Introduction
Recent advances in quantum physics have moved esoteric concepts from the realm of abstract mathematics into observable phenomena. Quantum distance — formally called the quantum metric tensor — quantifies the similarity between two quantum states; a value of one indicates identical states and zero means they are entirely differentprnewswire.com. Although theorised decades ago, direct measurement in solids remained elusive because the subtle geometric properties of electronic wave‑functions are difficult to proberdworldonline.com. In August 2025, a team led by Keun Su Kim (Yonsei University) and Bohm‑Jung Yang (Seoul National University) achieved the first direct measurement of this distance in black phosphorus using angle‑resolved photoemission spectroscopy (ARPES)prnewswire.com. Their breakthrough not only validates theoretical predictions but opens a path toward integrating quantum metrics into materials engineering, quantum computing and industrial metrology.
Implications of quantum distance measurement
Quantum geometry and condensed‑matter phenomena
The quantum metric tensor measures how rapidly an electron wave‑function changes with momentum. It appears in many condensed‑matter phenomena and can be regarded as a geometrical counterpart to the more familiar Berry curvature. The tensor influences quantum fluctuations, orbital magnetism, localisation, superfluidity and quantum phase transitionsrdworldonline.com. Theoretical studies suggest that large quantum metric contributions can enhance the transition temperatures of flat‑band superconductorsrdworldonline.com and play a role in fractionalised quantum Hall statesarxiv.org. In quantum information theory, it is equivalent to the quantum Fisher information and thus provides a measure of entanglementrdworldonline.com. Accurate knowledge of this “distance” therefore informs the design of fault‑tolerant quantum computers, since error‑correction schemes depend on the geometry of the computational Hilbert spacerdworldonline.com.
Practical measurement and its ripple effects
The Yonsei/SNU team demonstrated that it is possible to reconstruct the quantum metric tensor of electrons in a crystalline solid by analysing the pseudospin textures extracted from polarisation‑dependent ARPES measurementsprnewswire.com. They used black phosphorus because its simple layered structure simplifies interpretationprnewswire.com. By shining polarised synchrotron radiation on the material and tracking the resulting photoelectrons, the researchers reconstructed momentum‑resolved pseudospin textures and hence the full quantum metric tensorrdworldonline.com. The measured values agreed with theoretical predictions, turning a theoretical parameter into an observable quantity.
Professor Kim noted that understanding quantum distances is as critical for error‑free quantum technologies as accurate length measurements are for architectural safetyprnewswire.com. This measurement establishes a benchmark for evaluating the performance of candidate quantum materials and informs efforts to build fault‑tolerant quantum computers, high‑temperature superconductors, and secure quantum communication channelsprnewswire.com. As quantum devices leave the laboratory, precise geometric characterisation will become essential for quality control and certification.
Black phosphorus: a versatile platform for quantum technology
Electronic and optical properties
Black phosphorus (BP) is the most stable allotrope of phosphorus. Its layered crystal structure yields high carrier mobility (∼1,000 cm²/V·s along one axis) and anisotropic in‑plane propertiesrdworldonline.com. The band gap of few‑layer BP is strongly layer‑dependent, varying from ~0.3 eV in bulk to around 2 eV in monolayer form; this tunability, combined with a direct band gap, makes BP attractive for optoelectronic devicesfrontiersin.org. Because BP surfaces lack dangling bonds, they integrate well with silicon substrates, enabling on‑chip two‑dimensional optical modulatorsfrontiersin.org.
Photonics and sensing applications
BP’s ability to emit and detect mid‑infrared light has sparked interest in night‑vision, spectroscopy and gas‑sensing devices. Researchers at Lawrence Berkeley National Laboratory showed that ultrathin BP layers can emit light efficiently in the 2.3–5.5 μm range and that this emission is robust even when the surface is oxidisednewscenter.lbl.gov. The low surface recombination velocity means that thin BP sheets maintain brightness despite imperfectionsnewscenter.lbl.gov. This makes BP an excellent candidate for mid‑IR LEDs and photodetectorsnewscenter.lbl.gov.
