Entanglement – From a bizarre and long misunderstood quantum phenomenon to a key technology of the 21st century
In 1981 the famous theoretical physicist Richard Feynman gave a widely praised speech in which he developed a thought that has kept physicists and engineers up on their feet until today. He designed the vision of an entirely new kind of computer that would make today’s high-powered computers look like a Commodore 64 from the early 1980s: a „quantum computer“. The basis of such a computer is arguably the most peculiar phenomena in the quantum world, which already caused the founding fathers of quantum theory a lot of headaches: the entanglement of quantum particles.
At that time only a daring thought of a single visionary thinking physicist Feynman’s idea today drives the efforts of numerous physicists and engineers, and with them of investors with billions of dollars to deploy who are sensing the next technological revolution with considerable profit potential. They all know: quantum computers, once constructed, will define a new era of data processing. They could shape the 21st century as much as the development of digital circuits formed the 20th century. But it is not just the quantum computer that has been making physicists‘ hearts beat faster in the last few years. Since the beginning of the 2000s, a broad new quantum revolution is emerging. It already bears a name: Quantum 2.0.
Undoubtedly, quantum theory has been the most influential theory of the 20th century. Numerous technologies based on quantum physics are shaping our everyday lives today: electronic components and integrated circuits on semiconductor chips, lasers, electron microscopes, LED light, special solid state properties such as superconductivity, special chemical compounds, and magnetic resonance tomography. And last but not least, all nuclear technologies rely on the laws of the quantum world. Thus, the very first technical application of quantum theory was the most terrible weapon ever militarily used: the atomic bomb.
All of today’s quantum technologies have one thing in common: they are based on the properties of large ensembles of quantum particles and our ability to control them: the steering of the flow of many electrons, the excitation of a large number of photons, the measurement of the nuclear spin of numerous atoms. Examples are the tunnel effect in the transistor, the coherence of photons in the laser, the spin properties of many atoms in magnetic resonance tomography, Bose-Einstein condensation,or the discrete quantum jumps in an atomic clock. The physicists have long since become accustomed to the bizarre quantum effects such as quantum tunneling, the wraithlike synchronization of billions of particles, or the wave like properties of matter associated with these phenomena. For the statistical behavior of an ensemble of many quantum particles can be grasped very well with standard quantum theory (Schrödinger’s equation) established 90 years ago, and their underlying processes are still somewhat descriptive.
In the emerging second generation of quantum technologies, on the other hand, something completely new comes into play: the specific preparation, control, manipulation and subsequent evaluation of the states of individual quantum particles and their interaction with each other. It is precisely here where entanglement, the very characteristic of the quantum world which confused the founders of quantum theory around Einstein, Bohr, and others so much and the fundamental importance of which for quantum physics physicists fully recognized only many yearsafter the first establishment of quantum theory, takes the center stage. It describes how a limited number of quantum particles can be brought into a state in which they behave as if they were coupled together by a ghostly hand, even if they are far apart from each other. Each particle „knows“ so to speak what the others are doing. They all belong to a common physical entity (the physicists say: a single „wave function“). There thus exists a correlation between the particles, which allows for an instantaneous (i.e. without any time delay) prediction of which state is realized for one particle, just when another one has been measured, even if there are many kilometers between them. It’s like someone in Germany instantly felt what’s happening to his twin in Australia. It took nearly 50 years for the physicists to entirely understand this particularly strange phenomenon of the quantum world, and even today to many of them it still feels like magic. No less magical are the technologies that become possible with it.
In recent years numerous research centers for new quantum technologies have been set up around the world, and several generously funded government projects have been launched. Examples include the Canadian Institute for Quantum Computing with start-up funding of approximately $300 million, the Centre for Quantum Technologies in Singapore, the Joint Quantum Institute in the United States, the Engineering and Physical Sciences Research Council in the UK, and QuTech in the Netherlands. And the Europeans have meanwhile become active as well: in 2016 3,400 scientists signed the Quantum Manifesto, a call to promote the co-ordination between academia and industry to research and develop new quantum technologies in Europe. It states:
“Europe needs strategic investment now in order to lead the second quantum revolution. Building upon its scientific excellence, Europe has the opportunity to create a competitive industry for long-term prosperity and security.”
Politicians finally acted upon this appeal: The European Commission decided to promote a flagship project for research into quantum technologies with funding of one billion euros over the next ten years. That is a lot of money for the chronically weak public finances of European countries. The project focuses on four quantum technologies: communication, computing, sensors and simulations. Concrete new technologies that could arise from this are:
- Secure communication through quantum cryptology: The properties of entangled quantum particles make it possible to produce absolutely secure encryptions.
- Quantum information transfer: This includes the ability to transport quantum information (qubits) over large spatial distances, sometimes referred to as “quantum teleportation”. This could pave the way to a quantum internet.
- Highly sensitive quantum sensors: Entangled quantum states allow significantly more accurate measurements of various physical variables such as time, gravitational forces or electromagnetic fields. The basis for this is the extreme sensitivity of entanglement to external influences.
- Replicating biological systems, such as the production of an artificial leaf for energy conversion by photosynthesis, in which quantum effects play an important role.
- And finally, the ultimate goal: a new era of computing with the development of a quantum computer.
Companies have quickly grown aware of the new possibilities of quantum technologies. Firms like IBM, Google, and Microsoft regard them as billion-dollar businesses and are thus investing heavily into research on how to take advantage of entangled quantum states technologically. Examples include Google’s partnerships with numerous academic research groups, the Canadian company D-Wave Systems Quantum Computing, and the investment of many UK companies into the UK National Quantum Technologies Programme.
Government and companies have long understood that the Quantum Technologies 2.0 are key technologies of the 21st century. The understanding of the bizarre and for long inexplicable phenomenon of entanglement at last provides us a glimpse into a seemingly distant technological future, which we are sure to face soon.