Austrian and Chinese
scientists have succeeded in teleporting three-dimensional quantum states for
the first time. High-dimensional teleportation could play an important role in
future quantum computers.
Researchers from the
Austrian Academy of Sciences and the University of Vienna have experimentally
demonstrated what was previously only a theoretical possibility. Together with
quantum physicists from the University of Science and Technology of China, they
have succeeded in teleporting complex high-dimensional quantum states. The
research teams report this international first in the journal Physical
Review Letters.
In their study, the
researchers teleported the quantum
state of one photon (light particle) to another distant one.
Previously, only two-level states ("qubits") had been transmitted,
i.e., information with values "0" or "1". However, the
scientists succeeded in teleporting a three-level state, a so-called
"qutrit". In quantum
physics, unlike in classical computer science, "0" and
"1" are not an 'either/or' – both simultaneously, or anything in
between, is also possible. The Austrian-Chinese team has now demonstrated this
in practice with a third possibility "2".
Novel experimental method
It has been known since the
1990s that multidimensional quantum teleportation is theoretically possible.
However: "First, we had to design an experimental method for implementing
high-dimensional teleportation, as well as to develop the necessary
technology", says Manuel Erhard from the Vienna Institute for Quantum
Optics and Quantum Information of the Austrian Academy of Sciences.
The quantum state to be teleported
is encoded in the possible paths a photon can take. One can picture these paths
as three optical fibers. Most interestingly, in quantum physics a single photon
can also be located in all three optical fibers at the same time. To teleport
this three-dimensional quantum state, the researchers used a new experimental
method. The core of quantum teleportation is the so-called Bell measurement. It
is based on a multiport beam splitter, which directs photons through several
inputs and outputs and connects all optical fibers together. In addition, the
scientists used auxiliary photons—these are also sent into the multiple beam
splitter and can interfere with the other photons.
Through clever selection of
certain interference patterns, the quantum information can be transferred to
another photon far from the input photon, without the two ever physically
interacting. The experimental concept is not limited to three dimensions, but
can in principle be extended to any number of dimensions, as Erhard emphasizes.
Higher information
capacities for quantum computers
With this, the international
research team has also made an important step towards practical applications
such as a future quantum internet, since high-dimensional quantum systems can
transport larger amounts of information than qubits. "This result could
help to connect quantum computers with information capacities beyond
qubits", says Anton Zeilinger, quantum physicist at the Austrian Academy
of Sciences and the University of Vienna, about the innovative potential of the
new method.
The participating Chinese
researchers also see great opportunities in multidimensional quantum
teleportation. "The basics for the next-generation quantum network systems
is built on our foundational research today", says Jian-Wei Pan from the
University of Science and Technology of China. Pan recently held a lecture in
Vienna at the invitation of the University of Vienna and the Academy.
In future work, the quantum physicists will
focus on how to extend the newly gained knowledge to enable teleportation of
the entire quantum state of a single photon or atom.
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