Felix Tiefenbacher

Entanglement-based quantum communication over 144km

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. Bells 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).

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

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. Bells 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).

High-speed linear optics quantum computing using active feed-forward.

As information carriers in quantum computing, photonic qubits have the advantage of undergoing negligible decoherence. However, the absence of any significant photon–photon interaction is problematic for the realization of non-trivial two-qubit gates. One solution is to introduce an effective nonlinearity by measurements resulting in probabilistic gate operations. In one-way quantum computation, the random quantum measurement error can be overcome by applying a feed-forward technique, such that the future measurement basis depends on earlier measurement results. This technique is crucial for achieving deterministic quantum computation once a cluster state (the highly entangled multiparticle state on which one-way quantum computation is based) is prepared. Here we realize a concatenated scheme of measurement and active feed-forward in a one-way quantum computing experiment. We demonstrate that, for a perfect cluster state and no photon loss, our quantum computation scheme would operate with good fidelity and that our feed-forward components function with very high speed and low error for detected photons. With present technology, the individual computational step (in our case the individual feed-forward cycle) can be operated in less than 150 ns using electro-optical modulators. This is an important result for the future development of one-way quantum computers, whose large-scale implementation will depend on advances in the production and detection of the required highly entangled cluster states.

High-fidelity transmission of entanglement over a high-loss free-space channel

An experiment distributing entangled photons over 144 km significantly raises the bar on distance, channel loss and transmission time—encouraging news with regard to future long-distance quantum-communication networks.

Experimental Demonstration of Free-Space Decoy-State Quantum Key Distribution over 144 km

In this paper, we report on the successful quantum key distribution using attenuated laser pulses over a real distance of 144 km. This link between the Canary islands of La Palma and Tenerife has a path length through atmosphere much longer than from LEO satellites to a ground station and serves as a realistic test bed for future quantum communication to space.

Free-space quantum key distribution over 144 km

We report on the experimental implementation of a BB84-type quantum key distribution protocol over a 144 km free-space link using weak coherent laser pulses. The security was assured by employing decoy state analysis, and optimization of the link transmission was achieved with bi-directional active telescope tracking. This enabled us to distribute a secure key at a rate of 11 bits/s at an attenuation of about 35dB. Utilizing a simple transmitter setup and an optical ground station capable of tracking spacecraft in low earth orbit, this outdoor experiment demonstrates the feasibility of global key distribution via satellites.

Crossed-crystal scheme for femtosecond-pulsed entangled photon generation in periodically poled potassium titanyl phosphate

Thomas Scheidl, ∗ Felix Tiefenbacher, Robert Prevedel, 3 Fabian Steinlechner, Rupert Ursin, 5 and Anton Zeilinger 5 Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanng. 3, 1090 Vienna, Austria Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria Present address: Research Institute of Molecular Pathology (IMP) and Max F. Perutz Laboratories GmbH, Dr.-Bohr-Gasse 7-9, 1030 Vienna, Austria ICFO–Institut de Ciencies Fotoniques, 08860 Castelldefels (Barcelona), Spain Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria (Dated: April 29, 2014)

Free-Space Decoy-State Quantum Key Distribution

Quantum cryptography, the only method which can provide quantifiable security of a distributed key, became the first application of quantum information methods. Complementary to fiber based systems, free space optics enables one to establish a secure key in various new scenarios,e.g., authentication to money machines or short distance links in metropolitan areas. Here we report on secure communication over 144 km between the islands of Tenerife and La Palma. Decoy state analysis ensured the security of our attenuated pulse scheme for a link efficiency of about 35 dB and resulted in key rates of 231 bit/s, clearly demonstrating the feasibility of free space links to satellites enabling global secure key exchange.

QIPS: quantum information and quantum physics in space

The aim of the QIPS project (financed by ESA) is to explore quantum phenomena and to demonstrate quantum communication over long distances. Based on the current state-of-the-art a first study investigating the feasibility of space based quantum communication has to establish goals for mid-term and long-term missions, but also has to test the feasibility of key issues in a long distance ground-to-ground experiment. We have therefore designed a proof-of-concept demonstration for establishing single photon links over a distance of 144 km between the Canary Islands of La Palma and Tenerife to evaluate main limitations for future space experiments. Here we report on the progress of this project and present first measurements of crucial parameters of the optical free space link.

Applications of quantum entanglement on a ISS-spaceplatform

We proposed tests of quantum communication in space, whereby an entangled photon Source is placed onboard the ISS, and two entangled photons are transmitted via a simultaneous down link and received at two distant ground stations.