# Measurements on the Transmon Qubit

What is the point in running a quantum algorithm if you do not know the outcome? This video will be the first of three on how we can control superconducting - or transmon - qubits. Niels Butink will start explaining the way we read out the state of the qubit, which we do using a *readout resonator*. While doing this, he introduces an important concept, the *readout fidelity* of the measurement.

After single-qubit readout, Niels briefly touches upon how current state-of-the-art quantum processors measure multiple qubits at the same time. We will see that we need to make smart use of multiplexed signals. Letâ€™s get started!

## Prerequisite knowledge

## Further thinking

We have seen that in order to measure one qubit, a resonator coupled to it is used. When having multiple qubits, resonators with different resonance frequencies are needed. Can you identify each qubit and its resonator in the circuit shown during the video? We see in the picture there are more resonators than qubits, what do you think is the purpose of these?

## Further reading

In the video, Niels advises several articles for further reading. You can also first watch the entire series on transmon qubits (6 videos in total) and come back to this.

**Advanced pulse shaping**

- Rapid Driven Reset of a Qubit Readout Resonator
- Research by the DiCarlo group itself with Niels as the main author.

Active resonator reset in the nonlinear dispersive regime of circuit QED

**Benchmarking and improving superconducting amplifiers**

- Although the paper is not on arxiv, you can read the abstract on the Science website to get an idea.

A nearâ€“quantum-limited Josephson traveling-wave parametric amplifier - Research by the DiCarlo group itself with Niels as the main author.

General method for extracting the quantum efficiency of dispersive qubit readout in circuit QED

**Advanced readout topologies**

- Fast Scalable State Measurement with Superconducting Qubits
- Rapid high-fidelity multiplexed readout of superconducting qubits