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


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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    ABSTRACT: Non-classical states of light are of fundamental importance for emerging quantum technologies. All optics experiments producing multi-qubit entangled states have until now relied on outcome post-selection, a procedure where only the measurement results corresponding to the desired state are considered. This method severely limits the usefulness of the resulting entangled states. Here, we show the direct production of polarization-entangled photon triplets by cascading two entangled downconversion processes. Detecting the triplets with high efficiency superconducting nanowire single-photon detectors allows us to fully characterize them through quantum state tomography. We use our three-photon entangled state to demonstrate the ability to herald Bell states, a task which was not possible with previous three-photon states, and test local realism by violating the Mermin and Svetlichny inequalities. These results represent a significant breakthrough for entangled multi-photon state production by eliminating the constraints of outcome post-selection, providing a novel resource for optical quantum information processing.
    Nature Photonics 04/2014; 8(10). DOI:10.1038/nphoton.2014.218 · 32.39 Impact Factor
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    • "Besides the remarkable progress of photon state engineering using atomic memories (Kimble (2008); Yuan et al. (2008)) the majority of current experiments is based on the production of photon pairs in the process of spontaneous parametric down-conversion (SPDC), where the entangled photon pair is concluded from post-selection of randomly occurring coincidences. Here we present new insights into the heralded generation of photon states (Barz et al. (2010); Wagenknecht et al. (2010)) that are maximally entangled in polarization (Schrödinger (1935)) with linear optics and standard photon detection from SPDC (Kwiat et al. (1995)). We utilize the down-conversion state corresponding to the generation of three pairs of photons, where the coincident detection of four auxiliary photons unambiguously heralds the successful preparation of the entangled state ( ´ Sliwa & Banaszek (2003)). "

    Advanced Photonic Sciences, 03/2012; , ISBN: 978-953-51-0153-6
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