Conditional preparation of X (2) macroscopic entangled states
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Conditional Preparation of c(2) Macroscopic Entangled States¶ S. A. Podoshvedov School of Computational Sciences, Korea Institute for Advanced Study 130-722, Seoul, Republic of Korea e-mail: [email protected] Received September 26, 2005
Abstract—Two experimental arrangements consisting of coupled spontaneous parametric down-converters with type-I phase matching pumped simultaneously by a powerful optical field in a coherent state through a balanced beam splitter and linear optical elements are proposed for conditional preparation of macroscopic entangled states in output pumping modes of the studied system. Successful generation of the macroscopic entangled state in the pumping modes is unambiguously heralded by coincident detection of two photons in the generated signal and idler modes of the system. We calculate the amount of entanglement and probabilities of successfully observing the χ(2) macroscopic entangled states in the total wavefunction. We show that the proposed schemes can be used to obtain a new type of macroscopic entangled states. PACS numbers: 03.65.Ud, 42.50.Dv DOI: 10.1134/S1063776106040029
1. INTRODUCTION The theory of quantum computation promises to revolutionize the future of computer technology in factoring large integers [1] and combinational searches [2]. For quantum communication purposes, entangled states of light fields are of particular interest. Such states can also be used, for example, for quantum key distribution [3] and quantum teleportation [4]. The entangled states are useful for quantum processing, but they are hard to produce and tend to decohere fast. Spontaneous noncollinear parametric down-converter with type-II phase matching is well known to produce true entanglement along certain directions of propagation of the generated optical beams [5]. It is well known that at certain angles between the pump beam and the optical axis of the crystal, namely, along two intersecting directions, the emitted light becomes unpolarized or entangled [5]. In recent years, the problem of physical production of entangled states has been intensively studied, but despite enormous progress in generating entangled states of photons [5], deterministic generation of the states remains elusive [6]. Indeed, the majority of current experiments in optics is based on the use of spontaneous parametric down-conversion, which is inherently random. Consequently, we can determine whether a pair of photons has been generated only by postselection produced by detectors. In certain applications, for example, in testing Bell inequalities [7], the randomness of the generated pair is not essential. Nevertheless, ¶
The text was submitted by author in English.
the conditional preparation of entangled states is required in some applications of quantum information, for example, in experiments involving multiple photon pairs [8] and in constructing a quantum-controlled sign gate [9]. Therefore, it is important to study the problem of conditional preparation of entangled states by optical methods [1
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