Fig. 1. Conceptual art of quantum information masking. Gradient lines and shading indicate the site of information storage

Fig. 2. Circuit realizing quantum information masking. (a) A quantum controlled-NOT gate can realize bipartite quantum information masking in the limited qubit state space. Top: symbol of the quantum controlled-NOT gate in quantum circuit. Bottom: each state on a disk in the Bloch sphere corresponds to a maximum masking set; (b) realization of quadpartite and tripartite masking of high-dimensional quantum information; the composition is derived from reference [31]. "8"-shaped connection between the lines indicates that the corresponding bipartite subsystem is maximally entangled

Fig. 3. Experimental configuration of quantum information masking based on two-photon interference^[25]. BBO: beta barium borate (nonlinear crystal); HWP: half-wave plate; QWP: quarter-wave plate; PBS: polarizing beam splitter

Fig. 4. Experimental results of quantum information masking using two-photon interference^[25]. (a) A qubit maskable disk represented on the Bloch sphere. The data points are five quantum states on the maskable disk and the recovered state from masking, deduced by numerically invert the masking isometry; (b) marginal states of the five data points after masking almost completely overlap; the inset quantifies the trace distance between the experimental results and the theoretical predictions of the marginal states; (c)(d) bipartite density matrix after masking ρ₁ and ρ₄ inferred from quantum state tomography. The dashed boxes show the theoretical predictions

Fig. 5. Zero volume measure of the qubit maskable set^[25]. Each subfigure shows the trace distance between one of the reduced density matrix of the output state after masking and the reduced density matrix of the masked reference state when the input state deviates from the reference state on different latitudes along a parallel or a meridian. A trace distance of 0 indicates the success of masking. Under this experimental configuration, the maskable disks are encircled by the line of constant latitudes on the Bloch sphere. The error bars show the standard deviations deduced from the photon counting statistics, and the solid curves depict the theoretical predictions

Fig. 6. Experimental setup realizing real qudit information masking using quantum walks^[26]. BD: calcite crystal optical beam splitter; SPCM: single photon counting module

Fig. 7. Relationship between the concurrence of the output state from quantum information masking under the subtheory of real quantum mechanics and the robustness of imaginarity of the input state that characterizes the distance from the real state space^[26]. Testbed set of quantum states is the qubit maximally superposition states

Fig. 8. Quantum secret sharing using quantum information masking. (a) Conceptual art of quantum secret sharing^[25]. Three receivers use their corresponding marginal state to reconstruct the masked quantum state. (b) schematic plot of quantum secret sharing and image transmission through quantum information masking. Each receiver can use its own marginal state to fix the location of quantum state on a disk in the Bloch sphere, so three receivers can completely determine the position of the quantum state in the Bloch sphere after comparing their information. Moreover, the Bloch sphere and the color space are isomorphic establishing the one-to-one correspondence between the qubit states and all possible colors. (c) result of image transmission using quantum secret sharing. The left and right panels are the original and reconstruction image after transmission using quantum information masking