From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH) : “Single photon emitter takes a step closer to quantum tech”

From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH)

Raphaël Butté
Nik Papageorgiou

To get closer to quantum technology we need to develop non-classical light sources that can emit a single photon at a time and do so on demand. Scientists at EPFL have now designed one of these “single photon emitters” that can work at room temperature and are based on quantum dots grown on cost-effective silicon substrates.

Developing non-classical light sources that can emit, on-demand, exactly one photon at a time is one of the main requirements of quantum technologies. But although the first demonstration of such a “single photon emitter”, or SPE, dates back to the 1970s, their low reliability and efficiency has been stood in the way of any meaningfully practical use.

Conventional light sources like incandescent light bulbs or LEDs emit bunches of photons at a time. In other words, their probability to emit a single photon at a time is very low. Laser sources can emit streams of single photons, but not on-demand, which means that, sometimes, there will be no photons whatsoever emitted when we want them to.

So the main advantage of SPEs is that they can do both: emit a single photon and do so on-demand – or, in more technical terms, their single-photon purity, which they can maintain at an ultrafast timeframe. Thus, for a light source to qualify as an SPE, it must feature a single-photon purity above 50%; of course, the closer to 100%, the closer we will be to an ideal SPE.

Researchers at EPFL, led by Professor Nicolas Grandjean, have now developed “bright and pure” SPEs based on wide-bandgap semiconductor quantum dots grown on cost-effective silicon substrates.

The quantum dots are made of gallium nitride and aluminum nitride (GaN/AlN) and feature single-photon purity of 95% at cryogenic temperatures, while also maintaining excellent good resilience at higher temperatures, with a purity of 83% at room temperature.

The SPE also shows photon emission rates up to 1 MHz while maintaining a single-photon purity over 50%. “Such brightness up to room temperature is possible because of the unique electronic properties of the GaN/AlN quantum dots, which preserves the single-photon purity due to the limited spectral overlap with competing neighboring electronic excitation,” says Stachurski, the PhD student who investigated these quantum systems.

Single-photon emission by a self-assembled GaN/AlN quantum dot. Credit: J. Stachurski/EPFL.

“A very appealing feature of GaN/AlN quantum dots is that they belong to the III-nitride semiconductor family, namely that behind the solid‐state lighting revolution (blue and white LEDs) whose importance was recognized by the Nobel prize in Physics in 2014,” state the researchers. “It is nowadays the second semiconductor family in terms of consumer market right after silicon that dominates the microelectronic industry. As such, III-nitrides benefit from a solid and mature technological platform, which makes them of high potential interest for the development of quantum applications.”

An important future step will be to see if this platform can emit one photon and only one per laser pulse, which is an essential prerequisite to determine its efficiency.

“Since our electronic excitations exhibit room temperature lifetimes as short as 2 to 3 billionth of a second, single photon rates of several tens of MHz could be within reach,” state the authors. “Combined with resonant laser excitation, which is known to significantly improve single-photon purity, our quantum-dot platform could be of interest for implementing room-temperature quantum key distribution based on a true SPE, as opposed to current commercial systems that run with attenuated laser sources.”

Science paper:
Light: Science & Application

See the full article here .


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The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH) is a research institute and university in Lausanne, Switzerland, that specializes in natural sciences and engineering. It is one of the two Swiss Federal Institutes of Technology, and it has three main missions: education, research and technology transfer.

The QS World University Rankings ranks EPFL(CH) 14th in the world across all fields in their 2020/2021 ranking, whereas Times Higher Education World University Rankings ranks EPFL(CH) as the world’s 19th best school for Engineering and Technology in 2020.

EPFL(CH) is located in the French-speaking part of Switzerland; the sister institution in the German-speaking part of Switzerland is The Swiss Federal Institute of Technology ETH Zürich [Eidgenössische Technische Hochschule Zürich] (CH). Associated with several specialized research institutes, the two universities form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles Polytechniques Fédérales] (CH) which is directly dependent on the Federal Department of Economic Affairs, Education and Research. In connection with research and teaching activities, EPFL(CH) operates a nuclear reactor CROCUS; a Tokamak Fusion reactor; a Blue Gene/Q Supercomputer; and P3 bio-hazard facilities.

ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École Polytechnique Fédérale de Lausanne](CH), and four associated research institutes form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales] (CH) with the aim of collaborating on scientific projects.

The roots of modern-day EPFL(CH) can be traced back to the foundation of a private school under the name École Spéciale de Lausanne in 1853 at the initiative of Lois Rivier, a graduate of the École Centrale Paris (FR) and John Gay the then professor and rector of the Académie de Lausanne. At its inception it had only 11 students and the offices were located at Rue du Valentin in Lausanne. In 1869, it became the technical department of the public Académie de Lausanne. When the Académie was reorganized and acquired the status of a university in 1890, the technical faculty changed its name to École d’Ingénieurs de l’Université de Lausanne. In 1946, it was renamed the École polytechnique de l’Université de Lausanne (EPUL). In 1969, the EPUL was separated from the rest of the University of Lausanne and became a federal institute under its current name. EPFL(CH), like ETH Zürich (CH), is thus directly controlled by the Swiss federal government. In contrast, all other universities in Switzerland are controlled by their respective cantonal governments. Following the nomination of Patrick Aebischer as president in 2000, EPFL(CH) has started to develop into the field of life sciences. It absorbed the Swiss Institute for Experimental Cancer Research (ISREC) in 2008.

In 1946, there were 360 students. In 1969, EPFL(CH) had 1,400 students and 55 professors. In the past two decades the university has grown rapidly and as of 2012 roughly 14,000 people study or work on campus, about 9,300 of these being Bachelor, Master or PhD students. The environment at modern day EPFL(CH) is highly international with the school attracting students and researchers from all over the world. More than 125 countries are represented on the campus and the university has two official languages, French and English.


EPFL is organized into eight schools, themselves formed of institutes that group research units (laboratories or chairs) around common themes:

School of Basic Sciences
Institute of Mathematics
Institute of Chemical Sciences and Engineering
Institute of Physics
European Centre of Atomic and Molecular Computations
Bernoulli Center
Biomedical Imaging Research Center
Interdisciplinary Center for Electron Microscopy
MPG-EPFL Centre for Molecular Nanosciences and Technology
Swiss Plasma Center
Laboratory of Astrophysics

School of Engineering

Institute of Electrical Engineering
Institute of Mechanical Engineering
Institute of Materials
Institute of Microengineering
Institute of Bioengineering

School of Architecture, Civil and Environmental Engineering

Institute of Architecture
Civil Engineering Institute
Institute of Urban and Regional Sciences
Environmental Engineering Institute

School of Computer and Communication Sciences

Algorithms & Theoretical Computer Science
Artificial Intelligence & Machine Learning
Computational Biology
Computer Architecture & Integrated Systems
Data Management & Information Retrieval
Graphics & Vision
Human-Computer Interaction
Information & Communication Theory
Programming Languages & Formal Methods
Security & Cryptography
Signal & Image Processing

School of Life Sciences

Bachelor-Master Teaching Section in Life Sciences and Technologies
Brain Mind Institute
Institute of Bioengineering
Swiss Institute for Experimental Cancer Research
Global Health Institute
Ten Technology Platforms & Core Facilities (PTECH)
Center for Phenogenomics
NCCR Synaptic Bases of Mental Diseases

College of Management of Technology

Swiss Finance Institute at EPFL
Section of Management of Technology and Entrepreneurship
Institute of Technology and Public Policy
Institute of Management of Technology and Entrepreneurship
Section of Financial Engineering

College of Humanities

Human and social sciences teaching program

EPFL Middle East

Section of Energy Management and Sustainability

In addition to the eight schools there are seven closely related institutions

Swiss Cancer Centre
Center for Biomedical Imaging (CIBM)
Centre for Advanced Modelling Science (CADMOS)
École Cantonale d’art de Lausanne (ECAL)
Campus Biotech
Wyss Center for Bio- and Neuro-engineering
Swiss National Supercomputing Centre