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Frontiers in Optics

Generation and Reconstruction of Time-Bin Entangled Ququarts

Samantha J. Nowierski, Neal N. Oza, Prem Kumar, Gregory S. Kanter

Published Jan 1, 2016• 0 citations
Publisher

Abstract

We generate and reconstruct a maximally-entangled time-bin ququart using quantum state tomography and polarization-projective measurements. We measure a fidelity of 93.7 ± 0.4% to a maximally-entangled ququart with accidental coincidences subtracted.
DOI
10.1364/fio.2016.fw3b.2

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Quantum state tomography (QST) is an essential tool for characterizing an unknown quantum state. Recently, QST has been performed for entangled qudits based on orbital angular momentum, time-energy uncertainty, and frequency bins. Here, we propose a QST for time-bin qudits, with which the number of measurement settings scales linearly with dimension d . Using the proposed scheme, we performed QST for a four-dimensional time-bin maximally entangled state with 16 measurement settings. We successfully reconstructed the density matrix of the entangled qudits, with which the average fidelity of the state was calculated to be 0.950.
We generate time-bin entangled photons and measure the resulting quantum state with a tomography system that uses asymmetric interferometers having $3\ifmmode\times\else\texttimes\fi{}3$ output couplers. This configuration allows for measurements to be made simultaneously in all bases that are required for tomographic reconstruction. By eliminating the burden of tuning interferometer phases and by measuring all the spatial and temporal modes, substantial improvements in measurement speed are observed. Raw fidelities of 84% with respect to an ideal entangled state are measured in about 2 s using a 12-MHz entangled state generator, with corresponding accidental count subtracted fidelities exceeding 90%.