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arXiv:quant-ph/0607182

Free-Space distribution of entanglement and single photons over 144 km

Rupert Ursin, Felix Tiefenbacher, T. Schmitt-Manderbach, H. Weier, T. Scheidl, Michael Lindenthal, B. Blauensteiner, Thomas D. Jennewein, J. Perdigués, Pavel Trojek, Bernhard Ömer, M. Fuerst, M. Meyenburg, John Rarity, Zoran Sodnik, C. Barbieri, Harald Weinfurter, Anton Zeilinger

Published Jul 26, 2006• 503 citations

Abstract

Quantum Entanglement is the essence of quantum physics and inspires fundamental questions about the principles of nature. Moreover it is also the basis for emerging technologies of quantum information processing such as quantum cryptography, quantum teleportation and quantum computation. Bell's discovery, that correlations measured on entangled quantum systems are at variance with a local realistic picture led to a flurry of experiments confirming the quantum predictions. However, it is still experimentally undecided whether quantum entanglement can survive global distances, as predicted by quantum theory. Here we report the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality measured by two observers separated by 144 km between the Canary Islands of La Palma and Tenerife via an optical free-space link using the Optical Ground Station (OGS) of the European Space Agency (ESA). Furthermore we used the entangled pairs to generate a quantum cryptographic key under experimental conditions and constraints characteristic for a Space-to-ground experiment. The distance in our experiment exceeds all previous free-space experiments by more than one order of magnitude and exploits the limit for ground-based free-space communication; significantly longer distances can only be reached using air- or space-based platforms. The range achieved thereby demonstrates the feasibility of quantum communication in space, involving satellites or the International Space Station (ISS).

DOI: 10.48550/arxiv.quant-ph/0607182

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We report free-space distribution of entangled photon pairs over a noisy ground atmosphere of 13 km. It is shown that the desired entanglement can still survive after both entangled photons have passed through the noisy ground atmosphere with a distance beyond the effective thickness of the aerosphere. This is confirmed by observing a spacelike separated violation of Bell inequality of 2.45+/-0.09. On this basis, we exploit the distributed entangled photon source to demonstrate the Bennett-Brassard 1984 quantum cryptography scheme. The distribution distance of entangled photon pairs achieved in the experiment is for the first time well beyond the effective thickness of the aerosphere, hence presenting a significant step towards satellite-based global quantum communication.

Fundamental quantum optics test as well as quantum cryptography and quantum teleportation are based on the distribution of single quantum states and quantum entanglement respectively. We will discuss recent experimental achievements in the field of long-distance quantum communication via optical fiber as well as in free-space over a record breaking distance of 144 km. The European Space Agency (ESA) has supported a range of studies in the field of quantum physics and quantuminformation science in space for several years, and consequently a mission proposal Space-QUEST Quantum Entanglement for Space Experiments was submitted to the European Life and Physical Sciences in Space Program. This proposal envisions to perform space-to-ground quantum communication tests from the International Space Station (ISS) and will presented in this article.