Quantum Physics & the Quest for the Perfect Internet

Communication on the Internet takes place via tiny pulses of light that are continually becoming weaker as the network handles the increasing flow of information. Eventually we will reach the limit for how weak the pulses can be and still be able to function as information carriers. But a Quantum Internet, where information is encoded in quantum properties of tiny pulses, would open up a whole new world of online possibilities—a system without many of the limits faced by the current system.

A network of quantum computers communicating with each other reliably over macroscopic distances would be able to perform both quantum and classical computations in much more secure fashion.

But in order for a quantum-based network to function physicists must first create new ways to detect and store light information in atoms, a so-called quantum memory. And that is exactly what researchers have been attempting over the past several years.

Recently physicists at the University of Michigan have coaxed two separate atoms to communicate with a sort of quantum intuition that Albert Einstein referred to as "spooky." In doing so, the researchers have made another advancement toward super-fast quantum computing and a building block for a quantum Internet.

Scientists used light to establish what's called "entanglement" between two atoms, which were trapped a meter apart in separate enclosures (think of entangling like controlling the outcome of one coin flip with the outcome of a separate coin flip).

"This linkage between remote atoms could be the fundamental piece of a radically new quantum computer architecture," said principal investigator Christopher Monroe. "Now that the technique has been demonstrated, it should be possible to scale it up to networks of many interconnected components that will eventually be necessary for quantum information processing."

David Moehring, the lead author of the paper who did this research as a U-M graduate student, adds that the most important feature of this experiment is the distance between the two atoms.

"The separation of the qubits in our entangled state is the most important feature," Moehring said. "Localized entanglement has been performed in ion trap qubits in the past, but if one desires to build a scalable quantum computer network (or a quantum internet), the creation of entanglement schemes between remotely entangled qubit memories is necessary."

In this experiment, the researchers used two atoms to function as qubits, or quantum bits, storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process.

The atoms, which were actually ions of the rare-earth element ytterbium, are capable of emitting two different types of photon of different wavelengths. The type of photon released by each atom indicates the particular state of the atom. Because of this, each photon was entangled with its atom.

By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fiber optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Monroe says the fiber optic thread was necessary to establish entanglement of the atoms, but then the fiber could be severed and the two atoms would remain entangled, even if one were "(carefully) taken to Jupiter."

Each qubit's information is like a single bit of information in a conventional computer, which is represented as a 0 or a 1. Things get weird on the quantum scale, though, and a qubit can be a 0, a 1, or both at the same time, Monroe says. Scientists call this phenomenon "superposition." Even weirder, scientists can't directly observe superposition, because the act of measuring the qubit affects it and forces it to become either a 0 or a 1.

Entangled particles can default to the same position once measured, for example always ending in 0,0 or 1,1.

"When entangled objects are measured, they always result in some sort of correlation, like always getting two coins to come up the same, even though they may be very far apart," Monroe said. "Einstein called this 'spooky action-at-a-distance,' and it was the basis for his nonbelief in quantum mechanics. But entanglement exists, and although very difficult to control, it is actually the basis for quantum computers."

Scientists could set the position of one qubit and know that its entangled mate will follow suit.

Entanglement provides extra wiring between quantum circuits, Monroe says. And it allows quantum computers to perform tasks impossible with conventional computers. Quantum computers could transmit provably secure encrypted data, for example. And they could factor numbers incredibly faster than today's machines, making most current encryption technology obsolete.

Posted by Rebecca Sato

* Portions of this post were adapted from a University of Michigan news release

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Related Links:

http://w2c.blogspot.com/2004/09/quantum-internet-search.html\
http://chronos-st.blogspot.com/
http://www.physorg.com/news108217803.html

Comments

[Jeff Paul Scam]

Well the fiber optic thread was necessary to establish entanglement of the atoms but now its being used for many purposes

[Narendra Nath]

It gives a reasonably good idea about Quantum computer possibilities. However, it is not clear how a large system of two-atoms configuration may be controlled to act as a large computer. The entangling aspect permits cryptic information from leaking while being transmitted needs to be better explained. Hopefully, the same is possible only in a larger description than provided here.
It may also be nice if the practical difficulties being encountered presently in generating a larger memory system are also outlined so that innovative thinking may become possible by a larger group of persons the world over.

[Narendra Nath]

It is a nice basic information. It is not clear how the two atoms of a quantum switch are to kept apart at a certain distance from one another and how such a configuration may be accomplished for a very large system of such atoms. The benefit of entanglement lie perhaps in sending out encryptic data safely to a distant location. What else are the benefits of the third state in the ;ogic switch.