Biomedical subjects

Konrad Banaszek

Publications and source records attributed to Konrad Banaszek.

6 recordsLinked to original sources

PubMed2004

Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks.

Highly correlated photons or, accordingly, high-fidelity single-photon states are a prerequisite for closing detection loopholes in experimental tests of local realism and implementing scalable linear optical quantum computation. We demonstrate a parametric down-conversion source exhibiting a conditional detection efficiency of 51% (with corresponding preparation efficiency of 85%) and extraordinarily high detection rates of up to 8.5 x 10(5) coincidences/(s mW). We exploit a novel type-II phase matching configuration in a microstructured waveguide in conjunction with an ultrashort pump.

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PubMed2004

Experimental demonstration of entanglement-enhanced classical communication over a quantum channel with correlated noise.

We present an experiment demonstrating the entanglement enhanced capacity of a quantum channel with correlated noise, modeled by a fiber optic link exhibiting fluctuating birefringence. In this setting, introducing entanglement between two photons is required to maximize the amount of information that can be encoded into their joint polarization degree of freedom. We demonstrated this effect using a fiber-coupled source of entangled photon pairs based on spontaneous parametric down-conversion, and a linear-optics Bell state measurement. The obtained experimental classical capacity with entangled states is equal to 0.82+/-0.04 per a photon pair, and it exceeds approximately 2.5 times the theoretical upper limit when no quantum correlations are allowed.

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PubMed2003

Fiber-assisted detection with photon number resolution.

We report the development of a photon-number-resolving detector based on a fiber-optical setup and a pair of standard avalanche photodiodes. The detector is capable of resolving individual photon numbers and operates on the well-known principle by which a single-mode input state is split into a large number (eight) of output modes. We reconstruct the photon statistics of weak coherent input light from experimental data and show that there is a high probability of inferring the input photon number from a measurement of the number of detection events on a single run.

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PubMed2003

Direct measurement of the spatial Wigner function with area-integrated detection.

We demonstrate experimentally a novel technique for characterizing transverse spatial coherence by using the Wigner distribution function. The method is based on the measurement of interference between a pair of rotated and displaced replicas of the input beam with an area-integrating detector, and it provides an optimal signal-to-noise ratio in regimes when array detectors are not available. We analyze the quantum-optical picture of the presented measurement for single-photon signals and discuss possible applications in quantum information processing.

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PubMed2003

Managing photons for quantum information processing.

We study distinguishing information in the context of photonic quantum interference tailored for practical implementations of quantum information processing schemes. In particular, we consider the character of single-photon states optimized for multiple-source interference experiments and for experiments relying on Bell-state measurement and arrive at specific design criteria for photons produced by parametric down-conversion. Such states can be realistically implemented with available technology. We describe a novel method for characterizing the mode structure of single photons, and demonstrate it in the context of coherent light.

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PubMed2003

Photon counting with a loop detector.

We propose a design for a photon-counting detector that is capable of resolving multiphoton events. The basic element of the setup is a fiber loop, which traps the input field with the help of a fast electro-optic switch. A single weakly coupled avalanche photodiode is used to detect small portions of the signal field extracted from the loop. We analyze the response of the loop detector to an arbitrary input field and discuss both the reconstruction of the photon-number distribution of an unknown field from the count statistics measured in the setup and the application of the detector in conditional-state preparation.

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