Neutralizing antibodies could be antivirals against COVID-19 pandemics. Here, we report isolation of four human-origin monoclonal antibodies from a convalescent patient, all of which display neutralization abilities. B38 and H4 block the binding between virus S-protein RBD and cellular receptor ACE2. A competition assay indicates their different epitopes on the RBD, making them a potential virus-targeting MAb-pair to avoid immune escape in future clinical applications. Moreover, a therapeutic study in a mouse model validated that these antibodies can reduce virus titers in infected lungs. The RBD-B38 complex structure revealed that most residues on the epitope overlap with the RBD-ACE2 binding interface, explaining the blocking effect and neutralizing capacity. Our results highlight the promise of antibodybased therapeutics and provide a structural basis for rational vaccine design.

Transformations on quantum states form a basic building block of every quantum information system. From photonic polarization to two-level atoms, complete sets of quantum gates for a variety of qubit systems are well known. For multi-level quantum systems beyond qubits, the situation is more challenging. The orbital angular momentum modes of photons comprise one such high-dimensional system for which generation and measurement techniques are well-studied. However, arbitrary transformations for such quantum states are not known. Here we experimentally demonstrate a four-dimensional generalization of the Pauli X-gate and all of its integer powers on single photons carrying orbital angular momentum. Together with the well-known Z-gate, this forms the first complete set of high-dimensional quantum gates implemented experimentally. The concept of the X-gate is based on independent access to quantum states with different parities and can thus be easily generalized to other photonic degrees-of-freedom, as well as to other quantum systems such as ions and superconducting circuits.Introduction -High-dimensional quantum states have recently attracted increasing attention in both fundamental and applied research in quantum mechanics [1][2][3][4][5]. The possibility of encoding vast amounts of information on a single photon makes them particularly interesting for large-alphabet quantum communication protocols [6][7][8][9], as well as for investigating fundamental questions concerning local realism or quantum contextuality [10,11]. The temporal and spatial structure of a photon provides a natural multi-mode state space in which to encode quantum information. The orbital angular momentum (OAM) modes of light [12] comprise one such basis of spatial modes that has emerged as a popular choice for experiments on high-dimensional quantum information [13]. While techniques for the generation and measurement of photonic quDits carrying OAM are well known [14][15][16], efficient methods for their control and transformation remain a challenge. No general recipe is known so far, and experimentally feasible techniques are known only for special cases.Here we experimentally demonstrate a fourdimensional X-gate and all of its integer powers with the orbital angular momentum modes of single photons. The four-dimensional X-gate is a generalization of the two-dimensional σ x Pauli transformation and acts as a cyclic ladder operator on a four-dimensional Hilbert space. The cyclic transformation required for this gate was designed through the use of the computer algorithm MELVIN [17] and recently demonstrated with classical states of light [18]. The Z-gate for OAM quDits (the generalization of the two-dimensional σ z Pauli transformation) introduces a mode-dependent phase,