On October 2, 2019, the team of A. May, L. Schlieper, and J. Schwinger submitted a paper titled Practical Period Finding on IBM Q — Quantum Speedups in the Presence of Errors. The authors wrote about optimizing quantum circuits for the specific devices they are running on. They actually ran their tests on my favorite quantum computer: ibmq_16_melbourne.

According to the paper, and I’ve got experiments queued up as I write this, it makes a difference which qubits you entangle, and which qubit out of the pair is the control qubit. I can only recall one instance of seeing qubit1 controlling qubit0, and although it struck me as odd, it didn’t seem to be worth investigating. In hindsight, on ibmq_16_melbourne anyway, that’s the optimal way of entangling those 2 qubits.

For most published circuit diagrams, a non-optimized presentation is probably best. After all, the author doesn’t know what hardware you might run the circuit on. It would be unnecessarily confusing to have to first decompose one optimized circuit in order to optimally recompose the circuit for another device.

Anyway, I intend to re-run some old experiments and see how pronounced the differences are. I might end up having to redo some or all of the experiments that I ran for my paper.

This is the sort of thing I learn when I read one paper a day.