2006/08/15 by Agata M. Brańczyk, Agata M. Branczyk, Paulo E. M. F. Mendonca +4
Computer Science · Engineering · Mathematics · Physics and Astronomy · #Algorithm #Artificial intelligence #Computer science #Control (management) #Control theory (sociology) #Dephasing #Engineering #Image (mathematics) #Mathematics #Noise (video) #Physics #Quantum #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum mechanics #Quantum state #Qubit #State (computer science) #Task (project management) #Topology (electrical circuits) #Weak measurement #quant-ph
paper · pdf · doi:10.1103/physreva.75.012329
published as Phys. Rev. A, 75, 012329 (2007) · 12 pages, 7 figures, v2 includes new references and minor changes
arxiv created 2006/08/15 · openalex publication_date 2007/01/24 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyze a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two nonorthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a nonprojective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement backaction. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realizes the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.