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Seminar Physik funktioneller Materialien 12

Dipl.-Ing. Dr. Stephan Sponar

Experimental Demonstration of Direct Path State

Characterization by Strongly Measuring Weak Values in Neutron Interferometry

26.01.2017, 10:00, Kurt-Gödel-Hörsaal, EG, Strudlhofgasse 4, 1090 Wien


Unlike a measurement on a single system, which determines the system's current state after the measurement, quantum tomography works to determine the state prior to the measurements. Quantum tomography can be used for characterizing optical signals, including measuring the signal gain and loss of optical devices, as well as in quantum computing and quantum information theory to reliably determine the actual states of the qubits.

Quantum tomography has been around for quite a while. The usual approach to reconstruct a quantum state involves a lot of computational postprocessing of the data. So in 2011 a novel more direct tomographical method was established that makes it possible to determine the quantum state without the postprocessing. However, that novel method had a drawback. It uses so called weak measurements to determine the quantum state. Because of this weakness not a lot of information gain is very low for each measurement and the measurements have to be repeated many many times. Now we managed to combine both methods and got the benefits from both. We could use the method established in 2011 without the need of computational postprocessing, but at the same time we managed to use strong measurements, which spared us a lot of measurement time and made it possible to determine the quantum state with higher precision and accuracy. We performed a neutron interferometric experiment, but our results are not limited to that quantum system, but are in fact completely general. So they can be applied to many other quantum systems.



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