Neutral atom quantum computers promise solutions to many of the problems plaguing current devices, but the technology is still in its infancy. Recent advances in the ability to control and schedule these devices suggest that they may be close to prime time.
The best developed quantum technology today is based on superconducting qubits, which power processors from IBM and Google. But although these devices have been used to demonstrate quantum supremacy and build the largest universal quantum computer To date, they have some limitations.
To begin with, they must be cooled to near absolute zero, which requires bulky and expensive cryogenic equipment. Their quantum states are also very fragile, typically lasting only microseconds, and can only directly interact with their nearest neighbors, limiting the complexity of the circuits they can implement.
Neutral atom quantum computers circumvent these problems. They are built from a series of individual atoms that are cooled to ultra-low temperatures by firing lasers at them. The rest of the device needs no cooling and individual atoms can be arranged only micrometers apart, making the entire system incredibly compact.
Quantum information is encoded in low-energy atomic states that are very stable, so these qubits have much longer lives than superconductors. This stability also makes it difficult for qubits to interact, making it difficult to create entanglements, which are critical to most quantum algorithms. But these neutral atoms can be put into a highly excited state, called the Rydberg state, by firing laser pulses at them, which can be used to entangle them with each other.
Despite these promising features, until now the technology has been used primarily for quantum simulators that help understand quantum processes but cannot implement quantum algorithms. However, two studies NatureLed by researchers at quantum computing companies QuEra and ColdQuanta, it has shown that the technology can be used to implement multi-qubit circuits.
The two groups approach the problem in slightly different ways. The QuEra team takes a novel approach to connectivity into your device by using well-focused laser beams, known as optical tweezers, to physically move your qubits. This allows them to easily entangle distant qubits rather than limiting themselves to just the closest ones. the coldannta team, on the other hand, entangled its qubits by simultaneously exciting two of them in a Rydberg state.
Both groups were able to implement complex multi-qubit circuits. And as Hannah Williams of Durham University in the UK points out in a attached commentthe two approaches are complementary.
Physically rearranging the qubits means there are large gaps between operations, but flexible connectivity makes it possible to create much more complex circuits. However, the ColdQuanta approach 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 writes
However, a lot of improvement is required before that happens, according to Williams, from better gate fidelities (how consistently you can set the correct operation) to optimized laser beam shapes and more powerful lasers.
However, both companies seem confident that this won’t take long. QuEra already presented a 256-atom quantum simulator last year and, according to your website, a 64-qubit quantum computer is “coming soon”. ColdQuanta is more specific, with the promise that your Hilbert 100-qubit computer will be available this year.
How quickly neutral atoms can catch up with industry-leading technologies such as superconducting qubits and trapped ions remains to be seen, but it appears that a promising new competitor has entered the quantum race.
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