Implement generic MultiControlledBloq using single-controlled subbloq + And ladder.
#1155
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| @frozen | ||
| class MultiControlledBloq(Bloq): |
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I see @mpharrigan's point that having both Controlled(sub_bloq, ctrl_spec) and MultiControlledBloq(sub_bloq, ctrl_spec) can be confusing and the implementation of both would actually be identical.
Regarding interface vs implementation, it may make things cleaner if we rename MultiControlledBloq to be more descriptive of the implementation, like ControlledViaAndLadder() and explain that the implementation performs CtrlSpecAnd -> Bloq.controlled() -> CtrlSpecAnd.adjoint() to decompose a bloq controlled by arbitrary CtrlSpec to a singly controlled Bloq via an And / And^{dagger} ladder and uses
Then, this specific implementation can be used by users who want to depend upon this behavior instead of the behavior getting potentially updated if we decide to update the decomposition of Controlled Bloq later.
MultiControlledPauli can get removed and we will simply update the call sites to use ControlledViaAndLadder(ctrl_spec, XGate())
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I like the bloq name ControlledViaAndLadder, will use that
tanujkhattar
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Looking good. Left a final round of comments
| target = soqs.pop('target') | ||
| (target_reg_name,) = [reg.name for reg in self.target_bloq.signature] | ||
| if self.n_ctrls == 0: | ||
| # TODO discuss if we should remove support for this case. |
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#1131
ControlledViaAndthat computes a single qubit control usingCtrlSpecAnd, and uses a single-controlled subbloq.MultiControlPaulito delegate to this. For the moment I did not remove it fully as it breaks too many things that switch between cirq-style and qualtran-style defs. This should be cleaned up in a follow-up PR.