Research group Quantum photonics

Researchers from Stockholm University and the Indian Institute of Science Education and Research (IISER) Mohali have reported a practical way to spot one of physics’ strangest predictions: the Unruh effect, which says that an object speeding up (accelerating) would perceive empty space as faintly warm. But, trying to heat something up by accelerating it unimaginably fast is a non-starter in the lab. The team shows how to convert that tiny effect into a clear, timestamped flash of light.

2025 is UNESCO's International Year of Quantum Science, and as part of this initiative, a quantum light source was taken on a 12-month tour to 12 institutes in Europe. "We participated in the QuanTour project and conducted experiments on the quantum dot source in February,” said Ana Predojević and her research team at the Department of Physics.

Fysikum at Stockholm University is set to host a quantum dot that has been on a journey throughout Europe. The ‘QuanTour’ project is an initiative to showcase a quantum light source as it travels throughout 12 institutes within Europe all as part of the UNESCO’s international year of quantum science and technology, 2025, chosen to recognize the 100 years since the initial development of quantum mechanics. Whilst here in Sweden, the source will be hosted in the lab of Ana Predojević where they will verify the quantum nature of the light emitted from the Quantum dot. These semiconductor quantum dots are tiny structures, typically only a couple nanometers wide, that are engineered to have optical and electronic properties that allow for the production of single photons. This quantum dot is then embedded within a microscopic heterostructure shaped like a dartboard (4-𝜇m wide) in order to optimize the emission direction and efficiency in the direction perpendicular to the quantum dot.

Extremely efficient entangled photon pair sources can be achieved by employing a simple but effective approach – placing quantum dots in broadband pillar microcavities. - It's a novel device with potential to enhance digital security, says Professor Ana Predojević, head of Quantum Photonics group at Fysikum. Sources of entangled photons are a key enabler of quantum technology. Such sources can be achieved employing quantum dots, however, ensuring high efficiency with which the photon pairs are channeled from the quantum dot to the collection optics remains a challenge. Meeting this requirement calls for the use of broadband photonic structures that can efficiently extract pairs of photons that have different wavelengths.

Moungi G. Bawendi, Louis E. Brus and Alexei I. Ekimov were awarded the Nobel Prize in Chemistry 2023 for the discovery and development of quantum dots. These tiny quantum systems have unique properties and many applications: they emit light used in television screens and LED lamps, they catalyse chemical reactions, and their emission marks the borders of tumor tissue for a surgeon. Ana Predojević, is associate professor at Fysikum: "We use the best tools and methods available to modern science to generate quantum light, harness its unique properties, and bring it closer to real-world application."

Quantum technologies including quantum computing and quantum communication rely on a very intriguing natural phenomenon – entanglement. Using modern methods of machine learning enables quantification of this important and fragile feature of the quantum world.

Quantum mechanics predicts effects that are counter-intuitive and impossible to reconcile with our daily experience. One of the most intriguing examples of these predictions is that a pair of particles can be entangled. When two particles are entangled we cannot describe the properties of one of them without referring to the other, they behave as a single entity.

An emerging field of physics and engineering is quantum technology, encompassing technologies that rely on the properties of quantum mechanics. Quantum computing being one example of these technologies, representing a paradigm shift for computing technology, since it can outperform much more than existing computers. On February 21 at 13:00, in the: Svedberg salen (FD5), AlbaNova, Professor Akira Furusawa from University of Tokyo, RIKEN Center for Quantum Computing will have a presentation with the title THE FUTURE IS QUANTUM - The development of Quantum Computing.