Parameterized quantum comb and simpler circuits for reversing unknown
  qubit-unitary operations
Yin Mo Lei Zhang Yu-Ao Chen Yingjian Liu Tengxiang Lin Xin Wang
Quantum comb is an essential tool for characterizing complex quantum
protocols in quantum information processing. In this work, we introduce PQComb,
a framework leveraging parameterized quantum circuits to explore the
capabilities of quantum combs for general quantum process transformation tasks
and beyond. By optimizing PQComb for time-reversal simulations of unknown
unitary evolutions, we develop a simpler protocol for unknown qubit unitary
inversion that reduces the ancilla qubit overhead from 6 to 3 compared to the
existing method in [Yoshida, Soeda, Murao, PRL 131, 120602, 2023]. This
demonstrates the utility of quantum comb structures and showcases PQComb's
potential for solving complex quantum tasks. Our results pave the way for
broader PQComb applications in quantum computing and quantum information,
emphasizing its versatility for tackling diverse problems in quantum machine
learning.