Single-photon router

LB13197

- In recent years, quantum information science has advanced rapidly, both at the level of fundamental research and technological development. For instance, quantum cryptography systems have become commercially available. These systems are examples of quantum channels, serving mainly to distribute quantum information. There is a significant effort to combine these quantum channels with quantum nodes that would offer basic processing and routing capability. The combination of these channels and nodes would create a quantum network enabling applications simply impossible today. Quantum networks connecting simple quantum processing nodes are also a promising architecture for a scalable
quantum computer.

In this letter, we demonstrate an example of a rudimentary quantum node, a single-photon router. The active element of the router is a single ”artificial atom”, a superconducting qubit, strongly coupled to a superconducting transmission line. Exploiting the phenomenon of electromagnetically induced transparency (EIT), we show that we can route a single-photon signal from an input port to either of two output ports with an on-off ratio of 99%. The switching time of the device is shown to be a few nanoseconds, consistent with theoretical expectations and the device parameters. The device is a nanofabricated circuit offering a clear path to scalability. For instance, it is straight forward to extend this router
to select between multiple output channels.

Signature of hydrogen-bonded supramolecular assemblies at dye-sensitized solar cell interfaces

LC13086B


- Due to the growing global demand for energy, the development of efficient ways of harnessing solar power has become a key scientific challenge. Among promising low-cost alternatives to silicon photovoltaics, dye-sensitized solar cells based on mesoporous TiO2 films sensitized with the dye Ru(dcbpyH2)2(NCS)2 (N3 dye) have gained prominence due to their relatively high energy conversion efficiencies. In dye-sensitized cells the photocurrent is generated via ultrafast electron transfer from the photoexcited dye sensitizer to the semiconductor. As a result the atomistic nature of the semiconductor/dye interface plays a critical role in the performance of these solar cells. Substantial efforts have been devoted to elucidating the structure of this interface, and yet its atomistic nature remains highly controversial. Here we perform a systematic comparison between measured core-level photoemission spectra at the TiO2/N3 interface and the spectra calculated by us from first principles for a variety of atomistic interface models. This analysis suggests that systematic
hydrogen-bonding between dyes occurs on the TiO2 surface, leading to a supramolecular assembly. The present finding hails a paradigm shift in our understanding of dye-sensitized solar cells and bears on the design of more efficient nanoscale photovoltaics.