Making better quantum devices

(Nanowerk News) A UNSW-led collaboration found that removing random doping in quantum electronic devices greatly improves their reproducibility, a key requirement for future applications such as quantum information processing and spintronics (Letters of applied physics, “Improving the reproducibility of quantum devices with completely undoped architectures”). Left: wafer structures ?? undoped (top) and n-type doped (bottom). Right: completed device on undoped wafer and electron microscope image. (Image courtesy of the researchers)

The challenge of quantum reproducibility

The challenge in making quantum devices is that, until now, it has not been possible to make two quantum transistors that exhibit identical performance characteristics.

Although the devices have identical physical appearance, their electrical performance can vary greatly from one device to another. This makes it difficult to integrate multiple quantum components into a complete quantum circuit.

In the new study conducted by UNSW, the researchers show that the problem stems from the random spatial position of dopants in quantum devices.

The conventional approach to making semiconductors conduct electricity is to chemically dop it with another element. For example, a very small amount of phosphorus atoms added to silicon produces an excess of free electrons, allowing the flow of electric current

But in nanoscale quantum devices the random placement of these dopants means that no two devices with identical characteristics exist.

The UNSW-led team worked with collaborators at Cambridge to demonstrate that total dopant removal makes quantum devices significantly more reproducible. On the left, nine identical devices on a doped wafer exhibit different electronic behaviors, while on the right, nine non-doped devices are nearly indistinguishable. (Image courtesy of the researchers)

Lead author Ashwin Srinivasan commented: “The electrical gain of the undoped quantum contact transistors is up to three times more uniform for the new approach than conventional doped devices.”

Professor Hamilton, head of the Quantum Devices lab at UNSW, Sydney, said, “We suspected that removing the random doping would improve the reproducibility of the device, but the results were far better than we expected. Ashwin made nine. devices and all exhibited identical quantum properties and electrical performance – I had never seen anything like it before.

?? This work shows that quantum devices can be reproducibly produced.