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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 Sr + 88 qubits are entangled directly via an optical fibre link, and the entanglement is subsequently extended to Ca + 43 memory qubits cotrapped in each network node, using local mixed-species logic gates. We create remotely entangled Sr + − Ca + and Ca + − 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 ∼ 10     s , more than 100 × the state creation time.

Abstract:

Abstract Quantum entanglement allows for correlations between distant objects that go beyond any classical theory. These additional correlations can be exploited to gain practical advantage in certain non-local games. In recent years there has been interest in games defined on graph structures and involving mobile agents. One of these is the graph domination game, where quantum advantage has been discovered recently on some finite graphs by numerical optimization [1]. Here we study quantum advantage in the 1-step, 2-player version of this game, focusing on cycle graphs. We study it numerically, analytically and through the use of noisy, intermediate scale quantum (NISQ) processors. We find explicit strategies and show that they realise the numerical bounds that were found recently for the case of small graphs [1]. We then generalise our strategies to cycles of arbitrary size. Finally, we run our strategies for 5-, 6-, and 7-site cycles on NISQ hardware and find measurable advantage (compared to the optimal classical strategies) in all cases.

Abstract:

Quantum harmonic oscillators model phenomena from electromagnetic fields to molecular vibrations, with excitations represented by bosons such as photons or phonons. Linear interactions that create or annihilate single bosons generate coherent states of light or motion. Introducing higher-order nonlinear interactions produces richer quantum behaviour: second-order interactions enable squeezing, whereas higher-order interactions generate non-Gaussian states useful for continuous-variable quantum computation. However, such interactions are usually weak or require specialized hardware. Hybrid systems, where a linear interaction couples an oscillator to a spin, offer an alternative. Here we combine two spin-dependent linear bosonic interactions to implement up to fourth-order nonlinear bosonic interactions in a single trapped ion, focusing on generalized squeezing. We demonstrate and characterize squeezing, trisqueezing and quadsqueezing; reconstruct the Wigner functions of the resulting states; and achieve quadsqueezing over 100 times faster than conventional methods. The approach has no fundamental limit on the interaction order and applies to any platform supporting spin-dependent linear interactions.

Abstract:

We characterise an efficient optically-heated neutral atom source for ion trapping. We observe loading rates of up to 24(3) s−1 with heating powers below 85 mW, and demonstrate loading of a single ion in under 30 s with 41.4(4) mW of optical power in a room-temperature ion trap system with an ionisation probability of 1.50(5) × 10−5 . We calibrate a thermal model for the source’s internal temperature by imaging the fluorescence of a collimated flux of neutral calcium that effuses from the source at various optical heating powers. We show that the thermal performance of this source is mainly limited by radiative losses. We explore the effect of second-stage photo-ionisation laser power on the loading rate, and identify a path beyond the loading rates reported in this study. We predict that this source is also well-suited to a wide range of metals used in ion trapping.