He, R., Sazio, P. J. A., Peacock, A. C., Healy, N., Sparks, J. R., Krishnamurthi, M., et al. (2012). Integration of gigahertz-bandwidth semiconductor devices inside microstructured optical fibres. Nat. Photon., 6(3), 174–179.
Abstract: The prospect of an all-fibre optical communications network in which light can be generated, modulated and detected within the fibre itself without the need for discrete optoelectronic devices is an appealing one. However, to become a reality, this approach requires the incorporation of optoelectronic materials and functionalities into silica fibres to create a new breed of semiconductor-fibre hybrid devices for performing various tasks. Here, we report the integration of precisely doped semiconductor materials and high-quality rectifying semiconductor junctions into microstructured optical fibres, enabling high-speed, in-fibre functionalities such as photodetection at telecommunications wavelengths. These semiconductor-fibre hybrid devices exhibit a bandwidth of up to 3 GHz and seamless coupling to standard single-mode optical fibres.
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Crespi, A., Ramponi, R., Osellame, R., Sansoni, L., Bongioanni, I., Sciarrino, F., et al. (2011). Integrated photonic quantum gates for polarization qubits. Nat. Comm., 2(566), 6.
Abstract: The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. However, the technology for handling polarization-encoded qubits, the most commonly adopted approach, is still missing in quantum optical circuits. Here we demonstrate the first integrated photonic controlled-NOT (CNOT) gate for polarization-encoded qubits. This result has been enabled by the integration, based on femtosecond laser waveguide writing, of partially polarizing beam splitters on a glass chip. We characterize the logical truth table of the quantum gate demonstrating its high fidelity to the expected one. In addition, we show the ability of this gate to transform separable states into entangled ones and vice versa. Finally, the full accessibility of our device is exploited to carry out a complete characterization of the CNOT gate through a quantum process tomography.
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Feofanov, A. K., Oboznov, V. A., Bol'Ginov, V. V., Lisenfeld, J., Poletto, S., Ryazanov, V. V., et al. (2010). Implementation of superconductor/ferromagnet/ superconductor. Nat. Phys., 6(8), 593–597.
Abstract: High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metal-oxide-semiconductor logic. The remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to hold a magnetic flux quantum Φ0. Inserting a π-type Josephson junction in the cell is equivalent to applying flux Φ0/2 and thus makes it possible to solve this problem. Moreover, using π-junctions in superconducting qubits may help to protect them from noise. Here we demonstrate the operation of three superconducting circuits-two of them are classical and one quantum-that all utilize such π-phase shifters realized using superconductor/ferromagnet/superconductor sandwich technology. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a π-biased phase qubit, for which we observe coherent Rabi oscillations. We find no degradation of the measured coherence time compared to that of a reference qubit without a π-junction.
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Pile, D. (2012). How many bits can a photon carry. Nat. Photon., 6(1), 14–15.
Abstract: Quantum physics offers a way to enhance the amount of information a photon can carry, with potential applications in optical communication, lithography, metrology and imaging.
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Bason, M. G., Viteau, M., Malossi, N., Huillery, P., Arimondo, E., Ciampini, D., et al. (2012). High-fidelity quantum driving. Nat. Phys., 8(2), 147–152.
Abstract: Accurately controlling a quantum system is a fundamental requirement in quantum information processing and the coherent manipulation of molecular systems. The ultimate goal in quantum control is to prepare a desired state with the highest fidelity allowed by the available resources and the experimental constraints. Here we experimentally implement two optimal high-fidelity control protocols using a two-level quantum system comprising Bose-Einstein condensates in optical lattices. The first is a short-cut protocol that reaches the maximum quantum-transformation speed compatible with the Heisenberg uncertainty principle. In the opposite limit, we realize the recently proposed transitionless superadiabatic protocols in which the system follows the instantaneous adiabatic ground state nearly perfectly. We demonstrate that superadiabatic protocols are extremely robust against control parameter variations, making them useful for practical applications.
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