Three-intensity decoy state method for device independent quantum key distribution with basis dependent errors

We study the measurement device independent quantum key distribution (MDIQKD) in practice with limited resource, when there are only 3 different states in implementing the decoy-state method and when there are basis dependent coding errors. We present general formulas for the decoy-state method for two-pulse sources with 3 different states, which can be applied to the recently proposed MDIQKD with imperfect single-photon source such as the coherent states or the heralded states from the parametric down conversion. We point out that the existing result for secure QKD with source coding errors does not always hold. We find that very accurate source coding is not necessary. In particular, we loosen the precision of existing result by several magnitude orders for secure QKD.Comment: Published version with Eq.(17) corrected. We emphasize that our major result (Eq.16) for the decoy-state part can be applied to generate a key rate very close to the ideal case of using infinite different coherent states, as was numerically demonstrated in Ref.[21]. Published in PRA, 2013, Ja

Simple protocol for secure decoy-state quantum key distribution with a loosely controlled source

The method of decoy-state quantum key distribution (QKD) requests different intensities of light pulses. Existing theory has assumed exact control of intensities. Here we propose a simple protocol which is secure and efficient even there are errors in intensity control. In our protocol, decoy pulses and signal pulses are generated from the same father pulses with a two-value attenuation. Given the upper bound of fluctuation of the father pulses, our protocol is secure provided that the two-value attenuation is done exactly. We propose to use unbalanced beam-splitters for a stable attenuation. Given that the intensity error is bounded by $\pm5$, with the same key rate, our method can achieve a secure distance only 1 km shorter than that of an ideal protocol with exactly controlled source

Efectos de las claras en la productividad forestal y características del sitio en rodales de Pinus sylvestris

A clear-cutting system with soil preparation before replanting is usual for Scots pine stands in many European countries. Additionally, thinning regimes are applied during the rotation. Thus, forest floor is recreated in each rotation and can be influenced by thinning regime. The present study aimed to determine possible effects of thinning on production (evaluated by basal area) and forest-floor status (evaluated by dry mass, carbon and nitrogen content) in pine stands. We used data from four experiments established in 1962 in 25- to 45-year-old pine stands. In 2008, we analysed forest-floor characteristics under the observed stands. The results from basal area evaluation showed different development in treatments on all experiments during and at the end of observation. We observed substantial, but statistically non-significant, differences between treatments in quantity of dry mass (and of carbon and nitrogen) accumulated in humus horizons under Scots pine stands more than 40 years after first thinning.En muchos países europeos es habitual un sistema de tala rasa con preparación del suelo antes de la plantación para pino silvestre. Además, se aplican regímenes de claras durante la rotación. Por lo tanto, el suelo forestal se recrea en cada rotación y puede ser influenciado por el régimen de claras. El presente estudio tuvo como objetivo determinar los posibles efectos de las claras en la producción (evaluada por el área basal) y el estado del suelo forestal (evaluado por peso seco, contenido de carbono y nitrógeno) en los rodales de pino. Se utilizaron datos de cuatro experimentos, iniciado en 1962 en rodales de 25 a 45 años de edad. En 2008, se analizaron las características de suelo forestal de los rodales. Los resultados de la evaluación de área basal mostraron un crecimiento diferente entre los tratamientos en todos los experimentos durante y al final del periodo de observación. Se han observado diferencias importantes, pero estadísticamente no significativas, entre tratamientos en la cantidad de masa seca (y de carbono y nitrógeno) en el horizonte de humus acumulado en los rodales de pino silvestre durante más de 40 años después de la primera entresaca

Secure and efficient decoy-state quantum key distribution with inexact pulse intensities

We present a general theorem for the efficient verification of the lower bound of single-photon transmittance. We show how to do decoy-state quantum key distribution efficiently with large random errors in the intensity control. In our protocol, the linear terms of fluctuation disappear and only the quadratic terms take effect. We then show the unconditional security of decoy-state method with whatever error pattern in intensities of decoy pulses and signal pulses provided that the intensity of each decoy pulse is less than $\mu$ and the intensity of each signal pulse is larger than $\mu'$

Unconditional security of the Bennett 1992 quantum key-distribution scheme with strong reference pulse

We prove the unconditional security of the original Bennett 1992 protocol with strong reference pulse. We show that we may place a projection onto suitably defined qubit spaces before the receiver, which makes the analysis as simple as qubit-based protocols. Unlike the single-photon-based qubits, the qubits identified in this scheme are almost surely detected by the receiver even after a lossy channel. This leads to the key generation rate that is proportional to the channel transmission rate for proper choices of experimental parameters.Comment: More detailed presentation and a bit modified security proo

General theory of decoy-state quantum cryptography with source errors

The existing theory of decoy-state quantum cryptography assumes the exact control of each states from Alice's source. Such exact control is impossible in practice. We develop the theory of decoy-state method so that it is unconditionally secure even there are state errors of sources, if the range of a few parameters in the states are known. This theory simplifies the practical implementation of the decoy-state quantum key distribution because the unconditional security can be achieved with a slightly shortened final key, even though the small errors of pulses are not corrected.Comment: Our results can be used securely for any source of diagonal states, including the Plug-&-Play protocol with whatever error pattern, if we know the ranges of errors of a few parameter