Amplitude Of Pump Field Research Articles

Investigation of quadrature squeezing in parametric downconversion with a partially coherent pump

We investigate the behavior of squeezing in combined quadratures of biphotons generated in the parametric downconversion process for partially coherent pump beams in spatial, temporal, and spatiotemporal domains compared to fully coherent beams. These beams involve both stationary (continuous-wave) and non-stationary (pulsed) processes. This study also involves the derivation of complex Gaussian representation for a partially spatially coherent pump modeled as a Gaussian Schell model beam, which is more resistant to the effects of turbulence. Our findings illustrate that by employing the partially coherent pump, one can generate a squeezed state possessing partially coherent properties without compromising in squeezing by optimizing pump field amplitude, interaction length, and degree of coherence of the pump. We anticipate these results to be useful in limiting the possibility of eavesdropping in noisy channels and optical high-precision measurements in the case of continuous-variable quantum key distribution based on two-mode squeezed states.

Parametric Generation of Subharmonics in a Composite Multiferroic Resonator

Parametric generation of subharmonics in a composite multiferroic resonator is observed and investigated. The resonator has the form of a disk and contains two mechanically coupled layers, one of which is amorphous ferromagnet $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{C}$ and the other piezoelectric lead zirconate titanate. The resonator is placed inside two planar electromagnetic coils with orthogonal axes. A static magnetic field of 0--100 Oe is applied parallel to the plane of the resonator. The resonator is excited in the frequency range f = 9--10 kHz by either a harmonic magnetic field with an amplitude of up to 5 Oe generated by one of the coils, or a harmonic electric field with an amplitude of up to 500 V/cm applied to the piezoelectric layer. When the pump field is above a certain threshold, generation of a subharmonic of half-frequency (f/2) is observed for three different excitation methods. The first two employed either the direct magnetoelectric effect or the converse magnetoelectric effect, while in the third a transformer system is utilized. The subharmonic is generated in a limited range of pump frequencies and its amplitude is a nonlinear function of both the pump-field amplitude and the strength of static magnetic field. A theory of parametric generation of the subharmonic in a multiferroic resonator is developed, taking into account the magnetoacoustic nonlinearity of the ferromagnetic layer of the structure and excitation of acoustic resonances near the pump and subharmonic frequencies. The theory qualitatively describes the main characteristics of the subharmonic generation.

Mechanical squeezing of the tripod-type four-level atom-assisted optomechanical system

Quadrature squeezing of a mesoscopic mechanical oscillator is investigated in a driven hybrid optomechanical system with a membrane-in-middle configuration containing a tripod-type four-level atom on either side of the membrane. We analyze in detail the influence of the coupling constant between cavity field and atom, amplitude of pump field, cavity pump detuning and Rabi frequency of classical field on the squeezing of the position quadrature of the vibrating membrane. The results show that the mechanical squeezing can be controlled by choosing the evolved parameters and initial state of atom, appropriately. Also, it is shown that a noticeable amount of squeezing can be obtained by increasing the amplitude of the classical pump field and therefore effective coupling constant. More over, we investigate that such a system can lead to a larger squeezing than the case with Λ-type three-level atom.

The amplitude of the cavity pump field and dissipation effects on the entanglement dynamics and statistical properties of an optomechanical system

In this paper we consider a cavity optomechanics consists of a two-level atom that interacts with a single-mode quantized field in the presence of a strong driving laser. By evaluating the effective Hamiltonian of the whole system which contains the field dissipation, we derive the time-dependent state vector of the system corresponding to particular initial conditions for the cavity field and oscillatory mirror. In the continuation, we pay our attention to the dynamical properties of the considered system by choosing different initial conditions for the atom. In particular, the effects of amplitude of the pump field, various initial atomic states and cavity loss rate on the entanglement, atomic population inversion and photon and phonon statistical properties are numerically analysed. According to the obtained results, maximal entanglement for all chosen initial states of the system is visible as time develops. Moreover, the presence of dissipative field leads to decrease the entanglement and finally tends to a fixed positive value, while the Mandel parameter as well as the population inversion reduce and tend to a fixed value in the negative region. Also, the appearance of non-classicality feature such as typical collapse–revival phenomenon in the (negative values of) Mandel parameter is noticeable.

Autoresonant Excitation and Control of Solitons in Magnetics

The method of exciting a soliton and complicated nonlinear structures in easy axis (EA) magnets based on the autoresonance effect upon pumping by an external circularly polarized field with a slowly varying amplitude is proposed. The threshold conditions of the pumping field amplitude ensuring such an excitation are determined. It is shown that autoresonance can also be used to control the parameters of soliton spin waves, in particular, their velocity and amplitude. The conditions of capturing a soliton by external pumping are found. The equations describing the time evolution of soliton parameters under the action of an external ac fields are obtained. It is discovered that a soliton can also be controlled with the help of the scattering-at-resonance effect.

