David Lucas

Abstract:

We generate multipartite entangled states of two, three, and four matter qubits, where the entanglement is distributed over macroscopic distances via a photonic network link. Trapped-ion ${}^{88}{\mathrm{Sr}}^{+}$ qubits are entangled directly via an optical fibre link, and the entanglement is subsequently extended to ${}^{43}{\mathrm{Ca}}^{+}$ memory qubits cotrapped in each network node, using local mixed-species logic gates. We create remotely entangled ${\mathrm{Sr}}^{+}\text{−}{\mathrm{Ca}}^{+}$ and ${\mathrm{Ca}}^{+}\text{−}{\mathrm{Ca}}^{+}$ states, as well as mixed-species Greenberger-Horne-Zeilinger (GHZ) states of up to four qubits. We demonstrate storage of the remotely entangled memory qubits for $\sim 10\mathrm{s}$ , more than $100\times$ the state creation time.

Abstract:

Lattice gauge theories, which have both dynamical matter and gauge fields, are strongly coupled problems that lie beyond the reach of classical computation. Quantum simulations may provide a tractable approach for studying lattice gauge theories, but implementing gauge-invariant encodings and real-time evolution remains experimentally challenging. Here we demonstrate a resource-efficient encoding of a Z2$${{\mathbb{Z}}}_{2}$$ lattice gauge theory using a hybrid qubit–oscillator trapped-ion quantum device, with the qubits representing the gauge fields and the vibrational modes of the ions encoding the bosonic matter fields. We use synthetic dimensions to construct higher dimensional lattice geometries, and we combine digital and analogue techniques to prepare the initial states, realize the gauge-invariant real-time evolution and measure the relevant observables. After observing dynamics obeying Gauss’s law in a Z2$${{\mathbb{Z}}}_{2}$$ link, we extend this approach to a loop geometry formed by two qubits and two oscillators. In this quasi-two-dimensional set-up, we observe Aharonov–Bohm interference with dynamical gauge fields encoding the magnetic flux, thereby demonstrating the interplay between charge and flux. Our results establish a path for scalable quantum simulations of lattice gauge theories in higher dimensions.