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We demonstrate the control of entanglement of a single photon between several spatial modes propagating through a strongly scattering medium. Measurement of the scattering matrix allows the wavefront of the photon to be shaped to compensate the distortions induced by multiple scattering events. The photon can thus be directed coherently to a single or multi-mode output. Using this approach we show how entanglement across different modes can be manipulated despite the enormous wavefront disturbance caused by the scattering medium., Comment: 4 pages, 3 figures, reference added

We demonstrate the generation of an optical dipole wave suitable for the process of efficiently coupling single quanta of light and matter in free space. We employ a parabolic mirror for the conversion of a transverse beam mode to a focused dipole wave and show the required spatial and temporal shaping of the mode incident onto the mirror. The results include a proof of principle correction of the parabolic mirror's aberrations. For the application of exciting an atom with a single photon pulse we demonstrate the creation of a suitable temporal pulse envelope. We infer coupling strengths of 89% and success probabilities of up to 87% for the application of exciting a single atom for the current experimental parameters., Comment: to be published in Europ. Phys. J. D

Multimode nonclassical states of light are an essential resource in quantum computation with continuous variables, for example in cluster state computation. They can be generated either by mixing different squeezed light sources using linear optical operations, or directly in a multimode optical device. In parallel, frequency combs are perfect tools for high precision metrological applications and for quantum time transfer. Synchronously Pumped Optical Parametric Oscillators (SPOPOs) have been theoretically shown to produce multimode non-classical frequency combs. In this paper, we present the first experimental generation and characterization of a femtosecond quantum frequency comb generated by a SPOPO. In particular, we give the experimental evidence of the multimode nature of the generated quantum state and, by studying the spectral noise distribution of this state, we show that at least three nonclassical independent modes are required to describe it.

Quantum computation and communication protocols require quantum resources which are in the continuous variable regime squeezed and/or quadrature entangled optical modes. To perform more and more complex and robust protocols, one needs sources that can produce in a controlled way highly multimode quantum states of light. One possibility is to mix different single mode quantum resources. Another is to directly use a multimode device, either in the spatial or in the frequency domain. We present here the first experimental demonstration of a device capable of producing simultanuously several squeezed transverse modes of the same frequency and which is potentially scalable. We show that this device, which is an Optical Parametric Oscillator using a self-imaging cavity, produces a multimode quantum resource made of three squeezed transverse modes.

We show that an Optical Parametric Oscillator which is simultaneously resonant for several modes, either spatial or temporal, generates both below and above threshold a multimode non-classical state of light consisting of squeezed vacuum states in all the non-oscillating modes. We confirm this prediction by an experiment dealing with the degenerate TEM$_{01}$ and TEM$_{10}$ modes. We show the conservation of non-classical properties when the threshold is crossed. The experiment is made possible by the implementation of a new method to lock the relative phase of the pump and the injected beam.

We investigate the spatial quantum properties of the light emitted by a perfectly spatially degenerate optical parametric oscillator (self-imaging OPO). We show that this device produces local squeezing for areas bigger than a coherence are that depends on the crystal length and pump width. Furthermore, it generates local EPR beams in the far field. We show, calculating the eigenmodes of the system, that it is highly multimode for realistic experimental parameters.