# Spin qubits

Time for another type of qubits: spin qubits. Heavily based on the concept of transistors (the building block of classical computers), these qubits are very suitable for use in quantum circuits.

For these qubits, we need to trap single (!) electrons so that we can use its spin as the qubit. Wait... single electrons? Yes, and not only do we need to trap them, but we also need to know that we succeeded. How can we do this?

In this video, QuTech professor Lieven Vandersypen takes you through the basics of spin qubits. He first introduces the concepts of charging energy and Coulomb blockade, after which he explains how we can use it to form our qubit. Then Lieven explains charge sensing, yet another way to detect whether you have a single electron in your quantum dot. Finally, we take a look at scaling up our system, initially by looking at a system that consists of two quantum dots. Professor Vandersypen ends the video with a brief outlook on how spin qubits can ultimately be used in large-scale quantum integrated circuits.

## Prerequisite knowledge

- Quantum bits
- Electrochemical potentials (i.e., energy diagrams)
- (nice to have) Standard knowledge on transistors

## Further thinking

We have seen that to realize spin qubits it is important to understand how quantum dots work. Do you understand why using a quantum dot is crucial?

## Further reading

Take a look at this review paper discussing the field of spins in quantum dots.

- https://qutech.nl/wp-content/uploads/2020/03/2019_08_PhysicsToday_pt.3.4270.pdf (L. M. K. Vandersypen and M. A. Eriksson, Physics Today 72, 8, 38, 2019)
- https://arxiv.org/pdf/1204.5917.pdf (C. Kloeffel and D. Loss, 2012)

For more recent research, you might want to check out these papers:

- https://arxiv.org/abs/1904.11443 (Hendrickx et al., 2019)
- https://arxiv.org/abs/1910.05289 (Petit et al., 2019)

In the paper by Watson et al. (2018), they show the experimental realisation of two quantum algorithms with a two spin qubits quantum processor.

- https://arxiv.org/abs/1708.04214 (Watson et al., 2018)