Generation of optimal states for single-qubit rotations

We show how the interaction of a single-mode quantum field with a sequence of identically prepared two-level atoms converges to a field state that has some remarkable properties: starting from the given initial atomic state, it performs an error- and entanglement-free rotation in the Bloch sphere, while remaining unchanged itself. Starting from a random initial state, it minimizes the average rotation error. We discuss the similarities with the recently-introduced transcoherent states [1], and relate the preparation process to a recent proposal [2] for “cleaning up” a quantum field so as to be able to reuse it for quantum logic operations.

[1] A. Z. Goldberg, A. M. Steinberg, and K. Heshami “Field states for effecting optimal coherent rotations on single or multiple qubits,” Quantum 7, 963 (2023).

[2] J. Ikonen, J. Salmilehto and Mikko Möttönen, “Energy-efficient quantum computing,” npj Quantum Information 3:17 (2017).