Generalizing a brick-wall circuit acting on qubits to acting on qudits

Question

Recently, I have been creating a "brick layer" circuit of random unitary gates (each acting on 2 qubits) which acts on a n qubit register using cirq. A typical circuit looks like this.

(Where a top and bottom label symbolises one gate).

The code used to reproduce it is here. https://colab.research.google.com/drive/1Rs3knKOJV8CddSQLzl1HgO1L-GR7sfbK?usp=sharing

I wish to extrapolate my model to n qudits as opposed to qubits. I have been successful in applying this to qutrits. The code for this is below.

https://colab.research.google.com/drive/13xz7PP7WZ676-PSpg06U_QmRdg4kRXDr?usp=sharing

However, when I try to do this for some general qudit register. I always land up with a type error.

See the code below (which is very similar to the others)

https://colab.research.google.com/drive/1Ij0ZdNixv5krCIBa5-esKq92KpGzBo9Z?usp=sharing

Does anybody know how to fix this error? Help would be greatly appreciated :) I reckoned as it was easy to get the code working for qutrits it shouldn't be so hard to get it working for any general qudit register.

Cheers, Luke

Answer 1

Try these changes to your code:

class QuditPlusGate(cirq.Gate):
  def __init__(self, dimension):
    self._p = dimension
  def _qid_shape_(self):
    return (self._p, self._p)
  ...
  # the rest of your code

def quditopsmoment0(n,p):
  qudits = qudit_register(n,p)
  u_gate = QuditPlusGate(p)
  listofqops0 = []
  i = 0
  while i < n/2:
    listofqops0.append(u_gate.on(qudits[2*i],qudits[2*i + 1]))
    i = i + 1
  else:
    return listofqops0

quditopsmoment0(2,2)

Passing the dimension as an argument when initializing the QuditPlusGate class allows eliminating the extra argument you had for the _qid_shape_ method to match the method it was overriding. That seemed to fix it for me.