Physicists establish 'spooky' quantum communication

September 5, 2007

Physicists at the University of Michigan have coaxed two separate atoms to communicate with a sort of quantum intuition that Albert Einstein called "spooky."

In doing so, the researchers have made an advance toward super-fast quantum computing. The research could also be 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).

A paper on the findings appears in the Sept. 6 edition of the journal Nature.

"This linkage between remote atoms could be the fundamental piece of a radically new quantum computer architecture," said Professor Christopher Monroe, the principal investigator who did this research while at U-M, but is now at the University of Maryland. "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, says the most important feature of this experiment is the distance between the two atoms. Moehring graduated and now has a position at the Max-Planck-Institute for Quantum Optics in Germany.

"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 either 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 (most encryption today is based on the inability for man or machine to factor large numbers efficiently).

Source: University of Michigan

Explore further: 'Topological' graphene nanoribbons trap electrons for new quantum materials

Related Stories

New study could hold key to hack-proof systems

July 17, 2018

Major data breaches have made worldwide headlines of late but an international consortium of scientists—including a professor from Heriot-Watt—have developed a new technique that could result in hack-proof systems.

Physicists demonstrate new method to make single photons

July 23, 2018

Scientists need individual photons for quantum cryptography and quantum computers. Leiden physicists have now experimentally demonstrated a new production method. Publication in Physical Review Letters on July 23rd.

The marriage of topology and magnetism in a Weyl system

August 6, 2018

Topology is a global aspect of materials, leading to fundamental new properties for compounds with large relativistic effects. The incorporation of heavy elements gives rise to non-trivial topological phases of matter, such ...

Quantum mechanics: entanglements in ultracold atomic clouds

June 27, 2018

A system's state is characterised as entangled or quantum correlated if two or more particles cannot be described as a combination of separate, independent states but only as a whole. Researchers at the Kirchhoff Institute ...

Recommended for you

Gravitational wave detectors to search for dark matter

August 16, 2018

Gravitational wave detectors might be able to detect much more than gravitational waves. According to a new study, they could also potentially detect dark matter, if dark matter is composed of a particular kind of particle ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.