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In this paper, we propose a non-Markovian quantum channel approach to mitigating the degradation of the average fidelity in continuous-variable quantum teleportation. The non-Markovian quantum channel is modeled by an augmented system, where ancillary systems are introduced to represent the internal modes of non-Markovian environments. With a proper non-Markovianity, enhanced effects of the channels on continuous-variable quantum teleportation are observed. Also, the logarithmic negativity of entangled states can be effectively maintained so that the decay of the average fidelity of quantum teleportation is mitigated. In addition, the analysis on different teleported quantum states shows that coherent states exhibit stronger robustness than those of squeezed states and cat states in quantum teleportation with a non-Markovian channel., Comment: 16 pages, 16 figures

We proposed and analyzed a scheme to generate large-size Schr\"{o}dinger cat states based on linear operations of Fock states and squeezed vacuum states and conditional measurements. By conducting conditional measurements via photon number detectors, two unbalanced Schr\"{o}dinger kitten states combined by a beam splitter can be amplified to a large-size cat state with the same parity. According to simulation results, two Schr\"{o}dinger odd kitten states of $\beta=1.06$ and $\beta=1.11$ generated from one-photon-subtracted squeezed vacuum states of $-$3 dB, are amplified to an odd cat state of $\beta=1.73$ with a fidelity of $F=99\%$. A large-size Schr\"{o}dinger odd cat state with $\beta=2.51$ and $F=97.30\%$ is predicted when the input squeezed vacuum states are increased to $-$5.91 dB. According to the analysis on the impacts of experimental imperfections in practice, Schr\"{o}dinger odd cat states of $\beta>2$ are available. A feasible configuration based on a quantum frequency comb is developed to realize the large-size cat state generation scheme we proposed.

Precise knowledge of an optical device's frequency response is crucial for it to be useful in most applications. Traditional methods for determining the frequency response of an optical system (e.g. optical cavity or waveguide modulator) usually rely on calibrated broadband photo-detectors or complicated RF mixdown operations. As the bandwidths of these devices continue to increase, there is a growing need for a characterization method that does not have bandwidth limitations, or require a previously calibrated device. We demonstrate a new calibration technique on an optical system (consisting of an optical cavity and a high-speed waveguide modulator) that is free from limitations imposed by detector bandwidth, and does not require a calibrated photo-detector or modulator. We use a low-frequency (DC) photo-detector to monitor the cavity's optical response as a function of modulation frequency, which is also used to determine the modulator's frequency response. Knowledge of the frequency-dependent modulation depth allows us to more precisely determine the cavity's characteristics (free spectral range and linewidth). The precision and repeatability of our technique is demonstrated by measuring the different resonant frequencies of orthogonal polarization cavity modes caused by the presence of a non-linear crystal. Once the modulator has been characterized using this simple method, the frequency response of any passive optical element can be determined., Comment: 10 pages, 7 figures

A quantitative analysis is conducted on the impacts of experimental imperfections in the input state, the detector properties, and their interactions on photon-subtracted squeezed vacuum states in terms of a quantum non-Gaussian character witness and Wigner function. Limitations of the non-classicality and quantum non-Gaussian characteristic of Schr\"{o}dinger kitten states are identified and addressed. The detrimental effects of a photon-number detector on the generation of odd Schr\"{o}dinger kitten state at near-infrared wavelengths ($\sim$ 860 nm) and telecommunication wavelengths ($\sim$ 1550 nm) are presented and analysed. This analysis demonstrates that the high dark count probability of telecommunication-wavelength photon-number detectors significantly undermines the negativity of the Wigner function in Schr\"{o}dinger kitten state generation experiments. For a one-photon-subtracted squeezed vacuum state at $\sim$ 1550 nm, an APD-based photon-number-resolving detector provides no significant advantage over a non-photon-number-resolving detector when imperfections, such as dark count probability and inefficiency, are taken into account., Comment: Copyright belongs to IOP Publishing ltd. This is an author-created, un-copyedited version of an article accepted for publication in New Journal of Phyiscis. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.1088/1367-2630/15/2/023042