Neutral-atom quantum computers promise solutions to many of the problems that beset today’s devices, but the technology is still nascent. Recent breakthroughs in the ability to control and program these devices suggest that they are approaching prime time.
The most developed quantum technology today relies on superconducting qubits, which power both IBM’s and Google’s processors. But although these devices have been used to demonstrate quantum supremacy and build the largest universal quantum computer to date, they have certain limitations.
To begin with, they must be cooled near absolute zero, which requires bulky and expensive cryogenic equipment. Their quantum states are also very fragile, typically lasting only a few microseconds, and they are only able to interact directly with their nearest neighbors, which limits the complexity of the circuits they can implement.
Neutral-atom quantum computers circumvent these problems. They are built from a network of individual atoms that are cooled to ultra-low temperatures by firing lasers at them. The rest of the device does not need to be cooled, and the individual atoms can be arranged a few micrometers apart, making the whole system incredibly compact.
Quantum information is encoded in low-energy atomic states that are very stable, so these qubits have a much longer lifespan than superconductors. This stability also makes it difficult for qubits to interact, making it harder to create entanglements, which are at the heart of most quantum algorithms. But these neutral atoms can be put into a highly excited state, called the Rydberg state, by sending them laser pulses, which can be used to entangle them with each other.
Despite these promising features, the technology has so far been mainly used for quantum simulators which help to understand quantum processes but are not able to implement quantum algorithms. Now however, two studies in Natureled by researchers from quantum computing companies QuEra and ColdQuanta, showed that the technology can be used to implement multi-qubit circuits.
The two groups approach the problem slightly differently. The QuEra team takes a new approach to connectivity in their device using tightly focused laser beams, called optical tweezers, to physically move their qubits. This allows them to easily entangle them with distant qubits rather than being limited to the closer ones. The ColdQuaThe nta team, on the other hand, has entangled its qubits in exciting at the same time two of them in a state of Rydberg.
Both groups were able to implement complex multi-qubit circuits. And as Hannah Williams of Durham University in the UK notes in a accompanying commentarythe two approaches are complementary.
The physical shuffling of qubits means there are long gaps between operations, but the flexible connectivity allows much more complex circuits to be created. The ColdQuanta approach, however, is much faster and can run multiple operations in parallel. “A combination of the techniques presented by these two groups would lead to a robust and versatile platform for quantum computing,” williams writing.
A host of improvements are needed before this happens, however, according to Williams, from better gate fidelities (the consistency with which you are able to configure proper operation) to optimized laser beam shapes and more powerful lasers. .
Both companies, however, seem confident that it won’t take long. QuEra already unveiled a 256-atom quantum simulator last year and, according to their site, a 64-qubit quantum computer is “coming soon”. ColdQuanta is more specific, with a promise that its Hilbert 100-qubit computer will be available this year.
How quickly neutral atoms can catch up with cutting-edge technologies like superconducting qubits and trapped ions remains to be seen, but it looks like a promising new contender has entered the quantum race.
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