Welcome to Wenjun Zhang’s homepage! I am a graduate student at Physics Department, Tsinghua University. My research interests include atomic, molecular and optical (AMO) physics and quantum simulation. Advised by Prof. Wenlan Chen, I’m excited to investigate the physics of quantum many-body systems with long-range interactions by using Rydberg atom arrays.
News
Sep 16, 2023
I gave a talk at the 2023 Ph.D. forum at Tsinghua Physics and won the best oral presentation prize!
Cold atoms in an optical cavity have been widely used for quantum simulations of many-body physics, where the quantum control capability has been advancing rapidly in recent years. Here, we show the atom cavity system is universal for quantum optimization with arbitrary connectivity. We consider a single-mode cavity and develop a Raman coupling scheme by which the engineered quantum Hamiltonian for atoms directly encodes number partition problems. The programmability is introduced by placing the atoms at different positions in the cavity with optical tweezers. The number partition problem solution is encoded in the ground state of atomic qubits coupled through a photonic cavity mode, which can be reached by adiabatic quantum computing. We construct an explicit mapping for the 3-SAT and vertex cover problems to be efficiently encoded by the cavity system, which costs linear overhead in the number of atomic qubits. The atom cavity encoding is further extended to quadratic unconstrained binary optimization problems. The encoding protocol is optimal in the cost of atom number scaling with the number of binary degrees of freedom of the computation problem. Our theory implies the atom cavity system is a promising quantum optimization platform searching for practical quantum advantage.
@article{ye2023universal,title={Universal Quantum Optimization with Cold Atoms in an Optical Cavity},author={Ye, Meng and Tian, Ye and Lin, Jian and Luo, Yuchen and You, Jiaqi and Hu, Jiazhong and Zhang*, Wenjun and Chen, Wenlan and Li, Xiaopeng},journal={Physical Review Letters},volume={131},number={10},pages={103601},year={2023},doi={10.1103/PhysRevLett.131.103601},url={https://link.aps.org/doi/10.1103/PhysRevLett.131.103601},}
Accelerating the Assembly of Defect-Free Atomic Arrays with Maximum Parallelisms
Shuai Wang†, Wenjun Zhang†, Tao Zhang, Shuyao Mei, Yuqing Wang, Jiazhong Hu, and Wenlan Chen
Defect-free atomic arrays have been demonstrated as a scalable and fully controllable platform for quantum simulations and quantum computations. To push the qubit size limit of this platform further, we design an integrated measurement and feedback system, based on field-programmable gate array (FPGA), to quickly assemble two-dimensional defect-free atomic array using maximum parallelisms. The total time cost of the rearrangement is first reduced by processing atom detection, atomic occupation analysis, rearrangement strategy formulation, and acousto-optic deflectors driving signal generation in parallel in time. Then, by simultaneously moving multiple atoms in the same row (column), we save rearrangement time by parallelism in space. To best utilize these parallelisms, we propose an alternative algorithm named the Tetris algorithm to reassemble atoms to arbitrary target array geometry from two-dimensional stochastically loaded atomic arrays. For an L-by-L target array geometry, the number of moves scales as L, and the total rearrangement time scales at most as L2. Although in this work we do not test on actual atoms, we simulate the performance of our FPGA system experimentally with all components integrated except for the atoms. We present the overall performance for different target geometries, and demonstrate a dramatic boost in rearrangement time cost and the potential to scale up defect-free atomic array to 1000 atoms in room-temperature platform and 10 000 atoms in cryogenic environment.
@article{wang2023accelerating,title={Accelerating the Assembly of Defect-Free Atomic Arrays with Maximum Parallelisms},author={Wang†, Shuai and Zhang†, Wenjun and Zhang, Tao and Mei, Shuyao and Wang, Yuqing and Hu, Jiazhong and Chen, Wenlan},journal={Physical Review Applied},volume={19},number={5},pages={054032},year={2023},rights={All rights reserved},doi={10.1103/PhysRevApplied.19.054032},url={https://link.aps.org/doi/10.1103/PhysRevApplied.19.054032},}
Evidence of Potts-Nematic Superfluidity in a Hexagonal sp2 Optical Lattice
Shengjie Jin, Wenjun Zhang, Xinxin Guo, Xuzong Chen, Xiaoji Zhou, and Xiaopeng Li
As in between liquid and crystal phases lies a nematic liquid crystal, which breaks rotation with preservation of translation symmetry, there is a nematic superfluid phase bridging a superfluid and a supersolid. The nematic order also emerges in interacting electrons and has been found to largely intertwine with multiorbital correlation in high-temperature superconductivity, where Ising nematicity arises from a four-fold rotation symmetry C4 broken down to C2. Here, we report an observation of a three-state (Z3) quantum nematic order, dubbed “Potts-nematicity”, in a system of cold atoms loaded in an excited band of a hexagonal optical lattice described by an sp2-orbital hybridized model. This Potts-nematic quantum state spontaneously breaks a three-fold rotation symmetry of the lattice, qualitatively distinct from the Ising nematicity. Our field theory analysis shows that the Potts-nematic order is stabilized by intricate renormalization effects enabled by strong interorbital mixing present in the hexagonal lattice. This discovery paves a way to investigate quantum vestigial orders in multiorbital atomic superfluids.
@article{jin2021evidence,title={Evidence of Potts-Nematic Superfluidity in a Hexagonal sp2 Optical Lattice},author={Jin, Shengjie and Zhang, Wenjun and Guo, Xinxin and Chen, Xuzong and Zhou, Xiaoji and Li, Xiaopeng},journal={Physical Review Letters},volume={126},number={3},pages={035301},year={2021},publisher={{American Physical Society}},doi={10.1103/PhysRevLett.126.035301},url={https://link.aps.org/doi/10.1103/PhysRevLett.126.035301},}