Nonlinear magnetoelectric effects at high magnetic field amplitudes in composite multiferroics

Magnetoelectric effects (ME) in ferromagnetic-ferroelectric layered composites arise due to magnetostriction and piezoelectric effect in the ferroic phases and are mediated by mechanical strain. The ME coupling strength in such composites could be measured by electrical response to an applied ac magnetic field h and a bias magnetic field H. The coupling, in general, is linear for small ac field amplitudes, but one expects nonlinear ME interactions for high field strengths since the dependence of magnetostriction λ on magnetic fields is nonlinear. Here we report on nonlinear voltage response of a composite of ferromagnetic Metglas and piezoelectric lanthanum gallium tantalate (langatate) subjected to an ac and a bias magnetic fields, resulting in the generation of voltages at harmonics of the frequency of h. The dependences of the ME voltage of the first four harmonics on the magnetic fields for H = 0–20 Oe and h = 0–50 Oe were measured. Up to a hundred harmonics were observed in the voltage versus frequency spectra and was indicative of high nonlinearity of the ME coupling in the multiferroic structure. It is shown that for h smaller than the saturation magnetic field HS for magnetostriction in the ferromagnetic layer, the amplitudes of the ME voltages are proportional to the derivatives of λ with respect to H and show a power-law dependence on the pumping field amplitude An(H) ~ λ(n)(H)hn. We discuss a procedure for estimating the amplitudes of the harmonics for large pumping fields h, on the order of HS. The nonlinear ME effects in the composites are of interest for application in signal processing devices and highly sensitive magnetic field sensors.

Amplified emission and lasing in a plasmonic nanolaser with many three-level molecules

Steady-state plasmonic lasing is studied theoretically for a system consisting of many dye molecules arranged regularly around a gold nano-sphere. A three-level model with realistic molecular dissipation is employed to analyze the performance as function of the pump field amplitude and number of molecules. Few molecules and moderate pumping produce a single narrow emission peak because the excited molecules transfer energy to a single dipole plasmon mode by amplified spontaneous emission. Under strong pumping, the single peak splits into broader and weaker emission peaks because two molecular excited levels interfere with each other through coherent coupling with the pump field and with the dipole plasmon field. A large number of molecules gives rise to a Poisson-like distribution of plasmon number states with a large mean number characteristic of lasing action. These characteristics of lasing, however, deteriorate under strong pumping because of the molecular interference effect.

Role of interbranch pumping on the quantum-statistical behavior of multi-mode magnons in ferromagnetic nanowires

Theoretical studies are reported for the quantum-statistical properties of microwave-driven multi-mode magnon systems as represented by ferromagnetic nanowires with a stripe geometry. Effects of both the exchange and the dipole–dipole interactions, as well as a Zeeman term for an external applied field, are included in the magnetic Hamiltonian. The model also contains the time-dependent nonlinear effects due to parallel pumping with an electromagnetic field. Using a coherent magnon state representation in terms of creation and annihilation operators, we investigate the effects of parallel pumping on the temporal evolution of various nonclassical properties of the system. A focus is on the interbranch mixing produced by the pumping field when there are three or more modes. In particular, the occupation magnon number and the multi-mode cross correlations between magnon modes are studied. Manipulation of the collapse and revival phenomena of the average magnon occupation number and the control of the cross correlation between the magnon modes are demonstrated through tuning of the parallel pumping field amplitude and appropriate choices for the coherent magnon states. The cross correlations are a direct consequence of the interbranch pumping effects and do not appear in the corresponding one- or two-mode magnon systems.

Quantum statistics for a two-mode magnon system with microwave pumping: application to coupled ferromagnetic nanowires

A microscopic (Hamiltonian-based) method for the quantum statistics of bosonic excitations in a two-mode magnon system is developed. Both the exchange and the dipole–dipole interactions, as well as the Zeeman term for an external applied field, are included in the spin Hamiltonian, and the model also contains the nonlinear effects due to parallel pumping and four-magnon interactions. The quantization of spin operators is achieved through the Holstein–Primakoff formalism, and then a coherent magnon state representation is used to study the occupation magnon number and the quantum statistical behaviour of the system. Particular attention is given to the cross correlation between the two coupled magnon modes in a ferromagnetic nanowire geometry formed by two lines of spins. Manipulation of the collapse-and-revival phenomena for the temporal evolution of the magnon number as well as the control of the cross correlation between the two magnon modes is demonstrated by tuning the parallel pumping field amplitude. The role of the four-magnon interactions is particularly interesting and leads to anti-correlation in some cases with coherent states.

