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

Resch, Katharina; Lindenthal, M.; Blauensteiner, B.; Böhm, Hannes R.; Fedrizzi, Alessandro; Kurtsiefer, C.; Poppe, Andreas; Schmitt-Manderbach, T.; Taraba, Michael; Ursin, Rupert; Walther, Philip; Weier, Henning; Weinfurter, Harald; Zeilinger, Anton

doi:10.1364/opex.13.000202

Cited by 118 publications

(73 citation statements)

References 27 publications

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“…The compact entangledphoton source, being pumped by a low-power diode laser, can readily be integrated into a satellite-borne photonic terminal, which was previously [14,16] not the case. We expect that this will allow fundamental tests of the laws of quantum mechanics on a global scale [26].…”

Section: ψmentioning

confidence: 99%

“…Furthermore photons can be easily generated, manipulated and transmitted over large distances via optical fibres or free-space links. Since the maximal distance for the distribution of quantum entanglement in optical fibres is limited to the order [2, 3, 4, 5] of ∼ 100 km, the most promising option for testing quantum entanglement on a global scale is currently free-space transmission, ultimately using satellites and ground stations [6].In recent years, various free-space quantum communication experiments with weak coherent laser pulses [7,8,9,10,11] and entangled photons [12,13,14,15] have been performed on ever larger distance scales and with increasing bit rates. The to-date most advanced test bed for free-space distribution of entanglement is a 144 km free-space link between two Canary Islands, where the successful transmission of one photon of an entangled pair was recently achieved [16].…”

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confidence: 99%

“…In recent years, various free-space quantum communication experiments with weak coherent laser pulses [7,8,9,10,11] and entangled photons [12,13,14,15] have been performed on ever larger distance scales and with increasing bit rates. The to-date most advanced test bed for free-space distribution of entanglement is a 144 km free-space link between two Canary Islands, where the successful transmission of one photon of an entangled pair was recently achieved [16].…”

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

et al. 2009

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Quantum entanglement enables tasks not possible in classical physics. Many quantum communication protocols [1] require the distribution of entangled states between distant parties. Here we experimentally demonstrate the successful transmission of an entangled photon pair over a 144 km free-space link. The received entangled states have excellent, noise-limited fidelity, even though they are exposed to extreme attenuation dominated by turbulent atmospheric effects. The total channel loss of 64 dB corresponds to the estimated attenuation regime for a two-photon satellite quantum communication scenario. We confirm that the received two-photon states are still highly entangled by violating the CHSH inequality by more than 5 standard deviations. From a fundamental point of view, our results show that the photons are subject to virtually no decoherence during their 0.5 ms long flight through air, which is encouraging for future world-wide quantum communication scenarios.Entanglement is at the heart of many peculiarities encountered in quantum mechanics and has allowed many ground-breaking tests on the fundamentals of nature. Entangled photons are ideal tools to investigate the laws of quantum mechanics over long distances and timescales since they are not subject to decoherence. Furthermore photons can be easily generated, manipulated and transmitted over large distances via optical fibres or free-space links. Since the maximal distance for the distribution of quantum entanglement in optical fibres is limited to the order [2, 3, 4, 5] of ∼ 100 km, the most promising option for testing quantum entanglement on a global scale is currently free-space transmission, ultimately using satellites and ground stations [6].In recent years, various free-space quantum communication experiments with weak coherent laser pulses [7,8,9,10,11] and entangled photons [12,13,14,15] have been performed on ever larger distance scales and with increasing bit rates. The to-date most advanced test bed for free-space distribution of entanglement is a 144 km free-space link between two Canary Islands, where the successful transmission of one photon of an entangled pair was recently achieved [16]. In the present experiment we demonstrate a fundamentally more interesting scenario by sending both photons of an entangled pair over this free-space channel. By violating a Clauser-HorneShimony-Holt (CHSH) Bell inequality [17] we find that entanglement is highly stable over these long time spans -the photon-pair flight time of ∼ 0.5 ms is the longest lifetime of photonic Bell states reported so far, almost twice as long as the previous high [4,5] of ∼ 250 µs.The achieved noise-limited fidelity paves the way for free-space implementations of quantum communication protocols that require the transmission of two photons, e.g. quantum dense coding [18], entanglement purification [19], quantum teleportation [20] and quantum key distribution without a shared reference frame [21]. From a technological perspective, the overall two-photon loss bridged in our exper...

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Section: ψmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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

et al. 2009

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“…Entanglement distribution over fiber-based transmission lines has proven to maintain coherence over tens of kilometers [9,10,11]. However, the use of free-space links cannot be obviated when considering such purposes as airplane and satellite quantum links or hand-held communication devices [12,13,14].The increased quantum-channel capacity that is available when encoding the information in the OAM of the entangled photons was anticipated to be severely limited in a practical free-space link, due to atmospheric turbulence that causes wave front distortions. Several theoretical studies have addressed this aspect [15,16,17,18,19,20,21], but there is no unanimity on exactly how sensitive OAM entanglement is to atmospheric perturbations.…”

