Hoonsoo Kang

The Fock state is widely regarded as the most nonclassical quantum state of light and has great potential in the areas of quantum computation and quantum sensing. Numerous methods have been proposed to generate Fock states and extremely number-squeezed states, or quasi-Fock states. In order to utilize natural light for quantum technologies, it is necessary to develop methods for transforming classical light into quasi-Fock states. Thus, we demonstrated that through the collective interaction of light and atoms in the Tavis-Cummings model, we can amplify classical light, such as thermal states and coherent states, into quasi-Fock states. To analyze this process, we introduce theoretical tools for studying number state-multi-atom interactions and provide a comprehensive analysis of Tavis-Cummings dynamics, rather than relying on extensions of the Jaynes-Cummings model. Our results reveal that the emergence of nearly sinusoidal emission-absorption oscillations, periodic oscillation of photon number variance, and intrinisic nonlinear effects collectively establilshes the necessary condition for deterministic conversion of classical light into quasi-Fock states.

Continuous tuning of terahertz waves was demonstrated with seamless change in grating period in a periodically poled stoichiometric lithium tantalite (SLT) crystal. The periodically poled fan-out structure allows wide tunability such as 610 GHz with the bandwidth as narrow as 17 GHz at a carrier frequency of 1.00 THz. Temperature-dependent measurements show a gradual intensity increase of the THz pulses as the temperature decreases. Furthermore, absorption and refractive index of SLT in the THz range were estimated and compared with those of LiNbO3 (LN). The absorption coefficient of the LT crystal at ordinary wave was almost half of that in the LN crystal. SLT could be one of the powerful crystals for high-power THz generation with large optical aperture because of the fewer defects inside the crystal.

We report a new simple method for the signal enhancement of laser-induced breakdown spectroscopy using a pulsed buffer gas jet. The signal is enhanced up to more than 10 fold by using argon gas jets, which are injected through a pulsed nozzle onto the sample area to be analyzed. By synchronizing the buffer gas pulse with the laser pulse and optimizing the spatial arrangements between the gas jet and the sample surface, we have successfully exploited the useful properties of the buffer gas in open atmosphere. The signal-enhancement mechanism in our buffer gas jet has been discussed. Also, applications to various samples (metal, glass, and paper) have been demonstrated.

We present an evaluation of the frequency shifts in an optically pumped caesium-beam frequency standard caused by the neighbouring transitions. We analyse the shifts caused by the Rabi and Ramsey pulling effects and find a well-known result for the Rabi pulling but a new result for the Ramsey pulling. The revised Ramsey shift is found to be proportional to not the imaginary but the real part of the ground-state atomic coherence. The value of the Ramsey shift is proportional to the first power of the Rabi frequency defined by a small orthogonal component of the microwave field and the inverse value of the Zeeman splitting. We compare the shifts caused by the neighbouring transitions and show that the relative contributions of the Rabi and Ramsey pulling effects crucially depend on the quality of optical pumping. We estimate that the Rabi shift for the KRISS-1 caesium-beam frequency standard is at a relative level of 10⁻¹⁴ while the Ramsey shift is at a relative level of 10⁻¹².