Tensor-Network Quantum Circuit Simulation/PastaQ as Backend Simulator/Extension

[Fe-r-oz]

Hi, @GTorlai!

Is it correct to infer that PastaQ.jl is more suited for implementing tensor-network circuit simulations than ITensor.jl?

PastaQ.jl has even dedicated page on circuit simulation documentation: https://gtorlai.github.io/PastaQ.jl/stable/Circuits.html
There was no mention of circuit simulation atITensors.jldocumentation (is it because it is somehow assumed that we can do circuit simulation or it's better to use a package such as PastaQ.jl that is built on top of ITensor.jl?)

Please have a brief look at MPS quantum circuit simulation with non-local range gates as well.

I am working on this issue: amazon-braket/Braket.jl#81. The task is "Ideally the simulator should be able to consumeBraket.jlcircuits and translate them automatically". It seems to be thatPastaQ.jlwould be more suited for this task.

Kindly please provide guidance as there is no documentation about how to incorporate PastaQ.jl as backend/extension with other packages.

Thanks,

Best Regards,

[mtfishman]

The circuit simulation code in PastaQ.jl is just a wrapper around the one in ITensorMPS.jl, see for example https://itensor.github.io/ITensors.jl/dev/tutorials/MPSTimeEvolution.html and https://itensor.github.io/ITensors.jl/dev/MPSandMPO.html#Gate-evolution. It is just meant to be a little bit friendlier to users coming from quantum information, however I would recommend using ITensorMPS.jl now since PastaQ.jl has had limited development recently due to not having enough developers.

[Fe-r-oz]

Thanks for the update! After looking into src/circuits/runcircuit.jl , it makes better sense.

PastaQ.jl/src/circuits/runcircuit.jl

Lines 153 to 160 in d1a9116

	function runcircuit(
	M::Union{MPS,MPO,ITensor},
	circuit::Union{Tuple,AbstractVector};
	full_representation::Bool=false,
	noise=nothing,
	eltype=nothing,
	device=identity,
	kwargs...,

PastaQ.jl/src/circuits/runcircuit.jl

Lines 15 to 29 in d1a9116

	function buildcircuit(
	hilbert::Vector{<:Index},
	circuit::Union{Tuple,Vector{<:Any}};
	noise::Union{Nothing,Tuple,NamedTuple}=nothing,
	eltype=nothing,
	device=identity,
	)
	circuit_tensors = ITensor[]
	circuit = circuit isa Tuple ? [circuit] : circuit
	circuit = insertnoise(circuit, noise)
	circuit_tensors = isempty(circuit) ? ITensor[] : [gate(hilbert, g) for g in circuit]
	circuit_tensors = device(_convert_leaf_eltype(eltype, circuit_tensors))
	return circuit_tensors
	end

I look forward to future developments! I hope it finds more developers in the near future.

Best Regards,