Quantum computing promises to be a revolutionary tool, simplifying equations that classical computers would struggle to complete. Yet the workhorse of the quantum device, known as a qubit, is a delicate object susceptible to collapse.
Keeping enough qubits in their ideal state long enough for calculations has so far proven to be a challenge.
In a new experiment, scientists were able to maintain a qubit in this state for twice as long as normal. Along the way, they demonstrated the practicality of quantum error correction (QEC), a process that keeps quantum information intact longer by introducing room for redundancy and error suppression.
The idea of QEC has been around since the mid-90s, but has now been shown to work in real time. Part of the reason for the experiment’s success was the introduction of machine-learning AI algorithms to fine-tune the error-correction routine.
“For the first time, we have shown that making the system more redundant and actively detecting and correcting quantum errors leads to greater resilience of quantum information,” explains physicist Michel Devoret, from Yale University in Connecticut. .
Qubits are objects as they exist in a mixture of quantum states. Where classical objects can have absolute states, a qubit’s version of the same state would be best described using probability. When a qubit interacts with other qubits, their probabilities become entangled in computationally useful ways.
Unfortunately, it’s not just other qubits that can intertwine their states with an undecided object. Everything in the environment acts as ‘noise’, potentially influencing those tricky probabilities and leaving room for error.
Part of the reason scientists have struggled to implement QEC is that it can introduce its own errors. The extra space allowed for error correction can make the qubit even more vulnerable to interference from the surrounding environment.
Like many quantum physics experiments, this one was conducted at ultra-cold temperatures – a hundred times colder than outer space, in this case. The configuration must be carefully controlled in order to protect the qubit as much as possible.
The error-corrected qubit lasted 1.8 milliseconds – just a blink of an eye, as we might experience, but an impressive amount of time for a qubit operating at the quantum level. Now the research team will be able to further refine the process.
“Our experience shows that quantum error correction is a real practical tool,” says Devoret. “This is more than just a proof-of-principle demonstration.”
While scientists are making significant progress in the development of quantum computers – and rudimentary quantum computers currently exist – there is still a long way to go before the technology’s full potential is realized.
Reducing noise, improving stability, and upgrading error correction will all play an important role in moving closer to practical, large-scale quantum computers that anyone can use.
In this case, the breakthrough was due to several different factors, rather than a single change. The QEC code was actually from 2001, but improvements as well as upgrades to the quantum circuit fabrication process made the difference.
“No single breakthrough has enabled this result,” says Volodymyr Sivak, Google researcher and formerly at Yale University. “It’s actually a combination of a whole bunch of different technologies that have been developed over the last few years, which we’ve combined in this experiment.”
“Our experiment validates a fundamental assumption of quantum computing, and it makes me very excited about the future of this field.”
The research has been published in Nature.
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