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Unitary non-Gaussian nonlinearity is one of the key components required for quantum computation and other developing applications of quantum information processing. Sufficient operation of this kind is still not available, but it can be approximatively implemented with help of a specifically engineered resource state constructed from individual photons. We present experimental realization and thorough analysis of such quantum resource state, and confirm that the state does indeed possess properties of a state produced by unitary dynamics driven by cubic nonlinearity.

We develop an experimental scheme based on a continuous-wave (cw) laser for generating arbitrary superpositions of photon number states. In this experiment, we successfully generate superposition states of zero to three photons, namely advanced versions of superpositions of two and three coherent states. They are fully compatible with developed quantum teleportation and measurement-based quantum operations with cw lasers. Due to achieved high detection efficiency, we observe, without any loss correction, multiple areas of negativity of Wigner function, which confirm strongly nonclassical nature of the generated states., 5 pages, 2 figures

We observe -9.01$\pm$0.14 dB of squeezing and +15.12$\pm$0.14 dB of antisqueezing with a local oscillator phase locked in homodyne measurement. In reference [1], two main factors are pointed out which degrade the observed squeezing level: phase fluctuation in homodyne measurement and intracavity losses of an optical parametric oscillator for squeezing. We have improved the phase stability of homodyne measurement and have reduced the intracavity losses. We measure pump power dependences of the squeezing and antisqueezing levels, which show good agreement with theoretical calculations taking account of the phase fluctuation., Comment: 4 pages, 4 figures

Continuous-variable Gaussian cluster states are a potential resource for universal quantum computation. Here we report on the optical generation and theoretical verification of three different kinds of four-mode continuous variable cluster states.

Polyacrylamides of low molecular weights (average degrees of polymerization(‾DP) : 7.2, 18.3, 21.3, and 45.4) were prepared by radical polymerization, and their PMR spectra were observed over the temperature range of 30–90 °C. From the temperature dependence of the PMR spectra, the values of the energy barrier to the internal rotation about C–N bonds were determined by means of a total line-shape analysis. The energy barriers for the polymers above ‾DP : 18.3 were 10.6 kcal/mol, while those for the polymer of ‾DP : 7.2 were 9.2 kcal/mol. These results were interpreted in terms of the local environment around the amide groups. The intramolecular hydrogen bonding was also investigated.

We witness experimentally the presence of macroscopic coherence in Gaussian quantum states using a recently proposed criterion (E.G. Cavalcanti and M. Reid, Phys. Rev. Lett. 97, 170405 (2006)). The macroscopic coherence stems from interference between macroscopically distinct states in phase space and we prove experimentally that even the vacuum state contains these features with a distance in phase space of $0.51\pm0.02$ shot noise units (SNU). For squeezed states we found macroscopic superpositions with a distance of up to $0.83\pm0.02$ SNU. The proof of macroscopic quantum coherence was investigated with respect to squeezing and purity of the states., 5 pages, 6 figures

We experimentally demonstrate the highly efficient generation of arbitrary superpositions of zero- to three-photon-number states. One of the generated states can be used as an ancilla to realize the non-Gaussian quantum gate.