[Reading Science] The Core of Quantum Computers: 'Qubit'

Competition to Develop Qubits for Quantum Computers
Google and IBM Lead in Superconducting Approach
Ion Trap, Neutral Atom, and Other Methods Also Compete
The Winner Remains Uncertain,
But a Game Changer That Will Transform Human Life Is Expected

Google researchers are examining cooling equipment for superconducting quantum computers. Photo by Reuters and Yonhap News.

At the end of 2024, Google's unveiled 'Willow' chip was enough to raise expectations that the world of Quantum is about to open. The announcement that a problem taking 10 trillion years with the best existing supercomputer could be solved in just 5 minutes heated up not only the global science and technology sectors but also the stock market. Stocks of companies related to quantum surged more than tenfold, increasing public interest. Many people were enthusiastic about the word 'quantum.' Although 'quantum' remains unfamiliar and an unfinished technology to those not versed in physics, the anticipation for the changes quantum will bring is already a reality.

The reason quantum computers are special is that the way they process information is completely different. While the general computers we use express only 0 or 1 in units called 'bits,' quantum computers create a state called 'qubits' that can be 0 and 1 simultaneously. This is similar to a coin showing both heads and tails at the same time when flipped. Thanks to this characteristic, quantum computers can process numerous calculations simultaneously.

The core factor determining the performance of quantum computers lies in how well these qubits can be created. While error correction technology, which addresses errors increasing with repeated quantum computations, is important, research teams worldwide are currently engrossed in competing to produce qubits using different methods.

Quantum Computer Chip 'Willow' Released by Google Shocks the World Reuters Yonhap News

There are mainly seven dominant methods for qubits. Among them, the most notable method currently is the 'superconducting qubit' led by Google and IBM. It utilizes the phenomenon where electricity flows without resistance at ultra-low temperatures close to minus 273 degrees Celsius. Like sliding frictionlessly on an ice rink, this state allows quantum information to be maintained longer. IBM's quantum computer installed at Yonsei University operates using this technology. Google succeeded in creating the 'Sycamore' chip with this technology, solving a calculation that would take 10,000 years on a conventional computer in just 200 seconds, and continued research and achievements with the Willow chip.

Following superconductors, the most active research field is the 'ion trap' method. This technology controls electrically charged atoms suspended in the air with lasers, akin to delicately handling beads floating in the air. Professor Jeongsang Kim of Duke University, who founded IonQ, and researchers at Oxford University in the UK lead this field. It boasts very high accuracy but faces the challenge of handling many ions simultaneously.

There is also the 'photonic qubit' method using light. This approach processes information with photons, the particles of light, and operates at room temperature, transmitting information as fast as light. PsiQuantum and Xanadu in the United States are researching to commercialize this technology. However, entangling photons with each other is not easy, and efforts to solve this continue.

The 'spin qubit' method, which utilizes the spin behavior of electrons or atomic nuclei, is also gaining attention. It uses the state of particles spinning like the Earth’s rotation for information storage. Researchers at the University of New South Wales (UNSW) in Australia have already succeeded in linking two qubits using this method. It operates relatively long even at normal temperatures, but precisely controlling individual spins remains challenging.

Microsoft's research on 'topological qubits' is considered the most challenging method. Like there are multiple ways to untie a knot, this aims to create qubits resistant to errors by utilizing the topological properties of materials. Although still at the laboratory stage, success could lead to the most stable quantum computers.

Semiconductor company Intel is focusing on developing 'silicon-based qubits' that can utilize existing semiconductor processes. This is considered most advantageous for mass production as it can leverage current computer chip manufacturing facilities.

The 'neutral atom qubit' method, which controls neutral atoms with lasers, is also gaining attention. This technology precisely arranges and controls individual atoms using laser optical tweezers and has the advantage of stably handling hundreds of qubits. Research is actively underway mainly at Harvard University and MIT, with QuEra Computing leading commercialization efforts.

Korea has also entered this competition. The Electronics and Telecommunications Research Institute (ETRI) focuses on photonic qubits, and the Korea Research Institute of Standards and Science (KRISS) centers on superconducting methods, with various research institutions collaborating to study diverse qubit technologies. Although there is still a gap compared to the world’s top level, the government has expressed its determination to narrow this gap through full support, including pushing for exemption from preliminary feasibility studies on quantum technology, which it has designated as one of the three major game-changing technologies.

Several hurdles remain before quantum computers can be practically used. Maintaining quantum states for a long time, reducing computational errors, and increasing the number of qubits are major challenges. However, recent research achievements over the past one to two years show hopeful signs that these obstacles are being overcome one by one.

What will be possible once this technology is perfected? The time required for new drug development could be shortened from years to weeks. More powerful encryption systems will be created, and climate change predictions will become more accurate. The learning speed of artificial intelligence could increase hundreds of times.

Qubits hold infinite possibilities between 0 and 1. Although most are still laboratory-level prototypes, and countless researchers worldwide continue their efforts, it is impossible to say when quantum computers will enter our daily lives. It is also unknown who will be the winner in the already started qubit war.

Han Sangwook, president of the Korean Quantum Information Society, said, "It is still unknown which qubit will be the ultimate winner. Currently, ultra-low temperature qubits seem dominant, but ion traps have shown excellent error performance, and neutral atoms have also achieved good results. Earlier this year, potential was seen even in photonic qubits. These technologies are developing through healthy competition, but it is still difficult to say that a qubit capable of changing the world has emerged. Of course, when a winner emerges, it will undoubtedly be a game changer that can transform human life." He explained that regardless of who the winner is, the benefits will belong to all humanity.