distance signal transmission. However, unlike most of the high-transmission regions in gas media, the group-velocity dispersion, as we show in this work, is anomalous at these wavelengths due to the nearby asymmetric-stretch rovibrational band of atmospheric carbon dioxide. The spectrograms of ultrashort mid-infrared laser pulses transmitted over a distance of 60 m in our experiments provide a map of air dispersion in this wavelength range, revealing clear signatures of anomalous dispersion, with anomalous group delays as long as 1.8 ps detected across the bandwidth covered by 80-fs laser pulses.

Gerasimov, K.I., Moiseev, S.A. & Zaripov, R.B.

Appl. Magn. Reson. V. **48**, Issue 8, pp 795–804 (2017)

We have demonstrated a combination of frequency comb spin-echo protocol in a conventional microwave pulsed electron spin resonance spectrometer with gradient pulses of the external magnetic field applied for on-demand retrieval of signal microwave pulses at the required moments of time. A natural high-finesse periodic structure was used as a carrier of stored information. The structure is made out of hyperfine lines of electron spin resonance of tetracyanoethylene anion radicals in toluene at room temperature. Herein, we have also observed that using the pulses of gradient magnetic field can increase the memory capacity. The experimental results demonstrated promising opportunities for controlling electron nuclear spin coherence, which could be useful for implementation of broadband microwave or optical-microwave noise free quantum memory protocols.

Chun Xiao Zhou, Rui Zhang, Miao Di Guo, S. A. Moiseev, and Xue Mei Su

We investigate the quantum interference effect of single photon transfer in a two-atom cavity system caused by the excitation phase. In the proposed system, the two identical atoms are firstly put into a timed state by an external single photon field. During the excitation, the atoms grasp different phases which depend on the spatial position of the atoms. Due to the strong resonant interaction between the atoms and optical cavity mode, the absorbed input photon can be efficiently transferred from the atoms to the cavity mode. We show that photon transfer is sensitive to the quantum interference caused by the excitation phases of atoms. The atomic positions can also determine the coupling constants between the atoms and cavity mode as well as the interatomic dipole–dipole interaction which causes additional interference effects on the quantum transfer. Based on the characteristics of the excitation phase, we find that it is a feasible scheme to generate a long-lived dark state and it could be useful for storage and manipulation of single photon fields by controlling the excitation phase.

J. Phys. B: At. Mol. Opt. Phys. 50125501 (2017).

К. И. Герасимов, М. М. Миннегалиев, С. А. Моисеев, Р.В. Урманчеев,** **T. Chanelière and A. Louchet-Chauvet

Оптика и спектроскопия т. 123, № 2 (2017)

Экспериментально реализован протокол квантовой памяти, основанный на восстановлении спящего эха (ROSE) в кристалле Tm^{3+}:Y_{3}Al_{5}O_{12} в схеме с ортогональной геометрией распространения сигнального и контролирующего световых полей, которая наиболее удобна для дальнейшей реализации высокоэффективной квантовой памяти в одномодовом оптическом резонаторе. В данной схеме продемонстрирована эффективность восстановления сигнала спящего эха ~13% при времени хранения 36 mс. Также показана возможность записи и считывания последовательностей из нескольких световых импульсов. Рассмотрены достоинства и недостатки представленной схемы, предложены способы увеличения эффективности и времени хранения.

Moiseev S.A., Gubaidullin F.F., Kirillov R.S., Latypov R.R., Perminov N.S., Petrovnin K.V., Sherstyukov O.N.

Phys. Rev. A **95**, 012338 (2017)

**DOI: **10.1103/PhysRevA.95.012338

In this paper we present universal broadband multiresonator quantum memory based on the spatial-frequency combs of the microresonators coupled with a common waveguide. We find a Bragg-type impedance matching condition for the coupling of the microresonators with a waveguide field that provides an efficient broadband quantum storage. The analytical solution obtained for the microresonator fields enables sustainable parametric control of all the memory characteristics. We also construct an experimental prototype of the studied quantum memory in the microwave spectral range that demonstrates basic properties of the microwave microresonators, their coupling with a common waveguide, and independent control of the microresonator frequencies. Experimentally observed narrow lines of the microresonators confirm the possibility of multiresonator quantum memory implementation.

