Conduction mechanisms and voltage drop during field electron emission from diamond needles.

We report results of experimental investigation of field electron emission from diamond nanoemitters. The measurements were performed with single crystal diamond needles fixed at tungsten tips. The voltage drop along diamond needles during emission was revealed and measured using electron energy spectroscopy. The observed linear dependence of the voltage drop in diamond on voltage applied to the tungsten tip is explained in the frame of a simple macroscopic electrical model combining Poole-Frenkel conduction along the diamond tip and Fowler-Nordheim tunneling at the diamond-vacuum junction. Experimental evidences of electron emission sensitivity to laser illumination are discussed for possible modification of diamond emitter characteristics and voltage drop.

Generation and characterization of multimode quantum frequency combs.

Multimode nonclassical states of light are an essential resource in quantum computation with continuous variables, for example, in cluster state computation. We report in this Letter the first experimental evidence of a multimode nonclassical frequency comb in a femtosecond synchronously pumped optical parametric oscillator. In addition to a global reduction of its quantum intensity fluctuations, the system features quantum correlations between different parts of its frequency spectrum. This allows us to show that the frequency comb is composed of several uncorrelated eigenmodes having specific spectral shapes, two of them at least being squeezed, and to characterize their spectral shapes.

Direct generation of a multi-transverse mode non-classical state of light.

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 simultaneously 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.

Frequency doubling of low power images using a self-imaging cavity.

A self-imaging resonator can be simultaneously resonant for many transverse modes and therefore allows cavity build-up for images of various shapes. The stability properties of such a cavity are reviewed. We have used this device for the first time to enhance the efficiency of second harmonic generation of weak images. We characterize the global and local efficiency of the second harmonic generation, and discuss its limitation due to the spatial bandwidth of the cavity and the diffraction along the crystal length.