Just a few years ago, many researchers in quantum computing thought it would take several decades to develop machines that could solve complex tasks, such as predicting how chemicals react or cracking encrypted text. But now, there is growing hope that such machines could arrive in the next ten years.
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A ‘vibe shift’ is how Nathalie de Leon, an experimental quantum physicist at Princeton University in New Jersey, describes the change. “People are now starting to come around.”
The pace of progress in the field has picked up dramatically, especially in the past two years or so, along several fronts. Teams in academic laboratories, as well as companies ranging from small start-ups to large technology corporations, have drastically reduced the size of errors that notoriously fickle quantum devices tend to produce, by improving both the manufacturing of quantum devices and the techniques used to control them. Meanwhile, theorists better understand how to use quantum devices more efficiently.
“At this point, I am much more certain that quantum computation will be realized, and that the timeline is much shorter than people thought,” says Dorit Aharonov, a computer scientist at Hebrew University in Jerusalem. “We’ve entered a new era.”
Error prone
The latest developments are exciting to physicists because they address some of the main bottlenecks preventing development of viable quantum computers. These devices work by encoding information in qubits, which are units of information that can take on not just the values 0 or 1, like the bits in a classical computer, but also a continuum of possibilities in between. The prototypical example is the quantum spin of an electron, which is the quantum analogue of a magnetic needle and can be oriented in any direction in space.
Chao-Yang Lu is among those who expect a fault-tolerant quantum computer by 2035.Credit: Dave Tacon for Nature
The heart of a typical quantum computation consists of a series of gates, which are operations that manipulate the state of qubits. Gates can be performed on a single qubit, for example rotating a spin by a certain angle, or on more than one qubit. Crucially, a gate can put multiple qubits in collective entangled, or strongly correlated, states — exponentially boosting the amount of information that they can handle. Every computation then concludes with a measurement, which extracts information from the qubits, destroys the intricate quantum state produced by the gates and returns an answer in the form of a string of ordinary digital bits.
For decades, researchers questioned the viability of this computational paradigm owing to two main reasons. One is that, in practice, quantum states tend to naturally and randomly drift, and after a certain amount of time, the information they store is inevitably lost. The other is that gates and measurements can themselves introduce errors. Even operations as simple as using electromagnetic pulses to rotate a spin never work out exactly as intended.
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