Fig. 1. Phase control of metasurfaces. (a) Finite difference time domain (FDTD) simulation results of electric field scattered by metasurface show that vertically incident light waves are deflected; (b) using metasurfaces to generate vortex beams^[7]; (c) SEM micrograph of designed metalens^[34]; (d) holographic projection based on metasurface^[35]; (e) full-color printing with TiO₂ metasurface^[36]; (f) experimental light intensity profiles for achromatic metalens at various incident wavelengths (white dashed line indicates position of focal plane)^[37]

Fig. 2. Quantum surface plasmon polaritons. (a) Quantum entanglement property of surface plasmon polaritons is observed first^[61]; (b) energy-time entanglement after photon-SPP-photon conversion process of photon pairs^[63]; (c) quantum tunneling effect between two adjacent surface plasmon resonators^[65]; (d) single-photon source excites surface plasmon monopole propagating on nanowires^[66]

Fig. 3. Optimize quantum light sources with metasurfaces. (a) Combining CBR-HBR with quantum dots to produce entangled photon pairs^[70]; (b) metasurface is designed to convert QD emissions from the two paths (labeled by 1 and 2) into two opposite circularly polarized beams that propagate along directions with angles of θ₁ and θ₂ relative to the surface normal of metasurface, respectively^[71]; (c) quantum emitter stimulates SPP to couple with metasurface and produce spin single photons^[72]; (d) subwavelength pillars extending from surface of single-crystal diamond substrate are designed to create high-numerical-aperture metalens for coupling NV-center photoluminescence into collimated beam in air^[73]; (e) photoluminescence spectra of original and coupled single-photon emitters^[74]

Fig. 4. High-dimensional multiphoton entanglement source based on optical metasurface^[81]. (a) High-dimensional quantum source based on metalens array; (b) image of SPDC photon pair array recorded by EMCCD; (c) density matrices of four Bell states; (d) four-photon and six-photon coincidences dependence on pump power

Fig. 5. Measurement and manipulation of quantum states. (a) Metasurface decomposes input N-photons into M polarization states; (b) reconstruction of two density matrices of dual-photon states^[82]; (c) incident light reverses its spin and gains orbital angular momentum by applying geometric phase; (d) theoretically calculated density matrix of each Bell state; (e) measurement results of non-local spin and OAM correlation between two photons^[85]; (f) metasurface performs arbitrary U(2) operations on two-dimensional photon state^[86]; (g) utilize non-unitary metasurface to realize bunching and anti-bunching of photons^[87]

Fig. 6. Application of quantum optics combined with metasurfaces. (a) Combining loss of metal metasurface with quantum interference to break classical absorption limit^[88]; (b) combining the polarization multiplexing function of metasurface and polarization entanglement characteristics of quantum light source to realize remote control of quantum imaging; (c) when entanglement degree of entangled photon pair decreases, contrast of pattern decreases obviously^[91]; (d) metamaterial surfaces for remote manipulation of edge imaging^[95]; (e) metamaterial surface splits left-handed and right-polarized photons of NOON state^[96]

Fig. 7. Quantum vacuum engineering of quantum emitter^[102]. (a) Metasurface destroys quantum vacuum symmetry of quantum emitter, which induces quantum interference in decay channel of multi-level quantum emitter; (b) polarization-dependent response of metasurface; (c) simulated field intensity distribution of dipole source; (d) simulated reflection field intensity distribution of y dipole; (e) simulated reflection field intensity distribution of x dipole; (f) relationship between population of two excited states of quantum emitter and time