[sakras]

Basically, quantum gates are mathematically represented as multiplying your state by unitary matrices. Unitary matrices are ones where their inverse is their own conjugate transpose (i.e. XX*=I). Since each gate has an inverse, for any computation you can reverse it (in other words find a circuit that recovers the inputs from the outputs).

In practice this means that you sometimes have to keep around extra bits called Ancilla bits that just contain garbage, but are necessary for reversibility.

[bmacho]

So by 'reversibility' they mean that good graphics would require too much memory (bc quantum can't reuse memory as traditional computers do), and we don't have the resources for that yet.

[pyrolistical]

But what does this have to do with it being xray?

[kqr]

Layman speculating, but wouldn't occlusion throw away visual data? Discarding data is disallowed because it breaks reversibility.

Though I'm not sure about this becuase I would guess the current implementation also discards data where wireframes intersect.