**DOI**: 10.1103/PhysRevA.95.012338

Narkis M. Arslanov, Ali A. Kamli, Sergey A. Moiseev

Laser Physics **27**, 025103 (5pp) (2017).

Investigation of light in waveguide structures is a topical modern problem that has long-standing historical roots. A *parallel-plate waveguide* is a basic model in these studies and is intensively used in numerous investigations of nano-optics, integrated circuits and nanoplasmonics. In this letter we have first found an approximate analytical solution which describes the light modes with high accuracy in the subwavelength waveguides. The solution provides a way of obtaining a clear understanding of the light properties within the broadband spectral range in the waveguide with various physical parameters. The potential of the analytical solution for studies of light fields in the waveguides of nano-optics and nanoplasmonics has also been discussed.

Moiseev, E.S., Moiseev, S.A.

Laser Physics Letters, Volume 14, Number 1, 015202 (2017)

We demonstrate that a photon echo can be implemented by all-optical means using an array of on-chip high-finesse ring cavities whose parameters are chirped in such a way as to support equidistant spectra of cavity modes. When launched into such a system, a classical or quantum optical signal—even a single-photon field—becomes distributed between individual cavities, giving rise to prominent coherence echo revivals at well-defined delay times, controlled by the chirp of cavity parameters. This effect enables long storage times for high-throughput broadband optical delay and quantum memory.

R. V. Urmancheev, K. I. Gerasimov, M. M. Minnegaliev and S. A. Moiseev

Bulletin of RAS: Physics — 2017, Vol. 81, N. 5.

In this paper, we generalize McCall Hahn area theorem to the echo pulse irradiation in the optically depth medium where absorption line consists of several unresolved spectral optical transitions and is characterized by a symmetrical form. Some of the obtained analytical results are compared with experimental studies in Tm^{3+}:Y_{3}Al_{5}O_{12 } crystal at 793 nm.

N. S. Perminov, R. S. Kirillov, R. R. Latypov, S. A. Moiseev and O. N. Sherstyukov

Bulletin of RAS: Physics — 2017, Vol. 81, N. 5.

We study the dynamics of the interaction of microcavities that are connected to the common waveguide in the circuit multiresonator quantum memory. Were obtained optimal conditions for the implementation of quantum memory and dynamic picture of the energy exchange between different microcavities.

K.I. Gerasimov, M.M. Minnegaliev, B.Z. Malkin, E.I. Baibekov, and S.A. Moiseev

Phys. Rev. B **94**, 054429 (2016).

**DOI**: 10.1103/PhysRevB.94.054429

We performed high-resolution magneto-optical spectroscopy of the hyperfine transitions from 4I15/2 to the 4I13/2 and 4I9/2 multiplets of 167Er3+ and 166Er3+ in an isotopically purified 7LiYF4 crystal in various external magnetic fields up to 0.7 T. The obtained experimental results are interpreted in the framework of the generalized theoretical approach. The derived model successfully explains all the experimentally observed optical hyperfine transitions by using a single set of basic parameters found for the crystal-field interaction, magnetic dipole and electric quadrupole hyperfine interactions, together with Zeeman interactions at different orientations of the external magnetic field. A number of the studied quantum transitions appears to be promising for use in Raman quantum storage at optical telecommunication wavelengths.

Gleim A.V., Egorov V.I., Nazarov Y.V., Smirnov S.V., Chistyakov V.V., Bannik O.I., Anisimov A.A., Kynev S.M., Ivanova A.E., Collins R.J., Kozlov S.A., Buller G.

Optics express — 2016, Vol. 24, No. 3, pp. 2619-2633.

