11 papers
Quantum channel tomography: optimal bounds and a Heisenberg-to-classical phase transition
Kean Chen, Filippo Girardi, Aadil Oufkir +2
How many black-box queries to a quantum channel are needed to learn its full classical description? This question lies at the heart of quantum channel tomography (also known as qua…
Quantum Multi-Level Estimation of Functionals of Discrete Distributions
Kean Chen, Minbo Gao, Tongyang Li +2
We propose a quantum multi-level estimation framework for a functional of a discrete distribution . We partition the values into logarith…
Strict Hierarchy for Quantum Channel Certification to Unitary
Kean Chen, Qisheng Wang, Zhicheng Zhang
We consider the problem of quantum channel certification to unitary, where one is given access to an unknown -dimensional channel , and wants to test whether $\math…
Trace Estimation of Quantum State Powers: Sample Complexity and Computational Hardness
Kean Chen, Yupan Liu, Qisheng Wang
As often emerges in various basic quantum properties such as Rényi and Tsallis entropies, the trace of quantum state powers has attracted a lot of attention. The…
Approximation does not help in quantum unitary time-reversal
Kean Chen, Nengkun Yu, Zhicheng Zhang
Access to the time-reverse of an unknown quantum unitary process is widely assumed in quantum learning, metrology, and many-body physics. The fundamental task of unita…
Quantum channel tomography and estimation by local test
Kean Chen, Nengkun Yu, Zhicheng Zhang
We study the estimation of an unknown quantum channel with input dimension , output dimension and Kraus rank at most . We establish a connection between…