Photons & Phonons: A room-temperature diamond quantum memory

Abstract

This thesis presents demonstrations of the storage and manipulation of single photons in a room-temperature diamond quantum memory using a Raman memory protocol. We report on results from four experiments.

In the first we demonstrate single photon storage and, upon retrieval, verify the quantum nature of the light with a Hanbury Brown Twiss measurement of g^(2)(0) = 0.65±0.07. A measurement of g^(2)(0) < 1 is indicative of quantum light. This is the first demonstration of single photon storage where the bandwidth of the stored light is greater than 1 THz. The diamond memory stores light for over 13 times the duration of the input wavepacket. In the second experiment, we report the storage and retrieval of polarization-encoded qubits and demonstrate qubit storage above a classical bound. We also verify that entanglement between the input photon and an auxiliary persists through storage and retrieval. We then turn to additional uses of a Raman quantum memory. We demonstrate that a photon stored in the diamond memory can, upon retrieval, have its frequency and bandwidth converted. We report frequency conversion over a range of 4.2 times the bandwidth of the input photon (4.1 nm, 2.3 THz), and bandwidth modulation between 0.5 to 1.9 times the bandwidth of the input. We verify that the output light from storage and spectral manipulation is still non-classical in nature.

Finally, we demonstrate both single- and two-photon quantum interference mediated by the diamond memory, where the memory acts as a beamsplitter between photon and optical phonon modes in the diamond lattice. In a first experiment, a single photon is split into two time-bins. The first time-bin is stored in the memory, then recalled and made to interfere with the second time-bin producing fringes. In a second experiment, a photon from a weak coherent state is stored in the memory and, upon retrieval, undergoes Hong- Ou-Mandel interference with a second photon. We measure Hong-Ou-Mandel interference with a visibility of 59% giving a signature of non-classical interference (> 50%). This collection of experiments establishes the diamond memory as a prime candidate for certain quantum communication and processing applications. These results demonstrate the potential for the diamond memory to be an integrated platform for photon storage, spectral conversion, and information processing.