Photons emitted by the Strontium ions areĬollected using high numerical aperture objectives and used to generate remoteĮntanglement between the ions. Strontium (purple dots) and Calcium ions (green dots) are trapped in two 88 Sr + ions serve as our 'interface' qubits for entanglement generation.
We use two different ion species chosen to excel in different functions: 43 Ca + ions serve as our 'application' qubits, offering long-lived storage and precise manipulation using the well-established, laser-based techniques previously developed in our group (and elsewhere). At the heart of each trap is a surface-electrode trap chip, which allows us to trap multiple chains of ions that can be independently moved around, split up further or recombined to implement complex algorithms. In our laboratory, we operate an elementary version of such a quantum network: two dual-species ion trap nodes, 'Alice' and 'Bob', linked by a few metres of optical fibre. In particular, a key motivation behind our work is a proposal for a scalable quantum information processing architecture, where – in much the same fashion as how today’s supercomputers are built from racks upon racks of smaller servers – a number of relatively simple ion-trap processing nodes are banded together into one big computer using optical fibre links. This duality makes hybrid systems consisting of both trapped-ion and photonic qubits a fertile ground for scientific exploration as well as for technological applications.
Photons, on the other hand, naturally propagate at the speed of light and barely interact with each other or other matter, allowing single photons to travel over many kilometers of optical fibre without losing their quantum information.
In some aspects, they are diametrically opposite qubit technologies: Trapped ions are kept virtually at standstill in ultra-high vacuum systems, where they are routinely laser-cooled to just above absolute zero, and multiple trapped-ion qubits are readily made to interact using their electric repulsion (enabling the record-precision quantum logic gates demonstrated here in Oxford and elsewhere). Trapped ions and photons: complementary quantum systemsīoth trapped ions and photons – particles of light – behave in accordance with the rules of quantum mechanics, and can be manipulated with exquisite precision using room-temperature technology, making them interesting for quantum information processing.
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