[Jan.16] Physics Special Seminar - Dr. Wonjin Jang (École Polytechniqu…

물리학과에서는 특별세미나를 아래와 같이 개최하오니 관심있는 분들의 많은 참석을 바랍니다.

1. 연사: 장원진 박사 (École Polytechnique Fédérale de Lausanne (EPFL), Switzerland)

2. 일시: 2025. 1. 16(목), 오후 4시
3. 장소: 공학3동 302호 (세미나실)

4. 제목: Coherent control of quantum states in semiconductor quantum dot systems

Gate-defined semiconductor quantum dots (QDs) offer intriguing avenues for exploring various spin and charge degrees of freedom of electrons (or holes) confined in the QDs, which can be harnessed for quantum computations and simulations. This talk aims to present the control and engineering of the quantum states in 1) semiconductor QDs, and 2) semiconductor QD-superconducting cavity hybrid architectures.

The first part of the talk will focus on spin state manipulation in semiconductor QDs. Starting with a brief introduction to single-electron spin qubits in QDs, coherent control of the spin doublet states formed by three electrons will be mainly discussed. I will present a high-fidelity single-shot state detection scheme for the three-electron spin states, which facilitates coherent qubit operations based on exchange interactions. Moreover, I will show that the hyperfine interaction between the spin doublet and the environmental nuclear spins enables dynamic nuclear polarization (DNP), which allows bidirectional control over the nuclear Overhauser field. By tuning the local magnetic field experienced by the QDs via the DNP, a true decoherence-free-subspace (DFS) for spin qubit operations can be derived from the spin doublet structure. The true DFS is decoupled from both the long- and short-wavelength magnetic field noise, allowing highly coherent spin qubit operations.

In the second part of the talk, the semiconductor-superconductor hybrid architecture will be discussed. Analogous to an atom in a cavity, a semiconductor QD embedded in a superconducting cavity can interact with the microwave photons in the cavity. This allows various applications such as microwave photon detection, quantum simulations, and long-range interactions between remote QD spins. Here, I will mainly present strong hole charge-photon interaction enabled by high-impedance Josephson junction array cavity. In particular, holes in QDs have emerged as a front-runner for QD-based quantum computation, mainly owing to their sizable spin-orbit interaction, and scalability. Exploiting the tunability of our resonator, the signature of spin doublet structure in the cavity will also be shown. These findings pave the way toward coherent hole spin-photon interface which is a prerequisite for large-scale hole-based quantum processors.