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We show that oblivious transfer can be seen as the classical analogue to a quantum channel in the same sense as non-local boxes are for maximally entangled qubits.
The reflectivity of commercially available erbium-doped fiber amplifiers (EDFAs) was measured with coherent optical frequency domain reflectometry (C-OFDR). Reflections at the output isolator as well as the distributed gain along the erbium-doped fiber could be observed thanks to the high amplified spontaneous emission (ASE) rejection due to the coherent detection. Gain figures obtained with the OFDR technique are in good agreement with single-pass direct gain measurements.
The insertion loss of an integrated optic device is measured by means of the OFDR teclmique. Measurements of Rayleigh BackScattered intensity in the input and output fibers of the device allow direct detection of light power guided in the fiber before and after the component. The insertion and return losses of the component can thus be directly evaluated. Experimental results are in good agreement with measurements performed by the cut-back method.
We perform a transmission of polarization encoded quantum bits through 16 km of single mode optical fiber in the 1550 nm window.The polarization drift caused by the changing birefringence of the fiber is kept stable through the use of a polarization control system we developed.This system employs 2 classical reference signals with 0.8 nm spacing from the quantum channel.We also send through the same fiber an extra reference classical signal used to trigger the single-photon detector.To the best of our knowledge this is the first time a quantum channel is multiplexed with 3 classical signals in the same optical fiber.
The experiment performed aims to transfer the quantum information (QI) carried by "telecom photons" at 1310 nm to "visible photons". This is a necessary step to realize a quantum interface between photons and atoms. To this end, in the most general case, entanglement produced by parametric down-conversion is preserved when submitting one photon out of an entangled pair to a wavelength up-conversion process (i.e. sum frequency generation SFG) in a nonlinear crystal.
We implement a photon-counting Optical Time Domain Reflectometer (OTDR) at 1.55μm which exhibits a high 2-point resolution and a high accuracy.It is based on a low temporal-jitter photon-counting module at 1.55μm.This detector is composed of a periodically poled Lithium niobate (PPLN) waveguide, which provides a wavelength conversion from near infrared to visible light, and a low jitter silicon photon-counting detector.With this apparatus, we obtain centimetre resolution over a measurement range of tens of kilometres.
In the last few years the world in which Quantum Cryptography evolves has deeply changed. On the one side the revelations of Snowden, though he said nothing really new, made the world more aware of the importance to protect sensitive data from all kinds of adversaries, including sometimes "friends." On the other side, breakthroughs in quantum computation, in particular in superconducting qubits and surface-codes, made it possible that in 15 to 25 years there might be a quantum machine able to break today's codes. This implies that in order to protect today's data over a few decades, one has to act now and use some quantum-safe cryptography.
Generalized quantum measurements can be used to separate deterministically two nonorthogonal quantum states. However, such measurements also lead to inconclusive results, where the initial state remains unknown. We introduce a particular type of generalized quantum measurement, which we term loss induced generalized (LIGe) quantum measurement, and present an experimental realization. This LIGe measurement achieves optimal deterministic separation of two nonorthogonally polarized single photons. \textcopyright{} 1996 The American Physical Society.
We report on the experimental realization and characterization of an asynchronous heralded single-photon source based on spontaneous parametric down-conversion. Photons at 1550 nm are heralded as being inside a single-mode fibre with more than 60% probability, and the multi-photon emission probability is reduced by a factor of up to more than 500 compared to Poissonian light sources. These figures of merit, together with the choice of telecom wavelength for the heralded photons, are compatible with practical applications needing very efficient and robust single-photon sources.
Quantum cryptography could well be the first application of quantum mechanics at the single-quantum level. The rapid progress in both theory and experiment in recent years is reviewed, with emphasis on open questions and technological issues.
Here we present experimental realizations of two new entanglement detection methods: a three-measurement Bell inequality inequivalent to the Clauser-Horne-Shimony-Holt inequality and a nonlinear Bell-type inequality based on the negativity measure. In addition, we provide an experimental and theoretical comparison between these new methods and several techniques already in use: the traditional Clauser-Horne-Shimony-Holt inequality, the entanglement witness, and complete state tomography.
