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China's Quantum Supremacy Milestone; A Quantum Computer that Measures Light

Earlier this month a group of scientists led by Jian-Wei Pan from the University of Science and Technology of China in Hefei has claimed to achieve quantum supremacy by implementing a new type of quantum computing called "boson sampling" used on 76 photons with their photonic quantum computer, and as such is capable of calculations that no classical computer could or has ever accomplished in any reasonable amount of time. The paper issued by the group states that a classical supercomputer would require 600 million years of computation to generate the number of samples their quantum computer, named Jiuzhang, generates in just 20 seconds.

The Chinese team claims that their quantum computer is 10 billion times faster than that of Google which was released in 2019 (described later in this article). Assuming the claim. made by the team in their paper hold up, this supercomputer, Jiuzhang, will be the second quantum computer to achieve quantum supremacy anywhere in the world, after Google.

In this article, you'll find the most asked questions surrounding the Jiuzhang supercomputer and Quantum Supremacy, as well as what this means for the future of computing.

What is Quantum Supremacy and Boston Sampling?

Quantum supremacy is the ability to harness quantum technology to achieve computational power that can't be achieved by a conventional computer. In quantum computing, quantum supremacy, also known as quantum advantage is essentially the ability to demonstrate that a programmable quantum device can solve a problem substantially faster than a classical computer could solve in any feasible amount of time.

Conventional computers struggle to calculate problems that involve the complex quantum properties of photons, whereas quantum computers are based on quantum mechanics and aim to bring innovative changes to the development of materials and drugs, assessment of financial risks, and artificial intelligence using big data. There were historically were regarded as a "dream technology" due to the difficulty of development, but the Juizhang is now suspected to be the second quantum computer to achieve the advantage. The team who spearheaded the Juizhang quantum computer used the new type of quantum computing called "boson sampling' which is capable of calculations that no classical computer could accomplish in any reasonable amount of time.

Boson sampling relies on the quantum property of photons (particles of light) that are displayed when they travel through a beam splitter, the boson sampling device has a network of beam splitters that converts one set of photons arriving at a number of parallel input ports into a second set leaving through a number of parallel outputs, the task of which is to work out the probability that a certain input configuration will lead to a certain output.

Essentially, the beam splitter divides a single beam of light into two beams split in different directions, when two identical photons hit the beam splitter at the exact same time, they don’t split from one another but stick together and travel in the same direction. Whereas if you shoot numerous photons through a sequence of beam splitters repeatedly, patterns emerge in the paths of the photons that are extraordinarily difficult to simulate or predict with classical computers. Finding possible sets of photon paths in this set-up is called boson sampling.

What Makes "Juizhang" Ground-Breaking?

The associate professor at the University of Tokyo, Shuntaro Takeda stated that "The Chinese technology will undoubtedly contribute to the development of optical quantum computing". According to one of the professors in charge of the experiment, the Chinese computer contrasts with that of Google, which relies on ultra-cold superconducting chips, by utilizing the manipulation of particles of light, which was regarded as a 'breakthrough experiment' by a german expert in quantum optics, Christine Silberhorn. In contrast to Google computer, Juizhang uses photons traveling through circuits that combine 300 beam splitters, 75 mirrors, and various other materials, and because it doesn't require deep refrigeration and vacuum vessel equipment, it is much easier to use than that of Google.

The success of the experiment is measured by the number of photons detected. Jiuzhang, which itself is an optical circuit, detected a maximum of 76 photons in one test with an average of 43 across several tests. In quantum computing, a perfect boson sampler would have a fidelity of 1 over many trials, meaning that it completely matches up with theoretical predictions, where Jiuzhang had a fidelity of 0.99. Researchers that took part in the study calculated that simulating boson sampling with such a high fidelity on a classical computer would be impossible, further claiming that the Japanese Fugaku supercomputer, the current world’s most powerful classical computer, would take 600 million years to accomplish what Jiuzhang has the ability to do in just 200 seconds. Further, the fastest Chinese supercomputer, TaihuLight, would have taken 2.5 billion years to arrive at the same result. These results suggest that this quantum computer can do GBS 100 trillion times faster than a classical supercomputer.

While this doesn't confirm that China has a fully practical quantum computer, the device is specialized and mostly useful as a tool for doing GBS, but it is definitely a major milestone on the way to a practical quantum computer.

What Progress Was Made Before This year?

Huge progress has been made in the 21st century towards quantum supremacy, Google initially bought its first supercomputer in 20--, later in 2017 announcing their initiative to demonstrate quantum supremacy before the end of 2017, in 2018 the company even partnered with NASA to “analyze results from quantum circuits run on Google quantum processors, and... provide comparisons with classical simulation to both support Google invalidating its hardware and establish a baseline for quantum supremacy.” Late in October 2019, Google confirmed speculations made in the Financial Times report that"Google claims to have reached quantum supremacy with an array of 54 qubits out of which 53 were functional, which were used to perform a series of operations in 200 seconds that would take a supercomputer about 10,000 years to complete". IBM also became publically involved in the progress towards Quantum supremacy by demonstrating the simulation of 56 qubits on a classical supercomputer which increased computational power that was needed to make further progress. As the owner of the most powerful supercomputer at the time, IBM refuted Google's 2019 achievements by suggesting their claims were excessive and that the operations made by the computer could just take 2.5 days for a supercomputer rather than 10,000 years.

What Does This Mean for Computing?

The associate professor at the University of Tokyo, Shuntaro Takeda says that while Google's quantum computer is "overwhelmingly superior" to China's at present in terms of practicality because the Chinese computer is aimed specifically at achieving quantum supremacy and is not considered applicable to other calculations. Despite there being no current practical use of the Chinese technology, China is making huge progress in quantum computing technology, the country has made the development of quantum computers a key project, with plans to set up facilities in Anhui Province at a cost close to almost $10 billion, which will continue to accelerate development.

Further, the U.S. government have plans in place to invest $1.3 billion over five years from 2019 to develop quantum computing technologies, where competition between the U.S. and China is expected to further intensify in the field of quantum computing which will promote huge technological advancements overall.

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