abdullahkhalids
commented
1 year ago This is good starting work. Let me suggest some improvements.
In the current form, the code is not at all taking advantage of stac's abilities for constructing such circuits. Right now, most of the code is just figuring out the indices in a convoluted manner. The whole point of geometric addressing is to avoid doing this, and going mad.
Let us look at Fig 1. of the paper.
By drawing the two axes I have labelled each qubit by $(x, y)$. Now, from the diagram it is quite clear that for measurement qubit at $(x,y)$, the $CX$ gates will go between it and the qubits $(x+1,y), (x-1,y), (x,y+1), (x,y-1)$. So how do we do this in stac?
The key is when you create the physical qubits. Right now, you have
surface_code_circ.physical_register.elements = \
[stac.PhysicalQubit(i, i, []) for i in range(surface_code_circ.num_qubits)]In stac.PhysicalQubit(i, i, []) the second argument is the coordinate of the physical qubit. So, we want to turn this into $(x_i,y_j)$.
surface_code_circ.physical_register.elements = \
[stac.PhysicalQubit(row*i + j, (i, j), []) for i in range(row) for j in range(col)]
# double check the first argument.Next, in the following lines inside the for loop, you are assigning the physical qubits created above to the virtual qubits of the circuit.
surface_code_circ.register[(0,0,i)].constituent_register = surface_code_circ.physical_register.elements[i]
surface_code_circ.layout_map[(0,0,i)] = iYou want to rewrite the two loops, so you are alternatively assigning each physical qubit to either the data register or the syndrome register, as per the diagram.
Once you have done the above, the rest is trivial. Iterate through all the syndrome measurement qubits, look at its coordinates and do the $(x\pm 1, y\pm 1)$ business with the gates.
- To iterate through the virtual qubits in the syndrome register, just do
for qubit in circ.register[(0,1)].qubits() - To figure out the coordinates of physical qubit associated with the above virtual qubit, you can do
qubit.constituent_register.coordinates - With these physical coordinates in hand, add/subtract 1 etc and call
geo_append.
This should do the job. I hope the above is clear. If not, please ask.
JiQing000
Solutions for issue#1 Implementation of surface codes. Please let me know whether there is any mistake or adjustment required.