Optimal Universal Quantum Circuits for Unitary Complex Conjugation

May 31, 2022
20 pages
Published in:
  • IEEE Trans.Info.Theor. 69 (2023) 8, 5069-5082,
  • IEEE Trans.Info.Theor. 69 (2023) 8
  • Published: Aug, 2023
e-Print:

Citations per year

2022202320242025253
Abstract: (IEEE)
Let UdU_{d} be a unitary operator representing an arbitrary dd -dimensional unitary quantum operation. This work presents optimal quantum circuits for transforming a number kk of calls of UdU_{d} into its complex conjugate Ud\overline {U_{d}} . Our circuits admit a parallel implementation and are proven to be optimal for any kk and dd with an average fidelity of F=k+1d(dk)\left \langle{ {F}}\right \rangle =\frac {k+1}{d(d-k)} . Optimality is shown for average fidelity, robustness to noise, and other standard figures of merit. This extends previous works which considered the scenario of a single call ( k=1k=1 ) of the operation UdU_{d} , and the special case of k=d1k=d-1 calls. We then show that our results encompass optimal transformations from kk calls of UdU_{d} to f(Ud)f(U_{d}) for any arbitrary homomorphism ff from the group of dd -dimensional unitary operators to itself, since complex conjugation is the only non-trivial automorphism on the group of unitary operators. Finally, we apply our optimal complex conjugation implementation to design a probabilistic circuit for reversing arbitrary quantum evolutions.
Note:
  • 20 pages, 5 figures. Improved presentation, typos corrected, and some proofs are now clearer. Close to the published version
  • Quantum circuit
  • Quantum channels
  • Transforms
  • Task analysis
  • Logic gates
  • Quantum state
  • Decoding
  • optimisation
  • probability
  • quantum computing