2017/07/31 by Yuxiang Yang, Giulio Chiribella, Qinheping Hu · 1 citation
Computer Science · Physics and Astronomy · #Angular momentum #Bell state #Cartesian coordinate system #Degrees of freedom (physics and chemistry) #Quantum #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum entanglement #Rotation (mathematics) #Spin (aerodynamics) #Spins #State (computer science) #quant-ph
paper · pdf · doi:10.1088/1367-2630/aa94e5
published as New Journal of Physics 19, 123003 (2017) · 25 pages + appendix, 7 figures, new results added
openalex created_date 2017/07/31 · arxiv created 2017/09/30 · openalex publication_date 2017/10/20 · arxiv updated 2017/12/05 · openalex updated_date 2026/08/06
Entanglement in angular momentum degrees of freedom is a precious resource for quantum metrology and control. Here we study the conversions of this resource, focusing on Bell pairs of spin- J particles, where one particle is used to probe unknown rotations and the other particle is used as reference. When a large number of pairs are given, we show that every rotated spin- J Bell state can be reversibly converted into an equivalent number of rotated spin one-half Bell states, at a rate determined by the quantum Fisher information. This result provides the foundation for the definition of an elementary unit of information about rotations in space, which we call the Cartesian refbit . In the finite copy scenario, we design machines that approximately break down Bell states of higher spins into Cartesian refbits, as well as machines that approximately implement the inverse process. In addition, we establish a quantitative link between the conversion of Bell states and the simulation of unitary gates, showing that the fidelity of probabilistic state conversion provides upper and lower bounds on the fidelity of deterministic gate simulation. The result holds not only for rotation gates, but also to all sets of gates that form finite-dimensional representations of compact groups. For rotation gates, we show how rotations on a system of given spin can simulate rotations on a system of different spin.