Chuan-Feng Li

Pure-state manifestations of geometric phase are well established and have found applications across essentially all branches of physics, yet their generalization to mixed-state regimes remains largely unexplored experimentally. The Uhlmann geometric phase offers a natural extension of pure-state paradigms and can exhibit a topological character. However, observation of this invariant is impeded by the incompatibility between Uhlmann parallel transport and Hamiltonian dynamics, as well as the difficulty of preparing topologically nontrivial mixed states. To address this challenge, we report an experimentally accessible protocol for directly measuring the mixed-state topological invariant. By engineering controlled nonunitary dynamics in a photonic quantum walk, we prepare topologically nontrivial mixed states from a trivial initial state. Then, by machine learning the full density matrix in momentum space, we directly extract the quantized geometric phase of the nontrivial mixed states. Furthermore, we observe that this transition of the quantized mixed-state topological invariant from a trivial to a nontrivial value is closely associated with the emergence of a topological kink structure. These results highlight a geometric phase framework that naturally extends to open quantum systems both in and out of thermal equilibrium.

Neutral atoms coupled to optical microcavities provide an efficient atom‐photon interface for quantum computing, quantum networking and quantum metrology. However, the finite trapping lifetime of atoms generally requires cyclic atom transfer, which interrupts the atom‐cavity interaction and limits the applications of cavity QED experiments. Here, we realize continuous coupling of rubidium atoms to an optical microcavity. Continuous transfer of atoms from a magneto‐optical trap into the optical microcavity is achieved using a near‐resonant optical dipole trap, enabling strong coupling between an atomic ensemble and the microcavity with a vacuum Rabi splitting of 395(2) MHz. To demonstrate a potential application, we further realize continuous heralded single‐photon emission and measure a minimum value of the heralded second‐order correlation function, . These results pave the way for the continuous transfer of atoms into optical microcavities and broaden the application prospects of laser‐cooled atoms coupled to optical microcavities.

Random-access quantum memory (RAQM) is a fundamental building block for scalable quantum networks and photonic quantum computing. While existing realizations rely on gaseous physical systems, solid-state platforms—particularly integrated architectures—offer distinct practical advantages for scalable deployment. However, current integrated quantum memories are limited to single-channel operation, which precludes both RAQM and the manipulation of high-dimensional photonic states. Here, we demonstrate an 11-channel integrated quantum memory based on laser-written waveguide arrays in an ¹⁵¹ Eu ³⁺ :Y ₂ SiO ₅ crystals. On-chip electrode arrays allow independent control of the read-out time in each channel via Stark-shift-induced atomic interference. The device achieves random-access quantum storage of three time-bin qubits with a fidelity exceeding 99%, and stores five-dimensional path-encoded quantum states with a fidelity above 96%. This multichannel integrated quantum memory supports flexible functionality through its random-access operation and establishes a practical hardware platform for high-dimensional quantum networks implemented in integrated architectures.

Synthetic dimensions provide a powerful route for engineering topological matter beyond the constraints of real-space geometry, with enhanced tunability and measurement accessibility. Here, we implement two independent and extended synthetic dimensions based on photonic frequency and orbital angular momentum (OAM) in a zero-dimensional cavity system. With polarization serving as a pseudo-spin, we realize an anisotropic Dirac Hamiltonian with fully controllable coupling strengths, enabling unprecedented engineering of Dirac points, including their creation, motion, and merging, as well as a Lifshitz transition from type-I to type-II Dirac cones. Using angle- and time-resolved spectroscopic techniques, we experimentally reconstruct the full two-dimensional band structure, identify Dirac points, and measure the associated Berry phase. Our platform provides a versatile setting for exploring Dirac physics and topological phenomena and establishes a scalable pathway toward higher-dimensional quantum simulation.

Exceptional points (EPs), as an essential concept in non‐Hermitian systems, give rise to a variety of novel physical phenomena, most notably the exchange of eigenstates induced by encircling in parameter space. Here, we experimentally investigate eigenstate permutations in a parameter space containing three second‐order exceptional points (EP2s), realized on a programmable single‐photon platform capable of synthesizing four‐state non‐Hermitian Hamiltonians. By designing distinct parameter space loops that encircle the EP2s in different sequences, we observe eigenvalue and eigenstate permutations corresponding to the non‐Abelian dihedral group. Furthermore, using a branch‐cut representation of the underlying Riemann‐surface topology, we track the associated eigenstate permutations and show that different encircling paths generate distinct sequences of permutation operations. These results highlight the non‐commutative nature of eigenstate braiding in multi‐EP systems and establish an experimental connection between multi‐EP topology and non‐Abelian group structures in non‐Hermitian physics. More broadly, our work demonstrates the capability of programmable single‐photon platforms for investigating complex non‐Hermitian topological structures and their associated permutation dynamics.