Quantum physicists from the University of Innsbruck have achieved controlled entanglement of 14 quantum bits (qubits) and, thus, realized the largest quantum register that has ever been produced. Credit: University of Innsbruck |
The
term entanglement was introduced by the Austrian Nobel laureate Erwin
Schrödinger in 1935, and it describes a quantum mechanical phenomenon
that while it can clearly be demonstrated experimentally, is not
understood completely. Entangled particles cannot be defined as single
particles with defined states but rather as a whole system. By
entangling single quantum bits, a quantum computer will solve problems
considerably faster than conventional computers.
“It
becomes even more difficult to understand entanglement when there are
more than two particles involved,” says Thomas Monz, junior scientist in
the research group led by Rainer Blatt at the Institute for
Experimental Physics at the University of Innsbruck.
“And now our experiment with many particles provides us with new insights into this phenomenon,” adds Blatt.
World record: 14 quantum bits
Since
2005 the research team of Rainer Blatt has held the record for the
number of entangled quantum bits realized experimentally. To date,
nobody else has been able to achieve controlled entanglement of eight
particles, which represents one quantum byte. Now the Innsbruck
scientists have almost doubled this record. They confined 14 calcium
atoms in an ion trap, which, similar to a quantum computer, they then
manipulated with laser light. The internal states of each atom formed
single qubits and a quantum register of 14 qubits was produced. This
register represents the core of a future quantum computer. In addition,
the physicists of the University of Innsbruck have found out that the
decay rate of the atoms is not linear, as usually expected, but is
proportional to the square of the number of the qubits. When several
particles are entangled, the sensitivity of the system increases
significantly.
“This process is known as superdecoherence and has rarely been observed in quantum processing,” explains Thomas Monz.
It
is not only of importance for building quantum computers but also for
the construction of precise atomic clocks or carrying out quantum
simulations.
Increasing the number of entangled particles
By now the Innsbruck experimental physicists have succeeded in confining up to 64 particles in an ion trap.
“We
are not able to entangle this high number of ions yet,” says Thomas
Monz. “However, our current findings provide us with a better
understanding about the behavior of many entangled particles.”
And this knowledge may soon enable them to entangle even more atoms.
Some weeks ago Rainer Blatt’s research group reported on another important finding in this context in the scientific journal Nature:
They showed that ions might be entangled by electromagnetic coupling.
This enables the scientists to link many little quantum registers
efficiently on a micro chip.
“All
these findings are important steps to make quantum technologies
suitable for practical information processing,” Rainer Blatt is
convinced.
The
results of this work are published in the scientific journal Physical
Review Letters. The Innsbruck researchers are supported by the Austrian
Science Fund (FWF), the European Commission and the Federation of
Austrian Industries Tyrol.
