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How do we measure superconducting transmon qubits?
The qubit is coupled to a resonator. The resonance frequency of the resonator depends on the qubit state.
All data obtained from the free ibmq_armonk quantum device using @qiskit.
Thread below for details! #quantumcomputing
The qubit is coupled to a resonator. The resonance frequency of the resonator depends on the qubit state.
All data obtained from the free ibmq_armonk quantum device using @qiskit.
Thread below for details! #quantumcomputing
On the top left, you see the quantum state that I am creating using @qiskit visualized on a Bloch sphere. On the top right, you see a frequency sweep of the resonator coupled to the qubit. The resonator operates near 6.993 GHz, but shifts slightly depending on the qubit state.
If we monitor the resonator by measuring the amplitude and phase of reflected microwaves from it, we can perform readout of the qubit state. These are shown in the bottom left. Typically, this is done by sitting at a frequency midway between the response of |0> and |1>.
Finally, by classifying the two blobs in the bottom left into 0 and 1, we can obtain the histogram on the bottom right, which is what typically gets reported when we run quantum circuits over the cloud.
You can do all of these experiments yourself using @qiskit pulse!
You can do all of these experiments yourself using @qiskit pulse!
If you are interested in learning more about this measurement scheme (called dispersive readout of qubit state using a resonator), you can read this paper https://www.nature.com/articles/s41534-016-0004-0
Inspired by the animations of @j_bertolotti and @InertialObservr
