2.10 - Eigenstates and Eigenphases of QPU Instructions

The lecture slides are available here Download here.

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In this lecture, we introduce the concept of phase estimation in quantum computing. Similar to amplitude amplification and the quantum Fourier transform, phase estimation reveals information from superpositions. Unlike these other techniques, it uncovers attributes of operations acting on a quantum processing unit (QPU) register rather than the register's state itself.

The lecture presents the notion of eigenstates, which are states unaffected by a specific QPU operation except for global phases, and eigenphases, representing the global phase acquired by these eigenstates.

These eigenstates and eigenphases are unique to each QPU operation, defining that operation.

Phase estimation enables the determination of eigenphases associated with the eigenstates, facilitating the return to a superposition of all eigenphases.