"Schroedinger-ui Goyangi" Did Not Die Even When Slightly Opened

Domestic Research Team First Confirms Safety of Quantum Superposition and Measurement Principles
Solving Quantum Physics Challenge, Paving the Way for Practical Quantum Information Communication Technology

[Asia Economy Reporter Kim Bong-su] A domestic research team has demonstrated the fundamental principle that quantum information communication technologies such as quantum computers and quantum cryptography can be used practically and securely. This is regarded as a resolution to a long-standing problem in quantum physics.

The Korea Institute of Science and Technology (KIST) announced on the 7th that a research team led by Drs. Hong Seong-jin, Lim Hyang-taek, and Lee Seung-woo from the Quantum Information Research Group has, for the first time, derived and verified a perfect information preservation relation in quantum measurement. This perfectly proves that quantum technology is fundamentally secure even in the domain of weak measurement.

Quantum physics is based on principles such as quantum superposition and quantum entanglement. Quantum, the smallest unit of physical systems like electrons or ions, simultaneously exhibits wave and particle characteristics, and its state changes with each measurement or observation?this is the principle of quantum superposition. Quantum entanglement refers to the property where two 'entangled' quantum particles maintain a correlated relationship even when separated by large distances.

‘Schr?dinger’s cat’ is a thought experiment devised to explain the core properties of quantum physics: ‘quantum superposition’ and ‘quantum measurement.’ In this experiment, the cat inside the box can exist in a state of being both alive and dead simultaneously (quantum superposition), and the act of opening the box (measurement) determines the cat’s life or death. These quantum superposition and quantum measurement properties form the foundation of quantum physics and guarantee the security of technologies such as quantum computing and quantum cryptographic communication.

From an information perspective, interpreting the ‘Schr?dinger’s cat’ experiment means that to obtain information about the cat’s life or death, we open the box (quantum measurement), and this act changes the cat’s state from being simultaneously alive and dead (quantum superposition) to one definite state. In other words, the moment we obtain the information ‘the cat is dead,’ the cat is dead, and when we obtain ‘the cat is alive,’ the cat is alive. Due to the irreversibility of quantum measurement, the cat’s life or death cannot be reversed.

However, what happens if the measurement is not complete? For example, if the box is only slightly opened to see the cat’s tail? In quantum mechanics, this is called a ‘weak measurement.’ In such cases, we cannot obtain complete information about the cat’s life or death, and there is a possibility to reverse the cat’s fate through a ‘reversal’ of the measurement. Therefore, elucidating the ‘quantum information preservation relation’ that considers information gain, state change, and the probability of reversal has been a challenging problem in quantum physics and an important task to ensure the security of quantum technologies.

The research team theoretically derived an information preservation relation that extends the previously known relation between ‘information gain’ and ‘state change’ to also include the probability of ‘reversal.’ Using linear optical devices such as polarizers and polarization plates, they implemented ‘weak measurement’ and ‘reversal operations’ and applied them to three-dimensional quantum states realized with single photons. They experimentally verified the information preservation relation among ‘information gain,’ ‘state change,’ and ‘reversal.’ In other words, they proved for the first time a new information preservation relation showing that increasing measurement strength to gain more information about the quantum state causes greater disturbance to the quantum state, thereby lowering the probability of reversing to the initial quantum state before the weak measurement. If the probability of reversal to the initial quantum state exists, the security of quantum cryptographic communication cannot be guaranteed.

Dr. Lee Seung-woo stated, “By proving that the total amount of information in a quantum state cannot increase through measurement, we have perfectly clarified that quantum technology is fundamentally secure. We expect this to be applied as an optimization technology for quantum computing, quantum cryptographic communication, and quantum transmission.”

This research result was published as the cover paper in the latest issue of the international academic journal 'Physical Review Letters.'

This content was produced with the assistance of AI translation services.