Establishing polarization qubits from a photon-pair source and a design of an alternative scheme of universal optical programmable multi-qubit gates

Abstract

Due to the potential of quantum computers to revolutionize computation by solving some types of traditionally intractable problems by the classical computer, this field of study has become increasingly active and diverse, involving work on developing quantum processing hardware as well as research into applications with a potential large speed-up compared to simulations on classical (non-quantum) computers. One of the most promising methods for processing quantum information involves the use of photonic qubits, which allow for well-established and noise-free single-qubit operations. However, since there is no photon-photon interaction, processing the qubit-interaction property requires a nonlinear optical operation. Therefore, in the experiment section of this project, we created entangled photonic qubits by beginning with photon pair generation using a nonlinear crystal, then building up the complexity of the optical setup with the Hong-Oa-Mandel dip experiment, CHSH experiments, and eventually, photonic qubit generation and tomography. By optimizing the efficiency of the system in each experiment, the resultant qubit was successfully constructed with high fidelity to the designated Bell’s state. Additionally, we experimented with the optical structure of the photon pairs loop, which delivered some issues with noise and low signal in the results. Nonetheless, the structure still showed potential to be improved and utilized in future experiments. The entangled qubits and photon loop created in this project can be used as a foundation for various quantum optic algorithms, especially the photon loop structure, which can be used for the iteration of an operator, which is used regularly in the standard method for constructing multi-qubit gates. However, the method has some limitations in that only unitary operators can be created. Finally, in the second section of this project, we explored an alternative scheme for constructing quantum optical multi-qubit gates. This purposed scheme, which uses the Hilbert-space expansion technique, is capable of independently programming each matrix element of the operator, allowing many different types of quantum operators to be realized in quantum optic experiments. The advanced scheme can theoretically achieve n-polarization-qubit optical reconfigurable quantum gates by arranging linear optical elements.