Einstein received the 1922 Nobel Prize for his groundbreaking idea of 1905 that light consists of particles, today called photons. Together with Podolsky and Rosen, he proposed in 1935 that two quantum systems can be connected in a way that is much stronger than in classical physics. The Austrian Nobel Prize winner Erwin Schrödinger coined the name “entanglement” and called it “the essential feature of quantum mechanics”. By Einstein, it was dismissed as “spooky action at a distance”. Due to the enormous experimental progress today, not only the old predictions were confirmed, but novel phenomena were discovered, including, for example, multi-particle entanglement and quantum teleportation.
These are not just intellectual curiosities, but they lay the foundation for a possible future information technology, with applications such as quantum communication, quantum cryptography and quantum computation. In the talk, some of the most recent experimental results, particularly on long-distance quantum communication and on the implementation of quantum states in higher-dimensional Hilbert spaces, will be presented and future possible applications will be discussed. These will, for example, include experiments using satellite-based quantum communication on a world-wide scale. It would be interesting to hear Albert Einstein’s reaction to these developments, particularly in view of his statement towards the end of his life that despite years of conscious brooding, he did not come closer to answering the question “What is light?”