Korean scientists have succeeded in accurately measuring the 'quantum distance' of particles that are one-millionth the thickness of a human hair. This is the world's first development of core technology that can implement quantum computers or quantum sensors.
Professor Kim Geun-soo of Yonsei University and Professor Yang Beom-jeong of Seoul National University announced on the 6th that their joint research team has developed a method for measuring quantum distance that quantifies the distances in the microscopic world, which are smaller than atoms. The research results were published in the international journal Science on the same day.
Quantum distance quantitatively represents the quantum mechanical similarity between particles in the microscopic world. The microscopic world refers to a realm as small as atoms, one-millionth the thickness of a human hair. The principle that explains particle motion in the microscopic world is quantum mechanics.
In the microscopic world, the distance between particles is determined by how similar the two particles are. When both particles are in the same quantum state, the minimum value is '0', and the maximum value, when they are completely different, is '1'. This quantum distance is regarded as essential information for evaluating the accuracy of operations and tracking state changes in the fields of quantum computers and quantum sensors.
Until now, there has been no precedent for successfully measuring quantum distance accurately. The only instance was when Professor Yang Beom-jeong, along with researchers from the Massachusetts Institute of Technology (MIT), measured the quantum distance as an approximation. Professor Kim Geun-soo took on the challenge of measuring the quantum distance of electrons in solids together with Professor Yang.
The research team focused on black phosphorus, a material with a simple composition and structure. It is a substance made by applying high temperature and pressure to phosphorus to create a single layer, characterized by an atomic-level thinness and excellent electrical properties, making it suitable for use in semiconductor devices.
Professor Yang Beom-jeong discovered that the quantum distance of electrons is determined by the phase difference between the electrons due to the simple composition and symmetrical structure of black phosphorus. The phase difference refers to the spatial interval between the maxima of two waves with the same wavelength. Professor Kim Geun-soo successfully measured the phase difference of electrons in black phosphorus using advanced measuring equipment such as synchrotron radiation accelerators.
Accurately measuring quantum distance means that the precision of various applied technologies utilizing quantum mechanics can be improved. To construct buildings safely and stably, it is essential to first establish measurements and then accurately measure distances accordingly. Similarly, to advance quantum technology, it is necessary to accurately measure the states of particles in the microscopic world. Professors Kim and Yang have achieved this for the first time in the world.
Quantum technology refers to technologies based on the principles of quantum mechanics, such as quantum computers, quantum communication, and quantum sensors. When quantum computers are realized, they can solve problems that would take supercomputers 10,000 years to compute in an instant. Quantum encrypted communication can achieve information transmission that is impossible to hack, while quantum sensors can detect subtle signals that classical mechanical sensors cannot measure.
Professors Kim Geun-soo and Yang Beom-jeong stated, "Just as accurate distance measurement is essential for safely constructing buildings, precise quantum distance measurement is also crucial for developing quantum technology that operates accurately without errors," adding, "This research achievement can serve as a fundamental tool for various quantum technologies such as quantum computers and quantum sensors."
References
Science (2025), DOI : http://doi.org/10.1126/science.ado6049
Nature Physics (2025), DOI : https://doi.org/10.1038/s41567-024-02678-8