Mikhail V. Fedorov

Characterization of spectral entanglement of spontaneous parametric-down conversion biphotons in femtosecond pulsed regime

We verified the operational approach based on the direct measurement of the entanglement degree for bipartite systems. In particular spectral distributions of single counts and coincidence for pure biphoton states generated by a train of short pump pulses have been measured and the entanglement quantifier has been calculated. The approach gives an upper bound of entanglement stored in total biphoton states, which can reach extremely high values up to 104–105.

Two-color interference stabilization of atoms

The effect of interference stabilization is shown to exist in a system of two atomic levels coupled by a strong two-color laser field, the two frequencies of which are close to a two-photon Raman-type resonance between the chosen levels, with open channels of one-photon ionization from both of them. We suggest an experiment, in which a rather significant (up to 90%) suppression of ionization can take place and which demonstrates explicitly the interference origin of stabilization. Specific calculations are made for H and He atoms and optimal parameters of a two-color field are found. The physics of the effect and its relation with such well-known phenomena as LICS and population trapping in a three-level system are discussed.

Spectral Characterisation of Spontaneous Parametric-Down Conversion Entangled Photons Source in Femtosecond Pulsed Regime

We report on experimental measurements of coincidence and single particle spectral shapes of biphoton signals when frequency entangled states are generated by SPDC crystals pumped by short pulses.It is shown evidence for biphoton coincidence spectrum narrower and single-particle one wider than the pump spectrum, with a large contrast between coincidence and singles distributions.The investigation of biphoton correlations has been performed by fixing one monochromator at the maximal transmission wavelength on down-converted signal gate and scanning the one placed in the idler branch in order to observe the spectral distribution of single counts and coincidences.The degree of entanglement is evaluated by the ratio of the FWHM of single particle and coincidence distributions: the greater the ratio, the greater is the entanglement.The degree of entanglement in frequency variables can be very high: it increases linearly with the length of the crystal, and decreases with the growing pump pulse.

Diffraction as a reason for slowing down light pulses in vacuum

The mean velocity of a finite-size short light pulse in a far zone is defined as the vectorial sum of velocities of all rays forming the pulse. Because of diffraction, the mean pulse velocity defined in this way is always somewhat smaller than the speed of light. The conditions are found when this slowing-down effect is sufficiently pronounced to be experimentally measurable. Under these conditions the original Gaussian shape of a pulse is found to be strongly modified with significant lengthening of the rear wing of the field envelope. Schemes for measuring these effects are suggested and discussed.

Mechanisms of stabilization of Rydberg atoms in a strong light field

The main ideas and features of strong-field interference stabilization of Rydberg atoms are described. Both analytical and model calculations, as well as exact numerical solutions of the Schordinger equation are discussed and compared with each other. Experiments of the FOM Institute groups (The Netherlands) on stabilization of Ba and Ne atoms excited initially, correspondingly, to 27d and 5g levels are discussed. In both cases mechanisms of stabilization are argued in favor of different kinds of interference phenomena rather than adiabatic stabilization.