Statistics of discrete photodetection of resonance fluorescence in the Mollow sidebands
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Statistics of Discrete Photodetection of Resonance Fluorescence in the Mollow Sidebands G. P. Miroshnichenko St. Petersburg State University of Information Technologies, Mechanics, and Optics, St. Petersburg, 197101 Russia e-mail: [email protected] Received June 3, 2008
Abstract—A method is proposed for generating conditional single-photon states with a high degree of purity in a single-mode cavity by successive discrete photodetection. The cavity is pumped by resonance fluorescence emission from a source atom driven by a classical field. The cavity is tuned to a Mollow sideband. A relation between detector parameters is found that makes it possible to interpret the detection of a probe atom in the excited state as unambiguous evidence that a pure single-photon state has been prepared in the cavity. An expression is derived for the prior probability of such an event, and dependence of the one-photon state population of the cavity field on detuning, relaxation rate, and time is examined. PACS numbers: 42.50.-p, 42.50.Dv DOI: 10.1134/S1063776108120054
1. INTRODUCTION Quantum information technologies offer a new approach to information processing, transmission, and storage, based on manipulation of units of quantum information (qubits). Single photons propagating in optical media can be used as qubits [1]. Schemes have been proposed where antibunched light is used to produce single photons that can be detected as Gaussian wave packets within certain time intervals [2, 3]. Quantum logic operations on flying qubits of this kind are performed by using optical implementations of quantum phase gates [4]. Methods for creating nonclassical states of an electromagnetic field mode have been examined, such as Fock state generation in a high-Q cavity [5]. The feasibility of a single-photon quantum processor was discussed in [1]. In this paper, it is shown that resonance fluorescence light can be used to generate conditional single-photon states of a cavity field by successive discrete photodetection. The resonance fluorescence spectrum was originally calculated by Mollow in semiclassical approximation as the Fourier transform of the two-time atomic dipole correlation function [6]. A consistent quantum theory of photoelectron counting was developed in [7]. According to [7], each photon detection cycle consists of an interval of interaction between the coupled source–field system and the detector, an instantaneous transition to an unoccupied photoionization state, and an interval of free evolution of the source–field system (detector dead time). The cycle duration varies randomly. In [7], approximations were introduced that made it possible to express multitime joint photoionization probabilities in terms of the freefield annihilation and creation operators by using Glauber’s correlation functions. The key approxima-
tion in [7] is the calculation of the evolution operator for the total density matrix of the coupled source–field– detector system performed by retaining only the linear terms in the field–detector
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