The Spooky World of Quantum Entanglement
The phenomenon that spooked Albert Einstein.
|Why can’t we be in two places simultaneously? Why can’t we communicate instantaneously? Better yet, why can’t we teleport ourselves to another location instantly?|
Actually subatomic particles can. Unfortunately, even though we are comprised of these very particles, big objects don’t follow the rules of quantum mechanics, which, at the subatomic level, makes possible such incredible feats. But the weird nature of quantum behavior explicit in the subatomic world is gradually encroaching our classical world. Researchers are in pursuit of applications that would assist us in overcoming space-time constraints and the laws of classical physics. Future generations might see teleportation and a universal quantum web as a normal aspect of their daily life.
The underlying phenomenon that enables the seemingly impossible, is quantum entanglement – the mysterious way by which two particles are connected instantaneously irrespective of their spatial distance. Entanglement occurs when two particles (photons, atoms, electrons, etc.) become so deeply linked together that the changes that happen to one are instantly reflected on the other even if they are separated to the farthest corners of the universe. This means that any information imposed on one particle can be easily retrieved from the other without physically sending it across the distance that divides them. Not surprisingly, researchers and governments are frenetically chasing practical applications of entanglement, such as entanglement-assisted cryptography and teleportation.
A year ago, researchers led by Anton Zelinger at the University of Vienna in Austria set the record for transmitting entangled photons over a distance of 90 miles.The distance achieved in the experiment illustrates the possibility of quantum communication in space involving satellites. Their Space-QUEST (Quantum Entanglement for Space Experiments) proposal offers a step in that direction.
On Earth, which is less than 8,000 miles in diameter, we think our communications are instantaneous as signals travel at 186,000 miles per second, the speed of light. But consider the New Horizons spacecraft, which was launched in 2006 towards the boundary of our solar system to study Pluto. This spacecraft, cruising at thousands of miles per hour, will reach Pluto in 2015. At a distance of more than three billion miles, its communication with earth would take a few hours. If that is the timescale in our own backyard in the universe, imagine future missions to farther destinations. Perhaps future civilization will master the techniques of entanglement to communicate and transport instantaneously.
Entanglement defies some of our deepest perceptions about the nature of reality. It does not place a cap on speed, which Einstein’s special theory of relativity constrained to the speed of light. Instead, one particle (location) mysteriously shares the information with its entangled partner (another location) instantaneously. Information is not carried by electromagnetic waves at the speed of light, which is finite although it is very high. Instead, by observing one particle we instantly get the information about the other particle even if it is light years away. Until such observation (measurement) is made, no information exists – or, in the weird realm of quantum physics, all possible information exists.
Long accepted in microscopic systems, quantum entanglement has, more recently, been observed at the macroscopic level as well. In one recent study, John Martinis and his colleagues at the University of California used two superconductors to send streams of entangled electric currents. According to the laws of classical physics, the direction of the current should be completely independent of each other. But when Martinis and his team measured the direction of the current many times, they observed that when one current flowed clockwise the other flowed anticlockwise, demonstrating that both streams are linked to each other inexplicably. It was one of the most visible illustration of quantum entanglement in the classical world.
We presently have no explanation for such entanglement. In the orthodox version of quantum physics, objects do not have existence or any inherent properties and their existence become real only when minds interact with them through observation or measurements. Consequently, reality is created by interaction. Until that interaction, all possibilities are probable superposition of wave functions, and the wave functions collapse to create a measurable form of reality, which make other possible states disappear.
One of the leading figures of quantum physics, David Bohm, had a more deterministic approach, arguing that the quantum world can exist independently of the human mind: “In some sense man is a microcosm of the universe; therefore what man is a clue to the universe. We are enfolded in the universe. Indeed, the attempt to live according to the notion that the fragments are really separate is, in essence, what has led to the growing series of extremely urgent crises that are confronting us today.”
Many scientists believe that some hidden variables are behind the phenomena of entanglement. Einstein, who sought the ultimate truth through mathematical equations, ridiculed the concept of “the spooky action at a distance,” dismissively remarking, “I like to think that the moon is there even if I am not looking at it.” Yet, even he admitted to the evidence of entanglement, whose existence is established beyond any doubt through numerous experiments.
