Like any other manufactured chip, the wiring connecting the quantum dots is locked in place during chip manufacturing. Since different error correction schemes require different connections between qubits, this forces us to commit to specific error correction schemes during manufacturing. If a better scheme is developed after a chip is manufactured, it is probably not possible to switch to it. Less complex algorithms can benefit from simpler error correction schemes that require less overhead, but we wouldn’t be able to change the schemes with these chips.
So quantum dots seem to typify the trade-offs we face with quantum computing: it’s easier for us to create lots of quantum dots and all the hardware needed to manipulate them, but it’s apparently not possible for them to benefit from the flexibility that other types of qubits have.
The goal of this new article is to show that this is not necessarily true.
Mobile points
The new work was carried out in collaboration between researchers from Delft University of Technology and the startup QuTech. The team built a chip that had a linear array of quantum dots and started with single-electron spins at each end. Then, with the appropriate electrical signals, they were able to shift the spins toward the net point, gradually bringing them closer together. (And, gradually, here we mean a fraction of a second, but relatively slow compared to basic switching in electronics.)
Once the electrons were close enough, the spin wavefunctions overlapped, allowing the researchers to make two-qubit gates on them. These manipulations can be used to entangle the two spins and are therefore necessary to construct error-correcting logical qubits; These gates are also necessary to perform calculations.
The researchers then confirmed that they could move the electrons back to their initial positions, after which measurements confirmed that their spins were entangled. And since quantum teleportation also requires a two-qubit gate, they showed that the process could be used for teleportation. Teleportation can improve the type of mobility provided by moving qubits, as it can be used to move states after the qubits have spread widely apart.
