Research on quantum entanglement is posed to make yet another leap forward as European researchers outline an experiment involving the International Space Station.
Quantum entanglement, what Einstein termed “spooky action over a distance,” has remained puzzling to physicists since it was first predicted in the early years of quantum theory (1). In its simplest form, quantum entanglement can be described as a physical interconnection among particles, despite spatial separation. Specifically, each of the entangled particles takes on a common quantum state—an indefinite description of physical characteristics including spin, polarization, and momentum. When a state of one of the particles is measured and subsequently assigned a definite value, its entangled partner instantaneously assumes the same character.
Herein lies the most remarkable aspect of quantum entanglement and the justification for the attention it has garnered from the physics community—it entails instantaneous, faster-than-light interaction of particles. Since the quantum state of the measured particle instantly becomes that of its counterpart, there seems to be a transmission of information. Over the course of the last two decades, experiments in quantum entanglement demonstrating this result have been described as “quantum teleportation.” While claiming to have achieved teleportation may be a misnomer, as no classical information can be transmitted, the experiments have effectively demonstrated quantum state teleportation.
As a consequence, the future may yet hold the potential for the development of a quantum internet. According to current models, a quantum internet would guarantee secure and rapid communication, using the teleportation of qubits—the fundamental units of quantum communication—as the underlying mechanism for a global network (2). Driven by the potential realization of such a network, researchers have made significant progress honing the experimental methods of quantum teleportation.
In 2012 alone, there was a marked increase in the spatial separation of entangled particles. During the spring, a team of Chinese researchers from the University of Science and Technology of China in Shanghai successfully teleported 1,100 photons 97 km (1). Only months later, in September, an international team of researchers published the results of a similar experiment between La Palma and Tenerife, two of the Canary Islands (2). Once again breaking the record, they achieved a distance of 143 km between entangled photons. This year, hoping to build upon the significant progress already made, a team of European researchers has proposed a new experiment involving the International Space Station. If successful, achieving quantum teleportation via the ISS will transmit state information a distance of approximately 400 km (3).
In the experiment, a photon, entangled with another on Earth, would be transmitted to a photon detection module on the cupola of the ISS. After reception in space, the particle and its properties would be measured to determine the state similarities between the two. Assuming the preservation of entanglement, any changes detected in one photon would be present in the other (3). The long-range nature of the test would further allow researchers to explore the nature of quantum entanglement.
In addition to nearly tripling the current distance record, performing experiments with the ISS also resolves issues with current techniques confronting scientists. Firstly, the interference of weather is eliminated by the altitude of the ISS, which orbits between 330 km and 435 km above the surface of the Earth. Scientists hope that removing a significant portion of atmospheric interference will enable them to establish longer-distance networks. Secondly, because of the diminished pull of Earth’ gravitational field at the altitude of the ISS, performing experiments with the ISS will allow researchers to understand the influence of gravity on the entanglement of particles. Until now, the study of quantum entanglement has lacked an experimental method to effectively gauge the impact of gravity, or determine if gravity has any influence at all.
If the proposed experiment is both approved and successful, it will constitute the next step in the remarkable series of recent quantum entanglement experiments. Preserving present trends will, at the very least, lead to the development of more complex quantum networks and quantum computing systems in the coming years. But taking cues from Planck’s exploration of black-body radiation and Maxwell’s investigation of electromagnetism, examining the unknown frequently leads to remarkable twists and turns along the road to understanding the nature of the physical world.
1. Chinese Physicists Smash Quantum Record (2008). Available at http://www.wired.com/wiredscience/2012/05/quantum-teleportation-distance/ (12 April 2013).
2. Ma, Xiao-Song, et al., Nature. 489, 269–273 (2012).
3. Moskowitz, Clara. Space Station May Test ‘Spooky’ Entanglement Over Largest Distance Yet (2103). Available at http://www.livescience.com/28553-quantum-entanglement-distance-test.html (12 April 2013).