@article {3082, title = {Closing the Locality and Detection Loopholes in Multiparticle Entanglement Self-Testing}, journal = {Physical Review Letters}, volume = {128}, year = {2022}, month = {06/23/2022}, pages = {250401}, abstract = {

First proposed by Mayers and Yao, self-testing provides a certification method to infer the underlying physics of quantum experiments in a black-box scenario. Numerous demonstrations have been reported to self-test various types of entangled states. However, all the multiparticle self-testing experiments reported so far suffer from both detection and locality loopholes. Here, we report the first experimental realization of multiparticle entanglement self-testing closing the locality loophole in a photonic system, and the detection loophole in a superconducting system, respectively. We certify three-party and four-party GHZ states with at least 0.84 (1) and 0.86 (3) fidelities in a device-independent way. These results can be viewed as a meaningful advance in multiparticle loophole-free self-testing, and also significant progress on the foundations of quantum entanglement certification.

}, doi = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.250401}, url = {https://www.researchgate.net/profile/Dian-Wu/publication/361497881_Closing_the_Locality_and_Detection_Loopholes_in_Multiparticle_Entanglement_Self-Testing/links/62b55a8c1010dc02cc57530c/Closing-the-Locality-and-Detection-Loopholes-in-Multiparticle-Entangl}, author = {Dian Wu and Qi Zhao and Can Wang and Liang Huang and Yang-Fan Jiang and Bing Bai and You Zhou and Xue-Mei Gu and Feng-Ming Liu and Ying-Qiu Mao and Qi-Chao Sun and Ming-Cheng Chen and Jun Zhang and Cheng-Zhi Peng and Xiao-Bo Zhu and Qiang Zhang and Chao-Yang Lu and Jian-Wei Pan} } @article {2913, title = {Hamiltonian simulation with random inputs}, journal = {Phys. Rev. Lett. 129, 270502}, volume = {129}, year = {2022}, month = {12/30/2022}, abstract = {

The algorithmic error of digital quantum simulations is usually explored in terms of the spectral norm distance between the actual and ideal evolution operators. In practice, this worst-case error analysis may be unnecessarily pessimistic. To address this, we develop a theory of average-case performance of Hamiltonian simulation with random initial states. We relate the average-case error to the Frobenius norm of the multiplicative error and give upper bounds for the product formula (PF) and truncated Taylor series methods. As applications, we estimate average-case error for digital Hamiltonian simulation of general lattice Hamiltonians and k-local Hamiltonians. In particular, for the nearest-neighbor Heisenberg chain with n spins, the error is quadratically reduced from O(n) in the worst case to O(n\−\−\√) on average for both the PF method and the Taylor series method. Numerical evidence suggests that this theory accurately characterizes the average error for concrete models. We also apply our results to error analysis in the simulation of quantum scrambling.

}, doi = {https://doi.org/10.1103/PhysRevLett.129.270502}, url = {https://arxiv.org/abs/2111.04773}, author = {Qi Zhao and You Zhou and Alexander F. Shaw and Tongyang Li and Andrew M. Childs} } @article {3204, title = {A scheme to create and verify scalable entanglement in optical lattice}, journal = {npj Quantum Information}, volume = {8}, year = {2022}, month = {9/4/2022}, abstract = {

To achieve scalable quantum information processing, great efforts have been devoted to the creation of large-scale entangled states in various physical systems. Ultracold atom in optical lattice is considered as one of the promising platforms due to its feasible initialization and parallel manipulation. In this work, we propose an efficient scheme to generate and characterize global entanglement in the optical lattice. With only two-layer quantum circuits, the generation utilizes two-qubit entangling gates based on the superexchange interaction in double wells. The parallelism of these operations enables the generation to be fast and scalable. To verify the entanglement of this non-stabilizer state, we mainly design three complementary detection protocols which are less resource-consuming compared to the full tomography. In particular, one just needs two homogenous local measurement settings to identify the entanglement property. Our entanglement generation and verification protocols provide the foundation for the further quantum information processing in optical lattice.

