Ancilla Assisted Quantum Information Processing
PhD thesis — Indian Institute of Science Education and Research Pune, 2016. Full text: https://archive.org/details/arxiv-1601.00234
Arguments
Ancilla Assisted Quantum Information Processing
Quantum computers are only useful if you can verify what they're doing — one-shot state characterization attacks the calibration bottleneck behind qubit-scaling claims.
Extra "ancilla" qubits can be exploited to completely characterize a general quantum state — and even general quantum dynamics — in a single measurement (ancilla-assisted quantum state tomography), drastically reducing the number of independent measurements versus standard tomography; also enables the noninvasive quantum measurements needed for quantum-physics experiments. Demonstrated experimentally in nuclear magnetic resonance (NMR) systems.
Why it matters
Quantum computers are only useful if you can verify what they're doing — one-shot state characterization attacks the calibration bottleneck behind qubit-scaling claims.
Use when: Spare capacity is a tool — add well-placed auxiliary resources and a hard measurement problem collapses into one shot.