A Major Leap Toward Global Quantum Internet

Using an erbium-doped crystal, researchers prove quantum internet could connect to fiber optics.

Recently, a team of Australian researchers have discovered
that a particular rare earth crystal can store quantum information for longer
than one second. So, what?

Milos Rančić with the experimental setup used to investigate materials for a telecom-compatible quantum memory. (Image courtesy of Stuart Hay, ANU.)

Milos Rančić with the experimental setup used to investigate materials for a telecom-compatible quantum memory. (Image courtesy of Stuart Hay, ANU.)

Moore’s
law
is the observation that the number of transistors per square inch on an
integrated circuit has doubled every two years since their invention. The law
has held true for more than 50 years, but one day this rule is going to fail.
Eventually, we will reach a minimum size, under which there simply aren’t
enough atoms to build working semiconductors. Where are we supposed to go from
there?

The answer seems to be quantum computers. In a nutshell, in classical
computing, a bit shows the on/off state of a transistor. In quantum computing, Qubits
show the spin state of a particle. Because of the quantum effects subatomic
particles have on each other, the information storage potential of qubits is
exponentially greater than that of classical bits.

There are many technical challenges to building the first
quantum computer. David DiVincenzo, of IBM, listed the following requirements
for a practical quantum computer:

  • Scalable physically to increase the number of
    qubits 
  • Qubits that can be initialized to arbitrary
    values
  • Quantum gates that are faster than decoherence
    time
  • Universal gate set
  • Qubits that can be read easily

When these challenges are met, it will be possible to build
a quantum computer.

The researchers team, led by ANU professor Matthew Sellars,
are addressing that third challenge: decoherence time.

Coherence essentially refers to the stability of a
particle’s spin state. For qubits to be useful for storing data, they need to
be readable before their state changes. Prior to this crystal, quantum
information could only be stored for fractions of a second. Sellars and his
team have multiplied that by a factor of 10,000. In short, it’s quantum memory. 

Just as classical computers didn’t reach their full
potential until the advent of the Internet, Sellars believes that quantum
computers need to be interconnected to reach their full potential. This
discovery enables the sending of qubit data over a long range, potentially
around the globe.

Furthermore, the erbium-doped crystal developed by Sellars
and his team operates in the same 1550-nanometer band as today’s fiber-optic
telecom networks. This eliminates a complex conversion process and would enable
quantum computer systems to easily connect to existing fiber-optic systems.

The discovery also opens the door for other practical
devices, such as a quantum light source or photon emitter, or as an optical
link to connect quantum computers to a quantum internet.

The material’s versatility may make it possible to connect
the many types of quantum computers being developed at Google, IBM and other
facilities, including superconducting and silicon-based qubits.

The published work is accessible here through the journal Nature
Physics
. For more on quantum computing, click here.