**DOI**: 10.1364/OE.24.002619

A quantum key distribution system based on the subcarrier wave modulation method has been demonstrated which employs the BB84 protocol with a strong reference to generate secure bits at a rate of 16.5 kbit/s with an error of 0.5% over an optical channel of 10 dB loss, and 18 bits/s with an error of 0.75% over 25 dB of channel loss. To the best of our knowledge, these results represent the highest channel loss reported for secure quantum key distribution using the subcarrier wave approach. A passive unidirectional scheme has been used to compensate for the polarization dependence of the phase modulators in the receiver module, which resulted in a high visibility of 98.8%. The system is thus fully insensitive to polarization fluctuations and robust to environmental changes, making the approach promising for use in optical telecommunication networks. Further improvements in secure key rate and transmission distance can be achieved by implementing the decoy states protocol or by optimizing the mean photon number used in line with experimental parameters.

Gaidash A., Egorov V., Gleim A.

Journal of the Optical Society of America B: Optical Physics — 2016, Vol. 33, No. 7, pp. 1451-1455.

We discuss a method for revealing a photon-number-splitting (PNS) attack in a quantum key distribution (QKD) system, which is based on analyzing the statistical distribution of photon numbers detected in each time interval. A relation for estimating the difference between the expected photon-number distribution and the one appearing in the course of a PNS attack is derived. An equation defining the minimum number of counts necessary for revealing the attack with desired probability is given. Formulas for calculating the amount of raw keys known to an illegitimate user due to a PNS attack are obtained depending on the system’s total loss. The main advantage of the method is the possibility of using it in QKD systems without significant modifications in the protocol or experimental setup.

Ivanova A.E., Chivilikhin S.A., Gleim A.V.

Journal of Physics: Conference Series — 2016, Vol. 735, No. 1, pp. 012077.

**DOI**: 10.1088/1742-6596/735/1/012077

In this paper mathematical description of using of fiber Y-splitter and optical splitter with two input and two output ports in quantum random number generation systems were obtained.

Gaidash A.A., Kozubov A.V., Egorov V.I., Gleim A.V.

Journal of Physics: Conference Series — 2016, Vol. 741, No. 1, pp. 012090.

**DOI**: 10.1088/1742-6596/741/1/012090

Subcarrier wave quantum key distribution systems demonstrate promising capabilities for secure quantum networking. However for this class of devices no implementation of secure decoy states protocol was developed. It leaves them potentially vulnerable to photon-number splitting attacks on quantum channel and limiting the key distribution distance. We propose a practical solution to this problem by calculating the required parameters of light source and modulation indices for signal and decoy states in a subcarrier wave system and describing the corresponding experimental scheme.

Moiseev, E.S., Moiseev, S.A.

Journal of Modern Optics, Volume 63, Issue 20, pp 2081-2092(2016)

**DOI: **10.1080/09500340.2016.1182222

We have proposed a compact scheme of quantum random access memory (qRAM) based on the impedance matched multi-qubit photon echo quantum memory incorporated with the control four-level atom in two coupled QED cavities. A set of matching conditions for basic physical parameters of the qRAM scheme that provides an efficient quantum control of the fast single photon storage and readout has been found. In particular, it has been discovered that the efficient qRAM operations are determined by the specific properties of the excited photonic molecule coupling the two QED cavities. Herein, the maximal efficiency of the qRAM is realized when the cooperativity parameter of the photonic molecule equals to unity that can be experimentally achievable. We have also elaborated upon the new quantum address scheme where the multi-time-bin photon state is used for the control of the four-level atom during the readout of the photonic qubits from the quantum memory. The scheme reduces the required number of logical elements to one. Experimental implementation by means of current quantum technologies in the optical and microwave domains is also discussed.

Gerasimov, K.I., Minnegaliev, M.M., Malkin, B.Z., Baibekov, E.I., Moiseev, S.A.

