Generation and manipulation of photonic states and their characterization by quantum homodyne tomography

Zavatta A., Viciani S., Bellini M.

Merlin Cooper

This thesis is concerned with the generation of non-classical quantum states of light, the photon-level manipulation of quantum states and the accurate tomography of both quantum states and quantum processes. In optics, quantum information can be encoded and processed in both discrete and continuous variables. Hybrid approaches combining for example homodyne detection with conditional state preparation and manipulation are gaining increasing prominence. The development and characterization of a time-domain balanced homodyne detector (BHD) is presented. The detector has a bandwidth of 80 MHz, a signal-to-noise ratio of 14.5 dB and an efficiency of 86% making it well-suited to pulse-to-pulse measurement of quantum optical states. The BHD is employed to perform quantum state tomography (QST) of non-classical multi-photon Fock states generated by spontaneous parametric down-conversion. A detailed investigation of the mode-matching between the local oscillator used for homodyne detection and the generated Fock states is presented. The one-, two- and three-photon Fock states are reconstructed with a combined preparation and detection efficiency exceeding 50%. Fock states have a number of applications in quantum state engineering, where non-classical ancilla states and conditional measurements enable photon-level manipulation of quantum states. Fock state filtration (FSF) is investigated - an example of a post-selected beam splitter which is a basic building block for many quantum state engineering protocols. A model is developed incorporating the effect of experimental imperfections. An experimental implementation of a Fock state filter is fully characterized by means of coherent-state quantum process tomography (QPT). The reconstructed process is found to be consistent with the model. The filter preferentially removes the single-photon component from an arbitrary input quantum state. Calibration of optical detectors in the quantum regime is discussed. Quantum detector tomography (QDT) is reviewed and contrasted with a new technique for performing QST with a calibrated detector known as the fitting of data patterns (FDP). The first experimental characterization of a BHD is performed by probing the detector with phase-averaged coherent states. The FDP method is shown to be applicable to the estimation of quantum processes, where a detector response is not assumed - thus demonstrating the versatility of the FDP approach as a new method in the quantum tomography toolbox.

Giacomo Mauro D’Ariano, Matteo G. A. Paris, M. De Laurentis +2 more

Summary form only given. Quantum homodyne tomography (QHT) is the most successful technique for measuring the quantum state of light. It is based on numerical manipulation of balanced homodyne data. So far QHT is the only method successfully employed in a number of experiments to reconstruct the quantum state. We report QHT as a tool for the quantum characterization of optical devices. The goal is to link the estimation of relevant parameters with the results of homodyne detection.

Nicola Mosco, Lorenzo Maccone

Zavatta A., E. M. D'Angelo, Valentina Parigi +1 more

T. Hönigl-Decrinis, A. Yu. Dmitriev, Rais S. Shaikhaidarov +2 more