Estimation of Output Channel Noise for Continuous Variable Quantum Key Distribution

Estimation of channel parameters is important for extending the range and increasing the key rate of continuous variable quantum key distribution protocols. We propose a new estimator for the channel noise parameter based on the method of moments. The method of moments finds an estimator from the moments of the output distribution of the protocol. This estimator has the advantage of being able to use all of the states shared between Alice and Bob. Other estimators are limited to a smaller publicly revealed subset of the states. The proposed estimator has a lower variance for high loss channel than what has previously been proposed. We show that the method of moments estimator increases the key rate by up to an order of magnitude at the maximum transmission of the protocol.Comment: 5 pages, 3 figure

Real time demonstration of high bitrate quantum random number generation with coherent laser light

We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests

Raw-data attacks in quantum cryptography with partial tomography

We consider a variant of the BB84 protocol for quantum cryptography, the prototype of tomographically incomplete protocols, where the key is generated by one-way communication rather than the usual two-way communication. Our analysis, backed by numerical evidence, establishes thresholds for eavesdropping attacks on the raw data and on the generated key at quantum bit error rates of 10% and 6.15%, respectively. Both thresholds are lower than the threshold for unconditional security in the standard BB84 protocol.Comment: 11 pages, 2 figure

Crop production efficiency of sugarcane in the state of São Paulo: I. Climate and soil aspects.

Neste artigo, utilizou-se o método das zonas agroecológicas da FAO como energia de entrada e o rendimento real da cultura, observado em condições de campo ou tabulado em escala municipal pelos institutos de estatística, foi considerado como a energia resultante do processo de bioconversão. Este trabalho teve por objetivo gerar mapas de eficiência para o Estado de São Paulo e analisar qual a importância relativa do clima e do solo na variabilidade espacial da eficiência no Estado de São Paulo

Joint measurement of multiple noncommuting parameters

Although quantum metrology allows us to make precision measurements beyond the standard quantum limit, it mostly works on the measurement of only one observable due to the Heisenberg uncertainty relation on the measurement precision of noncommuting observables for one system. In this paper, we study the schemes of joint measurement of multiple observables which do not commute with each other using the quantum entanglement between two systems. We focus on analyzing the performance of a SU(1,1) nonlinear interferometer on fulfilling the task of joint measurement. The results show that the information encoded in multiple noncommuting observables on an optical field can be simultaneously measured with a signal-to-noise ratio higher than the standard quantum limit, and the ultimate limit of each observable is still the Heisenberg limit. Moreover, we find a resource conservation rule for the joint measurement