Phys. Rev. B, Volume 94, Issue 5, 054429 (2016)

**DOI:**** **10.1103/PhysRevB.94.054429

We performed high-resolution magneto-optical spectroscopy of the hyperfine transitions from I15/24 to the I13/24 and I9/24 multiplets of Er3+167 and Er3+166 in an isotopically purified LiYF47 crystal in various external magnetic fields up to 0.7 T. The obtained experimental results are interpreted in the framework of the generalized theoretical approach. The derived model successfully explains all the experimentally observed optical hyperfine transitions by using a single set of basic parameters found for the crystal-field interaction, magnetic dipole and electric quadrupole hyperfine interactions, together with Zeeman interactions at different orientations of the external magnetic field. A number of the studied quantum transitions appears to be promising for use in Raman quantum storage at optical telecommunication wavelengths.

Moiseev S. A. , Andrianov S. N.

Optics and Spectroscopy, Volume 121, Issue 6, pp 886–896(2016)

**DOI**: 10.1134/S0030400X16120195

A quantum transistor based quantum computer where the multiqubit quantum memory is a component of the quantum transistor and, correspondingly, takes part in the performance of quantum logical operations is considered. Proceeding from the generalized Jaynes–Cummings model, equations for coefficients of the wave function of the quantum system under consideration have been obtained for different stages of its evolution in processes of performing logical operations. The solution of the system of equations allows one to establish requirements that are imposed on the parameters of the initial Hamiltonian and must be satisfied for the effective operation of the computer; it also demonstrates the possibility of a universal set of quantum operations. Thus, based on the proposed approach, the possibility of constructing a compact multiatomic ensemble based on quantum computer using a quantum transistor for the implementation of two-qubit gates has been demonstrated.

S. A. Moiseev, and V. A. Skrebnev

Phys. Rev. A 91, 022329 (2015)

**DOI**: 10.1103/PhysRevA.91.022329

We propose an alternate pulse sequence for dynamical averaging of the dipole-dipole interactions and inhomogeneity of the magnetic fields in the nuclear-spin system. The sequence contains a short cycle of the periodic resonant pulse excitation that offers new possibilities for implementing the long-lived multiqubit quantum memory on the condensed spin ensembles that are so important for the construction of a universal quantum computer and long-distance quantum communications.

Agus Muhamad Hatta, Ali A. Kamli, Ola A. Al-Hagan and Sergey A. Moiseev

*J. Phys. B: At. Mol. Opt. Phys.* **48** 155502

**DOI: **10.1088/0953-4075/48/15/155502

Slow light with electromagnetically induced transparency (EIT) in the core of optical bre containing three-level atoms is investigated. The guided modes are treated in the weakly guiding approximation which renders the analysis into manageable form. The transparency window and permittivity prole of the core due to the strong pump eld in the EIT scheme is calculated. For a specic permittivity prole of the core due to EIT, the propagation constant of the weak signal eld and spatial shape of fundamental guided mode are calculated by solving the vector wave equation using the nite dierence method. It is found that the transparency window and slow light eld can be controlled via the optical bre parameters. The reduced group velocity of slow light in this conguration is useful for many technological applications such as optical memories, eective control of single photon elds, optical buer and delay line.

S A Moiseev and V A Skrebnev

J. Phys. B: At. Mol. Opt. Phys. 48 (2015) 135503 (5pp)

**DOI**: 10.1088/0953-4075/48/13/135503

We have proposed a new pulse sequence for the dynamical decoupling of decoherence effects in the ensemble of nuclear spins. The sequence provides a symmetric cycle that offers a strong suppression of the decoherence effects caused by the dipole–dipole interactions and the inhomogeneous local magnetic fields in nuclear spin ensemble dynamics. We have discussed a potential of the proposed pulse sequence for the long-lived storage of the multi-qubit quantum states.

S. A. Moiseev, A. I. Sidorova and B. S. Ham

Phys. Rev. A 89, 043802 (2014)

**DOI**: 10.1103/PhysRevA.89.043802

We have studied stationary and quasistationary signal light pulses in cold -type atomic media driven by counterpropagating control laser fields at the condition of electromagnetically induced transparency. By deriving a dispersion relation we present spectral and temporal properties of the signal light pulse and a significant influence of atomic decoherence on the coupled stationary light pulses for spatial splitting. Finally we discuss quasistationary light pulse evolution characterized by frozen spatial spreading for a robust coherent control of slow light pulses.

