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Using the Boolardy Engineering Test Array of the Australian Square KilometreArray Pathfinder (ASKAP BETA), we have carried out the first $z = 0 - 1$ surveyfor HI and OH absorption towards the gravitationally lensed quasarsPKSB1830$-$211 and MGJ0414$+$0534. Although we detected all previously reportedintervening systems towards PKSB1830$-$211, in the case of MGJ0414+0534 threesystems were not found, indicating that the original identifications may havebeen confused with radio frequency interference. Given the sensitivity of ourdata, we find that our detection yield is consistent with the expectedfrequency of intervening HI systems estimated from previous surveys for 21-cmemission in nearby galaxies and $z \sim 3$ damped Lyman $\alpha$ absorbers. Wefind spectral variability in the $z = 0.886$ face-on spiral galaxy towardsPKSB1830$-$211, from observations undertaken with the Westerbork SynthesisRadio Telescope in 1997/1998 and ASKAP BETA in 2014/2015. The HI equivalentwidth varies by a few per cent over approximately yearly time-scales. Thislong-term spectral variability is correlated between the north-east andsouth-west images of the core, and with the total flux density of the source,implying that it is observationally coupled to intrinsic changes in the quasar.The absence of any detectable variability in the ratio of HI associated withthe two core images is in stark contrast to the behaviour previously seen inthe molecular lines. We therefore infer that coherent opaque HI structures inthis galaxy are larger than the parsec-scale molecular clouds found atmm-wavelengths.

Illuminating the past 8 billion years of cold gas towards two gravitationally lensed quasars