Quantum Graph

Data structure

We represent our quantum program as a directed graph of quantum variables passing through operations called Bloqs. The container representing a program or subroutine is CompositeBloq. Since it is an immutable data structure, we use BloqBuilder to help us build composite bloqs. We use the abbreviated variable name cbloq for generic composite bloqs.

bb = BloqBuilder() q = bb.allocate(1) # allocate a quantum variable. q, = bb.add(H, qubit=q) # wire it into a new H op, get new quantum variable back. bb.free(q) # discard our quantum variable, get nothing back. cbloq = bb.finalize() # finish building, turn into a CompositeBloq

Components

Bloqs are analogous to functions. Any class attributes on a Bloq are analogous to C++ template parameters. Bloqs follow value-equality with respect to these parameters.

MultiCNOT(n=100) == MultiCNOT(n=100)

BloqInstances are unique instantiations of a Bloq contained in a CompositeBloq, because we could have many instances of the same Bloq and it matters (for data flow) which one is which.

binst1, (q,) = bb.add_2(H, q=q) binst2, (q,) = bb.add_2(H, q=q) binst1 != binst2 # one H comes before the other.

Signature are analogous to function (and return type) signatures and are a property of a Bloq.

Soquets are the "quantum variables" that follow linear typing rules (each must be used exactly once) and are instantiations of registers. There is generally a 1-to-many relationship between Register and Soquet because we support multidimensional quantum arrays.

SoquetT is a union type between Soquet and ndarray of Soquet. It means all the soquets for a given register. When you see variable names like soqdict, in_soqs, or final_soqs with type Dict[str, SoquetT]: this is a 1-to-1 mapping between register (by name) and all the Soquets for that potentially-multidimensional register. When you see names like idxed_soq, it means an individual Soquet has been plucked from a potentially-multidimensional array of them.

Soquets are the main quantum variables a user-developer uses to wire up bloqs. The user should assign meaningful names to the soquets or array of soquets and treat them as opaque types.

Gates

Bloqs support multi-dimensional, arbitrary-bitwidth, potentially asymmetric registers. As such, bloqs can represent high-level computations like "ModularExponentiation" or "Quantum Phase Estimation".

Low-level Bloqs where all Registers have bitsize=1, shape=(n,), and side=Side.THRU we generally name "gates". Bloqs that satisfy these conditions are similar to gates found in other quantum computing libraries.