K. I. Gerasimov, S. A. Moiseev, V. I. Morosov, and R. B. Zaripov

Proc. of SPIE Vol. 9533 953310-1

**DOI**: 10.1117/12.2185472

The controllable storage and on demand retrieval of the microwave pulses by using the photon echo quantum memory approach based on a spin frequency comb of inhomogeneous broadening (SFC- protocol) have been demonstrated. We have used an electron-nuclear spin ensemble of tetracyanoethylene anion radicals in toluene which has a natural periodic structure of narrow electron-spin resonance (ESR) hyperfine lines. On-demand retrieval of the stored field has been realized by using two pulses of the magnetic field gradient of an opposite polarity which hold the electron spins in a dephased excited state during the storage time. The obtained experimental results demonstrate promising properties for coherent controlling the electron-nuclear spin ensemble of radicals in liquid that could be useful for implementation of room-temperature broadband quantum memory.

S. N. Andrianov and S. A. Moiseev

Phys. Rev. A 90, 042303 (2014)

**DOI**: 10.1103/PhysRevA.90.042303

Recently, great progress has been made in the creation of a solid-state quantum computer using superconducting qubits on Cooper pairs of charged electrons.However, this approach hasmet limitations due to decoherence effects caused by the strong Coulomb interaction of the superconducting qubitwith the environment. Here, we propose the solution of this problem by switching to another Bose-Einstein condensate (BEC), uncharged long-livedmagnons, wherein the magnon BEC qubit can be realized due to themagnon blockade isolating a pair of themagnon condensate energy levels in the mesoscopic and nanoscopic ferromagnetic dielectric sample.We demonstrate the singlequbit gates by operating quantum transition between these states in the external microwave field.We also consider implementation of the two-qubit gates by using the interaction between such magnon BEC qubits due to exchange by virtual photons in a microwave cavity. Finally, we discuss the condition for long-lived magnon BEC qubits, a scalable architecture, and promising advantages of the multiqubit quantum computer based on the magnon qubit.

K. I. Gerasimov, S. A. Moiseev, V. I. Morosov and R. B. Zaripov

Phys. Rev. A 90, 042306 (2014)

**DOI**: 10.1103/PhysRevA.90.042306

We have demonstrated the storage of electromagnetic pulses by exploiting a spin-echo quantum memory protocol. Therein, we have used an electron-nuclear spin ensemble of tetracyanoethylene anion radicals in toluene which has a natural periodic structure of narrow electron-spin resonance (ESR) hyperfine lines. Robust storage up to three temporal modes has been achieved with storage time ∼1 μs at room temperature on a conventional pulsed ESR spectrometer. On-demand retrieval of the stored field has been realized by holding the electron spins in a dephased state during the storage time. A longer storage time and the highest overall finesse ∼20 of the ESR spectrum have been attained by using multipulse dynamical decoupling of the electron spins from the noisy environment. The obtained experimental results suggest that the electron-nuclear spin ensemble of radicals in liquid should be a promising system for the room-temperature quantum memory.

Sergey N. Andrianov, Vladimir V. Bochkarev, and Sergey Moiseev

Eur. Phys. J. B (2014) 87: 128

**DOI**: 10.1140/epjb/e2014-41028-3

We have analysed the kinetics of Bose-Einstein condensed (BEC) magnons after pulsed excitation in a ferromagnet at room and low temperatures. For this purpose, we have derived the kinetic

equations using the nonequilibrium statistical operator method to describe the general form of the interactions in the magnon system. On the basis of this approach, we have analysed the nonlinear properties of the magnon BEC kinetics caused by interactions with magnon reservoir modes and phonons. We have found that formation of a quasi-stationary BEC magnon state is possible not only at room temperature but also at low temperatures, where the magnon-phonon interaction leads to formation of a residual BEC state with magnon population much larger than at room temperature. It was also observed that a moderately strong four-particle part of the magnon-magnon interaction violating the number of magnons is sufficient to facilitate magnon BEC formation. The predicted long-lived magnon BEC state could be promising for realisation of macroscopic qubits.