arXiv subjects

Zhenhuan Liu

Publications and source records attributed to Zhenhuan Liu.

39 records · Page 3Linked to original sources

arXiv2022

Characterizing correlation within multipartite quantum systems via local randomized measurements

Given a quantum system on many qubits split into a few different parties, how many total correlations are there between these parties? Such a quantity, aimed to measure the deviation of the global quantum state from an uncorrelated state with the same local statistics, plays an important role in understanding multipartite correlations within complex networks of quantum states. Yet, the experimental access of this quantity remains challenging as it tends to be non-linear, and hence often requires tomography which becomes quickly intractable as dimensions of relevant quantum systems scale. Here, we introduce a much more experimentally accessible quantifier of total correlations, which can be estimated using only single-qubit measurements. It requires far fewer measurements than state tomography and obviates the need to coherently interfere multiple copies of a given state. Thus, we provide a tool for proving multipartite correlations that can be applied to near-term quantum devices.

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arXiv2020

Single-copies estimation of entanglement negativity

Entanglement plays a central role in quantum information processing, indicating the non-local correlation of quantum matters. However, few effective ways are known to detect the amount of entanglement of an unknown quantum state. In this work, we propose a scheme to estimate the entanglement negativity of any bi-partition of a composite system. The proposed scheme is based on the random unitary evolution and local measurements on the single-copy quantum states, which is more practical compared with former methods based on collective measurements on many copies of the identical state. Meanwhile, we generalize the scheme to quantify the total multi-partite correlation. We demonstrate the efficiency of the scheme with theoretical statistical analysis and numerical simulations. The proposed scheme is quite suitable for state-of-the-art quantum platforms, which can serve as not only a useful benchmarking tool to advance the quantum technology, but also a probe to study fundamental quantum physics, such as the entanglement dynamics.

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arXiv2020

Quantum gate verification and its application in property testing

To guarantee the normal functioning of quantum devices in different scenarios, appropriate benchmarking tool kits are quite significant. Inspired by the recent progress on quantum state verification, here we establish a general framework of verifying a target unitary gate. In both the non-adversarial and adversarial scenarios, we provide efficient methods to evaluate the performance of verification strategies for any qudit unitary gate. Furthermore, we figure out the optimal strategy and its realization with local operations. Specifically, for the commonly-used quantum gates like single qubit and qudit gates, multi-qubit Clifford gates, and multi-qubit Controlled-Z(X) gates, we provide efficient verification protocols. Besides, we discuss the application of gate verification for the detection of entanglement-preserving property of quantum channels and further quantify the robustness measure of them. We believe that the gate verification is a promising way to benchmark a large-scale quantum circuit as well as to test its property.

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