}, doi = {10.1038/s41534-022-00609-0}, url = {https://arxiv.org/abs/2209.01531}, author = {You Zhou and Bo Xiao and Meng-Da Li and Qi Zhao and Zhen-Sheng Yuan and Xiongfeng Ma and Jian-Wei Pan} } @article {2818, title = {Robust Self-Testing of Multiparticle Entanglement}, journal = {Phys. Rev. Lett. }, volume = {127}, year = {2021}, month = {12/7/2021}, pages = {230503}, abstract = {

Quantum self-testing is a device-independent way to certify quantum states and measurements using only the input-output statistics, with minimal assumptions about the quantum devices. Due to the high demand on tolerable noise, however, experimental self-testing was limited to two-photon systems. Here, we demonstrate the first robust self-testing for multi-particle quantum entanglement. We prepare two examples of four-photon graph states, the Greenberger-Horne-Zeilinger (GHZ) states with a fidelity of 0.957(2) and the linear cluster states with a fidelity of 0.945(2). Based on the observed input-output statistics, we certify the genuine four-photon entanglement and further estimate their qualities with respect to realistic noise in a device-independent manner.

}, doi = {https://doi.org/10.1103/PhysRevLett.127.230503}, url = {https://arxiv.org/abs/2105.10298}, author = {Dian Wu and Qi Zhao and Xue-Mei Gu and Han-Sen Zhong and You Zhou and Li-Chao Peng and Jian Qin and Yi-Han Luo and Kai Chen and Li Li and Nai-Le Liu and Chao-Yang Lu and Jian-Wei Pan} } @article {2572, title = {Constructing Multipartite Bell inequalities from stabilizers}, year = {2020}, month = {2/5/2020}, abstract = {

Bell inequality with self-testing property has played an important role in quantum information field with both fundamental and practical applications. However, it is generally challenging to find Bell inequalities with self-testing property for multipartite states and actually there are not many known candidates. In this work, we propose a systematical framework to construct Bell inequalities from stabilizers which are maximally violated by general stabilizer states, with two observables for each local party. We show that the constructed Bell inequalities can self-test any stabilizer state which is essentially device-independent, if and only if these stabilizers can uniquely determine the state in a device-dependent manner. This bridges the gap between device-independent and device-dependent verification methods. Our framework can provide plenty of Bell inequalities for self-testing stabilizer states. Among them, we give two families of Bell inequalities with different advantages: (1) a family of Bell inequalities with a constant ratio of quantum and classical bounds using 2N correlations, (2) Single pair inequalities improving on all previous robustness self-testing bounds using N+1 correlations, which are both efficient and suitable for realizations in multipartite systems. Our framework can not only inspire more fruitful multipartite Bell inequalities from conventional verification methods, but also pave the way for their practical applications.

}, url = {https://arxiv.org/abs/2002.01843}, author = {Qi Zhao and You Zhou} } @article {2646, title = {Quantum simulation with hybrid tensor networks}, year = {2020}, month = {7/2/2020}, abstract = {

Tensor network theory and quantum simulation are respectively the key classical and quantum methods in understanding many-body quantum physics. Here we show hybridization of these two seemingly independent methods, inheriting both their distinct advantageous features of efficient representations of many-body wave functions. We introduce the framework of hybrid tensor networks with building blocks consisting of measurable quantum states and classically contractable tensors. As an example, we demonstrate efficient quantum simulation with hybrid tree tensor networks that use quantum hardware whose size is significantly smaller than the one of the target system. We numerically test our method for finding the ground state of 1D and 2D spin systems of up to 8\×8 and 4\×3 qubits with operations only acting on 8+1 and 4+1 qubits, respectively. Our approach paves the way to the near-term quantum simulation of large practical problems with intermediate size quantum hardware, with potential applications in quantum chemistry, quantum many-body physics, quantum field theory, and quantum gravity thought experiments.

}, url = {https://arxiv.org/abs/2007.00958}, author = {Xiao Yuan and Jinzhao Sun and Junyu Liu and Qi Zhao and You Zhou} }