Global entangling gates on arbitrary ion qubits
Abstract
Quantum computers can efficiently solve classically intractable problems, such as the factorization of a large number^{1} and the simulation of quantum manybody systems^{2,3}. Universal quantum computation can be simplified by decomposing circuits into single and twoqubit entangling gates^{4}, but such decomposition is not necessarily efficient. It has been suggested that polynomial or exponential speedups can be obtained with global Nqubit (N greater than two) entangling gates^{59}. Such global gates involve alltoall connectivity, which emerges among trappedion qubits when using laserdriven collective motional modes^{1014}, and have been implemented for a single motional mode^{15,16}. However, the singlemode approach is difficult to scale up because isolating single modes becomes challenging as the number of ions increases in a single crystal, and multimode schemes are scalable^{17,18} but limited to pairwise gates^{1923}. Here we propose and implement a scalable scheme for realizing global entangling gates on multiple ^{171}Yb^{+} ion qubits by coupling to multiple motional modes through modulated laser fields. Because such global gates require decoupling multiple modes and balancing all pairwise coupling strengths during the gate, we develop a system with fully independent control capability on each ion^{14}. To demonstrate the usefulness and flexibility of these global gates, we generate a GreenbergerHorneZeilinger state with up to four qubits using a single global operation. Our approach realizes global entangling gates as scalable building blocks for universal quantum computation, motivating future research in scalable global methods for quantum information processing.
 Publication:

Nature
 Pub Date:
 July 2019
 DOI:
 10.1038/s4158601914284
 arXiv:
 arXiv:1901.03508
 Bibcode:
 2019Natur.572..363L
 Keywords:

 Quantum Physics;
 Physics  Atomic Physics;
 Physics  Optics
 EPrint:
 Main: 7 pages, 4 figures and Methods: 4 pages, 2 figures and 2 tables