Dec. 10, 2020 — In a blog post, Alex Hill, Senior Quantum Systems Engineer at Rigetti Computing, discussed the newly released Quil-T language extension to QUIL, Rigetti’s quantum instruction language, which aims to provide users more flexibility and control over their quantum algorithms. The blog post is included in part below.
Today’s quantum computers rely on careful measurements of hundreds of parameters that can vary over time. Take the humble X gate: to flip a qubit from the |0> to the |1> state, we have to know the qubit transition frequency and the optimal duration for a gate pulse (the “Rabi Flop”). If the pulse amplitude, time, or frequency are incorrect, then the X pulse will no longer exactly produce the intended gate, resulting in errors. We call the set of parameters that define all of the gates calibrations.
These calibrations are especially important for superconducting qubit architectures, as the physics of transmon qubits is very rich and can open a number of ways of performing the same gate. In the case of the X pulse, there are a number of pulse shapes (Flat Pulses, Gaussian Pulses, etc.) that more or less accomplish the same task; however, the usefulness of each of these pulse shapes depends on the pulse’s ability to minimize a wide variety of errors, for example, accidental transitions to the transmon’s |2> state, also called “leakage.” Clever design of pulse shaping can dramatically improve the error rate of both single-qubit and two-qubit quantum gates. Until now, these manipulations were hidden from view.
Today we’re releasing Quil-T, making gate definitions and pulse parameters completely editable across the entire Rigetti Aspen-8 processor. This gives Rigetti QCS users more fine-grained control over the parameters used to enact every gate operation, unlocking the ability to experiment with optimal control, control precise pulse timing, and construct novel gate schemes that can dramatically reduce overall gate depth. In the coming months, pulse level control functionality leveraging Quil-T will be available to more users through Amazon Braket.
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Source: Rigetti Computing
