Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements

We analyze the creation of spin squeezed atomic ensembles by simultaneous dispersive interactions with several optical frequencies. A judicious choice of optical parameters enables optimization of an interferometric detection scheme that suppresses inhomogeneous light shifts and keeps the interferometer operating in a balanced mode that minimizes technical noise. We show that when the atoms interact with two-frequency light tuned to cycling transitions the degree of spin squeezing $\xi^2$ scales as $\xi^2\sim 1/d$ where $d$ is the resonant optical depth of the ensemble. In real alkali atoms there are loss channels and the scaling may be closer to $\xi^2\sim 1/\sqrt d.$ Nevertheless the use of two-frequencies provides a significant improvement in the degree of squeezing attainable as we show by quantitative analysis of non-resonant probing on the Cs D1 line. Two alternative configurations are analyzed: a Mach-Zehnder interferometer that uses spatial interference, and an interaction with multi-frequency amplitude modulated light that does not require a spatial interferometer.Comment: 7 figure

Consumption of woody biomass in industry, commercial, and public facilities in Serbia: Present state and possible contribution to the share of renewable sources in final energy consumption

This paper is the continuation of the presentation of results obtained in comprehensive researches of woody biomass consumption in Serbia conducted as a part of the TCP/FAO project “Wood energy for sustainable rural development”. The previous paper (No. 3, 2011) showed results of wood fuels consumption for households heating and this paper shows their consumption for the needs of industry, commercial and public facilities. Research results show that total consumption of woody biomass in Serbia in 2010 was 7.41 million m3, out of which 7.03 million m3 was in the form of roundwood and 0.38 million m3 was in the form of wood residue from industry. The biggest consumers of woody biomass (roundwood, chips, residues) are households with the participation of 86.54%, followed by the production of wood-based panels with 4.47% and energy production for own purposes of wood processing companies with 2.96%. Compared to the officially registered consumption in energy balance in the amount of 0.281 Mtoe, actual consumption of wood energy in Serbia in 2010 was 1.37 Mtoe or 4.9 times higher. Participation of wood energy in final energy consumption in Serbia was 57,300 TJ or 13.6% in 2010. Current use of wood energy substitutes imports of light heating oil in the value of 1.3 billion € or 650 million € in the case of natural gas substituting. Use of wood fuel prevented emissions of about 7 million tonnes of CO2 from fossil fuels