A quantum computer could be one step closer as scientists at Oxford University have generated billions of quantum bits in silicon.
By creating 10 billions of pairs of bits simultaneously, the researchers hope to be able to link them together, and create a massive quantum computing device. Previous efforts have involved creating small numbers of bits and adding more one pair at a time, but that is difficult to do.
Using silicon was also an important achievement because it is used in computing technology today and doping silicon with other elements is a well-understood process.
The quantum bits were made of phosphorus atoms, scattered ijn a block of ultra-pure silicon. Only one of every 100 million atoms was an atom of phosphorus. (A cubic centimeter of silicon contains about a billion trillion atoms, or 1022, so there were plenty of phosphorus atoms).
Quantum computing would allow calculations to be done orders of magnitude faster than current computers. They would be much better at problems that require searching through large numbers of data points or combinations, and doing complicated simulations that require many variables.
It's a bit like the process in your brain, said Stephanie Simmons, a physicist at Oxford University's Department of Materials and the lead author of the study. When I say the word 'bear' you don't go through every animal you have ever encountered, it just resonates. While the human brain isn't a quantum system, it shows how researchers hope that quantum computers will be able to approach complicated problems.
The reason is that ordinary computer the circuits, each of which represents a bit, are either on or off. A quantum computer has bits also, but they can be in both states at the same time. In quantum mechanics, particles don't have a definite state until they are observed. Quantum bits can be strung together by 'entangling' the particles used. When particles are entangled, their state depends on one another, a condition called correlation. It is that correlation that allows the fast calculations because if you know something about one entangled particle you know the same thing about the other. The entanglement works no matter how far away the two are.
The Oxford team used electrons surrounding the atomic nuclei of phosphorus, with the spin of each electron and nucleus corresponding to an on or off state (1 or 0) one would find in an ordinary computer. (Spins are called up or down). Each atom made up a pair of quantum bits, or qubits. The team chose phosphorus because each atom has a single electron in its outer shell, making them behave like tiny magnets. That allows the manipulation of the spin with magnetic resonance.
The next step was to entangle the spins of the nuclei and electrons. Firing a high-frequency radio pulse at the doped silicon did that, and 'initialized' the system, said Simmons. That left the pairs of qubits in a superposed state -the spins in each atom were all aligned, but whether they were up or down had to be determined by measuring them. Until they are measured, the qubit pairs were in both states at once.
After that, the group wants to entangle all of the 10 billion pairs of qubits with each other. If millions can be entangled, then one can make a powerful quantum computer.
There are still obstacles. The silicon used was a very pure isotope of silicon, called silicon-28. About 5 percent of silicon in nature is silicon-29, which disrupts the kind of quantum system the Oxford team was building. The whole setup also has to be run at extremely low temperatures, approaching -420 degrees Fahrenheit (-253 C), cold enough to make most gases in the air solid.