INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS B: ATOMIC, MOLECULAR AND OPTICAL PHYSICS J. Phys. B: At. Mol. Opt. Phys. 39 (2006) 4853–4859 doi:10.1088/0953-4075/39/23/004 Squeezing in the output field from a one-dimensional atom Kazuki Koshino Faculty of Systems Engineering, Wakayama University, 930 Sakaedani Wakayama 640-8510, Japan and PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan E-mail: ikuzak@sys.wakayama-u.ac.jp Received 5 July 2006, in final form 15 August 2006 Published 10 November 2006 Online at stacks.iop.org/JPhysB/39/4853 Abstract It is revealed that quadrature squeezing occurs in the output field from a one- dimensional atom driven by a classical field. The degree of squeezing depends on the intensity of the input field, and reaches 28% at the maximum. It can roughly be regarded that the output field is in a superposition of coherent and number states. 1. Introduction In the field of cavity quantum electrodynamics (QED), highly isolated quantum systems composed of cavity photons and atoms can be realized [1]. The principal merit of a cavity QED system lies in its long coherence time. Such good quantum coherence has enabled us to observe experimentally the quantum oscillation among several quantum levels [2, 3]. This oscillatory dynamics has been applied to the preparation of non-classical states among cavity photons and atoms [4, 5], and also to quantum-state measurements [6–8]. The potential of cavity QED systems in quantum state engineering is further enriched with the help of laser- induced coherence among the atomic levels [9]. For example, the generation of single-photons with controllable pulse shapes has been accomplished [10, 11]. Recently, it was pointed out that the generation of entangled photons is also possible in cavity QED systems by utilizing the motional degrees of freedom of an atom [12, 13]. Besides isolation of the internal atom–photon system, the cavity also acts as an amplifier of the photon field. Thus, a cavity QED system is also promising as a giant χ (3) system, in which the atomic Kerr nonlinearity due to transition saturation is drastically enhanced by a cavity. One demonstration of this giant nonlinear effect is the photon blockade, in which the cavity photon mode behaves as an effective two-level system with transition saturation [14–16]. Another demonstration of the giant χ (3) effect is a significant nonlinear phase shift obtained by extremely weak input fields [17, 18]. The experimental results suggest realization 0953-4075/06/234853+07$30.00 © 2006 IOP Publishing Ltd Printed in the UK 4853