Silicon quantum bits reach accuracy that is necessary for quantum computation

15 October 2014

Researchers of the university of New South Wales in Sydney, including post-doctoral researcher Menno Veldhorst who works under a Rubicon grant awarded by the NWO, have realised a quantum bit in silicon with record performances, setting a new benchmark for quantum dots.

One of the greatest scientific challenges in this century is the realisation of a quantum computer. The many prospects of such a computer initiated research over several disciplines using different approaches to create the building block of a quantum computer: the quantum bit (qubit). Qubits have been realised for example using superconductors, by trapping ions and using single atoms. The researchers at UNSW demonstrate now that a qubit can also be realized using the same techniques and materials as that used to fabricate a billion transistors on a single chip.  The quantum device is fabricated by patterning nanostructures of aluminum on silicon. Using voltages applied on the aluminum layers, similar to the operation of a transistor, a quantum dot is realized that localizes a single electron. The spin of this electron represents the state of the qubit and using microwave pulses the researchers succeeded to direct the spin to any possible direction. While this has been done before, and exciting results are even mentioned previously in the press release of August 2014 [Long-lived qubits in silicon], all these previous quantum bits operated in the presence of other spins that are bound to the atom nuclei of the semiconductor. These nuclear spins limited the operation accuracy and the associated life-time of the qubit.

To operate a quantum computer successfully, it is crucial that the qubits can be operated with errors below 1%, such that so-called quantum error correction can be applied. Silicon is an exceptional material, as it can be purified to 28Si, leaving virtually no nuclear spins. The researchers demonstrate that after the isotopic purification, the qubit can be operated for almost 30 milliseconds, more than two orders longer than any previously realised quantum dot qubit. Consequently, the error-rate of the qubit dropped to a value of only 0.4%. The demonstration of qubits that allow error correction using conventional approaches is an important step towards the realm of quantum computation.

About Rubicon

Rubicon aims to encourage talented researchers at Dutch universities and research institutes run by KNAW and NWO to dedicate themselves to a career in postdoctoral research.

About NWO

With a budget of 625 million euros per year, the Netherlands Organisation for Scientific Research (NWO) is one of the biggest funding bodies for scientific research in the Netherlands. NWO promotes quality and innovation in science by selecting and funding the best research. It manages research institutes of national and international importance, contributes to strategic programming of scientific research in the Netherlands and brings science and society closer together. Research proposals are reviewed and selected by researchers of international repute. More than 5000 scientists can carry out research thanks to funding from NWO.

Further information

Source: NWO