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We discuss excess noise contributions of a practical balanced homodyne detector in Gaussianmodulated coherent-state (GMCS) quantum key distribution (QKD). We point out the key generated from the original realistic model of GMCS QKD may not be secure. In our refined realistic model, we take into account excess noise due to the finite bandwidth of the homodyne detector and the fluctuation of the local oscillator. A high speed balanced homodyne detector suitable for GMCS QKD in the telecommunication wavelength region is built and experimentally tested. The 3 dB bandwidth of the balanced homodyne detector is found to be 104 MHz and its electronic noise level is 13 dB below the shot noise at a local oscillator level of 8.5×10 8 photon per pulse.The secure key rate of a GMCS QKD experiment with this homodyne detector is expected to reach Mbits/s over a few kilometers. PACS numbers: 03.67.Dd * Electronic address: l.qian@utoronto.ca. If we assume E(W n ) = 0, E(W n W n+2 ) = 0 (only consecutive pulse value has a non-zero expectation), CC = a. In GMCS QKD, the variance of Bob's measurement of individual pulse will be contributed by the variances of its adjacent pulses. With the quadrature modulation of the coherent state prepared by Alice V , the excess noise due to the overlap between pulses ε overlap referring to

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Lowering either the administered activity or scan time is desirable in PET imaging as it decreases the patient's radiation burden or improves patient comfort and reduces motion artifacts. But reducing these parameters lowers overall photon counts and increases noise, adversely impacting image contrast and quantification. To address this low count statistics problem, we propose a cycleconsistent generative adversarial network (Cycle GAN) model to estimate diagnostic quality PET images using low count data.Cycle GAN learns a transformation to synthesize diagnostic PET images using low count data that would be indistinguishable from our standard clinical protocol. The algorithm also learns an inverse transformation such that cycle low count PET data (inverse of synthetic estimate) generated from synthetic full count PET is close to the true low count PET. We introduced residual blocks into the generator to catch the differences between low count and full count PET in the training dataset and better handle noise.The average mean error and normalized mean square error in whole body were −0.14% ± 1.43% and 0.52% ± 0.19% with Cycle GAN model, compared to 5.59% ± 2.11% and 3.51% ± 4.14% on the original low count PET images. Normalized cross-correlation is improved from 0.970 to 0.996, and peak signal-to-noise ratio is increased from 39.4 dB to 46.0 dB with proposed method.We developed a deep learning-based approach to accurately estimate diagnostic quality PET datasets from one eighth of photon counts, and has great potential to improve low count PET image quality to the level of diagnostic PET used in clinical settings.

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