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The 'extreme Population A (xA) quasars' approaching, sometimes exceeding theEddington limit, are a type of quasars that could serve as a standard candle tomeasure distances too large for supernovae type Ia (SNe Ia) to be observable.For using xA quasars as standard candles, it would be beneficial to know howtheir luminosities would vary if coupling constants varied over cosmic time.Alternatively, when calibrated using SN Ia standard candle, xA quasarobservations could constrain the variation of coupling constants. We show thatthe Hubble diagram of xA quasars provides the same constraint on the constants'variation as the Hubble diagram of SNe Ia from the Pantheon data. The couplingconstants vary concurrently in our model, i.e., the variation of the speed oflight $c$, the gravitational constant $G$, the Planck constant $h$, and theBoltzmann constant $k$, are interrelated as $G\thicksim c^{3}\thicksimh^{3}\thicksim k^{3/2}$. The constraint thus determined can be expressed interms of the Hubble constant $H_{0}$ as$(\dot{G}/G)_{0}=3(\dot{c}/c)_{0}=3(\dot{h}/h)_{0}=1.5 (\dot{k}/k)_{0}=5.4H_{0}=3.90(\pm 0.04)\times 10^{-10} yr^{-1}$, where subscript 0 is for the currenttime. This conclusion is corroborated with the analysis of data on the quasarswith correlated UV and X-ray emissions.

Constraining variability of coupling constants with bright and extreme quasars