According to the popular science mag Nature, the work is part of the quest for a functioning quantum computer which can use potentially dead or alive cats to do the adding up – unless we have got it wrong, which we might have.
The Nature paper, whose lead author is Magdalen College Junior Research Fellow Chris Ballance, demonstrates the all-important quantum ‘logic gate’ between two different species of ion – in this case two isotopes of calcium, the abundant isotope calcium-40 and the rare isotope calcium-43.
Calcium-43 makes the best single-qubit memory ever demonstrated, across all physical systems, while the calcium-40 ion has a simpler structure which is well-suited for use as an “interface qubit”.
The logic gate, which was first demonstrated for same-species ions at NIST Boulder (USA) in 2003, allows quantum information to be transferred from one qubit to another; in the present work, the qubits reside in the two different isotopes, stored in the same ion trap. The Oxford work was the first to demonstrate that this type of logic gate is possible with the demanding precision necessary to build a quantum computer.
In a piece of “spin-off science” from this technological achievement, we were able to perform a “Bell test”, by first using the high-precision logic gate to generate an entangled state of the two different-species ions, then manipulating and measuring them independently.
This was the first time such a test had been performed on two different type of atom separated by the atomic size.