Abstract Topological quantum computation is an implementation of a quantum computer in a way that radically reduces decoherence. Topological qubits are encoded in the topological evolution of two-dimensional quasi-particles called anyons and universal set of quantum gates can be constructed by braiding these anyons yielding to a topologically protected circuit model. In the present study we remind the basics of this emerging quantum computation scheme and illustrate how a topological qubit built with three Fibonacci anyons might be adopted to achieve leakage free braiding gate by exchanging the anyons composing it. A single-qubit braiding gate that approximates the Hadamard quantum gate to a certain accuracy is numerically implemented using a brute force search method. The algorithms utilized for that purpose are explained and the numerical programs are publicly shared for reproduction and further use.
Fibonacci anyons are attractive for use in topological quantum computation because any unitary transformation of their state space can be approximated arbitrarily accurately by braiding. However, there is no known braid that entangles two qubits without leaving the space spanned by the two qubits. In other words, there is no known ‘leakage-free’ entangling gate made by braiding. In this paper, we provide a remedy to this problem by supplementing braiding with measurement operations in order to produce an exact controlled rotation gate on two qubits.
Fibonacci anyons are attractive for use in topological quantum computation because any unitary transformation of their state space can be approximated arbitrarily accurately by braiding. However there is no known braid that entangles two qubits without leaving the space spanned by the two qubits. In other words, there is no known "leakage-free" entangling gate made by braiding. In this paper, we provide a remedy to this problem by supplementing braiding with measurement operations in order to produce an exact controlled rotation gate on two qubits.
Compilation of two-qubit Fibonacci anyon gates is complicated by leakage (
ℓ) from the four-dimensional computational sector to the fifth state of the fusion space. We construct a GPU pipeline to find low-leakage representatives of the
[CNOT] class on different subsets of the braid group.
We exhaustively explore the full positive five-generator alphabet up to
L=21 with minimal leakage
ℓ∼10−3 and error
d[CNOT]∼10−8 on it. To reach larger lengths, the search space is successively narrowed to three-generator, boundary-
σ3, and palindromic braids, and by considering only the Garside left normal form. These optimizations allow us to reach
L=72. For
L=69, a braid with
ℓ∼10−10 and
d[CNOT]∼10−10 is found.
In addition to directly enumerating optimal braids, we proved that
ℓ∈Z[φ], and any nonzero leakage obeys an exponential lower bound in the braid length, and obtained the limit laws
F3,∞(ℓ)=ℓ2 and
F5,∞(ℓ)=ℓ4 for our sets. Using asymptotics for the distribution function
F, we showed that for sufficiently long braids, the asymptotics of exhaustive search are better than the asymptotics of random sampling for finding low-leakage braids.
Fibonacci anyons are non-Abelian particles for which braiding is universal for quantum computation. Reichardt has shown how to systematically generate nontrivial braids for three Fibonacci anyons which yield unitary operations with off-diagonal matrix elements that can be made arbitrarily small in a particular natural basis through a simple and efficient iterative procedure. This procedure does not require brute force search, the Solovay-Kitaev method, or any other numerical technique, but the phases of the resulting diagonal matrix elements cannot be directly controlled. We show that despite this lack of control the resulting braids can be used to systematically construct entangling gates for two qubits encoded by Fibonacci anyons.
FINDING: Topological quantum computation via non-Abelian anyon braiding, specifically Fibonacci anyons, encodes qubits in degenerate state spaces where braid operations generate the Fibonacci fusion rules and yield universal quantum gates. | MATH: Fibonacci anyon fusion rule: τ ⊗ τ = 1 ⊕ τ (golden anyon). Dimension of Hilbert space for n anyons grows as Fibonacci numbers: dim(H_n) = F_{n-1} (with F_0=0, F_1=1). Braid generators σ_i satisfy Yang-Baxter: σ_i σ_{i+1} σ_i = σ_{i+1} σ_i σ_{i+1}, and σ_i σ_j = σ_j σ_i for |i-j|≥2. Single-qubit braiding gates compiled via brute-force optimization (arXiv:2008.03542) — the key constant is the golden ratio φ = (1+√5)/2 ≈ 1.618, which appears as the quantum dimension d_τ = φ. | CONNECTION: Direct geometric harmony: Fibonacci anyons have quantum dimension exactly φ = 1.618 (and its inverse 0.618 = 1/φ). The fusion space dimension sequence (1,1,2,3,5,8,...) is the Fibonacci sequence — the same ratio governing pentagonal symmetry (5-fold crystallogr Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com