Experts said China had grabbed the lead in quantum communications after a team of Chinese scientists used entangled photons from the country’s Micius satellite to make the world’s first quantum-secured video chat in 2017. According to a new study, lead has also been extended to quantum computing.
Physicists from the University of Science and Technology of China (USTC) announced significant advancements in quantum communication and quantum computing in three preprint articles published on arXiv.org last month. Researchers utilized nanometer-scale semiconductors called quantum dots in one of the tests to successfully transport single photons—an crucial resource for any quantum network—over 300 kilometers of fiber, considerably beyond prior attempts.
In another, scientists increased the number of detected photons in their photonic quantum computer from 76 to 113, resulting in a significant increase in its “quantum advantage,” or how much quicker it is than conventional computers at a given job.
The third article unveiled Zuchongzhi, a quantum computer made up of 66 superconducting qubits, and demonstrated that it could solve a problem with 56 of them, which is comparable to the 53 qubits utilized in Google’s quantum computer Sycamore, which established a performance record in 2019.
“This is a fascinating development. Scott Aaronson, a theoretical computer scientist at the University of Texas at Austin, says, “I had no idea they were coming out with not one but two of these [quantum computing findings] in the same week.” “Wow, that’s insane.”
All three accomplishments are world-class, but Zuchongzhi has scientists buzzing since it is the first independent confirmation of Google’s historic 2019 finding. John Martinis, a former Google researcher who spearheaded the effort to create Sycamore, says, “I’m extremely delighted that someone has repeated the experiment and proven that it works properly.” “This is great news for the field since superconducting qubits provide a stable base on which to develop these machines.”
Quantum computing and quantum communication are still in their infancy. For many years to come, none of this research will be of practical value. However, quantum technology has significant geopolitical implications: full-fledged quantum networks may provide unhackable communication routes, and a powerful quantum computer could potentially break most of the encryption used to safeguard e-mails and Internet transactions.
Tensions between the United States and China are at an all-time high, with the two nations squabbling over trade, human rights, espionage concerns, COVID, and Taiwan. Following China’s Micius satellite demonstration in 2017, American lawmakers responded by investing hundreds of millions of dollars in quantum information research through the National Quantum Initiative.
It was a strange sense of déjà vu. Fearmongering about a little Soviet spacecraft named Sputnik had prompted the United States to support another far-fetched project—space exploration—about 60 years before.
However, the battle for quantum advantage does not have to be a carbon copy of the space race. China and the United States are deeply connected in many sectors, including science, according to Zuoyue Wang, a scientific historian at California State Polytechnic University, Pomona, which might preclude a violent new competition in the quantum domain.
Hundreds of thousands of Chinese students study in the United States now, and experts from both nations work closely on projects ranging from agriculture to zoology. Despite growing geopolitical tensions, Wang claims that the two nations are “each other’s greatest international partnership partners.”
Richard Feynman, a physicist, proposed a simple hypothesis forty years ago: classical computers attempting to imitate a fundamentally quantum world may be outperformed by a computer that, like reality, is quantum. In 2019, a Google team led by Martinis demonstrated that the company’s Sycamore system could perform a specific, limited task exponentially faster than even the most powerful classical supercomputers (though a competing IBM team disputed that Google’s achievement represented a true quantum advantage). A year later, USTC researchers conducted a similar experiment with a photon-based quantum computer.
Why may simple quantum computers outperform traditional supercomputers in some tasks? The most popular refrain goes like this: A quantum computer employs qubits, which are somewhere between 0 and 1 before being measured—a so-called quantum superposition—instead of conventional bits that are either 0 or 1. Qubits must be entangled, or quantum correlated, with one another to function together in a computer.
It might be more obvious to think of the job Zuchongzhi and Sycamore did. Aaronson describes it as “nearly laughably easy.” “All you do is a series of quantum operations at random.” This jumble of instructions entangles all of the qubits into a single, jumbled state. For qubits, describing that state is easier than for bits. Four classical bits are required to describe two entangled qubits.
(You can get a 00, 01, 10, or 11 as a result.) The state complexity increases exponentially, thus describing a state that takes 50 qubits takes 250, or roughly one quadrillion, bits. Photonic quantum computers produce a similarly entangled and chaotic state, but with photons functioning as qubits instead of electrons.
