R&D INSIGHT News from the world of Research and Development with Harry O’Neill
Diamonds pave the way for quantum internet
The mighty silicon chip is ubiquitous in the 21st century, and the internet, which is equally pervasive in our everyday lives, is totally reliant on it.
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ew studies exploring the possibilities of quantum computing suggest that in the future it may be not be silicon, but diamonds, that hold the key to the web.
Physicists from the Delft University of
Technology in the Netherlands, have entangled information kept in pieces of diamond three metres apart, so that measuring the state of one quantum bit, or qubit, instantly fixes the state of the other, a feat which is necessary for exchanging quantum information over large distances. Quantum entanglement remains a very
mysterious phenomenon. Quantum particles have the capability of interacting with each other, seemingly instantaneously, over any distance, with Chinese physicists recently having clocked the speed as ‘at least 10,000 times faster than the speed of light.’ Despite this not making much sense at all to the casual follower of physics, it is one of the characteristics that make quantum devices so promising.
Qubits are similar to the bits used in present-
day computers, but can exist in a superposition of states, being both a ‘0’ and a ‘1’ at the same time. By linking these qubits, calculations which would have otherwise been impossible could theoretically be done very quickly. It could also allow for super-secure communication; an almost unbreakable encryption key could be formed if the sender and the receiver of a message both possess one part of two pairs of entangled qubits. Although entangling qubits at a distance
has been achieved before, the use of diamonds chips is thought to be a better system for scaling up, which has put it in pole-position for use in quantum networks. Qubits in diamonds are dependent on imperfections in the carbon lattice; when nitrogen atoms substitute for carbon atoms and appear next to gaps or vacancies in the structure, a qubit can be created based on the spin state of electrons held in the gap. Entangling qubits in separate diamond
pieces involves using lasers at a temperature of 10 kelvin, and the process remains quite
inefficient, with entanglement only being achieved once in every ten million attempts (this sounds a lot, but equates to around once every ten minutes). One important goal in the field is to provide
the basis for so-called quantum repeaters, which would make long-distance quantum communications possible. Photon-based entanglement fades after a few hundred kilometers due to light absorption in fibre- optic cables, and boosting the signal destroys the entanglement. But entangling chains of quantum repeaters
could link qubits over
longer distances. Although ion and atom systems are more
advanced than diamond in terms of linking close qubits for quantum computing, diamond has distinct advantages for linking remote processors in networks.. Unlike ions trapped in high vacuum, qubits in diamond can be maintained at room temperature, because the material’s surrounding carbon lattice shields them so well from stray magnetic fields or vibrations that might upset their superposition.
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