Atmospheric channel characteristics for quantum communication with continuous polarization variables

Heim, Bettina; Elser, Dominique; Bartley, Tim J.; Sabuncu, Metin; Wittmann, Christoffer; Sych, Denis; Marquardt, Christoph; Leuchs, Gerd

doi:10.1007/s00340-009-3838-8

Cited by 43 publications

(36 citation statements)

References 32 publications

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“…The experimental data were recorded within the framework of a setup on free-space quantum communication using continuous polarization variables, see figure 8 [42]. This experiment is a further development of earlier work performed in the laboratory [21] and on the roof of the MPL's building in Erlangen [20,22]. We use a grating-stabilized diode laser, with a wavelength of 809 nm that lies within an atmospheric transmission window.…”

Section: Real Fading Channelmentioning

confidence: 99%

“…In the case of discrete variable states and protocols, the impact of atmospheric channels on qubit-based QKD was actively investigated, for example, in [15][16][17][18][19]. The most negative effect of the free-space channel in this case is the background light (in the CV-based implementations, it is effectively filtered out by the homodyne detection [20]). The impact of fading channels on discrete variable protocols is similar to that of a constant attenuation and results in a decrease of the communication rate (which can also be partly compensated for by filtering [23]), but can preserve the entanglement properties upon post-selected measurements [24].…”

Section: Introductionmentioning

confidence: 99%

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Entanglement of Gaussian states and the applicability to quantum key distribution over fading channels

et al. 2012

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Entanglement of Gaussian states and the applicability to quantum key distribution over fading channels T h e o p e n -a c c e s s j o u r n a l f o r p h y s i c s New Journal of PhysicsEntanglement of Gaussian states and the applicability to quantum key distribution over fading channels Abstract. Entanglement properties of Gaussian states of light as well as the security of continuous variable quantum key distribution with Gaussian states in free-space fading channels are studied. These qualities are shown to be sensitive to the statistical properties of the transmittance distribution in the cases when entanglement is strong or when channel excess noise is present. Fading, i.e. transmission fluctuations, caused by beam wandering due to atmospheric turbulence, is a frequent challenge in free-space communication.We introduce a method of fading discrimination and subsequent post-selection of the corresponding sub-states and show that it can improve the entanglement 6 Authors to whom any correspondence should be addressed.Content from this work may be used under the terms of the Creative Commons Attribution-NonCommercialShareAlike 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New Journal of Physics 14 (2012) 0930481367-2630/12/093048+20$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft 2 resource and restore the security of the key distribution over a realistic fading link. Furthermore, the optimal post-selection strategy in combination with an optimized entangled resource is shown to drastically increase the protocol's robustness to excess noise, which is confirmed for experimentally measured fading channel characteristics. The stability of the result against finite data ensemble size and imperfect channel estimation is also addressed. Contents

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Section: Real Fading Channelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Entanglement of Gaussian states and the applicability to quantum key distribution over fading channels

et al. 2012

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“…However, systems using single-photon detectors suffer from background noise [6], while homodyne or heterodyne detection with bright local oscillator (LO) acting as a filter can reduce the background noise [7]. Experiments measuring Stokes operators [8][9][10][11][12][13] have shown the filtering effect of LO. Besides, quantum-limited coherent measurements between a geostationary Earth orbit satellite and a ground station has been conducted [14].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric effects on continuous-variable quantum key distribution

