Cages, chains and defects
The research groups involved in the global race for the quantum computer have chosen various ways to achieve this goal. The ideas for the heart of such computers, the physical storage cells, are manifold: some experts rely on defects, which they specifically incorporate into thin diamond layers, or on exotic materials, which are actually insulators but conduct electricity on their surface. Other researchers hold a chain of ions in suspension in a vacuum between two electrodes. David DiVincenzo is concerned with quantum dots. These are semiconductor cages into which individual electrons are locked. Their angular momentum – the direction of their own rotation, so to speak – can store the value of the qubit. “The advantage is that there is already a lot of know-how about the manufacturing of these semiconductor structures: conventional chip production is also based on semiconductors.”
Companies like IBM and Google favour superconducting circuits. In their conductor loops, the current can circle in different directions, thus reflecting the value of the qubit: clockwise, anti-clockwise or any superposition of the two directions of rotation. The outward appearance of these machines is not quite reminiscent of computers as we know them today: only the huge, barrel-shaped cooling container is visible. Inside, it hides the actual measuring apparatus: a maze of wires and metal parts resembling an avant-garde chandelier.