Over the last several decades quantum optical memory has been intensively studied to overcome limited retrieval efficiency and ultrashort storage time in a three-level optical system. Although alkali atoms have a long spin coherence time, the atom diffusion deteriorates its applications for quantum memories. On the contrary, solids normally have a short spin coherence time due to spin inhomogeneity, so that photon (Raman) echoes have been adapted to overcome the spin dephasing. Here, I report optical phase conjugation can be used for a near perfect retrieval efficiency in addition to the ultralong photon storage. Photon echoes combined with phase conjugation in a solid paves a road to scalability of qubits for quantum computing and entanglement swapping for long-distance quantum communications.

Prof. Ham’s research specialty is in quantum nonlinear optics of light matter interactions for the quantum coherence control of an ensemble. A typical example of the quantum coherence control is the ultraslow light and EIT, where he experimentally demonstrated both in solids for the first time. Over the last decade he has adapted quantum coherence control to photon echoes for ultralong quantum memory to make a breakthrough in quantum information processing. His recent interest is in quantum machine learning, quantum repeaters, and Optical DRAM via associative optical memories. With his research contribution, he won the award of “This month scientist” from the Korean government in 2010. He also won “The best Scholar Award” from the Optical Society of Korea in 2013. For academic activities, he organized several international conferences such as “Quantum Optics Workshop (2003, 2007, 2008, and 2013), SPIE Photonics Asia (Nonlinear quantum optics; 2014, 2016, 2018), and PIERS (quantum optics; 2014, 2017). Prof. Ham is now serving as a topical editor of Applied Optics (OSA) in addition to the advisory editorial board member of Optics Communications (Elsevier).