Coherent repopulation of hyperfine structure levels in the field of a bichromatic resonant radio-frequency wave

We consider the resonant interaction between atoms with hyperfine energy levels and a bichromatic radio-frequency field. Nuclear Zeeman levels of an impurity center in a magnetic host form a structure of this kind. Using the spin-density-matrix formalism, we solve the problem of coherent repopulation of a system of three of these levels under the action of a bichromatic resonant radio-frequency wave, taking into account transverse relaxation, and note the connection between this effect and the well-known phenomenon of coherent population capture when a laser bichromatic field interacts resonantly with a three-level system. We discuss various possibilities for observation of this effect experimentally. Zh. éksp. Teor. Fiz. 111, 1236–1244 (April 1997)     

Kinetics of atoms in a bichromatic field

The kinetics of atoms in a bichromatic field is considered. Analytic solutions are obtained for the force, friction coefficient, and diffusion coefficient in the model of a two-level atom without limitations imposed on the intensity of light fields. This effect is observed in the domain of global minima and maxima of the optical potential (i.e., at points where the relative phase of two standing waves is ? = 0, π/2.     

Atom in a femtosecond bichromatic laser field

The ionization of real hydrogen atom is studied under the action of a two-color pulsed laser field of duration 2.12 fs consisting of a fundamental frequencyω and one of its harmonics. We study the effect of phase difference (φ betweenω and its harmonic on the ionization probability. It is found that ionization can be switched on and off by varying the relative phaseφ betweenω and its harmonic.     

Second-harmonic generation in a doubly resonant semiconductor microcavity

We demonstrate second-harmonic generation in a doubly resonant semiconductor microcavity. The monolithic cavity consists of an AlGaAs active medium sandwiched between two AlGaAs/AlAs dual-wavelength mirrors. The mirrors do not have any apparent periodicity because, unlike single- or dual-wavelength Bragg reflectors, they are engineered with dispersion taken into account. Quasi-phase matching is obtained by addition of the appropriate phases at reflection so as to compensate for the dephasing between the fundamental and the second-harmonic fields.     

对称强双色共振场中弛豫效应对二能级系统斯塔克分裂的影响

本文应用半径典理论、密度矩阵方法和探索场中二能级系统的能级斯塔克(Stark)分裂。指出与无弛豫效应相比较,弛予效应不仅改变了由光学斯塔克效应所产生的分裂能级的权重、展宽了这些能级,而且还出现新的分裂能级。     

Dispersion of a three-level quantum system in a bichromatic field

We consider aspects of the interaction between a V-type three-level quantum system and the bichromatic field of two waves, one of which is assumed to be weak. We trace the dynamics of splitting into individual components for the spectral contours of the absorption coefficient (gain) for the signal wave. We discuss the effect of amplification of the signal wave for its frequency-degenerate two-wave interaction with pumping, when the field frequency is tuned to the “zero dispersion” point. We determine the conditions with respect to the concentration of resonant atoms and the spectral regions of the frequencies of the interacting waves for which, in order to correctly describe the effects under consideration, we need to take into account the effect of pumping and the signal in both dipole-allowed transitions of an ensemble of V type three-level quantum systems. We present the results of numerical calculations of the imaginary and real parts of the susceptibility of the resonant medium at the frequency of the signal wave, as a function of the parameters for the high-power radiation and resonant transitions of the quantum V system. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 631–636, September–October, 2007.     

Hopping of chaotic dynamics in a doubly resonant parametric oscillator

We study a doubly resonant optical parametric oscillator where the pump can feed two pairs of signal-idler modes. We assume the presence of gain at the pump frequency. We investigate the various oscillation states of interest, namely, when only the first pair oscillates with the other pair having null amplitudes and vice versa. We demonstrate the exchange of dynamics between the mode pairs when the relevant parameters of the cavity, namely, the phase mismatch factors or the decay rates switch because of fluctuations. The exchange of dynamics is shown to be independent of the nature of dynamics, i.e. independent of whether the motion isn-periodic or chaotic. We also investigate the case where both the pairs can exhibit chaotic dynamics though these states are difficult to realize because of fluctuations.     

Conversion efficiency of a doubly resonant optical parametric oscillator

The conversion efficiency of a doubly resonant optical parametric oscillator endowed with a Fabry-Perot type resonator is shown, by numerical analysis, to increase with decreasing reflectivity of the output mirror.     

Theory of multiphoton and tunnel ionization in a bichromatic field

The imaginary-time method [6, 7] is used to calculate the multiphoton and tunnel ionization probabilities for atoms in a laser radiation field part of which is converted into the second harmonic. We assume that the first harmonic has a linear or elliptical polarization and the second harmonic is polarized linearly, with its polarization vector making an arbitrary angle with that of the first harmonic. The mean momentum of the photoelectrons knocked out from atoms is shown to depend on the phase shift between the first and second harmonics and their mutual polarization and to be identically equal to zero for a monochromatic field. An important difference between the case of elliptical polarization and the case of linear polarization of both harmonics is the absence of conditions under which the conditions for dominance of one of the two generation mechanisms considered here can be identified during the generation of terahertz radiation from the region of optical breakdown in a gas.     

