Japanese RIKEN researchers are trying to adapt existing the silicon metal–oxide–semiconductor field-effect transistors (MOSFETs) to integrate qubits with current electronics, offering the potential for scaling up quantum devices and bringing quantum computing closer to becoming a reality.
Keiji Ono and colleagues from the RIKEN Center for Emergent Matter Science and the Toshiba Corporation in Japan, in collaboration with researchers from the United States, are investigating the properties of qubits produced by imperfections or defects in silicon MOSFETs. In particular, they are exploring their potential for developing quantum computing devices that are compatible with current manufacturing technologies.
“Companies like IBM and Google are developing quantum computers that use superconductors,” explains Ono. “In contrast, we are attempting to develop a quantum computer based on the silicon manufacturing techniques currently used to make computers and smart phones. The advantage of this approach is that it can leverage existing industrial knowledge and technology.”
After cooling a silicon MOSFET to 1.6 kelvin (−271.6 degrees Celsius), the researchers measured its electrical properties while applying a magnetic field and a microwave field. They found that when the silicon MOSFET was neither fully turned on nor off, a pair of defects in the silicon MOSFET formed two quantum dots in close vicinity to each other. This ‘double quantum dot’ generated qubits from the spin of electrons in the dots. It also produced quantum effects that can be used to control these qubits.
These observations are an important step toward controlling the quantum state of qubits in silicon MOSFETs and could pave the way for coupling qubits and making quantum devices using existing manufacturing techniques.
The researchers intend to raise the temperature at which the phenomena occur. “The work was carried out at temperatures an order of magnitude higher than previously reported,” says Ono. “So one important direction for our future research will be to achieve the same outcomes at even higher temperatures, of say 10 or 100 kelvin, or even at room temperature.”
We study hole spin resonance in a p-channel silicon metal-oxide-semiconductor field-effect transistor. In the subthreshold region, the measured source-drain current reveals a double dot in the channel. The observed spin resonance spectra agree with a model of strongly coupled two-spin states in the presence of a spin-orbit-induced anticrossing. Detailed spectroscopy at the anticrossing shows a suppressed spin resonance signal due to spin-orbit-induced quantum state mixing. This suppression is also observed for multiphoton spin resonances. Our experimental observations agree with theoretical calculations.