A Major Leap Toward Global Quantum Internet

Staff posted 2017-09-18

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.)

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.