According to some cosmologists, the universe began as a quantum fluctuation in a limitless void. The universe was a huge quantum superposition of all possible states until the first primordial mind observed it, causing it to collapse into one reality, eliminating all other probable states. In one version of quantum mechanics, each action opens up another universe, thereby creating an infinite number of parallel universes. Some physicists extend this argument even further, arguing that the creation of our universe from a singularity demands that everything that was created later (stars, planets, plants, animals and humans) are entangled with each other as the super entanglement that existed in the beginning is not broken, but has only spread to a larger extent. This explanation is very encouraging for proponents of paranormal phenomena, such as telepathy, which most scientists dismiss, who claim that the cells of our brain are entangled with everything else in the universe, thereby making it possible to decode information received from any other object or part of the universe.
Whatever the explanation for the quantum entanglement phenomenon, it has exciting real life applications. One immediate area where entanglement can play a crucial role is in computing. Computer binary codes of “1” and “0” are used in information exchanges in the digital age, which provides opportunities for eavesdropping or hacking of information. However quantum entanglement provides a better encryption tool using the properties of photons, such as spin. The traditional “bit” is replaced by “qubit” (quantum bits) to represent quantum information. If an attempt is made to intercept a photon-based message, the spin changes – signaling a possible compromise in security. MagiQ Technologies Inc. of Cambridge, Mass., sells technology built on quantum cryptography to banks and corporations. The encryption refreshes its quantum keys as often as 100 times a second during a transmission, making it extremely hard to break.
However, even though quantum encryption is possible, presently quantum computing is constrained by many practical challenges, including the breakdown of the spooky relation in systems because of interaction with the external world. So widespread quantum computing is a long way off. Theoretically, quantum computers would be much superior to classical ones. As they can hold all available values in qubits, rather than classical bits, they can search the right information through huge database faster and much more efficiently.
If quantum entanglement’s promise for information exchange is exciting, the possibility of quantum teleportation is downright dizzying. As the famous science writer Arthur C. Clarke once observed, “Any sufficiently advanced technology is indistinguishable from magic.”
In quantum teleportation, properties like the spin of a particle or the polarization of a photon, are transferred from one place to another without traveling through a physical medium, making it instantaneous. In 1993 an international group of scientists, confirmed the practical possibility of quantum teleportation – an idea, which until then had been exploited mostly by science fiction writers. Since then entanglement assisted teleportation has been tried successfully by different groups of researchers. Much as a fax machine scans and sends information to another location, hypothetical teleportation machine would reproduce an exact copy rather than an approximate duplicate.
In quantum teleportation, no material is sent from one location to another. Instead, quantum entanglement is used to impose information onto a particle at one location and retrieved through a different particle, which is entangled with the first particle, at another location. When all the information about the first particle is obtained at the other location, what is transported is the first particle itself. Strangely enough, the original is destroyed in the process of quantum teleportation. This year a team of scientists from the Joint Quantum Institute (JQI) at the University of Maryland and the University of Michigan succeeded in teleporting a quantum state directly from one atom to another over a substantial distance getting a step closer to practical quantum teleportation.
“There’s a lot of engineering that has to be done,” said Christopher Monroe, the leading scientist of the team. “But if you’ve ever seen the first solid-state transistor in 1957, it looked like this. It looked like it came out of a physics lab.” The group reported that in their protocol, atom-to-atom teleported information can be recovered with perfect accuracy about 90 percent of the time – and that figure can be improved.
Researchers hope to achieve the teleportation of complex systems, such as a virus, in coming decades. Applying the process to larger objects, including people, is largely a scientific engineering problem, which “is likely to be solved in time,” according to Michio Kaku, author of the bestseller Physics of the Impossible. Teleporting humans would involve scanning all the information in trillions and trillions of atoms that make up the person and the technology to perform such a task does not exist at this time and may not be available for centuries to come.
Scientists cannot explain why entanglement is not visible outside their labs right presently. But future generations might communicate instantly across the universe and may appear and disappear at will, no doubt a magical phenomenon by today’s standards. When we do master quantum entanglement, we may well be led to the eternal truth advocated in ancient philosophies and religions -that we live in the cosmos and the cosmos lives in us, that the space and time that separate us are just creations of the mind. As the Buddhist Mahayana Sukta says: “All such notions as causation, succession, atoms, primary elements, that make up personality, personal soul, Supreme Spirit, Sovereign God, Creator, are all figments of the imagination and manifestations of mind.”