Spooky Diamonds a Step Towards Quantum Computing

04 December 2011
Posted by Diana O'Carroll.

This week, researchers from the UK, Canada and Singapore have accomplished quantum entanglement on the macro scale, entangling two millimeter-sized diamonds.

Typically we think of objects moving and interacting according to classical mechanics - i.e. Newton's Second Law - you apply a force to one object and it will cause it to accelerate in a particular direction. But in quantum mechanics there are extra complications, such as entanglement, where an action performed on one object will affect another - even if they are at a distance: something described by Einstein as 'spooky'.

diamonds entangledStudying these quantum effects on objects any larger than an atomic particle is tough because there is so much environmental noise. Once in the 'macroscopic' scale, there are too many extra factors which are difficult to eliminate. The usual approach is to lower the temperature and so reduce thermal noise. Publishing in the journal Science, a team led by Ian Walmsley of Oxford University, took millimetre-wide pieces of diamond and tried to look at them in a more typical environment with an ambient temperature. To get around the problem of other noisy interactions that could interfere with results, they shortened the experiment to a matter of femtoseconds, and they did this using laser pulses.

Next came the entanglement, which they achieved by setting up a beam-splitter and detectors. They fired two laser pulses at each diamond, 350 femtoseconds apart. The second pulse picked up the energy the first pulse left behind before reaching the detector as an especially-energetic photon. If the system were classical, the second photon should pick up extra energy only half the time - only if it happened to hit the diamond where the energy was deposited in the first place.

But in 200 trillion trials, the team found that the second photon picked up extra energy every time. That means the energy was not contained within each diamond, but that they shared the same state as if they were one system. It had already been predicted that this could be done with larger objects at ambient temperature, but actually doing it is something else altogether so - although brief - this may be a step towards some real-world quantum computing, where entanglement allows you to store far more complex information than binary digits.

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