Macroscopic quantum information channel via the polarization-sensitive interaction between.pdf

a r X i v : q u a n t - p h / 0 5 0 9 2 2 0 v 1 3 0 S e p 2 0 0 5 Macroscopic quantum information channel via the polarization-sensitive interaction between the light and spin subsystems O.S. Mishina, D.V. Kupriyanov, Department of Theoretical Physics, State Polytechnic University, 195251, St.-Petersburg, Russia? E.S.Polzik QUANTOP - Danish Quantum Optics Center, Niels Bohr Institute, 2100 Copenhagen, Denmark? Abstract We discuss the quantum information channel, which is based on coherent and polarization sensi- tive interaction of light and atomic spin waves. We show that the joint Heisenberg dynamics of the polarization Stokes components of light and of the angular momenta of atoms has a wave nature and can be properly described in terms of the macroscopic polariton-type spin wave created in the sample. The principles of the quantum memory and readout protocols via the wave coupling of the output time modes in the light subsystem and the output spatial modes in the spin subsystem are demonstrated. PACS numbers: 03.67.Hk, 42.50.Ct ?Electronic address: ksana@quark.stu.neva.ru ?Electronic address: polzik@phys.au.dk 1 I. INTRODUCTION Quantum information processing based on continuous variables as an alternative to the discrete quantum schemes has been intensely studied during the last decade, see, for ex- ample, the review [1] and reference therein. Spin oriented atomic ensemble and polarized coherent light can be considered as convenient physical objects for storage and for transport of the quantum information, which can be written in the fluctuations of their polarizations. There are two experimental demonstrations of the entanglement and memory protocols in Refs.[2, 3], where the dynamical coupling of the spin fluctuations of an atomic ensemble consisting of cesium atoms with the polarization fluctuations of linearly polarized light via Faraday effect were implemented. The main feature and certain advantage of those protocols are in that only collective integr