Beam Me Up, Schrödinger: Bits of Quantum Light Teleported

Using a teleporter and a paradoxical cat, researchers have achieved the first-ever transfer of a particular complex set of quantum information from one point to another, opening the way for quantum communication networks.

The cat in the equation refers to "wave packets" of light representing the famous "thought experiment" known as Schrödinger’s cat. Schrödinger’s cat was a paradox proposed by early 20th century physicist Erwin Schrödinger to describe the situation in which normal, "classical" objects can exist in a quantum "superposition" — having two states at once.

The teleporter setup in the lab of professor Akira Furusawa at the University of Tokyo. (Images: Science/AAAS)

Professor Elanor Huntington in the School of Engineering and Information Technology at the University of New South Wales's (UNSW) Canberra campus at the Australian Defense Force Academy was part of a team led by University of Tokyo researchers.

"One of the limitations of high-speed quantum communication at present is that some detail is lost during the teleportation process. It’s the Star Trek equivalent of beaming the crew down to a planet and having their organs disappear or materialize in the wrong place. We’re talking about information, but the principle is the same – it allows us to guarantee the integrity of transmission.

Illustration representing teleportation of nonclassical wave packets.

"Just about any quantum technology relies on quantum teleportation. The value of this discovery is that it allows us, for the first time, to quickly and reliably move quantum information around. This information can be carried by light, and it’s a powerful way to represent and process information. Previous attempts to transmit were either very slow, or the information might be changed. This process means we will be able to move blocks of quantum information around within a computer or across a network, just as we do now with existing computer technologies.

"If we can do this, we can do just about any form of communication needed for any quantum technology," Huntington said.

A Schrödinger's cat state is a quantum superposition of two light waves. The two light waves are interpreted as, respectively, a living cat and a dead cat. Their quantum superposition hints of a "quantum" cat paradoxically alive and dead at the same time. (B) and (E) show the measured raw statistics of the light amplitude at the input and output of the experiment, respectively. (C) and (F) are the photon statistics of these input and output light states. (A) and (D) are numerical functions that behave like probability distributions and that completely define the statistical properties of the measured light amplitudes. They are reconstructed from the measurement results and are named Wigner's functions after their inventor. The two positive peaks seen in both figures represent the two light waves independently. The negative dip in the center is a sign of the interference caused by the quantum superposition of these two light waves put together. This negativity is a signature of the presence of a Schrodinger's cat state. The survival of the central negative dip in the output figure shows the success of quantum teleportation of Schrodinger's cat states.

The experiments were conducted on a machine known as "the teleporter" in the laboratory of professor Akira Furusawa at the University of Tokyo's department of applied physics.

Professor Huntington, who leads a research program for the Centre for Quantum Computation and Communication, developed the high-speed communication part of the teleporter at UNSW’s Canberra campus with PhD student James Webb.

For more information, visit: www.unsw.edu.au