Entangling Time-bin Qubits Using an Optical Switch: Source Alignment and Mach-Zehnder Interferometer Construction

Overview

Objectives/Goals Quantum mechanics is an extremely relevant topic of the day as it is being used in technology to increase the speed of information processing and to improve the security of cryptographic systems. These advancements largely involve the process of entangling qubits, which are basic units of quantum information (quantum bits). While polarization entanglement has been utilized frequently in current optics research, time-bin entanglement remains more in theory and has not been as thoroughly explored. A long-term, multi-stage experiment was planned out with the purpose of verifying the theoretical set-up by attempting to generate entangled time-bin qubits in real-time. Methods/Materials Single photon detector, fiber laser, fiber cutter/splicer, light attenuators, optical fibers, nonlinear crystal, polarizing beam splitters, couplers, mirrors, iris diaphragm, function generator, phase modulator, MXA signal analyzer The stages of the experiment included photon pair generation, time-bin qubit preparation, time-bin qubit entanglement with a switch, and measurement. Because of previous inefficiencies, the first stage is being reconstructed and retested to more efficiently generate photon pairs using a dual-Sagnac interferometer. The source is being built using free space components and aligned to maximize efficiency. An M-Z interferometer was built to test the functionality of the phase modulator, which is to be used in the third stage. Results The ideal laser settings to maximize efficiency were found. The M-Z interferometer was constructed and used to verify the functionality of the phase modulator. Some previous results suggested high loss, which is why the first stage is being reformulated to more efficiently generate photon pairs. Conclusions/Discussion Though various stages of the experiment were verified, the low efficiency of initial photon pair generation hinders the set-up from being fully assembled. Once the dual-Sagnac interferometer source is successfully aligned, all the components can be linked to generate time-bin qubits.