Quantum Optics

Most quantum information processes were first implemented in the real world with light, and many key aspects of quantum information science can be observed at the level of a few photons, the smallest detectable portion of electromagnetic energy.

A practical attraction of working with photons is that, thanks to the long history of optical science, a wide tool set exists to manipulate and encode information in the states of single photons. Photons can also be easily transported to distant places without deterioration of the encoded information.

CQT's research in quantum optics focuses on the preparation of entangled states between several photons, and the use of entangled photons for fundamental tests of quantum physics (Nature Physics 4, 681 (2008)), understanding and optimizing measurement processes and, on the applied side, for quantum communication tasks such as secure key distribution. We maintain a fully functional entanglement-based quantum key distribution system to investigate various protocols (Phys. Rev. A 78, 020301R (2008)) and possible vulnerabilities of real implementations.

Photon-pair sources are a workhorse for demonstration experiments of entanglement-related physics. We adapt those with very high fidelity of the prepared states to interconnect with other physical information carriers such as atoms. A high heralding efficiency for fundamental tests and operation in unconventional environments outside the lab are other goals. Using technology initially developed for quantum key distribution, we also investigate the statistical properties of light to find signatures of quantum effects in other physical systems – atomic systems, for example.

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