BP quantum dots (BPQDs) offer additional versatility. Researchers have prepared BPQDs with average diameters ~2 nm and fabricated Ormosil gel composites that exhibit nonlinear optical modulation in the ultraviolet regionfrontiersin.org. BPQDs’ tunable band gaps and strong edge states allow them to act as saturable absorbers, photodetectors, and biomedical imaging agentsfrontiersin.org. The combination of high mobility, tunable optics and integration capability positions BP as a platform for quantum photonics, sensing, and van der Waals quantum wells.
Quantum metric measurement using BP
The Yonsei/SNU experiment used BP as the testbed for measuring quantum distance. Its simple valence band structure enabled the reconstruction of pseudospin textures without excessive band mixingrdworldonline.com. The success of this measurement suggests that BP could serve not only as a device material but also as a metrological standard for calibrating quantum measurements in solids. Understanding the geometric properties of BP’s electronic states will aid in engineering devices that exploit quantum geometric phases and topological responses.
Future directions in quantum metric tensor research
The quantum geometry of solids remains a relatively unexplored landscape. The 2025 review by Verma, Moll and co‑authors outlines several key research directions. They argue that quantum geometry introduces new length and time scales through orbital mixing and dipole fluctuations; these scales can fundamentally alter materials’ responsesarxiv.org. Future research should focus on:
- Better models: Developing effective theories that incorporate quantum geometric corrections to capture orbital mixing without relying on full multi‑orbital modelsarxiv.org.
- Materials discovery: Using quantum geometry as a guide to identify materials with large geometric contributions that may exhibit exotic phases, such as flat‑band superconductivity or fractionalised topological ordersarxiv.org.
- Low‑temperature phenomena: Understanding how interactions and dipole fluctuations near the Fermi surface affect transport and superconductivityarxiv.org.
- Interpretation of experiments: Employing quantum geometry to reconcile discrepancies between different experimental probes and to explain non‑semiclassical responsesarxiv.org.
- Unifying Landau‑level and band physics: Exploring how geometric frequencies and lengths in moiré heterostructures mimic magnetic fields, potentially enabling quantum Hall effects without external fieldsarxiv.org.
As quantum metric measurements become routine, these directions will help integrate geometric effects into mainstream condensed‑matter theory, computational materials science, and device engineering.
Korean advancements in quantum computing
Government strategy and funding
South Korea has transitioned from modest quantum research programs to a comprehensive national strategy. The National Strategic Plan for Quantum Science and Technology (April 2021) and the subsequent Quantum Technology Promotion Act (May 2023) elevated quantum technologies to essential strategic statuspostquantum.com. At the first meeting of the Quantum Strategy Committee in March 2025, the government launched a ₩1 trillion Science and Technology Innovation Fund with ₩20 billion per year earmarked for quantum start‑upspostquantum.com. Ambitious technical goals include developing 1,000‑qubit quantum computers, building quantum repeaters for long‑distance communication, and creating GPS‑free quantum navigation sensorspostquantum.com. The strategy also plans to train 2,500 new quantum researchers by 2035postquantum.com.
In June 2025, the Quantum Korea 2025 conference showcased the country’s growing ecosystem. The event brought together 57 companies and organisations from eight countries and over 5,500 attendeeskoreaherald.com. Oskar Painter of Amazon Web Services noted that the coming five years would be decisive for quantum error correction and performance improvementskoreaherald.com. Roundtables with delegates from the European Union, the US Quantum Economic Development Consortium and Finland highlighted Korea’s drive for international collaborationkoreaherald.com. The government organised conferences covering quantum computing, communications, sensing and sciencekoreaherald.com and emphasised the need to build global quantum clusterskoreaherald.com.
Private and academic progress
South Korea invests heavily in quantum hardware and infrastructure. IQM, a Finnish‑German company, installed its first Asia‑Pacific quantum computer (a 5‑qubit superconducting “IQM Spark” system) at Chungbuk National University in early 2025 and plans to open a Seoul officemeetiqm.com. This installation provides researchers with on‑premises access to quantum hardware and positions South Korea as a regional hubmeetiqm.com.
