Spooky interaction: quantum computing will take advantage of the entangled relationship between pairs of particles.
Credit: iStockphoto
Another physical architecture being investigated for quantum information processing are neutral atoms. Scientists from the U.S. National Institute of Standards, in Gaithersburg, Maryland, led by Nobel laureate William Phillips, have developed a way to separate atoms in a supercool state and trap them in a lattice of lasers.
Most of the atoms in the laser energy traps are linked with a partner in the opposite quantum state – with an electron spin up or down. This is the first time scientists have been able to pair up atoms in this way (see, New bits for qubits, Cosmos Online).
Flipping magnetic
The research, published in Nature in July 2007, is one step closer to making pairs of atoms capable of transferring quantum information. The next step is to scale up the process to work on arrays of atoms. Getting an array of atoms to act together in this way could create logical connections among data – the starting point for the logical processing necessary for computing to happen.
"Recent experiments have made progress towards this goal by demonstrating entanglement among an ensemble of atoms confined in an optical lattice," the researchers wrote. "Until now, however, there has been no demonstration of a key operation: controlled entanglement between atoms in isolated pairs... Our experiment realises proposals to use controlled exchange coupling in a system of neutral atoms."
Another study – conducted by researchers at institutions including John Hopkins University in Baltimore, Maryland, and published in U.S. journal Science in July – looked at how excitations in the magnetic 'flips' or fluctuations of the electron spins propagate across a ceramic substance.
While predominantly quantum mechanical, the research showed a previously unknown quantum 'order' that propagates along otherwise magnetically disordered material (low temperature ceramics).
The propagation of the quantum order, known as phase coherence, can be controlled by introducing defects into the ceramic substrate or by changing its temperature – controlling the decoherence of the quantum order.
"We had two objectives," said study co-author Gabriel Aeppli, of the London Centre for Nanotechnology in Britain, "The first was to show that we could actually image the quantum order, which is sometimes referred to as 'phase coherence'. The second aim was to manipulate the distance over which it can be maintained."
This distance – and how sensitive it is to changes in temperature or chemical impurities in the material – can be essential in determining whether a material will have real-life applications, he said.
Reaching the chequered flag
The key factor to which physical architecture wins the day is the ability to scale upwards — creating enough qubits to complete a logic process — and the ability to withstand the effects of decoherence.
Whatever wins the day, White is excited about the final potential of quantum computer.
"It will change everything, in the same way current computers have changed everything. Think of MP3 players and mobile communication. In the early stages of classical computing, no-one predicted any of that would happen," says White.
Whatever the future holds for quantum computers, it may well be 20 more years before we see their final potential. It seems even technology that works like magic takes time to realise.
Heather Catchpole is a Sydney-based science writer and regular contributor to Cosmos.
