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Yu. M. Golubev

Publications and source records attributed to Yu. M. Golubev.

At least 19 recordsLinked to original sources
arXiv2021

High-fidelity quantum gates for OAM qudits on quantum memory

The application of high-dimensional quantum systems (qudits) in quantum computing and communications seems to be a promising avenue due to the possibility of increasing the amount of information encoded in one physical carrier. In this work, we propose a method for implementing single-qudit gates for qudits based on light modes with orbital angular momentum. Method for logical qudits encoding, which ensures the quasi-cyclicity of operations, is introduced. Based on the protocol for converting the orbital angular momentum of light in the Raman quantum memory scheme [Vashukevich E.A. et. al. PRA, 101, 033830 (2020)], we show that the considered gates provide an extremely high level of fidelity of single-qudit transformations. We also compare quantum gates' properties for systems of different dimensions and find the optimal conditions for carrying out transformations in the protocol under consideration.

quant-ph↗
arXiv2020

Two-photon bunching inside a quantum memory cell

We demonstrate the effect of interference, similar to the Hong-Ou-Mandel effect, for two single-photon pulses by writing them sequentially inside a quantum memory cell in a tripod configuration.

quant-ph↗
arXiv2020

Finding the optimal cluster state configuration. Minimization of one-way quantum computation errors

In this paper, we estimate the errors of Gaussian transformations implemented using one-way quantum computations on cluster states of various configurations. From all possible cluster state configurations, we choose those that give the smallest computation error. Furthermore, we evaluate errors in hybrid computational schemes, in which Gaussian operations are performed using one-way computations with additional linear transformations. As a result, we find the optimal strategy for the implementation of universal Gaussian computations with minimal errors.

quant-ph↗
arXiv2019

Quantum theory of a laser soliton

The Heisenberg-Langevin equation for a spatial laser soliton in a wide-aperture laser with saturable absorption is constructed within the framework of consistent quantum electrodynamics. We discuss in detail the canonical variables for the generation field and the material two-level medium, consisting of centres providing amplification and absorption. It is assumed that laser generation evolves in time much more slowly than an atomic media. This assumption makes it possible to apply the adiabatic approximation and construct a closed equation for the amplitude of a laser field. Much attention is paid to the formulation of Langevin sources when deriving the equation since they play a decisive role in the formation of solitons' quantum statistical features. To provide an appropriate procedure for observing the quantum squeezing of a soliton, synchronization of laser generation by an external weak electromagnetic field is considered. Here we also present the results of the analysis of a classical laser soliton (neglecting the quantum fluctuations), which serves as the basis for further consideration of quantum effects.

quant-ph↗
arXiv2019

Criteria of minimum squeezing for quantum cluster state generation

In this paper, we assess possibilities of generating cluster states with different topologies being possessed of a finite squeezing resource of the initial oscillators used to generate a cluster state. We obtained the condition on minimum squeezing required for generating a cluster with a given topology as a simple estimation in terms of the coefficients of the adjacency matrix

quant-ph↗
arXiv2018

Effect of saturated absorption on sub-Poissonian lasing

This paper discusses the effect of saturated absorption on the quantum features of a sub-Poissonian laser. It is shown that when both media (laser and absorbing) are saturated, the appearance of an additional element in the cavity does not lead to the demolition of the quantum properties (regular statistics of photons and quadrature squeezing) of laser radiation.

quant-ph↗
arXiv2018

Squeezed supermodes and cluster states based on modes with orbital angular momentum

In this paper we discuss the possibility of building a linear cluster state based on modes with a certain orbital angular momentum (OAM). We show that in the system under consideration a field with a rich mode structure is generated in the cavity. We also analyze the conditions under which an infinite system of Heisenberg-Langevin equations describing the dynamics of intracavity fields can be shortened and solved analytically. To analyze the genuine number of quantum degrees of freedom, we use the supermodes technique. This approach allows us to build the most entangled cluster state.

