First quantization of braided Majorana fermions

TL;DR

This paper develops a first quantization framework for braided Majorana fermions using a graded Hopf algebra, revealing how braiding parameter roots of unity influence the structure and dimensionality of multiparticle Hilbert spaces.

Contribution

It introduces a novel first quantization approach for braided Majorana fermions within a graded Hopf algebra framework, connecting braiding parameters to multiparticle state truncations.

Findings

Derived the graded dimension of multiparticle Hilbert spaces for various braiding parameters.

Identified roots of unity as truncation points affecting the number of allowed Majorana fermions.

Showed that nontrivial braiding is essential for encoding quantum information beyond classical bits.

Abstract

A ${\mathbb Z}_2$-graded qubit represents an even (bosonic) "vacuum state" and an odd, excited, Majorana fermion state. The multiparticle sectors of $N$, braided, indistinguishable Majorana fermions are constructed via first quantization. The framework is that of a graded Hopf algebra endowed with a braided tensor product. The Hopf algebra is ${U}({\mathfrak {gl}}(1|1))$, the Universal Enveloping Algebra of the ${\mathfrak{gl}}(1|1)$ superalgebra. A $4\times 4$ braiding matrix $B_t$ defines the braided tensor product. $B_t$, which is related to the $R$-matrix of the Alexander-Conway polynomial, depends on the braiding parameter $t$ belonging to the punctured plane ($t\in {\mathbb C}^\ast$); the ordinary antisymmetry property of fermions is recovered for $t=1$. For each $N$, the graded dimension $m|n$ of the graded multiparticle Hilbert space is computed. Besides the generic case, truncations occur when $t$ coincides with certain roots of unity which appear as solutions of an ordered set of polynomial equations. The roots of unity are organized into levels which specify the maximal number of allowed braided Majorana fermions in a multiparticle sector. By taking into account that the even/odd sectors in a ${\mathbb Z}_2$-graded Hilbert space are superselected, a nontrivial braiding with $t\neq 1$ is essential to produce a nontrivial Hilbert space described by qubits, qutrits, etc., since at $t=1$ the $N$-particle vacuum and the antisymmetrized excited state encode the same information carried by a classical $1$-bit.