Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
Non-Adiabatic Holonomic Quantum Gates
Vera Neef, Julien Pinske, Matthias Heinrich, Stefan Scheel, Alexander Szameit
Abstract
Implementing quantum gates as non-Abelian holonomies, a class of topologically protected unitary operators, is a particularly promising paradigm for the design of intrinsically stable quantum computers [1]. In contrast to dynamic phases, the geometric phase accumulated by a quantum system propagating through a Hilbert space$\mathcal{H}$depends exclusively on its path. In general, geometric phases can exhibit arbitrary dimensionality. Wilczek and Zee introduced the idea of multi-dimensional, non-Abelian geometric phases - so called holonomies [2]. Anandan later dropped the requirement of adiabaticity to create holonomies, that are truly time-independent [3]. Non-adiabatic holonomies rely on a subspace$\mathcal{H}_{\text{geo}}$of the Hilbert-space that is spanned by states$\{\vert \Phi_{k}\rangle\}_{k}$that fulfill$(\Phi_{k}\vert \hat{H}\vert \Phi_{j}\rangle=0$, where$\hat{H}$is the system's Hamiltonian. Restricting the propagation to$\mathcal{H}_{\text{geo}}$ensures parallel transport and, thus, a purely geometric phase (see Fig. 1a) [4], [5]. Quantum optics constitutes a particularly versatile platform for quantum information processing, and in particular for the construction of non-adiabatic holonomic quantum computers: In addition to integration and miniaturization provided by the platform, the bosonic nature of photons also conveniently allows for multiple excitations of the same mode, readily expanding$\mathcal{H}_{\text{geo}}$and enabling the synthesis of holonomies from higher symmetry groups$\mathrm{U}(N)$as larger and more capable computational units [6], [7].