quant-ph↗
arXiv2017

Noiseless signal shaping and cluster state generation with quantum memory cell

In this article, we employ multimode radiation of a synchronously pumped optical parametric oscillator (SPOPO) to build a cluster state through a conversion on the base of quantum memory cell. We demonstrate that by choosing an appropriate driving field we can ensure the effective writing of the only one supermode from the entire set of the SPOPO squeezed supermodes. Further, by changing the driving field profile at the readout, we convert the time profile of the retrieved signal while maintaining its quantum state. We demonstrate the possibilities of using the presented scheme by the example of creating a four-mode linear cluster state of light.

quant-ph↗
arXiv2016

Manipulation of quantum states in memory cell: controllable Mach-Zehnder interferometer

In this article, we consider the possibility of manipulation of quantum signals, ensured by the use of the tripod-type atomic memory cell. We show that depending on a configuration of driving fields at the writing and reading, such a cell allows both to store and transform the signal. It is possible to provide the operation of the memory cell in a Mach-Zehnder interferometer mode passing two successive pulses at the input. We proposed a procedure of partial signal read out that provides entanglement between the retrieved light and the atomic ensemble. Thus, we have shown that tripod atomic cell is a promising candidate to implement of quantum logical operations, including two-qubit ones, that can be performed on the basis of only one cell.

quant-ph↗
arXiv2016

Preservation of quantum correlations in femtosecond light pulse train within atomic ensemble

In this paper, we examined a possibility of preservation of a substantially multimode radiation in a single cell of quantum memory. As a light source we considered a synchronously pumped optical parametric oscillator (SPOPO). As it was shown in [1-4], SPOPO radiation has a large number of the correlated modes making it attractive for the purposes of the quantum communication and computing. We showed that these correlations can be mapped on the longitudinal spin waves of the memory cell and be restored later in the readout light. The efficiencies of the writing and readout depend on the mode structure of the memory determined by a mechanism of the light-matter interaction under consideration (the non-resonance Raman interaction) and by the profile of the driving light field. We showed that like the initial light pulse train, the restored one can be represented by a set of squeezed supermodes. The mapping of the quantum multimode correlations on the material medium offers opportunities to manipulate the quantum states within the memory cell followed by the reading of the transformed state.

quant-ph↗
arXiv2016

Storage and conversion of quantum-statistical properties of light in the resonant quantum memory on tripod atomic configuration

We have considered theoretically the feasibility of the broadband quantum memory based on the resonant tripod-type atomic configuration. In this case, the writing of a signal field is carried out simultaneously into two channels, and characterized by an excitation of two spin waves of the atomic ensemble. With simultaneous read out from both channels quantum properties of the original signal are mapped on the retrieval pulse no worse than in the case of memory based on Lambda-type atomic configuration. At the same time new possibilities are opened up for manipulation of quantum states associated with sequential reading out (and/or sequential writing) of signal pulses. For example, the pulse in squeezed state is converted into two partially entangled pulses with partially squeezed quadratures. Alternatively, two independent signal pulses with orthogonal squeezed quadratures can be converted into two entangled pulses.

quant-ph↗
arXiv2015

Quantum correlations and non-classicality in a system of two coupled vertical external cavity surface emitting lasers

Here we demonstrate that photocurrent noise reduction below the standard quantum limit and modal anticorrelation can arise in two mode coupled two-VECSEL system with common pump. This effect occurs due to correlated loss of laser modes. It is possible to suppress noise below the standard quantum limit even for Poissonian coherent pumping, whereas the regularity of the pump can be harmful for non-classicality.

quant-ph↗
arXiv2010

Quantum correlations and fluctuations in the pulsed light produced by a synchronously pumped optical parametric oscillator below its oscillation threshold

