Researchers from Vandersypen’s lab at QuTech, a collaboration between Delft University of Technology (TU Delft) and the Netherlands Organization for Applied Scientific Research (TNO) that was founded in 2014, have published a paper in Nature Communications, Electron cascade for distant spin readout, that has come up with a new approach for reading qubits. This discovery, excitingly for the quantum computing (QC) community, may go some way in assisting the development of bigger and much more efficient quantum computer systems.
Credit for the research also goes to the Dutch Research Council (NWO), and the Swiss National Science Foundation, which partly funded it.
“Our new readout method is based on a phenomenon that all of us know from our childhood: toppling dominoes. A first transition triggers a second transition, a second transition triggers a third transition, and so on — much like dominoes toppling over in a chain reaction,” said Sjaak van Diepen, lead author of the paper and a Ph.D. researcher at QuTech.
The Vandersypen’s group, which van Diepen is a part of, wants to build a quantum computer based on spin qubits in quantum dot arrays. These quantum dots are ‘tiny islands’, according to Qutech, “that can each confine one or multiple electrons and are tunnel coupled to their neighbours.”
Qubits are produced off the spin of electrons, and the ‘spin qubits’ — as they are called — in quantum dots are ‘read out via a very sensitive detector that measures the charge in its environment’.
On this phenomenon, Van Diepen said: “Charge sensors work well, but only locally: they need to be in close proximity to the charge they measure. Scaling up the current approach towards a large number of interconnected qubits will therefore limit qubit connectivity, because we would need to place sensors close to all qubits.”
The readout scheme guarantees spin qubits at a great distance from the charge sensor will still be read out with a high level of accuracy.
Postdoctoral researcher and second author of the paper, Tzu-Kan Hsiao said: “Our readout method is based on the fact that charges interact with one another. Therefore, a first charge transition can trigger other charge transitions — forming a cascade of transitions.”
QuTech — along with other initiatives in Europe and beyond — are proving that quantum information science (QIS) has a future. And with more research, more money invested from different funding sources, this decade should see a rise in its potential and actual implementation as a technology worth investing in.