Chinese scientists say physics breakthrough is a step towards scalable quantum computation

Scientists in China say they have made a breakthrough on the way to developing practical processors for quantum computers by achieving the entanglement of multiple ultracold atoms in a laser trap.

While previous studies had only been able to entangle two atoms at a time, the team developed new experimental devices and methods to link eight and 10 atoms in two-dimensional blocks and one-dimensional chains, respectively, marking a crucial step towards preparing and manipulating large-scale atom entanglement.

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The 10-body fully-entangled state. Photo: Handout
The study offered “a new platform towards scalable quantum computation and simulation,” wrote Pan Jianwei and his colleagues from the University of Science and Technology of China (USTC), Tsinghua University and Fudan University in their paper published in the peer-reviewed journal Physical Review Letters last month.
Quantum entanglement is a bizarre phenomenon in the world of quantum mechanics in which two or more particles are linked and always share a unified quantum state no matter how far apart they are in space.

It is a key ingredient in quantum algorithms and can help develop much faster and more powerful computers.

For instance, a quantum computer with 10 quantum bits, or qubits, represents the same amount of memory as 2^10 bits of a conventional computer, and its computing power increases exponentially with the number of particles entangled.

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Scientists have been using a device known as optical lattices, which are webs of laser beams for trapping atoms like eggs in a carton, as a promising platform for quantum computers. However, they got stuck at a critical step – how to entangle more than two atoms at a time to allow scalability.


Pan’s team at USTC has been studying optical-lattice-based ultracold atomic systems since 2010, and they have achieved entanglement of more than 1,000 pairs of rubidium atoms in previous experiments.

However, their work lacked the precise control of individual atomic qubits and an effective method to confirm the multi-atom entanglement state.

For the new study, Pan, known as China’s “father of quantum”, and his colleagues developed a number of new instruments and technologies, including a so-called optical superlattice, a quantum gas microscope and three digital micromirror devices, to create and verify the entanglement of multiple atoms at single-atom resolution, according to the paper.

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Using about 100 ultracold rubidium atoms, they could make entangled pairs with a fidelity of over 95 per cent and more than two-second lifetime. Then, they connected the entangled pairs into one-dimensional 10-atom chains and 2D eight-atom plaquettes, and observed to ensure all the atoms in each group were simultaneously entangled.

Their experiment showed essential ingredients in the road map towards generating multipartite entangled states, and the “building blocks” of entangled groups opened the revenue to larger scale, practical quantum computing, the researchers said.


South China Morning Post

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