Isabelle Zaquine

Ferrite thin films for microwave applications

Production of ferrite thin films is the key to integration of microwave ferrite devices (circulators for phased array antennas, for instance). The interesting materials are the usual microwave ferrites: garnets, lithium ferrites, barium hexaferrites. The required thicknesses are a few tens of micrometers, and it will be important to achieve high deposition rates. Different substrates can be used: silicon and alumina both with and without metallization. The films were deposited by rf sputtering from a single target. The as‐deposited films are amorphous and therefore require careful annealing in oxygen atmosphere. The sputtered films are a few micrometers thick on 4 in. substrates. The optimum annealing temperature was found by trying to obtain the highest possible magnetization for each ferrite. The precision on the value of magnetization is limited by the precision on the thickness of the film. We obtain magnetization values slightly lower than the target’s. The ferromagnetic resonance linewidth was measu...

Intracavity Bragg grating

Bragg diffraction of a read beam is studied theoretically when the refractive-index grating is placed inside a Fabry–Perot cavity. Diffraction efficiency, angular selectivity, and signal-to-noise ratio are largely enhanced compared with those for the bare Bragg grating, which may permit the use of low-efficiency or short-length materials as well. The results are much better for an asymmetric cavity operated in reflection than for a symmetric cavity in transmission.

Experimental wavelength-division-multiplexed photon-pair distribution

We have experimentally implemented the distribution of photon pairs produced by spontaneous parametric downconversion through telecom dense-wavelength-division-multiplexing filters. Using the measured counts and coincidences between symmetric channels, we evaluate the maximum fringe visibility that can be obtained with polarization-entangled photons and compare different filter technologies.

Experimental investigation of intracavity Bragg gratings

We report the results of an experimental investigation of the diffractive properties of a thick index grating embedded in a Fabry-Perot resonator, the so-called intracavity Bragg grating. We compare the performance of this device with that of a bare Bragg grating with same thickness and the same index modulation and establish the improvement in performance with the resonator. The experimental data also fit predictions calculated from a theoretical model.

Spontaneous four-wave mixing in liquid-core fibers: towards fibered Raman-free correlated photon sources

We experimentally demonstrate, for the first time to our knowledge, the generation of correlated photon pairs in a liquid-core photonic crystal fiber. Moreover, we show that, thanks to the specific Raman properties of liquids, the Raman noise (which is the main limitation of the performance of silica-core fiber-based correlated photon pair sources) is highly reduced. With a demonstrated coincident-to-accidental ratio equal to 63 and a pair generation efficiency of about 10

Multi-user quantum key distribution with entangled photons from an AlGaAs chip

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Decoherence effects on the nonlocality of symmetric states

per pump pulse, this work opens the way for the development of high quality correlated photon pair sources for quantum communications.

Band-edge-induced Bragg diffraction in two-dimensional photonic crystals

In view of real world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip emitting polarization entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.

Efficient Bragg-like operation of intracavity low-efficiency plane gratings

The observation of the non-local properties of multipartite entangled states is of great importance for quantum information protocols. Such properties, however, are fragile and may not be observed in the presence of decoherence exhibited by practical physical systems. In this work, we investigate the robustness of the non-locality of symmetric states experiencing phase and amplitude damping, using suitable Bell inequalities based on an extended version of Hardys paradox. We derive thresholds for observing non-locality in terms of experimental noise parameters, and demonstrate the importance of the choice of the measurement bases for optimizing the robustness. For

Optimal photon-pair single-mode coupling in narrow-band spontaneous parametric downconversion with arbitrary pump profile

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