Rui-Zhen Huang

Observation of Emergent ℤ2 Gauge Invariance in a Superconducting Circuit

  1. Zhan Wang,
  2. Zi-Yong Ge,
  3. Zhongcheng Xiang,
  4. Xiaohui Song,
  5. Rui-Zhen Huang,
  6. Pengtao Song,
  7. Xue-Yi Guo,
  8. Luhong Su,
  9. Kai Xu,
  10. Dongning Zheng,
  11. and Heng Fan
Lattice gauge theory (LGT) is one of the most fundamental subjects in modern quantum many-body physics, and has recently attracted many research interests in quantum simulations. Here
we experimentally investigate the emergent ℤ2 gauge invariance in a 1D superconducting circuit with 10 transmon qubits. By precisely adjusting the staggered longitude and transverse fields to each qubit, we construct an effective Hamiltonian containing a LGT and gauge-broken terms. The corresponding matter sector can exhibit localization, and there also exist a 3-qubit operator, of which the expectation value can retain nonzero for long time in a low-energy regime. The above localization can be regarded as confinement of the matter field, and the 3-body operator is the ℤ2 gauge generator. Thus, these experimental results demonstrate that, despite the absent of gauge structure in the effective Hamiltonian, ℤ2 gauge invariance can still emerge in the low-energy regime. Our work paves the way for both theoretically and experimentally studying the rich physics in quantum many-body system with an emergent gauge invariance.
arxiv pdf

Approximating Lattice Gauge Theories on Superconducting Circuits: Quantum Phase Transition and Quench Dynamics

  1. Zi-Yong Ge,
  2. Rui-Zhen Huang,
  3. Zi Yang Meng,
  4. and Heng Fan
We propose an implementation to approximate Z2 lattice gauge theory (LGT) on superconducting quantum circuits, where the effective theory is a mixture of a LGT and a gauge-broken term.
Using matrix product state based methods, both the ground state properties and quench dynamics are systematically investigated. With an increase of the transverse (electric) field, the system displays a quantum phase transition from a disordered phase to a translational symmetry breaking phase. In the ordered phase, an approximate Gaussian law of the Z2 LGT emerges in the ground state. Moreover, to shed light on the experiments, we also study the quench dynamics, where there is a dynamical signature of the spontaneous translational symmetry breaking. The spreading of the single particle of matter degree is diffusive under the weak transverse field, while it is ballistic with small velocity for the strong field. Furthermore, due to the existence of an approximate Gaussian law under the strong transverse field, the matter degree can also exhibit a confinement which leads to a strong suppression of the nearest-neighbor hopping. Our results pave the way for simulating the LGT on superconducting circuits, including the quantum phase transition and quench dynamics.
arxiv pdf