Engineering a noise-free quantum memory for temporal mode manipulation

Thesis

An optical quantum memory, a device which can store and retrieve on demand an arbitrary quantum state at the single photon level, has been identified as a significant cornerstone of photonic quantum technologies. The development of such a memory would allow the creation and development of a large number of quantum technologies. These would range from the ability to synchronise processing steps in an optical quantum computer, to the construction of a quantum repeater which would allow faithful transmission of quantum states over arbitrarily long distances.

In this thesis I investigate broadband light storage in a room-temperature Raman memory for purposes of quantum information processing with photons. During the course of this thesis, a novel scheme to suppress four-wave mixing noise is simulated, based on equations derived to describe the physics of the memory interaction. The experimental arrangement to test the suppression method is described and an original method using photon statistics is demonstrated. The results of these experiments prove the ability of the memory to retrieve and maintain the non-classicality of the state, given a single photon input.

Following the affirmation that, using this noise suppression technique, the memory can function at the single-photon level, I go on to consider how the temporal-spectral properties of a pulsed mode of light may be manipulated using the memory. There are two primary reasons for this investigation: 1) Increasing the efficiency of the read-in process by carving the optimum mode of the memory 2) Using the memory as a device operating in a high dimensional quantum information basis. The restrictions of such applications are considered and a method to test the efficacy of transformations in this basis is devised and experimentally tested. I also perform demonstrations of light storage using conventional temporal modes using a novel method of velocity selection within warm vapour.

Finally I detail further experiments that are achievable with the Raman quantum memory given the progress that has been achieved during my DPhil research. The results show that the Raman memory is a viable candidate for a practical route towards low-noise quantum storage and for manipulation of temporal modes of light.

Authors: Hird, TM

• DOI: 10.5287/ora-yjbn1myad
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Quantum memories; Quantum; Atom-light interactions; Physics
• Subjects: Physics; Quantum computing