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Can nuclear qubits points point the way?
A new technique lines up more nuclear spins than was previously possible.
Qubits might very well be the vehicle for the next revolution in computing. Silicon technology has made our computers faster and faster, but now it seems that we are reaching the limits of what is possible with ones and zeros. One of the answers could be the transition from the “good-old” bit to the flashy qubit.
The “qu” in qubit stands for quantum, and one way to realize such a qubit is to use the tiny magnetic fields (called spins) that are associated with the nucleus and the electrons of atoms. However, in order to build a “quantum computer” from these spin-qubits, scientists first need to learn how to effectively manipulate these spins.
A team of researchers from the USA and the UK recently added to the quantum-computing roadmap by developing a new technique that uses high magnetic fields and low temperatures to line up far more nuclear spins than has been possible so far.
The research team said the new technique will allow the initialization of the nuclear qubit in schemes to exploit N@C60 molecules as components of a quantum information processing device. The technique is outlined in a paper, “Efficient Dynamic Nuclear Polarization at High Magnetic Fields,” published in Physical Review Letters[1].
Dynamic nuclear polarization of N@C60 molecules (one is shown inset). The resonance on the left is due to the polarized nuclei, while the smaller one comes from the remaining unpolarized nuclei.
“We suggest a new technique for dynamic nuclear polarization that is more than twice as effective as previous versions,” said lead author Gavin Morley, who is currently on staff at the London Centre for Nanotechnology. “Our N@C60 fullerene molecules have a nitrogen atom in the very center with a nuclear spin and an electron spin. We want to use both spins to store quantum information as they can each point up or down. Then each molecule will be a quantum computer with two qubits.”
The researchers needed to have both of the spins in the molecule pointing up at the beginning of the quantum computation. They made the electron spin point up by using a strong magnetic field (8.6 tesla) and a low temperature (3 kelvin), but still the nuclear spin had about a 50-50 chance of pointing up or down.
“We used the fact that the electron was already pointing up to make the nuclear spin do the same,” said Morley. “This increased the number of useful molecules by over 1,000 times.”
This technique has drawn great interest from scientists working on nuclear magnetic resonance, because 1,000 times more useful molecules could greatly shorten the time it takes to perform an NMR experiment.
The co-authors on the paper are Johan van Tol from the National High Magnetic Field Lab in Florida and Arzhang Ardavan, Kyriakos Porfyrakis, Jinying Zhang, and G. Andrew D. Briggs, all of the University of Oxford.
[1] Gavin W. Morley, Johan van Tol, Arzhang Ardavan, Kyriakos Porfyrakis, Jinying Zhang, and G. Andrew D. Briggs, Physical Review Letters 98, 220501 (2007).
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