4 papers
Mixed state tomography reduces to pure state tomography
Angelos Pelecanos, Jack Spilecki, Ewin Tang +1
A longstanding belief in quantum tomography is that estimating a mixed state is far harder than estimating a pure state. This is borne out in the mathematics, where mixed state alg…
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…
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…
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…