Faster Than the Speed of Light
Quantum entanglement is a very weird phenomena that occurs when particles such as photons and electrons interact physically and instantaneously even when separated. It may be the only environmental phenomena that works faster than the speed of light. Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the sites of measurement. Recent experiments have shown that this transfer occurs at least 10,000 times faster than the speed of light. In a new study, the Institute of Physics and German Physical Society's New Journal of Physics, researchers have proposed using the International Space Station (ISS) to test the limits of this "spooky action" and potentially help to develop the first global quantum communication network. Their plans include a so-called Bell experiment which tests the theoretical contradiction between the predictions of quantum mechanics and classical physics, and a quantum key distribution experiment which will use the ISS as a relay point to send a secret encryption key across much larger distances than have already been achieved using optical fibres on Earth.
Quantum systems can become entangled through various types of interactions. If entangled, one object cannot be fully described without considering the other. They remain in a quantum superposition and share a single quantum state until a measurement is made.
An example of entanglement occurs when subatomic particles decay into other particles. These decay events obey the various conservation laws, and as a result, pairs of particles can be generated so that they are in some specific quantum states. For instance, a pair of these particles may be generated having a two-state spin: one must be spin up and the other must be spin down. In simple language when one changes from up to down the other will change from down to up. Distance does not seem to matter. It is an odd behavior that does not seem to be logical in our universe where the speed of light cannot be exceeded.
Quantum theory was originally developed to describe the smallest entities in physics. Later it turned out that it also makes predictions over macroscopic distances. Establishing quantum technology in space enables quantum systems to become available as a resource for quantum physics experiments on a global scale and beyond.
The successful implementation of such experiments, which are based on the transmission and detection of single photons or entangled photon pairs, would validate the key technology of a quantum transceiver, involving an entangled photon source (EPS), a faint laser pulse source (FPS) and a single-photon counting module. This would represent the first-ever demonstration of a fundamental quantum test experiment and of a quantum communication application in space. In this work, it is proposed to do a series of experiments with photons, making use of pre-existing infrastructure on board the International Space Station (ISS), and also of a dedicated small quantum optics payload based solely on state-of-the-art optical and electronic components.
The proposed experiments involve the distribution of entangled photon pairs and faint laser pulses from ground to space. For the Bell experiment, a pair of entangled photons would be generated on the ground; one would be sent from the ground station to the modified camera aboard the ISS, while the other would be measured locally on the ground for later comparison.
Entangled photons have an intimate connection with each other, even when separated over large distances, which defies the laws of classical physics. A measurement on one of the entangled photons in a pair will determine the outcome of the same measurement on the second photon, no matter how far apart they are.
"According to quantum physics, entanglement is independent of distance. Our proposed Bell-type experiment will show that particles are entangled, over large distances -- around 500 km -- for the very first time in an experiment," continued Professor Ursin.
"Our experiments will also enable us to test potential effects gravity may have on quantum entanglement."
The researchers also propose a quantum key distribution experiment, where a secret cryptographic key is generated using a stream of photons and shared between two parties safe in the knowledge that if an eavesdropper intercepts it, this would be noticed.
Up until now, the furthest a secret key has been sent is just a few hundred kilometers, which would realistically enable communication between just one or two cities.
Research teams from around the world are looking to build quantum satellites that will act as a relay between the two parties, significantly increasing the distance that a secret key could be passed.
Entanglement will provide a potential path for instantaneous communication as well as lay the ground work for even more fascinating quantum computer possibilities.
For further information see Entanglement.
ISS image via Wikipedia.