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A. A. Pukhov

Publications and source records attributed to A. A. Pukhov.

At least 37 records · Page 2Linked to original sources
arXiv2017

Single-photon upconversion

The phenomenon of upconversion, in which a system sequentially absorbs two or more photons and emits a photon of a higher frequency, has been used in numerous applications. These include high-resolution non-destructive bioimaging, deep-penetrating photodynamic therapy, and photovoltaic devices. Due to the multi-photon mechanism of upconversion, its quantum yield cannot exceed 50%. We propose a new mechanism of upconversion, which is based on single-photon absorption; in this process, unlike in multiple-photon upconversion, the quantum yield can be higher than 50%. We show that in a system of two atoms interacting with a reservoir, a low-frequency excitation of one atom can be upconverted into a high-frequency excitation of another atom. The energy required for such an upconversion is drawn from the reservoir, which destroys coherence. Decoherence leads to the transition of the system from the pure state with a small energy dispersion to the mixed state with greater dispersion of energy, while the system entropy increases. The phenomenon of single-photon upconversion can be used to increase the efficacy of devices utilizing upconversion.

physics.optics↗
arXiv2017

Optimum gain for plasmonic distributed feedback lasers

Although nanolasers typically have low Q-factors and high lasing thresholds, they have been successfully implemented with various gain media. Intuitively, it seems that an increase in the gain coefficient would improve the characteristics of nanolasers. For a plasmonic nanolaser, in particular, a distributed-feed-back (DFB) laser, we propose a self-consistent model that takes into account both spontaneous emission and the multimode character of laser generation to show that for a given pumping strength, the gain coefficient has an optimal value at which the radiation intensity is at a maximum and the radiation linewidth is at a minimum.

cond-mat.mes-hall↗
arXiv2016

Approach for describing spatial dynamics of quantum light-matter interaction in dispersive dissipative media

Solving the challenging problem of the amplification and generation of an electromagnetic field in nanostructures enables to implement many properties of the electromagnetic field at the nanoscale in novel practical applications. A first-principles quantum mechanical consideration of such a problem is sufficiently restricted by the exponentially large number of degrees of freedom, and does not allow the electromagnetic field dynamics to be described if it involves a high number of interacting atoms and modes of the electromagnetic field. Conversely, the classical description of electromagnetic fields is incorrect at the nanoscale due to the high level of quantum fluctuations connected to high dissipation and noise levels. In this paper, we develop the framework with a significantly reduced number of degrees of freedom, which describes the quantum spatial dynamics of electromagnetic fields interacting with atoms. As an example, we consider the interaction between atoms placed in a metallic subwavelength groove, and demonstrate that a spontaneously excited electromagnetic pulse propagates with the group velocity. The developed approach may be exploited to describe non-uniform amplification and propagation of electromagnetic fields in arbitrary dispersive dissipative systems.

cond-mat.mes-hall↗
arXiv2016

Superradiance of non-Dicke states

In 1954, Dicke predicted that a system of quantum emitters confined to a subwavelength volume would produce a superradiant burst. For such a burst to occur, the emitters must be in the special Dicke state with zero dipole moment. We show that a superradiant burst may also arise for non-Dicke initial states with nonzero dipole moment. Both for Dicke and non-Dicke initial states, superradiance arises due to a decrease in the dispersion of the quantum phase of the emitter state. For non-Dicke states, the quantum phase is related to the phase of long-period envelopes which modulate the oscillations of the dipole moments. A decrease in dispersion of the quantum phase causes a decrease in the dispersion of envelope phases that results in constructive interference of the envelopes and the superradiant burst.

quant-ph↗
arXiv2015

Lowering the lasing threshold of distributed feedback lasers with loss

We study laser generation in 1D distributed feedback lasers with amplifying and lossy layers. We show that when the lasing frequency differs from the transition frequencies of the amplifying medium, loss induced lasing may occur due to the broadening of the resonator mode with increasing loss in the absorbing layers. This broadening leads to a shift in the lasing frequency towards the transition frequency. As a result, the cavity mode interaction with the amplifying medium is enhanced, and the lasing threshold is lowered.

physics.optics↗
arXiv2015

Spaser operation below threshold: autonomous vs. driven spasers

At the plasmon resonance, high Joule losses in a metal nanoparticle of a spaser result in its low Q-factor. Due to the latter, to achieve the spasing regime, in which the number of coherent plasmons exceeds the number of incoherent plasmons, unsustainably high pump rates may be required. We show that under the condition of loss compensation by a spaser driven by an external optical wave, the number of coherent plasmons increases dramatically, and the quantum noise is suppressed. Since the compensation of losses of the driving wave may occur even near the spasing threshold, the number of coherent plasmons may exceed the number of spontaneously excited plasmons at achievable pump rates.

cond-mat.mes-hall↗
arXiv2015

Noisy metamolecule: strong narrowing of fluorescence line

We consider metamolecule consisting of bosonic mode correlated with the two-level system: it can be, for example, plasmonic mode interacting with the quantum dot. We focus on the parameter range where all the correlations are strong and of the same order: interaction between bosonic mode correlated with the two-level system, external coherent drive and dissipation. Quantum Monte-Carlo simulations show a fluorescence of this system at dissipation larger than the driving amplitude and strong (by the order of magnitude) narrowing of its spectral line. This effect may be related to kind of a quantum stochastic resonance. We show that the fluorescence corresponds to finite domain over the coherent drive with sharp lower threshold and there is splitting of the Wigner function.

cond-mat.mes-hall↗
arXiv2015

Superradiance of a subwavelength array of independent classical nonlinear emitters

