Reply to "Comment on `Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography'"

This is a Reply to the Comment by Lydersen et al. [arXiv: 1106.3756v1]

Gigahertz quantum key distribution with InGaAs avalanche photodiodes

We report a demonstration of quantum key distribution (QKD) at GHz clock rates with InGaAs avalanche photodiodes (APDs) operating in a self-differencing mode. Such a mode of operation allows detection of extremely weak avalanches so that the detector afterpulse noise is sufficiently suppressed. The system is characterized by a secure bit rate of 2.37 Mbps at 5.6 km and 27.9 kbps at 65.5 km when the fiber dispersion is not compensated. After compensating the fiber dispersion, the QKD distance is extended to 101 km, resulting in a secure key rate of 2.88 kbps. Our results suggest that InGaAs APDs are very well suited to GHz QKD applications.Comment: 4 pages, 4 figure

EPR studies of phase transitions in cadmium calcium acetate hexahydrate as a function of different paramagnetic impurity-ion concentrations

The phase tt':lnsition in cadmium calcium acetate hexahydrate (CCDAH) has been studied in detail with electron paramagnetic resonance (J;PR) as a function of two different paramagnetic ion concentrations. namely. Cu:• and Mn:• ions. The change in transition temperature (1:!2-143 Kl with Cuz• ion concentrations is explained in terms of mean-field theory and a soft vibrational mode of the -Ca-Cd1 _ ,Cu,-Ca- chain along the c axis of the crystal. While the same theory can also explain our observed transition temperature ( 118-128 K) as a function of the Mn2• ion concentration in this crystal. it does not explain why the limiting value of the transition temperature (i.e .• 145 K) of CaCd1 -.,CuzCCH3C00)4 ·6H~O as x tends to zero, is strikingly different from the limiting value of ( -128..+ K) of CaCd1_.,Mn,(CH3C00)4·6H:O as x tends to zero. The same theory also successfully c:xplains the absence of any phase transition in isomorphous CaCu(CH 3C00)~·6H 20. The value of -dT~Id.t is significantly higher with Mn:• than with Cu!• in CCDAH. [50163-1829(97)01329-5

Coexistence of high-bit-rate quantum key distribution and data on optical fiber

Quantum key distribution (QKD) uniquely allows distribution of cryptographic keys with security verified by quantum mechanical limits. Both protocol execution and subsequent applications require the assistance of classical data communication channels. While using separate fibers is one option, it is economically more viable if data and quantum signals are simultaneously transmitted through a single fiber. However, noise-photon contamination arising from the intense data signal has severely restricted both the QKD distances and secure key rates. Here, we exploit a novel temporal-filtering effect for noise-photon rejection. This allows high-bit-rate QKD over fibers up to 90 km in length and populated with error-free bidirectional Gb/s data communications. With high-bit rate and range sufficient for important information infrastructures, such as smart cities and 10 Gbit Ethernet, QKD is a significant step closer towards wide-scale deployment in fiber networks.Comment: 7 pages, 5 figure