High-fidelity transmission of entanglement over a high-loss free-space channel (original) (raw)

Entanglement-based quantum communication over 144 km

Nature Physics, 2007

Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. In view of applications such as quantum cryptography or quantum teleportation, extension of quantum-entanglement-based protocols to global distances is of considerable practical interest. Here we experimentally demonstrate entanglement-based quantum key distribution over 144 km. One photon is measured locally at the Canary Island of La Palma, whereas the other is sent over an optical free-space link to Tenerife, where the Optical Ground Station of the European Space Agency acts as the receiver. This exceeds previous free-space experiments by more than an order of magnitude in distance, and is an essential step towards future satellite-based quantum communication and experimental tests on quantum physics in space.

Long-distance quantum communication with entangled photons using satellites

IEEE Journal of Selected Topics in Quantum Electronics, 2003

The use of satellites to distribute entangled photon pairs (and single photons) provides a unique solution for long-distance quantum communication networks. This overcomes the principle limitations of Earth-bound technology, i.e. the narrow range of some 100 km provided by optical fiber and terrestrial free-space links.

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

. 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 [25] 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).

Quantum Information and Quantum Physics in Space: Experimental Evaluation

2000

Space links offer an ideal solution for global Quantum Communication, e.g. for secure key exchange. At the same time, the space environment enables fundamental tests of quantum phenomena, in particular quantum non-locality. Within the first part of this study, the detailed designs of mid-term and long-term experiments for the demonstration of Quantum Communications applications as well as fundamental principles of Quantum Physics have been further investigated, both from the scientific impact point of view, and in terms of the technical feasibility of the required space infrastructure. In the second part of the study, a multipurpose ground-based proof-of-concept experiment was defined and its detailed design was carried out. Its flexible and modular design of the demonstrator ensured compatibility with the testing of several phenomena (single photon channel, testing of atmospheric effects, entanglement distribution). Using this demonstrator, we performed basic ground-to-ground Quantum Communications experiments, that are representative of the needs of space systems in order to identify and evaluate the main limitations of future space-to-ground (or fully space-based) experiments. These experiments established single photon links between the Canary islands of La Palma and Tenerife over a distance of 144 km. Utilising schemes with an entangled photon source and attenuated laser pulses, we demonstrated secure key exchange at optical attenuation values expected for a downlink from a low earth orbit (LEO) satellite. We also demonstrated that the Optical Ground Station (OGS) on Tenerife, developed for standard optical communication to and from satellites, can be adapted for the use in quantum communication protocols. The results thus clearly demonstrate the feasibility of satellite-based quantum key distribution. On the way towards a quantum communication experiment in space, further developments of components and technologies are required. We identified associated critical areas and proposed future activities for the development of a space-based quantum communication terminal. The work described in this report was done under ESA contract. Responsibility for the contents resides in the author organisation that prepared it.

QUANTUM COMMUNICATIONS IN SPACE ("QSpace") Executive Summary Report

Quantum information science is an intriguing example where purely fundamental and even philosophical research can lead to a new technology. The developments in this young field experience a worldwide boom. Quantum communication provides qualitatively new concepts, which are much more powerful than their classical counterparts. This report is a detailed study of the feasibility for adopting the concepts of fundamental quantum physics and quantum communications to a space infrastructure. It also develops physical and technological concepts specifically designed for a space environment. After reviewing the basics of physics of quantum information we characterize and compare quantum communications and classical optical communications. We discuss how to produce, manipulate, and measure qubits to be employed in quantum communication systems. Emphasis is put on photonic qubits, but we also review the present status of non-photonic realizations of qubits. We show that the various protocols discussed in connection with quantum information (like quantum cryptography or quantum teleportation) are feasible with today's technology when being based on photonic entanglement. Several space scenarios are analyzed in detail both with respect to quantum communication applications and to novel fundamental quantum physics experiments. With the latter one may address, e.g., open questions on quantum non-locality and on the possible influence of relativity on quantum coherence. In the last chapter we establish selection criteria for first proof-of-principle quantum communication experiments in space. Specifically, we propose to realize down-links from the International Space Station (ISS) to optical ground stations. For this scenario, we suggest a series of four experiments, one following in a logical way from the other, with increasing complexity and expenditure. We also present a preliminary design of the experiments. This includes block diagrams for space and ground terminals, a rough cost estimate, and a description of the quantum measurements to be performed. For these experiments we propose the use of entangled photon pairs. They do not only allow the implementation of "standard" quantum cryptography schemes but also open up new avenues both for fundamental research and for quantum communication.

Witnessing effective entanglement over a 2km fiber channel

Optics Express, 2010

We present a fiber-based continuous-variable quantum key distribution system. In the scheme, a quantum signal of two non-orthogonal weak optical coherent states is sent through a fiber-based quantum channel. The receiver simultaneously measures conjugate quadratures of the light using two homodyne detectors. From the measured Q-function of the transmitted signal, we estimate the attenuation and the excess noise caused by the channel. The estimated excess noise originating from the channel and the channel attenuation including the quantum efficiency of the detection setup is investigated with respect to the detection of effective entanglement. The local oscillator is considered in the verification. We witness effective entanglement with a channel length of up to 2 km.

Space-quest, experiments with quantum entanglement in space

Europhysics News, 2009

The European Space Agency (ESA) has supported a range of studies in the field of quantum physics and quantum information science in space for several years, and consequently we have submitted the mission proposal Space-QUEST (Quantum Entanglement for Space Experiments) to the European Life and Physical Sciences in Space Program. We propose to perform space-to-ground quantum communication tests from the International Space Station (ISS). We present the proposed experiments in space as well as the design of a space based quantum communication payload.

Distributing entanglement and single photons through an intra-city, free-space quantum channel

Optics Express, 2005

We have distributed entangled photons directly through the atmosphere to a receiver station 7.8 km away over the city of Vienna, Austria at night. Detection of one photon from our entangled pairs constitutes a triggered single photon source from the sender. With no direct time-stable connection, the two stations found coincidence counts in the detection events by calculating the cross-correlation of locally-recorded time stamps shared over a public internet channel. For this experiment, our quantum channel was maintained for a total of 40 minutes during which time a coincidence lock found approximately 60000 coincident detection events. The polarization correlations in those events yielded a Bell parameter, S=2.27±0.019, which violates the CHSH-Bell inequality by 14 standard deviations. This result is promising for entanglement-based freespace quantum communication in high-density urban areas. It is also encouraging for optical quantum communication between ground stations and satellites since the length of our free-space link exceeds the atmospheric equivalent.

Entangled quantum key distribution over two free-space optical links

Optics Express, 2008

We report on the first real-time implementation of a quantum key distribution (QKD) system using entangled photon pairs that are sent over two free-space optical telescope links. The entangled photon pairs are produced with a type-II spontaneous parametric down-conversion source placed in a central, potentially untrusted, location. The two free-space links cover a distance of 435 m and 1,325 m respectively, producing a total separation of 1,575 m. The system relies on passive polarization analysis units, GPS timing receivers for synchronization, and custom written software to perform the complete QKD protocol including error correction and privacy amplification. Over 6.5 hours during the night, we observed an average raw key generation rate of 565 bits/s, an average quantum bit error rate (QBER) of 4.92%, and an average secure key generation rate of 85 bits/s.