Quantum process randomness
Abstract
We argue that the optimization of a quantum process based on the customarily used fidelity between the actual and the expected outputs may not be sufficient. We introduce a quantity namely the "quantum process randomness", which is the standard deviation of the distribution of Born probabilities corresponding to the orthonormal measurement that projects the expected output onto the eigenstates of the actual output, and obtain a tradeoff between fidelity and randomness for an arbitrary quantum process. We consider approximate quantum cloning and teleportation processes to illustrate the concept. We find that the optimal approximate universal and statedependent quantum cloning machines obtained by maximizing the fidelity is the same as that obtained by optimizing the difference between randomness and fidelity.
 Publication:

Physics Letters A
 Pub Date:
 January 2021
 DOI:
 10.1016/j.physleta.2020.127024
 arXiv:
 arXiv:1903.03564
 Bibcode:
 2021PhLA..38727024D
 Keywords:

 Quantum processes;
 Optimal quantum processes;
 Fidelity;
 Quantum process randomness;
 Statedependent quantum cloning;
 Quantum teleportation;
 Quantum Physics
 EPrint:
 v2: 6 pages, 2 figures, a generalization included, previous results unchanged