Incorrect on_classical_vals overrides for non classical bloqs

[anurudhp]

I ran into this while implementing #1514. The tensors of these bloq examples seem to have non-trivial phases, which makes them non-classical. The following bloq examples fail in #1514 (I've restricted to bloqs with up to 9 qubits):

sub_from_small

E Mismatched elements: 144 / 65536 (0.22%)
E Max absolute difference: 1.
E Max relative difference: 1.
E x: array([[1., 0., 0., ..., 0., 0., 0.],
E [0., 1., 0., ..., 0., 0., 0.],
E [0., 0., 1., ..., 0., 0., 0.],...
E y: array([[1.+0.j, 0.+0.j, 0.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],
E [0.+0.j, 1.+0.j, 0.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],
E [0.+0.j, 0.+0.j, 1.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],...

cmod_add_k_small

E Mismatched elements: 18 / 1024 (1.76%)
E Max absolute difference: 1.
E Max relative difference: 0.
E x: array([[1., 0., 0., ..., 0., 0., 0.],
E [0., 1., 0., ..., 0., 0., 0.],
E [0., 0., 1., ..., 0., 0., 0.],...
E y: array([[1.+0.j, 0.+0.j, 0.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],
E [0.+0.j, 1.+0.j, 0.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],
E [0.+0.j, 0.+0.j, 1.+0.j, ..., 0.+0.j, 0.+0.j, 0.+0.j],...

moddbl_small

E Mismatched elements: 3 / 256 (1.17%)
E Max absolute difference: 1.
E Max relative difference: 1.
E x: array([[1., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
E [0., 0., 0., 0., 0., 0., 0., 1., 0., 0., 0., 0., 0., 0., 0., 0.],
E [0., 1., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],...
E y: array([[1.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j,
E 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j],
E [0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 0.+0.j, 1.+0.j,...

approx_cswap_small

E Mismatched elements: 120 / 262144 (0.0458%)
E Max absolute difference: 2.
E Max relative difference: 2.
E x: array([[1., 0., 0., ..., 0., 0., 0.],
E [0., 1., 0., ..., 0., 0., 0.],
E [0., 0., 1., ..., 0., 0., 0.],...
E y: array([[1.000000e+00+6.471125e-32j, 0.000000e+00+0.000000e+00j,
E 0.000000e+00+0.000000e+00j, ..., 0.000000e+00+0.000000e+00j,
E 0.000000e+00+0.000000e+00j, 0.000000e+00+0.000000e+00j],...

[mpharrigan]

Do you know where the non-trivial phases are being introduced? Presumably if you write a decomposition of e.g. ModDbl using only classical operations (whose matrices only have +1 entries) then you can't get any phases popping up, right?

[tanujkhattar]

fyi -- approx_cswap_small's tensor would have a non-trivial phases since it implements an approximate cswap which is correct upto a phase, in order to have 4 T count instead of 7, which gets inverted when the approx cswap inverse is applied. This is similar to the 4 T version of Toffoli which applies a toffoli upto a relative phase (we don't explicitly have a bloq for this yet)

[mpharrigan]

Yeah, the approx cswap is clearer. It's got "approx" in the name, so it's less surprising that there are phases. The other ones are surprising to me