Photograph of the quantum chip housing the 16 crossbar array of quantum dots, seamlessly integrated into a checkerboard pattern. Each quantum dot, like a pawn on a chessboard, is uniquely identifiable and controllable using a coordinate system of letters and numbers. Photo credit: Marieke de Lorijn for QuTech. Credit: Marieke de Lorijn for QuTech

A new approach to tackling quantum dots offers the prospect of increasing the number of qubits in quantum systems and represents a breakthrough for quantum computing.

Researchers have developed a way to handle many quantum dots with just a few control lines using a checkerboard-like method. This enabled the operation of the largest gate-defined quantum dot system ever built. Their result represents an important step in the development of scalable quantum systems for practical quantum technology.

Quantum dots can be used to hold qubits, the building blocks of a quantum computer. Currently, each qubit requires its own address line and dedicated control electronics. This is highly impractical and in stark contrast to today’s computer technology where billions of transistors are handled with only a few thousand lines.

Addressing like a chessboard

Researchers in the QuTecha collaboration between Delft University of Technology (TU Delft) and TNO have developed a similar method for tackling quantum dots. Just as chess pieces’ positions are indicated using a combination of letters (A to H) and numbers (1 to 8), their quantum dots can be addressed using a combination of horizontal and vertical lines. Any point on a board can be defined and addressed using a specific combination of a letter and number. Their approach takes the state of the art to the next level and enables the operation of a system of 16 quantum dots in an array of 44.

Lead author Francesco Borsoi explains: This new way of approaching quantum dots is beneficial for reaching many qubits. If a single qubit is controlled and read using a single wire, millions of qubits will require millions of control lines. This approach doesn’t fit very well. However, if qubits could be controlled using our checkerboard system, millions of qubits could be addressed using just thousands of lines, corresponding to a ratio very similar to that of computer chips. This line reduction offers the possibility of increasing the number of qubits and represents a breakthrough for quantum computers, which will eventually require millions of qubits.