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Quantum Dot, Quantum Technology


A team of researchers from Sapienza University, the University of Florence and the CNR Institute for Photonics and Nanotechnology (IFN) have proposed an innovative method for the development of position-controlled quantum dots (QDs). The study, conducted as part of FIRB Project “DeLIGHTeD”, coordinated by Professor Marco Felici from the Sapienza Department of Physics, represents a further step towards the quantum information revolution. The results of the study have been published on Advanced Materials.

Quantum dots are agglomerates of semiconducting material that have a radius of a few nanometres (1 nm = a billionth of a metre). Their properties are closely related to their minute dimensions as the charge bearers (i.e., electrons) in the dots are affected by the fact that they are “forced” to stay in a confined area, thereby presenting quantum phenomena.

“When a QD is provided with energy,” explains Prof. Felici, “via luminous radition or electric impluses, for example, the system first shifts to an excited state and then loses energy by emitting light or photons. By correctly exciting a QD, it can be primed to emit a single photon for each excitation impulse. This ability is extremely interesting, especially in view of the use of single photons as “quantum bits” or qubits in computing and quantum information protocols.

Classic information on our computers is based on bits: binary numbers based on 0s and 1s are assigned to two easily distinguished states, such as a power signal which can be low (0) or high (1). Quantum information, on the other hand, is based on qubits. After assigning two states (values 0 and 1) to a quantum system (such as a single photon), these systems can also exhibit a combination of states (i.e., 30% state 0 and 79% state 1).

“This,” comments Prof. Felici, “provides us with the possibility to store an exponentially higher quantity of information than with a classic system. Moreover, the use of quantum algorithms makes the solution of problems that are extremely difficult to perform with our current computers, much easier. Quantum systems, for example, make it far easier to factor whole numbers thousands of places, and this is what currently used cryptographic protocols for computer security are based on.”

The development of quantum computers will, however, probably have to wait for the development of integrated photonic circuits (as opposed to the integrated circuits on which classic computers are based) that will be capable of managing operations based on a high number of qubits. Indeed, the QDs developed with the methods proposed by the Italian research team are ideal candidates for an “on chip” qubit generation: not only will they emit photons on request (i.e., in response to an electric impulse), but they can also be placed in a device with a precision greater than 100 nm, which is fully compatible with photonic circuits.


Site‐Controlled Single‐Photon Emitters Fabricated by Near‐Field Illumination - Francesco Biccari, Alice Boschetti, Giorgio Pettinari, Federico La China, Massimo Gurioli, Francesca Intonti, Anna Vinattieri, MayankShekhar Sharma, Mario Capizzi Mario Capizzi, Annamaria Gerardino, Luca Businaro, Mark Hopkinson, Antonio Polimeni, Marco Felici - Advanced Materials First published: 02 April 2018

For further information:

Marco Felici - Department of Physics, Sapienza University