Paradoxes of the influence of small Ni impurity additions in a NaCl crystal on the kinetics of its magnetoplasticity

A comparative study of magnetoplasticity in two types of NaCl crystals differing in impurity content only by a small Ni addition (0.06 ppm) in one of them, NaCl(Ni), has been carried out. Two methods of sample magnetic exposure were used: in a constant field B = 0–0.6 T and in crossed fields in the EPR scheme—the Earth’s field BEarth (50 μT) and a variable pumping field \(\tilde B( \sim 1 \mu T)\) at frequencies ν ~ 1 MHz. In the experiments in the EPR scheme, the change of the field orientation from \(\tilde B \bot B_{Earth}\) to \(\left. {\tilde B} \right\|B_{Earth}\) led to almost complete suppression of the effect in the NaCl(Ni) crystals and reduced only slightly (approximately by 20%) the height of the resonance peak of dislocation mean paths in the crystals without Ni, with the amplitude of the mean paths in NaCl(Ni) in the orientation \(\tilde B \bot B_{Earth}\) having been appreciably lower than that in NaCl. In contrast, upon exposure to a constant magnetic field, a more intense effect was observed in the crystal with Ni. The threshold pumping field amplitude \(\tilde B\), below which the effect is absent under resonance conditions, for the NaCl(Ni) crystals turned out to be a factor of 5 smaller than that for NaCl, while the thresholds of a constant magnetic field coincide for both types of crystals. All these differences are discussed in detail and interpreted.

The new ultra high-speed all-optical coherent streak-camera

In the present paper a new type of ultra high-speed all-optical coherent streak-camera was developed. It was shown that a thin resonant film (quantum dots or molecules) could radiate the angular sequence of delayed ultra-short pulses if a transverse spatial periodic distribution of the laser pump field amplitude has a triangle shape.

Resonant dislocation motion in NaCl crystals in the EPR scheme in the Earth’s magnetic field with pulsed pumping

Resonant dislocation motions in NaCl(Ca) crystals under the simultaneous action of the Earth’s magnetic field BEarth (∼66 μT) and a pulsed pump field \(\tilde B\) of sufficient amplitude \(\tilde B_m \) and certain duration τ have been detected and studied. The measured dislocation path peaks l(τ) have a maximum at τ = τr ≈ 0.53 μs. The resonance criterion has been found to be the ordinary EPR condition in which the g-factor is close to 2 and the optimum inverse pulse duration τr−1 is used instead of the harmonic pump field frequency νr. The largest peak l(τ) height is reached at mutually orthogonal dislocation (L) and magnetic field (BEarth and \(\tilde B\)) orientations. Pulsed field rotation to the position \(\tilde B\) ‖ BEarth significantly decreases but does not “kill” the effect. For dislocations parallel to the Earth’s field (L ‖ BEarth), the resonance almost disappears even at \(\tilde B\) ⊥ BEarth. In the optimum geometry of experiments, as the pump field amplitude \(\tilde B_m \) decreases from 17.6 to 10 μT, the path peak height lr = l(τr) decreases only by 7.5%, remaining at the level of lr ∼ 102 μm, and at a \(\tilde B_m \) further fall-off to 4 μT, it rapidly decreases to background values. In this case, the relative density of mobile dislocations similarly decreases from ∼90 to 40%. Possible physical mechanisms of the observed effect have been discussed.

Time-modulated type-II optical parametric oscillator: Quantum dynamics and strong Einstein-Podolsky-Rosen entanglement

We investigate semiclassical dynamics and quantum properties of light beams generated in time-modulated nondegenerate optical parametric oscillator (NOPO). Having in view production of continuous-variable (CV) entangled states of light beams we propose two experimentally feasible schemes of NOPO: (i) driven by continuously modulated pump field; (ii) under action of a periodic sequence of identical laser pulses. It is shown that the time modulation of pump field amplitude essentially improves the degree of CV entanglement in NOPO. On the whole the level of integral two-mode squeezing, which characterizes the degree of CV entanglement, goes below the standard limit established in an ordinary NOPO with monochromatic pumping. We develop semiclassical and quantum theories of these devices for both below- and above-threshold regimes of generation. Properties of CV entanglement for various operational regimes of the devices are discussed in the time domain in application to time-resolved quantum information technologies. Our analytical results are in well agreement with the results of numerical simulation and support a concept of CV entangled states of time-modulated light beams.

