Dublin researchers develop single photon emitter from quantum dots

21 Jul 2020

Scientists from CRANN and Trinity College School of Physics say this offers a better route to quantum computing.

Researchers at Trinity College Dublin's CRANN (Centre for Research on Adaptive Nanostructures and Nanodevices) and School of Physics have created a new device that will emit single photons from quantum dots. They say this approach could be key to practical quantum computers, quantum communications, and other quantum devices.

The team has made what they are calling "a significant improvement on previous designs in photonic systems" via their device, which enables controllable, directional emission of single photons and which produces entangled states of pairs of quantum dots.

Qubits and quantum computing

The promise of quantum computers leverages the properties of quantum bits – “qubits” – to execute computations. The Dublin team says that such quantum computers will have much greater computational powers over and above classical computers.

Quantum entanglement, a fundamental property of quantum mechanics, occurs when a pair or group of particles are quantum-mechanically linked such that the quantum state of each particle of the pair cannot be described independently of the state of the other's. Essentially, two entangled quantum dots can emit entangled photons.

Scientists are exploring different options and designs to make quantum computing a viable reality. One proposed idea utilises photonic systems, making use of quantum properties of light at the nanoscale, as qubits. The Trinity team describes their work in Nano Letters.

The new system utilizes single photons that are emitted in a controlled fashion in time and space from quantum dots. For applications such as quantum computing, it is necessary to control emissions from these dots and to produce quantum entanglement of emission from pairs of these dots.

Professor John Donegan, CRANN and Trinity’s School of Physics, commented, “Our device works by placing a metal tip within a few nanometers of a surface containing the quantum dots. The tip is excited by light and produces an electric field of such enormous intensity that it can greatly increase the number of single photons emitted by the dots.

“This strong field can also couple emission from pairs of quantum dots, entangling their states in a way that is unique to quantum emitters of light.” The other significant advantage is the mechanism by which the device works over current state-of-the-art photonic devices for quantum computing applications.

'Simple design'

Professor Ortwin Hess, Professor of Quantum Nanophotonics in Trinity’s School of Physics and CRANN, added, “By scanning the metal tip over the surface containing the quantum dots, we can generate the single photon emission as required. Such a device is much simpler than current systems that attempt to fix a metal tip, or a cavity, in close proximity to a quantum dot.

“We now expect that this device and its operation will have a striking effect on research in quantum emitters for quantum technologies.”

The collaboration between Professors Hess and Donegan began while Professor Hess was working at Imperial College London and will continue with his recent appointment to Trinity through Ireland's SFI Research Professorship Programme. The team plans to fabricate devices that will demonstrate controlled single photon emission and contribute strongly to the research effort in quantum technologies in Ireland.