We suggest a mechanism for the emergence of a superradiance burst in a subwavelength array of nonlinear classical emitters. We assume that the emitters interact via their common field of radiative response and that they may have an arbitrary distribution of initially phases. We show that only if this distribution is not uniform, a non-zero field of radiative response arises leading to a superradiance burst. Although this field cannot synchronize the emitters, it forces fast oscillations of a classical nonlinear emitter to have long-period envelopes. Constructive interference in the envelopes creates a large dipole moment of the array which results in a superradiance pulse. The intensity of the superradiance is proportional to the squared number of the emitters, which envelopes participate in the fluctuation.

physics.optics↗
arXiv2014

Lacunas in the optical force induced by quantum fluctuations of quasicontinuum of multipole plasmons

We investigate the force between plasmonic nanoparticle and highly excited two-level system (molecule). Usually van der Waals force between nanoscale electrically neutral systems is monotonic and attractive at moderate and larger distances and repulsive at small distances. In our system, the van der Waals force acting on molecule has optical nature. At moderate distances it is attractive as usual but its strength highly increases in a narrow distance ranges ("lacunas"). We show that quantum fluctuations of (quasi)continuum of multipole plasmons of high, nearly infinite degree altogether form effective environment and determine the interaction force while their spectral peculiarities stand behind the large and narrow lacunas in force. We solve exactly the Hamiltonian problem and discuss the role of the dissipation.

cond-mat.mes-hall↗
arXiv2014

Spontaneous radiation of a two-level atom into multipole modes of a plasmonic nanoparticle

We consider the relaxation of an excited two-level system (TLS) positioned near a spherical plasmonic nanoparticle (NP). The transition frequency of the TLS is assumed to coincide with the frequency of the condensation point of NP plasmonic resonances. We show that the relaxation of the TLS excitation is a two-step process. Following an initial exponential decay, the TLS breaks in to Rabi oscillations. Depending upon the distance between the TLS and NP, the probability of the TLS being in the excited state exhibits either chaotic or nearly regular oscillations. In the latter case, the eigenfrequency of the TLS-NP system coincides with one of NP multipole modes.

cond-mat.mes-hall↗
arXiv2014

Causality and phase transitions in PT-symmetrical optical systems

We discuss phase transitions in PT-symmetric optical systems. We show that due to frequency dispersion of the dielectric permittivity, an optical system can have PT-symmetry at isolated frequency points only. An assumption of the existence of a PT-symmetric system in a continuous frequency interval violates the causality principle. Therefore, the ideal symmetry-breaking transition cannot be observed by simply varying the frequency.

physics.optics↗
arXiv2013

Nanolaser in the selfgenerated nonequilibrium environment: quantum fluctuations and entanglement

We investigate the dynamics of the spaser-based nanolaser in the strong incoherent pumping regime in the quantum limit when the photon number is the order of unity. We consider the situation where the newly irradiated photon finds itself in the cloud of earlier irradiated photons that are not thermalized. As the result the entanglement of nanoparticle with quantum dot degrees of freedom in the nanolaser and the lasing intensity increases several times. In fact the nonthermal bath effectively makes the nanolaser "more quantum" and master equation for the nanolaser density matrix nonlinear and selfconsistent.

cond-mat.mes-hall↗
arXiv2013

Loss compensation by spasers in metamaterials

We show that exact loss compensation can be achieved in active metamaterials containing spasers pumped over a wide range of pumping values both below and above the spasing threshold. We demonstrate that the difference between spaser operation below and above spasing threshold vanishes, when the spaser is synchronized by an external field. As the spasing threshold loses its significance, a new pumping threshold, the threshold of loss compensation, arises. Below this threshold, which is smaller than the spasing threshold, compensation is impossible at any frequency of the external field.

cond-mat.mes-hall↗
arXiv2012

Superradiance of a 2D-spaser array

We demonstrate that interacting spasers arranged in a 2D array of arbitrary size can be mutually synchronized allowing them to supperradiate. For arrays smaller than the free space wavelength, the total radiated power is proportional to the square of the number N of spasers. For larger arrays, the radiation power is linear in N. However, the emitted beam becomes highly directional with intensity of radiation proportional to N^2 in the direction perpendicular to the plane of the array. Thus, spasers, which mainly amplify near fields, become an efficient source of far field radiation when they are arranged into an array.

cond-mat.mes-hall↗
arXiv2012

Spaser chains

We show that depending on the values of the coupling constants, two different scenarios for the stationary behavior of a chain of interacting spasers may be realized: (1) all the spasers are synchronized and oscillate with a unique phase and (2) a nonlinear autowave travels along the chain. In the latter scenario, the traveling wave is harmonic unlike excitations in other known nonlinear systems. The amplitude of this wave is determined by pumping and the wavenumber is determined by the coupling constants. Due to the nonlinear nature of the system, any initial distribution of spasers' states evolves into one of these steady states.

cond-mat.mes-hall↗
arXiv2012

Rabi oscillations in spasers during the nonradiative plasmon excitation

In the approach to the stationary regime, a spaser exhibits complicated and highly nonlinear dynamics with anharmonic oscillations.1 We demonstrate that these oscillations are due to Rabi oscillations of the quantum dot in the field of the nanoparticle. We show that the oscillations may or may not arise dependent on the initial conditions.

cond-mat.mes-hall↗
arXiv2011

Channel spaser

We show that net amplification of surface plasmons is achieved in channel in a metal plate due to nonradiative excitation by quantum dots. This makes possible lossless plasmon transmission lines in the channel as well as the amplification and generation of coherent surface plasmons. As an example, a ring channel spaser is considered.

cond-mat.mes-hall↗