Manipulation of photonic quantum states: From generation, engineering, and characterization to storage and retrieval

Abstract

The quantum state is the building block of every technology based on quantum mechanics. Its manipulation is critical for real applications, and is thus an important area of investigation within various physical systems, even after decades of study. As one of the types of information carrier, the photon is suitable for transmission, is relatively easy to control, and interacts only weakly with its environment. These features make it an ideal candidate for quantum information protocols. This thesis presents various new techniques in the manipulation of photonic quantum states. Photon-pair states generated in optical fiber exhibit ideal spatial modes for integration in quantum communication fiber networks. We demonstrate polarization-entangled photon-pair generation in commercially available polarization-maintaining fiber. The use of birefringent phase-matching makes the source free of Raman noise and tunable across a wide range of wavelengths. We then use a new approach to engineer the photon-pair state. We show that a gradual turning-on and turning-off of the interaction between two pumps can tailor the photon correlation such that individual photons are in pure wave-packets without filtering, which is crucial for applications requiring multiple indistinguishable photons. We develop a novel characterization technique called stimulated emission tomography. This method overcomes the difficulty of characterizing photonic quantum states due to the low efficiency of spontaneous emission. We demonstrate that a classical measurement can be performed to reveal the properties of the quantum state with unprecedented efficiency and accuracy. Finally, storage of quantum states in a so-called quantum memory is important as a synchronization device for both long-distance communication and local computational operations. It can also be used as an alternative way to produce on-demand single photons. We demonstrate ultra-broadband storage using hot atomic barium vapor based on off-resonant Raman interaction. This paves the way for the storage of femtosecond photons at telecom wavelengths