Probing noise in flux qubits via macroscopic resonant tunneling

Macroscopic resonant tunneling between the two lowest lying states of a bistable rf SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian-shaped profile that is not peaked at the resonance point but is shifted to a bias at which the initial well is higher than the target well. The rms amplitude of the noise, which is proportional to the dephasing rate 1/tauphi, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low energy flux noise in this device is a quantum mechanical environment in thermal equilibrium.     

Susceptibility of a three-level V-type quantum system in a bichromatic field

A theory of interaction of a three-level V-type quantum system with a bichromatic field of two waves, one of which is weak, has been developed. It is suggested that the upper two levels of this system are closely spaced and, therefore, both waves interact simultaneously with both allowed transitions. An expression for nonlinear macroscopic polarization of the V-system has been obtained by the density-matrix method.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 67–71, January–February, 2005.     

Coherent hole-burnings induced by a bichromatic laser field

In a Doppler-broadened three-level Λ-type system driven simultaneously by a coupling laser and two equal-amplitude saturating laser fields with a frequency difference 2δ, the absorption spectrum of a weak probe laser exhibits multiple deep spectral holes through coherent hole-burning CHB with controllable numbers, widths, depths, and positions. More significant, changing δ or lasers directions, CHBs can degenerate into narrower and deeper spectral holes where the slope of the refractive index is very steep. The multiple narrow spectral holes in a single absorption profile are expected to have potential applications in high density storage, optical information processes, and slow-light.     

Kroll-Watson-type theorem for potential scattering in a bichromatic laser field

Summary We show that for potential scattering of electrons in a bichromatic laser field a Kroll-Watson type of theorem can be derived in which the scatteringT-matrix element is composed of a renormalized on-shell matrix element for scattering without a field times a generalized Bessel function factor. The radiation field has two components of frequency ω₁ and sω₁ (s=2,3,…) and both components are out of phase by an angle ϕ. Our paper is a generalization of earlier investigations which were performed in the first-order Born approximation.     

Thermal self-frequency locking of a doubly resonant optical parametric oscillator

The increase in the circulating signal and idler fields that occurs in a high- Q doubly resonant optical parametric oscillator (OPO) as it approaches resonance results in a small increase in the crystal temperature owing to absorption of the generated fields. The temperature change affects the refractive index of the crystal and alters the optical path length of the cavity. This effect may lead to self-frequency locking of the OPO to a specific resonance of the signal and idler fields, and it also results in peculiarities in the transient response of the system as it is scanned through resonance. We show that the experimentally observed effects are consistent with the results of a numerical model of the OPO.     

Nonlinear mode coupling in doubly resonant frequency doublers

The concept of a doubly resonant frequency doubler can be used for a variety of experiments concerning both classical phenomena like efficient frequency doubling at low power levels and quantum effects like squeezed states of light or Quantum Non Demolition (QND) measurements. In many of these experiments the strength of the nonlinear coupling of fundamental and second-harmonic modes is of crucial importance. First we treat the general theory for the calculation of the coupling parameter, which depends not only on properties of the nonlinear material but also on resonator geometry and some optical phases. On this basis we discuss in detail the situation for two different monolithic resonator geometries, namely a linear (standing-wave) and a ring (travelling-wave) cavity. Finally we compare theoretical predictions for these resonators to the experimentally achieved results.     

Multiphoton transitions in a spin system driven by strong bichromatic field

EPR transient nutation spectroscopy is used to measure the effective field (Rabi frequency) for multiphoton transitions in a two-level spin system bichromatically driven by a transverse microwave (MW) field and a longitudinal radio-frequency (RF) field. The behavior of the effective field amplitude is examined in the case of a relatively strong MW field, when the derivation of the effective Hamiltonian cannot be reduced to first-order perturbation theory in ω₁/ω_rf(ω₁ is the microwave Rabi frequency, ω_rf is the RF frequency). Experimental results are consistently interpreted by taking into account the contributions of second and third order in ω₁/ω_rf evaluated by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously broadened EPR line, the third-order correction modifies the nutation frequency, while the second-order correction gives rise to a change in the nutation amplitude due to a Bloch-Siegert shift.     

Dynamics of interacting qubits in a strong alternating electromagnetic field

The populations of energy levels of interacting qubits have been studied as functions of the field amplitude and other control parameters for a constant frequency of the external electromagnetic field. It has been found that the qubit coupling constant strongly affects the quantum-coherent Landau-Zener transitions between the qubit states and the formation of an interference pattern in level populations, depending on the field parameters. It has been demonstrated that it is possible to determine the qubit coupling constant by Landau-Zener interferometry.