Symmetry is among the most fundamental and powerful concepts in nature, whose existence is usually taken as given, without explanation. We explore whether symmetry can be derived from more fundamental principles from the perspective of quantum information. Starting with a two-qubit system, we show there are only two minimally entangling logic gates: the identity and the $\mathrm{SWAP}$, which interchanges the two states of the qubits. We further demonstrate that, when viewed as an entanglement operator in the spin-space, the $S$-matrix in the two-body scattering of fermions in the $s$-wave channel is uniquely determined by unitarity and rotational invariance to be a linear combination of the identity and the $\mathrm{SWAP}$. Realizing a minimally entangling $S$-matrix would give rise to global symmetries, as exemplified in Wigner’s spin-flavor symmetry and Schrödinger’s conformal invariance in low energy quantum chromodynamics. For $N_q$ species of qubit, the identity gate is associated with an $[SU(2){]}^{N_q}$ symmetry, which is enlarged to $SU(2N_q)$ when there is a species-universal coupling constant.

• Received 7 May 2021
• Accepted 13 September 2021

DOI:https://doi.org/10.1103/PhysRevD.104.074014

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society