Quantum Dots “Made in Italy”: A Step Forward for Quantum Technology
An innovative method for the realization of site-controlled quantum dots was recently proposed by a team of researchers working at Sapienza (coordinator: Marco Felici), at the University of Florence (coordinator: Francesco Biccari) and at the Institute for Photonics and Nanotechnologies (IFN; coordinator Giorgio Pettinari) of the National Research Council (CNR).
The study was carried out within the framework of the FIRB (Futuro In Ricerca di Base) project “DeLIGHTeD”, funded by the Italian Ministry of Education, University and Research (MIUR) and coordinated by Marco Felici of the Physics Department of Sapienza University. The results of this investigation, published in Advanced Materials, could be useful in view of the practical implementation of quantum information protocols.
Quantum dots (QDs) are small, nanometer-sized (1 nm = 1 billionth of a meter) particles of a semiconducting material. Their properties are directly linked to their small size, in the sense that charge carriers (e.g., electrons) inside a QD are deeply affected by their being trapped within such a small region of space, presenting clear quantum confinementphenomena.
“When energy is provided to a QD,” as Marco Felici explains, “for example through light, or via an electrical pulse, the system is brought into an excited state, from which it relaxes by emitting photons. Under very specific excitation conditions, a QD can be made to emit a single photonper excitation pulse; this ability is potentially very interesting for applications, especially if we consider that single photons may be employed as ‘quantum bits’ (qubits) in quantum information and computation protocols.”
Classical computing, upon which currently available commercial computer systems are based, has the bitas its basic unit of information. A bit can take values of either 0 or 1, typically assigned to two easily recognizable states of a physical system (e.g., a high –1– or low –0– voltage signal). Quantum computation, on the other hand, is based on the qubit(quantum bit): after labeling two states of a quantum system —for example, a single photon— as 0 and 1, quantum protocols exploit the fact that such systems can be prepared as a probabilistic combination of states (e.g., for 30% in state 0 and for 70% in state 1).
“This,” as noted by Felici, “results in the possibility to store more information with respect to classical systems; moreover, quantum algorithms can more efficiently solve problems that are inherently difficult to handle for classical computers, such as the factorization of large integers. In this respect, it should be noted that integer factorization is at the heart of many cryptographic protocols, widely used in cybersecurity”.
However, the development of quantum computers that are truly superior to their classical counterpart will likely have to go through the realization of integrated photonic circuits(akin to the “standard” integrated circuits at the heart of classical computers), capable of handling operations based on a large number of qubits. The QDs realized with the method proposed by the Italian research team are ideally suited for the on-chip generation of such qubits: in addition to the ability to emit single photons on demand (for example in response to an electrical pulse), indeed, these QDs can be deterministically integrated within a device with positioning precision better than 100 nm, 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 https://doi.org/10.1002/adma.201705450