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The development of large-scale optical quantum information processing circuits ground on the stability and reconfigurability enabled by integrated photonics. We demonstrate a reconfigurable 8x8 integrated linear optical network based on silicon nitride waveguides for quantum information processing. Our processor implements a novel optical architecture enabling any arbitrary linear transformation and constitutes the largest programmable circuit reported so far on this platform. We validate a variety of photonic quantum information processing primitives, in the form of Hong-Ou-Mandel interference, bosonic coalescence/anticoalescence and high-dimensional single-photon quantum gates. We achieve fidelities that clearly demonstrate the promising future for large-scale photonic quantum information processing using low-loss silicon nitride., Comment: Added supplementary materials, extended introduction, new figures, results unchanged

International audience; We demonstrate the possibility to generate squeezed vacuum states of light by four wave mixing (FWM) enabled coherent population trapping in a metastable helium cell at room temperature. Contrary to usual FWM far detuned schemes, we work at resonance with an atomic transition. We investigate the properties of such states and show that the noise variances of the squeezed and anti-squeezed quadratures cannot be explained by the simple presence of losses. A specific model allows us to demonstrate the role played by spontaneous emitted photons, which experience squeezing while propagation inside of the cell. This theoretical model, which takes into account both residual absorption and spontaneous emission, leads to an excellent agreement with the experimental data without any adjusted parameter.

We report a bright and tunable source of spectrally pure heralded single photons in the telecom O-Band, based on cross-polarized four wave mixing in a commercial birefringent optical fiber. The source can achieve a purity of 85%, heralding efficiency of 30% and high coincidences to accidentals ratio of 108. Furthermore, the possibility of building multiple identical sources is explored. Through the measurements of joint spectral intensities, we find that the fiber is homogeneous over atleast 45 centimeters and can potentially realize 4 identical sources. This paves the way for a cost-effective fiber-optic approach to implement multi-photon quantum optics experiments., Comment: 14 pages, 10 figures

We implement a nondegenerate polarization-correlated photon-pair source on titanium-diffused nonperiodically-poled lithium niobate waveguides. The nonperiodic domains are optimized using genetic algorithm to maximize and equalize efficiencies of the spontaneous parametric down-conversion processes.

Universal linear optical networks made of on-chip tunable beam splitters and phase shifters form a very promising platform for quantum information processing (QIP). Thanks to their phase stability and reconfigurability, they are robust and enable a variety of quantum information and communication protocols such as quantum teleportation [1], quantum key distribution [2], photonic qubit gate protocols [3] and boson sampling [4]. Two known materials for on-chip platforms are silicon-on-insulator (SOI) and doped silica, where SOI allows for a high component density due to its high index contrast and silica has a low loss.

Variable measurement operators enable the optimization of strategies for testing quantum properties and the preparation of a range of quantum states. Here, we experimentally implement a weak-field homodyne detector that can continuously tune between measuring photon numbers and field quadratures. We combine a quantum signal with a coherent state on a balanced beam splitter and detect light at both output ports using photon-number-resolving transition edge sensors. We observe that the discrete difference statistics converge to the quadrature distribution of the signal as we increase the coherent state amplitude. Moreover, in a proof-of-principle demonstration of state engineering, we show the ability to control the photon-number distribution of a state that is heralded using our weak-field homodyne detector., Comment: 12 pages, 10 figures; includes Supplemental Material

We interfere weak coherent states with heralded Fock states on a balanced beam splitter and detect the output with photon-number-resolving detectors. Our setup constitutes a versatile detector that can perform both Gaussian and non-Gaussian measurements.

Integrated universal linear optical networks are essential for the development of quantum information processing (QIP). We demonstrate a universal, reconfigurable, 8×8 photonic processor based on Si3N4 waveguides showing a variety of QIP primitives.

Integrated universal linear optical networks are essential for the development of quantum information processing (QIP). We demonstrate a universal, reconfigurable, 8×8 photonic processor based on Si3N4 waveguides showing a variety of QIP primitives.

