6 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…
Formalizing CHSH Rigidity in Lean 4
Tianrun Zhao, Nengkun Yu
Violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality certifies genuine quantum correlations. In this work, we formalize in Lean 4 the rigidity theorem -- any strategy achi…
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…
Optimal lower bound for quantum channel tomography in away-from-boundary regime
Kean Chen, Zhicheng Zhang, Nengkun Yu
Consider quantum channels with input dimension , output dimension and Kraus rank at most . Any such channel must satisfy the constraint , and the parame…
Pauli Measurements Are Near-Optimal for Single-Qubit Tomography
Jayadev Acharya, Abhilash Dharmavarapu, Yuhan Liu +1
We provide the first non-trivial lower bounds for single-qubit tomography algorithms and show that at least copies are required…