Implement a square root of Swap gate in using qiskit

Question

Does the √SWAP gate have a ready-to-use function on the Qiskit circuit library?

If not, how to implement it?

https://quantumcomputing.stackexchange.com/questions/2228/how-to-implement-the-square-root-of-swap-gate-on-the-ibm-q-composer — Jaimin, Oct 29 '21 at 04:26
related: https://quantumcomputing.stackexchange.com/q/21708/55 — glS, Oct 29 '21 at 08:30
Does this answer your question? Expressing "Square root of Swap" gate in terms of CNOT — user1271772 No more free time, Nov 02 '21 at 13:07

score 2 · Accepted Answer · answered Oct 29 '21 at 11:18

I don't think √SWAP gate has a ready-to-use function in Qiskit. But it is easy to implement.

√SWAP unitary is: $$\sqrt{swap} = \left( {\begin{array}{*{20}{c}} 1&0&0&0 \\ 0&\frac{1}{2}(1 + i)&\frac{1}{2}(1 - i)&0 \\ 0&\frac{1}{2}(1 - i)&\frac{1}{2}(1 + i)&0 \\ 0&0&0&1 \end{array}} \right)$$

It is equivalent to:

So, it can be implemented as follows:

from qiskit import QuantumCircuit
circ = QuantumCircuit(2)
circ.cx(0, 1)
circ.csx(1, 0)
circ.cx(0, 1)

To verify:

from qiskit.quantum_info.operators import Operator
from qiskit.visualization import array_to_latex
op = Operator(circ)
array_to_latex(op)

And to use it as a gate:

sr_swap = circ.to_gate(label = '√SWAP')
qc = QuantumCircuit(2)
qc.append(sr_swap, [0, 1])

Thanks for this comprehensive answer. Is there a command that prints out the truth table for this circuit? — Bekaso, Oct 29 '21 at 11:43

Implement a square root of Swap gate in using qiskit

1 Answers1