How a Chinese diamond experiment may help crack one of the world’s toughest codes
An experiment in China using diamonds has put quantum code-breaking a step closer to reality, threatening to one day break the digital encryption technologies that safeguard banks, governments and the military.
In their experiment, quantum physicists in Hefei, Anhui province, reportedly broke down the number 35 into its factors – the numbers five and seven – on a new type of quantum computing device built inside a diamond.
The process, known as factorisation, is the key to cracking the most popular digital algorithm used in encryption today.
The research was led by quantum physicist Professor Du Jiangfeng at the University of Science and Technology of China, and details of the results were published in the journal Physical Review Letters in March.
In the experiment, laser and microwave beams were fired at particles trapped inside the diamond’s “nitrogen-vacancy centre”, a tiny space ideal for subatomic interaction. The particles came up with the solution in two microseconds, less than half of the time it takes for lightning to strike.
Speed is key to code-cracking and quantum computers have the potential to dramatically cut the time needed to break an encryption thanks to a phenomenon called entanglement.
The popular RSA algorithm, developed by Ron Rivest, Adi Shamir and Leonard Adleman in the 1970s, uses the product of two large prime numbers to encrypt a message.
Only people who know the two prime numbers can decode the message, because it is practically impossible to factor the product of two prime numbers when they were sufficiently large.
An enormous amount of digital computing power and thousands of years would be needed to determine the prime numbers used in the RSA system.
But, in theory, a quantum computer could break a RSA code in the blink of an eye.
Some researchers say the country’s first quantum computer could be up and running in the next few years but there are still problems to overcome.
The work in Hefei has caught the attention of cryptographers like Gao Jundao. Gao is an associate professor of cryptography at Xidian University in Xian, Shaanxi, and writes algorithms for the defence industry.
“[The finding] is code-breaking, strictly speaking, albeit still in its infancy,” Gao said. “It is no doubt a breakthrough.”
In 2012, Du’s team set a record by factorising the number 143, but it was achieved with nuclear magnetic resonance technology in a liquid, a medium not easy to scale up for practical applications.
Two years later, a multinational team of researchers from Japan, Britain and Microsoft set a new record by breaking down the number of 56,153 using the same technology.
But for the first time, the Chinese experiment factorised a number in a setting built entirely on solid material, making the system more stable.
Dr Xu Kebiao, first author of the paper, said the team’s diamond device could factor certain types of numbers of six digits or even higher.
“And it is scalable, which is a huge advantage of our system,” he said.
By summoning more entangled particles and creating more nitrogen-vacancy centres in the diamond, the quantum device may eventually harness enough capacity to outperform conventional computers.
China hits milestone in developing quantum computer ‘to eclipse all others’
And the diamond provided other advantages, according to Xu. Existing prototype quantum computers are extremely sensitive to disturbance from outside environments such as heat and electromagnetic interference. They needed to be kept in liquid helium for extremely low temperature, or heavily shield rooms.
“Our device just sits out in the open in the laboratory. It works in room temperature. We do not even bother to turn off the Wi-fi,” Xu said.
Professor Duan Changkui, another researcher involved in the experiment, said many technical challenges had to be overcome before the device could be used to break a code. These problems ranged from precise control of particles to better diamonds.
“The artificial diamonds must be extremely pure, and their nitrogen-vacancy centres perfectly aligned. The manufacturing process is very difficult,” he said.
“It is not easy to predict when the first practical machine could be built.”
But cryptographers were bracing for a battle, according to Gao.
“RSA is just one type of algorithm. There are other mathematical methods of encryption that cannot be decoded by large-number factorisation, and these will be the second or third line of defence,” he said.
Gao said a whole new branch of research, post-quantum cryptography, had been established to break those defences.