11:00 〜 11:15
▲ [21a-E207-8] Experimental quantum process tomography of time-bin qubit controlled-phase gate
キーワード：quantum gate, quantum information processing
Quantum logic gates are an essential element required to enable quantum information and computation tasks to be performed. So far, several two-qubits gates have been demonstrated using polarization or path-encoded photonic qubits. Previously, we have implemented the generation of an entangled state using a controlled-phase (C-Phase) [Appl. Phys. Exp. 11 092801 (2018).] and showed the truth table of controlled-NOT gate for time-bin qubits using a two-input, two-output (2x2) optical switch based on a lithium niobate waveguide. By inputting a temporally modulating signal and DC bias to the switch, it can work as a time-dependent beam splitter for different temporal mode of time-bin qubits. However, the experiment was performed with only a specific pair of input states, and thus the functionality of the C-Phase gate could not be fully characterized. Quantum process tomography (QPT) is an excellent method for analyzing how a state is transformed by a quantum gate. So, we reconstructed the process matrix by performing the QPT with 16 separable input states. After the maximum-likelihood estimation, the process fidelity was calculated to be 89 %. So, our optical switch was capable of the required quantum gate operation. We expected that quantum logic gates for time-bin qubits will be useful for advanced quantum communication systems.