3 papers
quant-ph2025
Are controlled unitaries helpful?
Ewin Tang, John Wright
Many quantum algorithms, to compute some property of a unitary , require access not just to , but to , the unitary with a control qubit. We show that having access to $cU…
quant-ph2025
Amplitude amplification and estimation require inverses
Ewin Tang, John Wright
We prove that the generic quantum speedups for brute-force search and counting only hold when the process we apply them to can be efficiently inverted. The algorithms speeding up t…
quant-ph2025
Beating full state tomography for unentangled spectrum estimation
Angelos Pelecanos, Xinyu Tan, Ewin Tang +1
How many copies of a mixed state are needed to learn its spectrum? To date, the best known algorithms for spectrum estimation require as many copies…