Article

Experimental demonstration of a heralded entanglement source

Nature Photonics (Impact Factor: 32.39). 07/2010; 4(8). DOI: 10.1038/nphoton.2010.123
Source: arXiv

ABSTRACT

The heralded generation of entangled states is a long-standing goal in
quantum information processing, because it is indispensable for a number of
quantum protocols. Polarization entangled photon pairs are usually generated
through spontaneous parametric down-conversion, but the emission is
probabilistic. Their applications are generally accompanied by post-selection
and destructive photon detection. Here, we report a source of entanglement
generated in an event-ready manner by conditioned detection of auxiliary
photons. This scheme benefits from the stable and robust properties of
spontaneous parametric down-conversion and requires only modest experimental
efforts. It is flexible and allows the preparation efficiency to be
significantly improved by using beamsplitters with different transmission
ratios. We have achieved a fidelity better than 87% and a state preparation
efficiency of 45% for the source. This could offer promise in essential
photonics-based quantum information tasks, and particularly in enabling optical
quantum computing by reducing dramatically the computational overhead.

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    • "Non-classical properties of such states enable heralded emission of photon pairs [1] [2] [3] as well as preparation of three-body entangled states (for example, Greenberger-Horne- Zeilinger (GHZ) states [4] [5]). There are several proposed solutions for the problem of three-photon generation such as cascaded or postselective second-order nonlinear processes [6] [7] [8] [9] [10] [11] [12] and formation of approximate photon triplets by SPDC photon pairs together with an attenuated coherent state [13]. "
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    • "However, these experiments have much lower heralding efficiencies; to the best of our knowledge, the best reported heralding efficiency for these systems is 3.3 × 10 −9 , five orders of magnitude lower than what we measure here [43]. Experiments based on six-photon schemes resulted in two-photon states with a fidelity of 84% [39] and 87% [40]. The measured heralding efficiency of approximately 10 −2 (including coupling and detection losses) reported by the six-photon experiments is higher, but with the changes discussed above our measured heralding efficiency would approach or even surpass this value. "
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    • "Indeed, the direct generation of CP light is far more favourable in terms of simplicity , compactness, energy efficiency and product cost. The high interest in CP light-emitting devices is due to their enormous potential in a wide range of current and future applications, including highly efficient liquid-crystal display (LCD) backlights [2], stereoscopic three-dimensional (3D) displays, optical quantum information processing and communication [3] [4], and optical spintronics [5]. For example, current backlit LCD technologies rely on polarising filters, alongside an electrically controlled, orientational birefringent LC material to generate an image. "
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