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FRECQUAM Report Summary

Project ID: 240486
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - FRECQUAM (Frequency Combs Quantum Metrology)

Ultrafast frequency combs have found tremendous utility as precision instruments in domains ranging from frequency metrology, optical clocks, broadband spectroscopy, and absolute distance measurement. This sensitivity originates from the fact that a comb carries a huge number of co-propagating, coherently-locked frequency modes. Accordingly, it is the aggregate noise arising from these individual teeth that limits the achievable sensitivity for a given measurement. Correlations among various frequencies are the key factor in describing and using an optical frequency comb. The project FRECQUAM lead to the development of unique methods, inspired from quantum optics, to extract amplitude and phase correlations among a multitude of spectral bands. From these, we can deduce the spectral/temporal eigenmodes of a given optical frequency comb (OFC), structure that contains all the information carried by this comb. These methods have been study the dynamics of lasers, and confirm for the first time 20 years old theoretical predictions.
Furthermore, these techniques were applied to metrology experiments such as, for instance, ranging in turbulent medium. We could reach the fundamental limit imposed by the quantum nature of the optical link, and demonstrate for the first time simultaneous parameter estimation within that regime.
But beyond characterizing the classical covariance matrix of an OFC, one can, using non-linear effects, manipulate this noise and eventually reduce it even bellow quantum vacuum noise, producing squeezed optical frequency combs. We have demonstrated that by proper control of non-linear crystals, optical cavities and pulse shaping it was possible to embed within an optical frequency comb up to 16 spectral/temporal modes with non-classical noise properties, a unique achievement in the quantum optics community. Furthermore, dividing the spectrum of this comb into 10 frequency bands, entanglement is certified for all of the 115974 possible nontrivial partitions of this 10 mode state. This is the first demonstration of full multipartite entanglement. Using this source, we did demonstrate theoretically that it is a very promising candidate for scalable measurement based quantum computing, and did perform first proof of principle experiments along these lines.

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