Takeoka, Masahiro



Faculty of Science and Technology, Department of Electronics and Electrical Engineering (Yagami)




Papers 【 Display / hide

  • Limit of Gaussian operations and measurements for Gaussian state discrimination and its application to state comparison

    Roberson D.E., Izumi S., Roga W., Neergaard-Nielsen J.S., Takeoka M., Andersen U.L.

    Physical Review A (Physical Review A)  103 ( 2 )  2021.02

    ISSN  24699926

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    We determine the optimal method of discriminating and comparing quantum states from a certain class of multimode Gaussian states and their mixtures when arbitrary global Gaussian operations and general Gaussian measurements are allowed. We consider the so-called constant-p displaced states, which include mixtures of multimode coherent states arbitrarily displaced along a common axis. We first show that no global or local Gaussian transformations or generalized Gaussian measurements can lead to a better discrimination method than simple homodyne measurements applied to each mode separately and classical postprocessing of the results. This result is applied to binary state comparison problems. We show that homodyne measurements, separately performed on each mode, are the best Gaussian measurement for binary state comparison. We further compare the performance of the optimal Gaussian strategy for binary coherent states comparison with these of non-Gaussian strategies using photon detections.

  • Classical simulation of boson sampling with sparse output

    Roga W., Takeoka M.

    Scientific Reports (Scientific Reports)  10 ( 1 )  2020.12

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    Boson sampling can simulate physical problems for which classical simulations are inefficient. However, not all problems simulated by boson sampling are classically intractable. We show explicit classical methods of finding boson sampling distributions when they are known to be highly sparse. In the methods, we first determine a few distributions from restricted number of detectors and then recover the full one using compressive sensing techniques. In general, the latter step could be of high complexity. However, we show that this problem can be reduced to solving an Ising model which under certain conditions can be done in polynomial time. Various extensions are discussed including a version involving quantum annealing. Hence, our results impact the understanding of the class of classically calculable problems. We indicate that boson samplers may be advantageous in dealing with problems which are not highly sparse. Finally, we suggest a hybrid method for problems of intermediate sparsity.

  • Challenges in Coding, DSP and Parallel Operation of Quantum Key Distribution and Coherent Data Transmission

    Eriksson T.A., Luis R.S., Rademacher G., Puttnam B.J., Gumus K., Schmalen L., Alvarado A., Furukawa H., Wada N., Hirano T., Sasaki M., Takeoka M.

    2020 European Conference on Optical Communications, ECOC 2020 (2020 European Conference on Optical Communications, ECOC 2020)   2020.12

    ISSN  9781728173610

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    We discuss challenges and recent progress on coding, digital signal processing and joint transmission with classical data channels, for quantum key distribution.

  • Franck-Condon factors via compressive sensing

    Jacob K.V., Kaur E., Roga W., Takeoka M.

    Physical Review A (Physical Review A)  102 ( 3 )  2020.09

    ISSN  24699926

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    The probabilities of vibronic transitions in molecules are referred to as Franck-Condon factors (FCFs). Although several approaches for calculating FCFs have been developed, such calculations are still challenging. Recently it was shown that there exists a correspondence between the problem of calculating FCFs and boson sampling. However, if the output photon number distribution of boson sampling is sparse, then it can be classically simulated. Exploiting these results, we develop a method to approximately reconstruct the distribution of FCFs of certain molecules. We demonstrate its proof of concept by applying it to formic acid and thymine at 0 K. In our method, we first obtain the marginal photon number distributions for pairs of modes of a Gaussian state associated with the molecular transition. We then apply a compressive sensing method called polynomial-time matching pursuit to recover FCFs.

  • Ultra-high-rate nonclassical light source with 50 GHz-repetition-rate mode-locked pump pulses and multiplexed single-photon detectors

    Wakui K., Tsujimoto Y., Fujiwara M., Morohashi I., Kishimoto T., China F., Yabuno M., Miki S., Terai H., Sasaki M., Takeoka M.

    Optics Express (Optics Express)  28 ( 15 ) 22399 - 22411 2020.07

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    Heralded single photons (HSPs) and entangled photon pairs (EPPs) via spontaneous parametric down-conversion are essential tools for the development of photonic quantum information technologies. In this paper, we report a novel ultra-high-rate nonclassical light source realized by developing 50 GHz-repetition-rate mode-locked pump pulses and multiplexed superconducting nanowire single-photon detectors. The presence of the single-photon state in the heralded photons with our setup was indicated by the second-order intensity correlation below 1/2 at the heralding rate over 20 Mcps. Even at the rate beyond 50 Mcps, the nonclassicality was still observed with the intensity correlation below unity. Moreover, our setup is also applicable to the polarization-EPP experiment, where we obtained the maximum coincidence rate of 1.6 Mcps with the fidelity of 0.881 ± (0.254 × 10 ) to the maximally entangled state. Our versatile source could be a promising tool to explore various large-scale quantum-photonic experiments with low success probability and heavy attenuation. −3

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