We present a simple quantum theory for the pulsed light generated by a synchronously pumped optical parametric oscillator (SPOPO) in the degenerate case where the signal and idler trains of pulses coincide, below threshold and neglecting all dispersion effects. Our main goal is to precise in the obtained quantum effects, which ones are identical to the c.w. case and which ones are specific to the SPOPO. We demonstrate in particular that the temporal correlations have interesting peculiarities: the quantum fluctuations at different times within the same pulse turn out to be totally not correlated, whereas they are correlated between nearby pulses at times that are placed in the same position relative to the centre of the pulses. The number of significantly correlated pulses is of the order of cavity finesse. We show also that there is perfect squeezing at noise frequencies multiple of the pulse repetition frequency when one approaches the threshold from below on the signal field quadrature measured by a balanced homodyne detection with a local oscillator of very short duration compared to the SPOPO pulse length.

quant-ph↗
arXiv2005

Laser photon statistics in the feedback loop

A mere correspondence between the electron statistics and the photon one vanishes in the feedback loop (FBL). It means that the direct photodetection, supplying us with the electron statistics, does not provide us with a wished information about the laser photon statistics. For getting this information we should think up another measurement procedure, and we in the article suggest applying the three-level laser as a auxiliary measuring device. This laser has impressive property, namely, its photon statistics survive information about the initial photon statistics of the laser which excites coherently the three-level medium. Thus, if we choose the laser in the FBL as exciting the three-level laser, then we have an possibility to evaluate its initial photon statistics by means of direct detecting the three-level laser emission. Finally, this approach allows us to conclude the feedback is not capable of creating a regularity in the laser light beam. Contrary, the final photon fluctuations turn out to be always even bigger. The mentioned above feature of the three-level laser takes place only for the strong interaction between the lasers (exciting and excited). It means the initial state of the exciting laser is changed dramatically, so our measurement procedure can not be identified with some non-demolition one.

quant-ph↗
arXiv2005

Quantum parallel dense coding of optical images

We propose quantum dense coding protocol for optical images. This protocol extends the earlier proposed dense coding scheme for continuous variables [S.L.Braunstein and H.J.Kimble, Phys.Rev.A 61, 042302 (2000)] to an essentially multimode in space and time optical quantum communication channel. This new scheme allows, in particular, for parallel dense coding of non-stationary optical images. Similar to some other quantum dense coding protocols, our scheme exploits the possibility of sending a classical message through only one of the two entangled spatially-multimode beams, using the other one as a reference system. We evaluate the Shannon mutual information for our protocol and find that it is superior to the standard quantum limit. Finally, we show how to optimize the performance of our scheme as a function of the spatio-temporal parameters of the multimode entangled light and of the input images.

quant-ph↗
arXiv2004

A Langevin analysis of fundamental noise limits in Coherent Anti-Stokes Raman Spectroscopy

We use a Langevin approach to analyze the quantum noise in Coherent Anti-Stokes Raman Spectroscopy (CARS) in several experimental scenarios: with continuous wave input fields acting simultaneously and with fast sequential pulsed lasers where one field scatters off the coherence generated by other fields; and for interactions within a cavity and in free space. In all the cases, the signal as well as the quantum noise due to spontaneous decay and decoherence in the medium are shown to be described by the same general expression. Our theory in particular shows that for short interaction times, the medium noise is not important and the efficiency is limited only by the intrinsic quantum nature of the photon. We obtain fully analytic results \emph{without} making an adiabatic approximation, the fluctuations of the medium and the fields are self solved consistently.

cond-mat.stat-mech↗
arXiv2004

Polarization statistical properties of the emission from the single mode Vertical-Cavity Surface-Emitting Lasers with the equally living laser levels

The full quantum-statistical theory of the Vertical-Cavity Surface-Emitting Laser (VCSEL) in the form of the Langevin equations is constructed for arbitrary relations between the frequency parameters. The same theoretical treatment as in Ref.[1,2] are used. For detailed analysis the theory is applied for lasers with equally living laser levels and on this basis the analytical expressions for the spectral densities of the Stokes parameter fluctuations are obtained in the explicit dependence on the physical phenomena, including the spin-flip and the optical anisotropy. It is demonstrated the arbitrary distribution of electrons between the sub-levels under pumping does not restrict a possibility to achieve the noise reduction below the quantum limit. Under comparison with phenomenological treatment Ref.[3] it is shown this approach turns out to be not quite satisfied.

quant-ph↗