There is a question in another answer about how it would look scaled to favicon size (32x32).
This is about as good it gets using a cellphone and the available tools.
That's the original source image from which the smaller size was derived.
That's the result of reducing it to 32x32 using a smart resizing algorithm (not simple scaling).
That's what it looks like with the Bloch sphere overlaid, lots of detail lost.
Converted to B&W, so it can be overlaid on to the greenish background.
The rules for submitting a design made no mention of developing a version for the icons used on the site, perhaps someone intends to take what is submitted and hand it over to a professional Graphics Designer (to preserve the Stack Exchange image and avoid sketchy looking sketches, along with providing some uniformity to the look).
If other people create a design there will likely be a better result and certainly more for people to vote on. That's what a sphere would look like, don't know what a cube had to do with QC; now we have both.