Two types of qubits

NARRATOR: For quantum computing to become a reality we need super-high accuracy quantum bits with very low error rates. Our two teams at UNSW, who work side by side, have created two types of quantum bit, the basic units of the quantum computer, and each of these has the fidelity, or an accuracy, of 99 per cent or better. This is a huge breakthrough for us.

ANDREW DZURAK, UNSW Australia, Director ANFF-NSW: The common theme is that we’ve both achieved this exquisite control of a single qubit, and we’ve done it with two different types of qubit—one which is a natural atom, made of phosphorus, and the other one is what we call an artificial atom. 

ASSOCIATE PROFESSOR ANDREA MORELLO, UNSW Australia, Head Quantum spin control group: My team has worked on the natural atom of phosphorus which actually contains two quantum bits, the electron and the nuclear spin, and on that one in particular we have achieved an incredible 99.99 per cent accuracy, which means an average of one error in every 10,000 quantum operations.

ANDREW DZURAK: In contrast, the artificial atom qubit is made with the same sorts of silicon transistors that are used in all of our smartphones and laptops. The super-high accuracy, or the fidelity, of all of our qubits is achieved by putting them inside a thin layer of very pure silicon known as silicon-28. 

ASSOCIATE PROFESSOR ANDREA MORELLO: Natural occurring silicon contains isotopes that produce magnetic noise and therefore disturb the operation of the qubit. But in these latest experiments we have removed these isotopes and therefore removed the source of noise.

ANDREW DZURAK: With the spin noise that occurs in natural silicon, it’s like a normal computer adding together 3 and 4 and coming up with 9 as an answer. Basically, it’s impossible for a practical quantum computer to work with such high levels of error.

ASSOCIATE PROFESSOR ANDREA MORELLO: With the nucleus of the phosphorus atom we have also established the new world record for how long a quantum state can be preserved in a solid state single quantum bit. We achieved 35 seconds, which is like an eternity in the quantum world. And this means we can do very complicated, extensive calculations on this quantum bit. We have succeeded in demonstrating two different ways to make very high accuracy quantum bits, and we think that in the future these two methods can be actually combined together in a single quantum computer that exploits the best of both methods.