Quantum computing operates using quantum bits (qubits) that exploit uniquely quantum phenomena such as superposition and entanglement to solve problems that are challenging for classical computers. One-way quantum computer, also known as measurement-based quantum computing (MBQC) performs complex algorithms by making a sequence of measurements on a highly entangled state called a cluster state. Large cluster states can be realized by fusing smaller cluster states, which can be done using linear optics with photonic qubits. Our lab focuses on generating multi-qubit cluster states using photonic qubits generated via spontaneous parametric down conversion (SPDC). We are also working toward demonstrating complex quantum algorithms and quantum simulations based on large cluster states and feedforward measurements. 

Stationary light pulse (SLP) represents a striking manifestation of coherent light-matter interaction, where a light pulse is effectively brought to a standstill within an atomic medium. This phenomenon arises through the interplay of counter-propagating control fields in systems exhibiting electromagnetically induced transparency (EIT). At POSTECH, we explore experimental techniques to generate and control SLP using cold atomic ensembles and tailored laser fields. Our research aims to implement stationary pulse as a platform for quantum memory, nonlinear optics at the single-photon level, and quantum information processing. Ultimately, SLP offers a promising route toward controlled light-matter quantum interfaces.  

Quantum cryptography utilizes the fundamental principles of quantum mechanics to achieve secure communication. At POSTECH, we conduct research on developing and implementing entanglement-based quantum communication, where security is guaranteed by the nonlocal correlations of entangled photon pairs. We explore efficient methods for generating and distributing entangled photons using spontaneous parametric down-conversion. In particular, we investigate hyperentanglement, where multiple degrees of freedom, such as polarization and time-bin, are entangled simultaneously, to enhance the performance and scalability of quantum communication systems. Such multi-dimensional entanglement offers advantages in noise resilience and information capacity, paving the way for the next generation of quantum communication networks.

Quantum metrology and sensing can achieve high sensitivity and resolution beyond the standard quantum limit. While entangled states of N photons are traditionally associated with reaching the so-called Heisenberg limit—where measurement uncertainty scales as 1/N—this is not the only pathway to such precision. Our lab has demonstrated Heisenberg-limited scaling using iterative interactions, a practical approach that enhances measurement sensitivity without requiring entanglement. Another central concept in quantum metrology is the Quantum Cramér-Rao Bound (QCRB), which is the theoretical lower bound on estimation uncertainty for a given quantum state and measurement scheme. We have developed and experimentally implemented adaptive estimation techniques that saturate the QCRB, thereby achieving optimal precision.
 Our work spans both theoretical and experimental aspects of high-precision parameter estimation using quantum resources and techniques, including weak value amplification, iterative measurement strategies, and other advanced quantum measurement protocols.