We realize an end-to-end no-switching quantum key distribution protocol using continuous-wave coherent light. We encode weak broadband Gaussian modulations onto the amplitude and phase quadratures of light beams. Our no-switching protocol achieves high secret key rate via a post-selection protocol that utilizes both quadrature information simultaneously. We establish a secret key rate of 25 Mbits/s for a lossless channel and 1 kbit/s for 90% channel loss, per 17 MHz of detected bandwidth, assuming individual Gaussian eavesdropping attacks. Since our scheme is truly broadband, it can potentially deliver orders of magnitude higher key rates by extending the encoding bandwidth with higher-end telecommunication technology.Quantum key distribution (QKD) [1] is a technique for generating a shared cryptographic key between two parties, Alice and Bob, where the security of the shared key is guaranteed by the laws of quantum mechanics. QKD based on continuous variables (CV) [2], in particular coherent state QKD [4,5,6,7,8,9], promises significantly higher secret key rates in comparison to single photon schemes [1,3]. They are relatively simple to implement, in contrast to QKD protocols employing "non-classical" states [10]. Coherent states are readily produced by a stabilized laser and can be detected using high quantum efficiency detectors. Confidence in the practicability of coherent state QKD protocols has increased since it was shown that the security of these protocols can be ensured for channel losses greater than 50% using post-selection [6] or reverse reconciliation [7] procedures. In principle, it is therefore possible to generate a secure key even in the presence of arbitrarily high loss. This development, coupled with potentially high secret key rates, render coherent state QKD protocols viable contenders for real-world cryptographic applications.Our coherent state QKD protocol builds on previous protocols presented in [5,6,7] and is an advance on random switching by simultaneously measuring both measurement bases [8]. The QKD protocol operates as follows. Alice draws two random numbers x A and p A from two Gaussian probability distributions with zero mean and variances of V (x A ) and V (p A ) respectively. Alice prepares a coherent state |x A + ip A and sends it to Bob. As a result of losses in the quantum channel, vacuum noise is coupled into the transmitted state. On receiving the state, Bob simultaneously measures both the amplitude (x B ) and phase (p B ) quadratures of the state via a 50/50 beam splitter. At this stage, Alice and Bob share correlated random data from which they can generate a secret key. They use postselection [6] to reverse any initial "information advantage" a potential eavesdropper (Eve) might have obtained, and perform information reconciliation and privacy amplification to distill a final secret key. Although no-switching coherent state QKD protocols have been demonstrated to be secure against coherent (collective) attacks [11] and progress has been made towards proving the uncondi...

The generation of random numbers via quantum processes is an efficient and reliable method to obtain true indeterministic random numbers that are of vital importance to cryptographic communication and large-scale computer modeling. However, in realistic scenarios, the raw output of a quantum random-number generator is inevitably tainted by classical technical noise. The integrity of the device can be compromised if this noise is tampered with, or even controlled by some malicious party. To safeguard against this, we propose and experimentally demonstrate an approach that produces side-information independent randomness that is quantified by min-entropy conditioned on this classical noise. We present a method for maximizing the conditional min-entropy of the number sequence generated from a given quantum-to-classical-noise ratio. The detected photocurrent in our experiment is shown to have a real-time random-number generation rate of 14 (Mbit/s)/MHz. The spectral response of the detection system shows the potential to deliver more than 70 Gbit/s of random numbers in our experimental setup.

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Purpose – The purpose of this paper is to investigate the impact of lean production practices on performance measures in machine tool industry and determines the lean criteria that can have significant positive impact on performance. Design/methodology/approach – The research paper presents a blend of theoretical framework and practical applications. Extant literature was reviewed and to achieve the research objectives, an exploratory survey was carried out in machine tool supply chains located in the national capital region of India. Reliability test, factor analysis and stepwise multiple regression analysis bring out several lean criteria that can affect key performance measures. Findings – It was found that two lean criteria, namely, strategic partnership with suppliers and cross-functional cross-organizational design and development teams significantly influenced most of the key performance measures. Some lean criteria were found to negatively affect the overall competitive potential of machine tool firms. Originality/value – The findings can encourage the management of non-adopter firms to adopt lean thinking and to select the lean production criteria that can be implemented to have significant positive impact on key performance indicators in machine tool value chains. This study is perhaps among the first few that focus on machine tool industry in India. The paper provides useful insights to the lean production implementers, consultants and researchers.