et al. 2018

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Compared to fiber continuous-variable quantum key distribution (CVQKD), atmospheric link offers the possibility of a broader geographical coverage and more flexible transmission. However, there are many negative features of the atmospheric channel that will reduce the achievable secret key rate, such as beam extinction and a variety of turbulence effects. Here we show how these factors affect performance of CVQKD, by considering our newly derived key rate formulas for fading channels, which involves detection imperfections, thus form a transmission model for CVQKD. This model can help evaluate the feasibility of experiment scheme in practical applications. We found that performance deterioration of horizontal link within the boundary layer is primarily caused by transmittance fluctuations (including beam wandering, broadening, deformation, and scintillation), while transmittance change due to pulse broadening under weak turbulence is negligible. Besides, we also found that communication interruptions can also cause a perceptible key rate reduction when the transmission distance is longer, while phase excess noise due to arrival time fluctuations requires new compensation techniques to reduce it to a negligible level. Furthermore, it is found that performing homodyne detection enables longer transmission distances, whereas heterodyne allows higher achievable key rate over short distances. heterodyne detection. Based on the deduced key rate formula, we consider three key parameters that affect the key rate. First, the transmittance change due to beam extinction [21] and turbulence effects (temporal pulse broadening, beam wandering, broadening, deformation, and scintillation) [22] are considered, where extinction likes the attenuation in an optical fiber. Our results demonstrate that beam wandering, broadening and deformation are the main turbulence effects affecting the achievable key rate. Second, we consider the communication interruption caused by angle-of-arrival fluctuations [20], and we found that the interruption probability is noticeable in the case of long-distance transmission. Third, we estimate the excess noise caused by pulse arrival time fluctuations which is found to be quite large. Based on the impacts mentioned above, we conduct a performance analysis.This paper is organized as follows. In section 2, we deduce the achievable secret key rate over the atmospheric channel. In section 3, with the result of section 2, we show how atmospheric effects affect the performance of GMCS CVQKD. In section 4, We consider all the implications mentioned in section 3 and perform a performance analysis. Finally we come to the conclusion and discussion in section 5.

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“…We fulfilled this demand by means of a specially developed protocol using the polarization degree of freedom to multiplex signal and LO in the same spatial channel mode already at the sender [26,27]. A successful pilot project proved the feasibility of CV QKD via a 100 m free-space link on the roof of our institute [28,29]. We now succeeded to established a point-to-point free-space link connecting two buildings at a distance of 1.6 km in an urban environment within the city of Erlangen.…”

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confidence: 99%

Atmospheric continuous-variable quantum communication

et al. 2014

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We present a quantum communication experiment conducted over a point-topoint free-space link of 1.6 km in urban conditions. We study atmospheric influences on the capability of the link to act as a continuous-variable (CV) quantum channel. Continuous polarization states (that contain the signal encoding as well as a local oscillator (LO) in the same spatial mode) are prepared and sent over the link in a polarization multiplexed setting. Both signal and LO undergo the same atmospheric fluctuations. These are intrinsically autocompensated which removes detrimental influences on the interferometric visibility. At the receiver, we measure the Q-function and interpret the data using the framework of effective entanglement (EE). We compare different state amplitudes and alphabets (two-state and four-state) and determine their optimal working points with respect to the distributed EE. Based on the high entanglement transmission rates achieved, our system indicates the high potential of atmospheric links in the field of CV quantum key distribution. 6 Contributed equally to this work.Quantum communication refers to the distribution of quantum states between two parties via a quantum channel. With regard to this, it is crucial that this quantum channel preserves the quantum properties of the distributed states. The most common channel implementations are optical fibers and free space. The latter offers great flexibility in terms of infrastructure establishment and links to moving objects are also feasible, see e.g. [1]. For a review of representative free-space quantum communication experiments see [2].Quantum key distribution (QKD) [3,4] is probably the most practical branch of quantum communication and concerns the establishment of a secret key jointly between two legitimate parties, Alice and Bob. As the security is based on the laws of quantum mechanics, in principle information theoretic-security can be achieved [4].Free-space QKD over a real atmospheric channel was first demonstrated in 1996 [5]. Since then, a number of prepare-and-measure as well as entanglement based schemes have been implemented in free space; the longest distance so far achieved on Earth is 144 km [6,7]. Nowadays, even quantum communication between earth and space is being conceived [8][9][10][11][12][13][14]. All of the systems so far referred to here have one major aspect in common: they are based on discrete quantum variables and use single photon threshold ('click') detectors, which involves spatial, spectral and/or temporal filtering in order to reduce background noise (see e.g. [15,16] for the first point-to-point demonstrations of free-space QKD in daylight).As already shown by Bennett [17], any two non-orthogonal quantum states suffice to ensure secure key distribution. This paved the way for continuous-variable (CV) protocols (for a review see [18,19]), based on a different approach: performing homodyne measurements on weak coherent states with the help of a bright local oscillator (LO). Generally, homodyne detectors offer immunity to st...

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Atmospheric channel characteristics for quantum communication with continuous polarization variables

Cited by 43 publications

References 32 publications

Entanglement of Gaussian states and the applicability to quantum key distribution over fading channels

Entanglement of Gaussian states and the applicability to quantum key distribution over fading channels

Atmospheric effects on continuous-variable quantum key distribution

Atmospheric continuous-variable quantum communication

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