This is why even a tiny quantum computer with 50 qubits can outperform a huge conventional supercomputer. “There haven’t been a lot of people talking about duplicating [Google’s 2019] experiment in the West—the United States, Europe,” Martinis adds. “I respect China for wanting to take this seriously.”
The USTC systems described in two of the recent preprints now have 56 qubits and 113 observed photons, making them the world’s most powerful quantum computers—with two major limitations. To begin with, neither quantum computer is capable of doing any meaningful tasks.
(Because photonic quantum computing is not a universal computer platform, it would not be a typical programmable computer even if scaled up.) Second, it’s not obvious how big of a quantum edge they have over traditional computers. Several research has claimed the capacity to mimic such chaotic entangled state in recent months, particularly for photonic quantum computers.
Despite the challenges of working with photonic quantum computers, USTC researchers have a strong motivation to master the platform since photons constitute the communication medium for China’s developing quantum network.
Thousands of kilometers of fiber-optic cables have already been laid between Beijing and Shanghai, forming the first quantum connection. Because photons can only go so far before succumbing to fiber noise, the link is not a fully realized quantum connection: it is split up by nodes.
Precision synchronization and unhackable communications are two of the most important uses of a genuine quantum network.
Quantum networks will need entangled single photons for quantum key distribution and other activities that need entanglement, among other things, to deliver on that promise. Single photons are believed to be suitable sources for quantum dots.
Quantum dots had never transmitted a single photon across more than a kilometer of fiber until recently. (In general, the longer the fiber, the more noise.) However, the USTC team was able to improve the transmission distance while lowering the single photon’s noise level.
It achieved success by using stringent controls, such as maintaining the temperature of the 300-kilometer fiber to within a tenth of a degree Celsius.
IN THE QUANTUM REALM RACING
Is China on the verge of surpassing the United States in quantum information technology? The answer is contingent on how you calculate it. While estimates vary, both countries appear to invest more than $100 million each year in research.
China has more total patents in quantum technology, while the United States has a significant advantage in quantum computing patents. China, of course, has a more advanced quantum network and currently controls the top two quantum computers.
Mitch Ambrose, a science policy analyst at the American Institute of Physics, says, “It’s such a novel challenge for the United States to be addressing.” “It hasn’t had to think much about what it means to be behind since it has been ahead for so long and in so many areas.”
In general, quantum research on China is nearly exclusively funded by the government and is focused on a few universities and enterprises. In contrast, research in the United States is dispersed across dozens of funding organizations, institutions, and private firms.
“The Chinese government takes science and technology far more seriously than the US administration,” Wang argues. “No one else is going to pay the bill.”
The US government is now deciding how to support the future of quantum information science, with legislation like the Innovation and Competition Act of 2021 proposing $1.5 billion for communications research, including quantum technologies.
The law also emphasizes semiconductor production in response to security worries about China and includes a clause that would limit collaboration with China on nuclear energy and armament.
This isn’t the first time the two countries have put a stumbling block in the way of scientific cooperation. The Wolf Amendment, which prohibits NASA from cooperating with China’s space program without a waiver, has been in effect since 2011.
In contrast, the United States and China have spent more than four decades openly working on scientific topics, thanks to the 1979 United States-China Agreement on Cooperation in Science and Technology.
Quantum research finds itself in an uncomfortable position as tensions between the two countries rise: while it is still fundamental research with few present applications, its strategic potential is apparent and vast.
“What are the ground rules for future scientific exchanges in any discipline, let alone quantum?” Ambrose inquires. Hawkish funding of quantum research might exacerbate tensions, but it also has the potential to encourage increased collaboration and openness among competing governments wanting to demonstrate their quantum expertise.
During the Cold War, the United States and the Soviet Union attempted to establish parity, if not superiority, in nuclear weapons, spaceflight, and other strategically vital technological endeavors.
Olga Krasnyak, a science diplomacy expert at Moscow’s National Research University Higher School of Economics, claims that the resultant US-Soviet scientific interactions contributed to the end of the Cold War.
“Science diplomacy has this advantage,” adds Krasnyak, “in that it employs science, which is universal.” And, perhaps most significantly, it employs scientists, who have long relied on their shared humanity and thirst for knowledge to bridge ideological divides.
Quantum computing and communications have the potential to change the planet. “I believe in the power of human communication, too,” Krasnyak says.