Soliton shape stabilization in a superlattice with next-to-nearest neighbor spectrum in a field of a nonlinear wave

The effect of an electric field of a nonlinear (cnoidal) electromagnetic wave (pumping field) upon the shape of the solitary electromagnetic wave (soliton) in the quantum semiconductor superlattice with two harmonics of the electron spectrum is studied. Propagation of electromagnetic waves is shown in this case to be described by the modified double sine-Gordon equation. The possibility of the amplification of the pulse and its transformation into the dissipative soliton is noticed. The speed and width of a soliton depend on the presence of the second harmonic in the superlattice electron energy spectrum. The dependence of the dissipative soliton parameters on temperature and pumping field amplitude is also noticed. The possibility of propagation of electromagnetic waves described by solutions of the modified sine-Gordon equation in the superlattice with the spectrum under study is found.

Direct observation of the excitonic ac Stark splitting in a quantum well

Ultrafast pump-probe measurements evidence the dynamical Stark splitting in the exciton absorption spectrum of a single semiconductor quantum well. The intensity of the Stark sidebands in the spectrum is comparable to the linear absorption and their separation scales as the pump field amplitude. In the time domain the Rabi oscillations are observed. The semiconductor Bloch equations solved in the Hartree-Fock approximation demonstrate that the coherent exciton-light coupling dominates over the many-body dephasing.

Collective dynamical cooling of neutral particles in a high-Qoptical cavity

We show that an ensemble of two-level atoms commonly coupled to a single, driven, damped high-$Q$ cavity mode could be cooled and trapped via the correlated dynamics of cavity field and the atomic motion. For sufficiently large detuning between the atoms and the field, spontaneous emission plays no role in the dynamics, and the cooling scheme can be applied to all particles with a sufficient optical dipole moment. The time scale of this collective cooling process increases with the particle number and can be optimized by suitably tailoring the pump field amplitude and frequency. The key properties of the underlying mechanism are discussed using a linearized model, where one can derive a closed set of equations for certain ensemble averages and the field. The results are then compared with N-particle dynamical simulations of the full equations.

On the transient and stationary parametric excitation of spin waves

Buildup times and the stationary values of spin wave excitations near the Suhl instability threshold are calculated numerically. The study is done in the framework of the two-mode model. The time evolution of the excitation may approach the steady state via oscillations that may last for a very long time. The stationary excitation N 0, and the buildup time τ b depend on the pumping power p, and the pumping field h via power laws: N 0= B( p/ p c−1) δ and τ b= A( h/ h c−1) − Δ . For the case of no de-tuning of the mode frequencies from ω p/2, δ=0.5 and Δ=0.98. In the case of modes that are de-tuned from ω p/2, δ=0.42 and Δ=1.1. The values for δ are consistent with experiments but the values for Δ are in bad agreement with experiment. It is shown that if a finite medium correction term is introduced into the equations of motion the threshold of the pumping field amplitude is below γ/ V where γ is the spin wave relaxation rate and V is the coupling of the spin waves to the pumping field. This result is very strange and raises serious doubts about the justification of the finite medium correction term.

Quantum fluctuations in the optical parametric oscillator in the limit of a fast decaying subharmonic mode.

The quantum fluctuations in a nondegenerate optical parametric oscillator are calculated without the standard linearization assumption. Analytical results are obtained with the help of a mean-field approximation, which is exact in the limit of a fast decaying subharmonic mode. This approach is equivalent to a linearization around a self-consistently determined pump field amplitude that takes into account fluctuations of the subharmonic mode. The range of validity of the mean-field approximation is analyzed, and the influence of the system size on field amplitudes and squeezing is discussed.

Interband quantum coherence in intersubband coupled quantum wells.

When two electron conduction subbands in a doped quantum well are coupled by a coherent laser pumping, electromagnetically induced transparency and Rabi splitting in the interband absorption spectrum of a probe light are found for steady electron dressed states. The effect of light-electron interaction on electron and hole eigenenergies and states are calculated using a generalized density-functional approach. The change of absorption coefficient with the pump field amplitude is studied and explained.

Electromagnetically induced transparency of interband transitions in quantum wells

In the presence of a coherent coupling between two electron conduction sub-bands within doped quantum wells, both the Coulomb and light induced electronic renormalizations on electron and hole eigenenergies and eigenstates are studied by employing a generalized density functional approach. The dynamic properties of interband absorption of a probing laser are investigated. Electromagnetically induced transparency in interband transitions and optical switching is shown. The effects on the absorption coefficient due to pump field amplitude, electron area density, inhomogeneous level broadening, and delta -doping layer position are investigated and explained.