Papers by B. Blauensteiner
Optics Express, 2005
We have distributed entangled photons directly through the atmosphere to a receiver station 7.8 k... more 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.
33rd European Conference and Exhibition on Optical Communication - ECOC 2007, 2007
ABSTRACT We use standard CWDM-telecom equipment and optical switches to combine entangled photons... more ABSTRACT We use standard CWDM-telecom equipment and optical switches to combine entangled photons with all needed signalling channels and perform QKD via a single optical fiber over a distance of 25km.
2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
ABSTRACT
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
ABSTRACT Most quantum communication protocols rely on the distribution of entangled photon pairs.... more ABSTRACT Most quantum communication protocols rely on the distribution of entangled photon pairs. If the transmission channel is an optical fiber both photons should have a wavelength around 1550nm. We present a source of polarisation entanglement based on spontaneous parametric down-conversion (SPDC) at telecom wavelengths. Using fiber-pigtailed ppLN crystals we can profit from the clean χ2 SPDC process, as opposed to four-wave mixing techniques, and also from a stable and efficient coupling to single mode fibers. Using a cw-pump, a tight energy correlation between the entangled photons is achieved. This fact is used here to distribute the entanglement through multiple channels employing only passive wavelength multiplexing. We demonstrate a possible application scenario with a single central source distributing entanglement to four users simultaneously. The source can also be used for creating tri-partite entanglement using the recently demonstrated cascaded SPDC scheme.
Optics Express, 2013
We implement an entanglement distribution network based on wavelength-multiplexing and optical sw... more We implement an entanglement distribution network based on wavelength-multiplexing and optical switching for quantum communication applications. Using a high-brightness source based on spontaneous parametric down-conversion in periodically-poled lithium niobate waveguides, we generate polarisation entangled photon pairs with a broad spectrum covering the telecom wavelengths around 1550 nm. The photon pairs have entanglement fidelities up to 99%, and are distributed via passive wavelength multiplexing in a static multi-user network. We furthermore demonstrate a possible network application in a scenario with a single centralised source dynamically allocating two-party entanglement to any pair of users by means of optical switches. The whole system, from the pump laser up to the receivers, is fibre and waveguide based, resulting in maximal stability, minimal losses and the advantage of readily integrable telecom components in the 1550 nm range.
Advanced Free-Space Optical Communication Techniques/Applications II and Photonic Components/Architectures for Microwave Systems and Displays, 2006
We report on the experimental implementation of a BB84-type quantum key distribution protocol ove... more 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.
2005 European Quantum Electronics Conference, EQEC '05, 2005
ABSTRACT In quantum communication and cryptography experiments which utilize the properties of si... more ABSTRACT In quantum communication and cryptography experiments which utilize the properties of single-photons and/or photon pairs, knowledge of the spectral bandwidth of the photons is of great importance. A mobile fiber-coupled single-photon monochromator was constructed which possesses the necessary efficiency and resolution for spectral characterization of photons.
ABSTRACT It is well-known that multi-photon signals in quantum key distribution (QKD) with weak l... more ABSTRACT It is well-known that multi-photon signals in quantum key distribution (QKD) with weak laser pulses represent a security threat resulting in a reduced rate for secret-key production. Similarly, multi-pair contributions from spontaneous-parametric-down-conversion (SPDC) sources may cause information leak. In particular, in the case of polarization coding (i.e., when the polarization of photons is used to encode the logical qubits) a security risk occurs when the polarizations show some degree of correlation. In such a case an eavesdropper can perform a photon number splitting (PNS) attack by getting hold of, and analyzing, one photon out of the multi-photon state without causing any disturbance to the polarization of the other ones. It is therefore important to estimate the relative amount of polarization- correlated multi-pairs in SPDC signals. We present and discuss the results of a recent investigation on this subject. In our study, we consider a CW-SPDC-source scheme of Kwiat type, fully based on polarization-entanglement. The down-converted field is produced continuously, and a suitably chosen coincidence window replaces the concept of pulses.
Physical Review Letters, 2006
Interference of photons emerging from independent sources is essential for modern quantuminformat... more Interference of photons emerging from independent sources is essential for modern quantuminformation processing schemes, above all quantum repeaters and linear-optics quantum computers. We report an observation of nonclassical interference of two single photons originating from two independent, separated sources, which were actively synchronized with a rms timing jitter of 260 fs. The resulting (two-photon) interference visibility was (83 4)%.
Physical Review A, 2009
The first direct measurement of photon bunching (g (2) correlation function) in one output arm of... more The first direct measurement of photon bunching (g (2) correlation function) in one output arm of a spontaneous-parametric-down-conversion source operated with a continuous pump laser in the single-photon regime is demonstrated. The result is in agreement with the statistics of a thermal field of the same coherence length, and shows the feasibility of investigating photon statistics with compact cw-pumped sources. Implications for entanglement-based quantum cryptography are discussed.
Optics Express, 2007
We demonstrate non-degenerate down-conversion at 810 and 1550 nm for long-distance fiber based qu... more We demonstrate non-degenerate down-conversion at 810 and 1550 nm for long-distance fiber based quantum communication using polarization entangled photon pairs. Measurements of the two-photon visibility, without dark count subtraction, have shown that the quantum correlations (raw visibility 89%) allow secure quantum cryptography after 100 km of non-zero dispersion shifted fiber using commercially available single photon detectors. In addition, quantum state tomography has revealed little degradation of state negativity, decreasing from 0.99 at the source to 0.93 after 100 km, indicating minimal loss in fidelity during the transmission.
Nature Physics, 2007
Quantum entanglement is the main resource to endow the field of quantum information processing wi... more 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.
e & i Elektrotechnik und Informationstechnik, 2007
ABSTRACT Zusammenfassung Die Quantenkryptographie ist die erste Anwendung von direkten Quanteneff... more ABSTRACT Zusammenfassung Die Quantenkryptographie ist die erste Anwendung von direkten Quanteneffekten, die heutzutage bereits in diversen Labors zu Produkten weiterentwickelt wird. Der von den Autoren verfolgte Ansatz verwendet quantenmechanische Verschrnkung zwischen Photonen. Die deshalb auftretenden, neuartigen Effekte bewirken, dass ein "bedingungslos geheimer Schlssel" zwischen den Kommunikationspartnern ausgetauscht werden kann. In diesem Artikel wird erstmalig die Verteilung von Polarisationsverschrnkung ber lngere Distanzen in Glasfasern gezeigt. Die auftretenden Korrelationen zeigen solch hohe Gte, wie sie fr den Aufbau eines geheimen Schlssels notwendig ist.
Optics Express, 2005
We have distributed entangled photons directly through the atmosphere to a receiver station 7.8 k... more 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.
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Papers by B. Blauensteiner