High-fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber

Abstract

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.

Coherent dynamics of a telecom-wavelength entangled photon source

“…However, successful distribution of photonic qubits depends on availability of suitable high-fidelity sources for links. Most experiments involving the distribution of entanglement over fibre have used downconversion as the source of entangled photons [6][7][8][9][10][11] . The Poissonian emission statistics of such systems produces an increasing number of multiple pairs as the generation probability increases 12 , and the probability of generating multiple pairs simultaneously is proportional to the probability of generating two single pairs separated by a chosen time, irrespective of pump power.…”

Secure Long-Distance Quantum Communication over Optical Fiber Quantum Channels

“…Moreover, the DPS QKD protocol can be implemented in long-distance quantum communications, between the quantum repeater nodes. As follows, we will focus on this QKD scheme, however there are many other QKD schemes available, see (Branciard et al, 2005), (Dušek et al, 2006), (Hübel et al, 2007), (Gomez-Sousa & Curty, 2009), (Kwiat et al, 2001), (Niederberger et al, 2005), (Renner et al, 2005).…”

“…The DPS QKD protocol has deep relevance to practical applications, since the differential phase shift QKD protocol is much simpler in hardware design than the well known QKD protocols, such as BB84 or the Six-state QKD protocols. Results on the security of DPS QKD protocol was published by Assche (Van Assche et al, 2004), Branciard, Gisin, and Scarani (Branciard et al, 2008), and several other attacks against various QKD schemes have been studied by Acín04 (Acín et al, 2004) (Dušek et al, 2006), Fasel (Fasel et al, 2004), Branciard (Branciard et al, 2005), and Gomez-Sousa and Curty (Gomez-Sousa & Curty, 2009), Hübel (Hübel et al, 2007), Niederberger (Niederberger et al, 2005), Renner05 (Renner et al, 2005).…”

“…As has been shown, the loss in the optical fiber link mostly depends on the length L of the channel (Fasel et al, 2004), (Galtarossa & Menyuk, 2005), (Gomez-Sousa & Curty, 2009), (Hübel et al, 2007). This length parameter affects the value of the transmission parameter t exponentially: 10 10 ,…”

Quantum entanglement distribution with 810 nm photons through telecom fibers

“…We extracted the entanglement visibility ͑a measure of the quality of entanglement͒, 8 raw coincidences, and secure key rate for QKD based on realistic error correction and privacy amplification 13 ͑Table I͒. To set a benchmark for comparison, measurements were performed locally with short 810 nm fibers ͑2 m͒, resulting in 95.7Ϯ 0.4% visibility.…”