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Transport of orbital-angular-momentum entanglement through a turbulent atmosphere

et al. 2011

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We demonstrate experimentally how orbital-angular-momentum entanglement of two photons evolves under influence of atmospheric turbulence. We find that the quantum channel capacity is surprisingly robust: Its typical horizontal decay distance is of the order of 2 kilometers, demonstrating the potential of photonic orbital angular momentum for free-space quantum communication in a metropolitan environment.PACS numbers: 03.67. Hk, 42.50.Dv, 42.68.Ay, 42.25.Kb Quantum communication by means of entangled photon pairs allows for an intrinsically secure transmission of data, by distributing the pairs via a free-space or fiber channel to distant parties [1]. Most popular is polarization entanglement, which has dimensionality 2. Higher dimensionalities can be achieved using orbital-angularmomentum (OAM) entanglement [2,3,4] or energy-time entanglement [5,6]; this route provides for a larger channel capacity and an increased security against eavesdroppers [7,8]. However, the performance of a practical highdimensional quantum channel is an open issue. Here, we address this issue for the case of OAM entanglement distribution via a free-space channel.For quantum communication to be of practical relevance, it is imperative that the entanglement between the photons carrying the information survives over a reasonably long propagation distance. Entanglement distribution over fiber-based transmission lines has proven to maintain coherence over tens of kilometers [9,10,11]. However, the use of free-space links cannot be obviated when considering such purposes as airplane and satellite quantum links or hand-held communication devices [12,13,14].The increased quantum-channel capacity that is available when encoding the information in the OAM of the entangled photons was anticipated to be severely limited in a practical free-space link, due to atmospheric turbulence that causes wave front distortions. Several theoretical studies have addressed this aspect [15,16,17,18,19,20,21], but there is no unanimity on exactly how sensitive OAM entanglement is to atmospheric perturbations. So far, no experimental verdict has been obtained to clarify this issue.In this Letter, we present the first such experiment. We start with bipartite OAM entanglement of dimensionality 6, and demonstrate how the corresponding quantum correlations evolve when one of the photons traverses a turbulent atmosphere, emulated by controlled mixing of cold and hot air. Our experimental results are in excellent agreement with our theoretical model, which is based on a Kolmogorov description of atmospheric turbulence. Specifically, we show how increasing strengths of turbulence degrade the Shannon dimensionality, which was introduced in Ref.[4] as a simple measure to quantify the channel capacity. Scaling up our system to reallife dimensions, we find that its typical horizontal decay distance is about 2 km.Our experimental setup is depicted in Fig. 1. The PPKTP crystal emits correlated photon pairs with complementary OAM, in a state of the form |Ψ = The entanglement i...

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“…[9,10], and references therein). Currently, there is much interest in testing quantum mechanics for large space distances and eventually in implementing quantum information protocols in global scales [11][12][13][14][15]. Photons seem to be the ideal physical objects for this purpose.…”

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Influence of detector motion in entanglement measurements with photons

2010

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We investigate how the polarization correlations of entangled photons described by wave packets are modified when measured by moving detectors. For this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a function of the apparatus velocity. Our analysis is motivated by future experiments with entangled photons designed to use satellites. This is a first step toward the implementation of quantum information protocols in a global scale. Entanglement plays a central role in quantum theory as one of its most distinguishing features [1,2]. It allows for the proof that no theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics [3]. As for applications, entanglement is crucial to quantum cryptography [4][5][6], teleportation [7], dense coding [8], and to the conception of quantum computers (see, e.g., Refs. [9,10], and references therein). Currently, there is much interest in testing quantum mechanics for large space distances and eventually in implementing quantum information protocols in global scales [11][12][13][14][15]. Photons seem to be the ideal physical objects for this purpose. Since present technology limits the use of fiber optics in this context up to about 100 km [16], the most viable alternative to go beyond happens to be free-space transmission using satellites and ground stations [17][18][19]. Here, rather than discussing the paramount technical challenges related to these experiments, we focus on an intrinsic physical restriction posed by the motion of the satellites when special relativity is taken into consideration (see also Ref. [20], and references therein). We address this issue by investigating the ClauserHorne-Shimony-Holt (CHSH) Bell inequality [21] for two entangled photons when one of the detectors is boosted with some velocity. Hereafter we assumeh = c = 1 unless stated otherwise.Let us assume a system composed of two photons, A and B, as emitted in opposite directions along the z axis in a SPS cascade [22]. The polarization of photons A and B is measured along arbitrary directions as defined by the unit vectorsâ i andb j (i, j = 1, 2), respectively, which are orthogonal to the z axis. The distance between the two detectors is large enough to make both measurements causally disconnected. It is well known that the CHSH Bell inequalityis satisfied for local hidden variable theories. Hereis the polarization correlation function obtained after an arbitrarily large number N of experiments is performed, and P A n (â i ) assume +1 or −1 values depending on whether the polarization of photon A is measured alongâ i or orthogonally to it, respectively, and analogously for P B n (b j ). Now, we investigate inequality (1) in the context of quantum mechanics when we allow one of the detectors to move along the z axis (say, carried by a satellite). Let us write the normalized state of a two-photon system as [23,24] where s X , andHere, X = A, B distinguishes between both particles, k X = ( k X , k X ) are the corresponding four-momenta, and s X...

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

Cited by 118 publications

References 27 publications

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

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

Transport of orbital-angular-momentum entanglement through a turbulent atmosphere

Influence of detector motion in entanglement measurements with photons

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