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We report the detection of high excitation CO emission from the most distantquasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at aredshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAMPlateau de Bure interferometer, showing a width of ~280 km/s. An upper fluxlimit for the CO (J=1-0) line was obtained from observations with theEffelsberg 100-meter telescope. Assuming no gravitational magnification, weestimate a molecular gas mass of ~2x10^10 M_sun. Using the CO (3-2)observations by Walter et al. (2003), a comparison of the line flux ratios withpredictions from a large velocity gradient model suggests that the gas islikely of high excitation, at densities ~10^5 cm^-3 and a temperature ~100 K.Since in this case the CO lines appear to have moderate optical depths, the gasmust be extended over a few kpc. The gas mass detected in J1148+5251 can fuelstar formation at the rate implied by the far-infrared luminosity for less than10 million years, a time comparable to the dynamical time of the region. Thegas must therefore be replenished quickly, and metal and dust enrichment mustoccur fast. The strong dust emission and massive, dense gas reservoir at z~6.4provide further evidence that vigorous star formation is co-eval with the rapidgrowth of massive black holes at these early epochs of the Universe.Comment: 4 pages, 3 figures, A&A Letter

High-excitation CO in a quasar host galaxy atz $\mathsf{=6.42}$