A single molecule, wired between two nanoelectrodes, will be turned into a device that emits exactly one particle of light at a time. Today’s quantum technologies—faster computing, unhackable communication, ultra-sensitive sensors—depend on reliable single-photon sources. Existing options, such as quantum dots or crystal defects, suffer from inefficiency, high cost, or difficulty scaling beyond laboratory demonstrations. Single molecules are theoretically ideal two-level systems, but until recently they could not be stably integrated into electronic circuits. This project solves that integration problem by chemically soldering individual molecules between electrodes, creating “single-molecule junctions” that convert electrical current into light, photon by photon. If successful, SPUD will deliver a new class of on-demand single-photon emitters that are cheap, made from non-toxic materials like carbon and nitrogen, and easily tunable by changing the molecule’s chemical structure. This could lower the barrier to building quantum communication networks and quantum sensors that operate at room temperature. The work merges molecular electronics with molecular photonics, opening a platform for tailoring quantum light sources that simply does not exist today.
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Single-photon emitters play a key role in quantum information processing, with the prospect of faster and more secure communication, computing with increased efficiency and metrology/sensing with unprecedented sensitivity. Of the possible existing technologies, electrically-driven sources based on "single-quantum" emitters - isolated two-level systems - offer significant advantages in terms of future scalability, low operational costs, ease of integration in existing classical devices and possible monolithic fabrication. There is, however, still no "ideal" on-demand (deterministic) single-photon emitter, and every proposed technology suffers from efficiency drawbacks or provides challenges in scaling beyond the laboratory proof-of-concept. The race for the ideal single-photon source is on. In SPUD, I propose to use single molecules, electrically wired and chemically soldered to two nanoelectrodes ("single-molecule junctions"), as single-photon sources. The two-level nature of isolated single-molecules results in a theoretically ideal behaviour for non-classical light emission, and they can also offer reduced size, a vast explorable chemical space of myriad of structures, ease of integration in hybrid devices and they rely on inexpensive and non-toxic materials - carbon, nitrogen, oxygen, etc. All these properties have been known since the early 1990s, but only recent development allow their stable and reproducible integration in electronic circuits, thus offering the enticing possibility of using them to convert electrical current into light, one photon at a time. In this project, we will demonstrate that single-molecule junctions can be efficient, on-demand single-photon sources, and that the experimental freedom granted by their structure offers a unique platform for the exploitation of their properties, merging the fields of molecular electronics and molecular photonics to deliver a uniquely tailorable class of devices for future quantum technologies.
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