CO SLED of J036+03 and J2054−0005 compared with those of other QSOs at z > 6 and at lower redshift. The CO SLEDs for J036+03 and J2054−0005 are shown as pink circles and cyan markers, respectively. For J2054−0005, the star refers to the CO(6−5) line studied in this work and the circle to the CO(7−6) in Decarli et al. (2022). The results for J036+03 are taken from Decarli et al. (2022). All other sources are displayed as shadowed squares: J1007+2115 at z = 7.5419 in red (Feruglio et al. 2023); J0439+1634 at z = 6.511 in gray (Yang et al. 2019); J1148+5251 at z = 6.419 in brown (Riechers et al. 2009; Gallerani et al. 2014); J0100+2802 at z = 6.327 in purple (Wang et al. 2019b); J2310+1855 at z = 6.003 in blue (Li et al. 2020); APM08279+5255 at z = 3.911 in green (Papadopoulos et al. 2001; Weiß et al. 2007); and Cloverleaf at z = 2.560 in orange (Bradford et al. 2009; Uzgil et al. 2016).