Cavity QED of electron spins in diamond

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Non-Technical AbstractIn a quantum communication network, information is carried by light pulses containing single photons and is processed by individual quantum systems or quantum bits, such as single atoms or single electron spins. This new information processing paradigm can enable secure or unbreakable communication and can tackle computational problems that would otherwise be impossible with conventional computers. A key requirement for developing this new paradigm is the control of interactions between light and quantum systems at the level of single photons and single quantum bits. This experimental project uses individual electron spins in a thin diamond membrane as quantum bits. Strong interactions between single photons and single spins are enabled by confining the photons in an optical micro-resonator with a dimension less than 50 micrometers. The primary goal is to use a single electron spin to control the quantum state of a single photon, thus realizing an optical switch that can operate at the level of single photons. These switches can serve as an important component in a quantum network. This research project also provides excellent training opportunities for graduate and undergraduate students in areas including nanophotonics and nanofabrication as well as quantum science and technology. This training prepares the students for careers in academia, industry, or government.Technical AbstractThis project develops a unique composite cavity QED system, in which an electron spin in a thin diamond membrane couples to the evanescent field of an optical whispering gallery mode in a silica microresonator via a resonant Raman transition. Fundamental optical interactions at the level of single electron spins and single photons are explored in a solid state environment. The research activity focuses on the experimental demonstration of the Duan-Kimbe scheme, which realizes a pi-phase shift for a single photon, conditioned on the quantum state of an atom. This cavity QED process takes place in the limit that cooperativity, a dimensionless parameter characterizing the strength of atom-photon or spin-photon coupling, exceeds 1, but does not require strong coupling at the single-photon level. The near term objective is to achieve single-spin-induced optical transparency and to realize a photonic switch that can control the quantum state of a single photon through its interaction with a single electron spin. These switches can enable the generation and distribution of quantum entanglement in a quantum network, potentially playing a significant role in the development of quantum information technologies.