We present a scheme for generation and characterization of entangled spatial qubits based on type-II spontaneous parametric down-conversion (SPDC) in a periodically poled titanyl phosphate (PPKTP) multimode nonlinear waveguide [1]. Our scheme exploits intermodal dispersion which has been hitherto successfully employed to produce spatially pure SPDC photon pairs from a multimode waveguide without spatial filtering [2]. Production of discrete entanglement relies on driving simultaneously two SPDC processes that involve different combinations of transverse spatial modes for which phase matching bandwidths significantly overlap. We propose a procedure for experimental identification of the spatial qubit subspace based on a scan of the spatial Wigner function via the displaced parity measurement using an inverting Sagnac interferometer and photon counting. We numerically verified the robustness of the mode reconstruction procedure against experimental imperfections. We also propose an experimental method for detecting spatial entanglement in the position-wave vector phase space. Numerical simulations indicate that waveguide parameters required for experimental demonstrations are compatible with current manufacturing capabilities. Using simulated mode profiles we calculate the maximum attainable Clauser-Horne- Shimony-Holt combination value reaching 2.12, which clearly violates the classical limit and confirms the feasibility of observing non-classical features of the generated state. [1] M. Jachura et al. Physical Review A, 95, 032322 (2017). [2] M. Jachura, M. Karpinski, C. Radzewicz, K. Banaszek, Optics Express, 22, 8624-8632 (2014).

In this Letter, we report our experimental results on phase-sensitive amplification (PSA) in a nondegenerate signal-idler configuration using ultranarrow coherent population oscillations in metastable helium at room temperature. We achieved a high PSA gain of nearly 7 with a bandwidth of 200 kHz by using the system at resonance in a single-pass scheme. Further, the measured minimum gain is close to the ideal value, showing that we have a nearly pure PSA. This is also confirmed from our phase-to-phase transfer curves measurements, illustrating that we have a nearly perfect squeezer, which is interesting for a variety of applications.

We discuss intermodal dispersion as a versatile tool to control photon pairs produced in chi(2) waveguides, present experimental generation of spatially pure photons exhibiting high-visibility nonclassical interference, and describe schemes to produce spatial entanglement.

We propose a scheme for generating spatial modal entangled photon pairs; using a modified integrated optic Mach-Zehnder interferometer and show the possibility of manipulating the output entangled state using an electro-optic switch.

In this paper, we address the issue of the generation of non-degenerate cross-polarization-entangled photon pairs using type-II periodically poled lithium niobate. We show that, by an appropriate engineering of the quasi-phase-matching grating, it is possible to simultaneously satisfy the conditions for two spontaneous parametric down-conversion processes, namely ordinary pump photon down-conversion to either extraordinary signal and ordinary idler paired photons, or to ordinary signal and extraordinary idler paired photons. In contrast to single type-II phase-matching, these two processes, when enabled together, can lead to the direct production of cross-polarization-entangled state for non degenerate signal and idler wavelengths. Such a scheme should be of great interest in applications requiring polarization-entangled non degenerate paired photons with, for instance, one of the entangled photons at an appropriate wavelength being used for local operation or for quantum storage in an atomic ensemble, and the other one at the typical wavelength of 1550 nm for propagation through an optical fiber., 9 pages, 5 figures, 2 tables

In this paper, we propose an integrated optic waveguide device employing a modified Mach–Zehnder interferometer, capable of generating nondegenerate, hyperentangled photon pairs. The geometry enables multiple (eight) type-II phase-matched spontaneous parametric downconversion processes simultaneously, resulting in a biphoton state, which is simultaneously entangled in polarization and spatial modes. Using an electro-optic phase modulator, we show the possibility of altering modal entanglement without affecting polarization entanglement. Such switchable, maximally entangled photon pairs, entangled in multiple degrees of freedom, should be very useful in various on-chip quantum optics experiments and in the implementation of quantum information protocols employing higher dimensional entanglement.

In this Letter, we propose and analyze a switchable integrated optical waveguide device employing a modified Mach-Zehnder interferometer, capable of generating nondegenerate, maximally spatial-mode entangled photon pairs. Using an integrated electro-optic phase modulator, we show the possibility of on-demand switching of spatial-mode entangled state from a Φ+ to a Ψ+ state and vice versa. Such a versatile device with the potential of easy manipulation of the "spatial-mode" degree of freedom, should be very interesting in realizing integrated optical chips for quantum information processing.

We propose a new scheme of domain engineering in Lithium Niobate for generating non degenerate polarization entangled photon pairs by simultaneously satisfying the conditions for two different SPDC processes.

We show theoretically that microstructured optical fibers filled with nonlinear liquids are capable of generating photon-pairs with highly tunable properties, suitable for applications in quantum spectroscopy and as sources of heralded single photons.

We propose a scheme for the generation of hyper-entangled photon pairs using an integrated optical waveguide device; the biphoton output state is simultaneously entangled in polarization and spatial modal degrees of freedom.

We demonstrate both experimentally and theoretically a new form of light storage based on Coherent Population Oscillations. It is shown to be phase preserving and robust to dephasing effects.