Korean universities have created dedicated quantum graduate schools and research centers. POSTECH’s quantum graduate school aims to train 180 experts over nine yearspostquantum.com, while Yonsei University operates an Institute for Quantum Information Technology and partners with IBM to access a 127‑qubit processorpostquantum.com. Government‑funded institutes such as the Korea Institute of Science and Technology (KIST) and the Electronics and Telecommunications Research Institute (ETRI) have advanced photonic quantum computing; ETRI demonstrated entanglement of 6 qubits on an 8‑photon silicon photonic chip in 2024postquantum.com. These programmes, combined with corporate investment from Samsung, SK Telecom and LG Electronics, create a vibrant quantum ecosystem.
Investment commitments
Beyond the national strategy, the Ministry of Science and ICT approved a ₩645.4 billion (≈£370 million) investment over eight years to develop a 1,000‑qubit quantum computer and a 100 km quantum internetquantumzeitgeist.com. The funding focuses on building superconducting quantum chips with error‑correction and includes research on quantum algorithms and applicationsquantumzeitgeist.com. The initiative also supports green technologies such as hydrogen‑reduction steelmaking, demonstrating the government’s holistic approach to high‑tech industriesquantumzeitgeist.com.
Integrating quantum measurements into industry
Quantum metrology and sensing
Quantum measurements leverage properties such as entanglement and superposition to achieve sensitivities unattainable with classical sensors. McKinsey identifies quantum sensing as the most mature quantum technology, projecting a market between US$0.7 billion and US$1 billion by 2030 and US$1–6 billion by 2040mckinsey.com. Quantum sensors can measure magnetic and electric fields, rotation, acceleration, temperature, gravity, time and pressuremckinsey.com. Use cases include:
- Imaging and diagnostics: Arrays of neutral‑atom or diamond NV centres could pinpoint magnetic signals in the human body within millimetres, enabling wearable magnetoencephalography devicesmckinsey.com.
- Navigation: Quantum inertial sensors may allow vehicles to navigate without GPS and with greater accuracy in cluttered or shielded environmentsmckinsey.com.
- Microelectronics: NV‑diamond sensors can detect flaws in integrated circuits during fabrication, improving quality control and reducing defectsmckinsey.com.
- Underground measurement: Quantum gravimeters and magnetometers can map mineral deposits and underground structures, aiding mining and environmental monitoringmckinsey.com.
The U.S. Government Accountability Office notes that quantum sensors are already used in atomic clocks and MRI machines and that further breakthroughs could revolutionise navigation, resource exploration and healthcaregao.gov. However, challenges remain: translating prototypes into commercial devices requires coordination between academia and industry, training an interdisciplinary workforce and ensuring the supply of specialised components such as high‑quality diamondsgao.gov.
Precision measurement research
Fundamental research continues to refine quantum measurements. An international team including scientists from Jena developed a measurement method that uses entangled photons to reduce noise, reaching the physical limits of measurement precisionuni-jena.de. Their method, tested on the Fraunhofer QSystemOne quantum computer, could improve interferometry for semiconductor manufacturing, radio‑frequency technology (6G), and biological microscopyuni-jena.de. The research illustrates how quantum computers can serve both as platforms for computation and as precision measurement toolsuni-jena.de. These advances will be crucial for industries such as lithography, metrology and telecommunications, where nanometre‑scale precision is essential.
Conclusion
The direct measurement of quantum distance in black phosphorus marks a milestone in quantum science. By converting an abstract geometric concept into a measurable quantity, the Yonsei/SNU team has provided a powerful tool for characterising quantum materials and designing more robust quantum devices. Black phosphorus emerges from this narrative not only as a convenient testbed for quantum geometry but also as a versatile platform for optoelectronics, sensing and van der Waals quantum wells.
South Korea’s comprehensive strategy — encompassing ambitious R&D targets, significant funding, academic programmes and industry partnerships — positions the country as a major player in the global quantum race. Its investment in a 1,000‑qubit quantum computer, quantum internet and advanced sensing technologies underscores the recognition that quantum geometry and precision measurement will underpin next‑generation technologies. At the same time, progress in quantum metrology and sensing demonstrates how industrial applications — from chip fabrication to medical diagnostics and navigation — are ready to benefit from quantum mechanics’ unique properties.
Together, these developments illustrate how quantum distance measurement, black phosphorus and quantum metrology converge to shape a future where precise control of quantum states drives innovation across disciplines.
