Scientists have made a significant improvement on previous designs in photonic systems that could make quantum computing a viable reality in the near future.

Researchers at CRANN and the School of Physics at Trinity College Dublin have created a new device that will emit single particles of light, or photons, from quantum dots that are the key to practical quantum computers, quantum communications, and other quantum devices.

The device allows for controllable, directional emission of single photons and which produces entangled states of pairs of quantum dots.

The promise of quantum computers leverages the properties of quantum bits or qubits to execute computations. Quantum bit is the basic unit of quantum information—the quantum version of the classical binary bit physically realised with a two-state device.

Current computers process and store information in bits of either 0s or 1s whereas qubits can be 0 and 1 simultaneously. That means quantum computers will have much greater computational powers over and above classical computers.

The Trinity team, who explored different options and designs, have published their studies in the high-profile journal Nano Letters.

The team looked at utilising photonic systems, making use of quantum properties of light at the nanoscale, as qubits.

Their system utilises single photons of light emitted in a controlled fashion in time and space from quantum emitters (nanoscale materials known as 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.

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

“The 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,” said Professor John Donegan, CRANN and Trinity’s School of Physics.

The other significant advantage is the mechanism by which the device works over current state-of-art photonic devices for quantum computing applications.

“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,” said Ortwin Hess, Professor of Quantum Nanophotonics in Trinity’s School of Physics and CRANN.

 

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