I have worked on this aspect on quantum computation [1]. The main problem is that reversibility is a feature of isolated quantum systems. In practice, they are not isolated.
Why? It's not just because of small interactions with the environment that we cannot control. It's that even the apparatuses that we use to control/drive the logical instructions (lasers, electrical transmission lines) should be taken into account if the computer is to be considered isolated. But usually they aren't, and this leads to inevitable losses of reversiblity in the data register.
In other words, unitary (reversible) operations do not come for free.
I think that in quantum computers it is more likely that energy-efficiency will come from some sort of algorithmic advantage.
Why? It's not just because of small interactions with the environment that we cannot control. It's that even the apparatuses that we use to control/drive the logical instructions (lasers, electrical transmission lines) should be taken into account if the computer is to be considered isolated. But usually they aren't, and this leads to inevitable losses of reversiblity in the data register.
In other words, unitary (reversible) operations do not come for free.
I think that in quantum computers it is more likely that energy-efficiency will come from some sort of algorithmic advantage.
[1] https://arxiv.org/abs/2210.10470