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Register a new userExperimental wavelength-multiplexed entanglement-based quantum cryptography
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In state-of-the-art quantum key distribution (QKD) systems, the main limiting factor in increasing the key generation rate is the timing resolution in detecting photons. Here, we present and experimentally demonstrate a strategy to overcome this limitation, also for high-loss and long-distance implementations. We exploit the intrinsic wavelength correlations of entangled photons using wavelength multiplexing to generate a quantum secure key from polarization entanglement. The presented approach can be integrated into both fiber- and satellite-based quantum-communication schemes, without any changes to most types of entanglement sources. This technique features a huge scaling potential allowing to increase the secure key rate by several orders of magnitude as compared to non-multiplexed schemes.
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We propose a quantum transmission based on bi-photons which are doubly-entangled both in polarisation and phase. This scheme finds a natural application in quantum cryptography, where we show that an eventual eavesdropper is bound to introduce a larger error on the quantum communication than for a single entangled bi-photon communication, when steeling the same information.
In counterfactual QKD information is transfered, in a secure way, between Alice and Bob even when no particle carrying the information is in fact transmitted between them. In this letter we fully implement the scheme for counterfactual QKD proposed in [T. Noh, PRL textbf{103}, 230501 (2009)], demonstrating for the first time that information can be transmitted between two parties without the transmission of a carrier.
Highly entangled quantum networks cluster states lie at the heart of recent approaches to quantum computing cite{Nielsen2006,Lloyd2012}. Yet, the current approach for constructing optical quantum networks does so one node at a time cite{Furusawa2008,Furusawa2009,Peng2012}, which lacks scalability. Here we demonstrate the emph{single-step} fabrication of a multimode quantum network from the parametric downconversion of femtosecond frequency combs. Ultrafast pulse shaping cite{weiner2000} is employed to characterize the combs spectral entanglement cite{vanLoock2003}. Each of the 511 possible bipartitions among ten spectral regions is shown to be entangled; furthermore, an eigenmode decomposition reveals that eight independent quantum channels cite{Braunstein2005} (qumodes) are subsumed within the comb. This multicolor entanglement imports the classical concept of wavelength-division multiplexing (WDM) to the quantum domain by playing upon frequency entanglement as a means to elevate quantum channel capacity. The quantum frequency comb is easily addressable, robust with respect to decoherence, and scalable, which renders it a unique tool for quantum information.
Entanglement-measurement attack is a well-known attack in quantum cryptography. In quantum cryptography protocols, eavesdropping checking can resist this attack. There are two known eavesdropping checking methods. One is to use decoy photon technology for eavesdropping checking. The other is to use the entanglement correlation of two groups of non-orthogonal entangled states for eavesdropping checking. In this paper, we prove the security against entanglement-measurement attack for the qudit-system-based quantum cryptography protocols which use the two methods for eavesdropping checking. Our security proof is useful to improve the eavesdropping checking method used in quantum cryptography protocols.
We report an experiment that demonstrates full function of a quantum router using entangled photons, where the paths of a single-photon pulse are controlled in a coherent fashion by polarization of another single photon. Through a projective measurement, we prepare the polarization of the control photon in arbitrary superposition states, leading to coherent routing of the target photon in quantum superposition of different paths. We demonstrate quantum nature of this router through optical measurements based on quantum state tomography and show an average fidelity of $(93.24pm 0.23)%$ for the quantum routing operation.
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