Phonon scattering inhibits simultaneous near-unity efficiency and indistinguishability in semiconductor single-photon sources
Authors: Jake Iles-Smith, Dara P. S. McCutcheon, Ahsan Nazir, Jesper Mørk
Journal: Nature Photonics
Publication Date: 03 July, 2017
Department of: Physics and Astronomy
Vibrations place fundamental bounds on semiconductor single-photon quantum devices
Very small packets of light, known as single photons, are expected to be a key resource for future quantum technologies. For example, they can be used to transfer information around a quantum network in a rapid and robust fashion. Yet, quantum device requirements are notoriously stringent, with the result that potential photon sources need to emit identical photons in a desired direction with almost perfect efficiency. Nevertheless, recent progress in controlling the emission properties of nanoscale islands of semiconductor, known as quantum dots, had led to speculation that realising such a high-quality source was now simply a matter of time.
However, as part of a team of collaborating researchers, a quantum theorist at the University of Manchester has now established that vibrations inherent to such quantum dots place fundamental bounds on their ability to perform as single photon sources. Specifically, they prevent the generation of perfectly indistinguishable (i.e. identical) photons with 100% efficiency. Though this result places important intrinsic limits on the potential use of current quantum dot single photon sources in quantum technologies, it also points the way towards new strategies and device designs that may be able to overcome the detrimental impact of vibrations in the future.
- A photon is the quantum of light (or more generally electromagnetic radiation); that is, the smallest packet of light that can be created. Likewise, the quantum of vibration is known as a phonon.
- Quantum dots are small man-made islands of semiconductor, usually of nanometre scale, that have properties similar to naturally occurring atoms or molecules.
- During emission of a photon, it is possible for a quantum dot to send out a vibrational wave into its surrounding environment, which steals away a portion of the photon energy. This photon will then be different to the others that did not give rise to any vibrations.
- One can improve how identical the photons are by simply filtering out and removing these undesired photons, but this ultimately comes at the cost of efficiency, as now not all photons that are emitted are used.