**Quantum Entanglement and Atom-Photon Interactions**

Quantum entanglement was first recognized by Schrödinger and Einstein as one of the most fundamental features of quantum physics. At POSTECH, we do research on how to experimentally generate, manipulate, and detect various entangled states of photons.

For example, we are searching for methods to effectively generate high-flux entangled photon states using spontaneous parametric down-conversion as well as other non-linear optical processes.

We are also interested in quantum optical interference due to coherent atom-photon interaction. An example of such quantum interference is electromagnetically induced transparency (EIT). Such coherent atom-photon interaction may one day be used for storage devices for photons.

**Photonic Quantum Information**

By utilizing the most fundamental principles of quantum physics, superposition and entanglement, it is possible to build an information processing device which functions inherently differently from its classical counterpart. Such a machine would use the “quantum bit” (qubit) instead of the “bit” as the basic information unit.

We are doing basic research on photonic quantum information where the photon is the carrier of the quantum information. Our research include multi-photon entanglement generation and detection, quantum state tomography, development of single-photon and multi-photon quantum gates, quantum cryptography, and quantum teleportation.

**Quantum-Enhanced Imaging and Metrology**

Every quantum mechanical particle (e.g., electron, photon, …) has the de Broglie wavelength associated with it. Interferometry using such particles has the resolution limit called the Rayleigh limit which is determined by the de Broglie wavelength of the individual particles. For N entangled particles, however, the de Broglie wavelength is reduced by a factor of N. Therefore, quantum interferometry and imaging system which utilize entangled photons can be made have the resolution limits that surpass the classical Rayleigh limit.

We are doing research on entangled photon interferometry and imaging methods as well as multi-photon detection schemes for next generation high-resolution metrology, imaging, and quantum lithography.