Fig. 1. Schematic representation of a switchable quantum bright–dark phase contrast imaging system. (a) The metasurface enables bright–dark phase contrast imaging. The quantum state of a polarization-entangled photon pair is 1/2(|HV⟩+|VH⟩). Signal photons pass through the PO and are modulated by the metasurface (at the Fourier plane) for imaging. The imaging arm outputs a quantum superposition of bright–dark phase contrast images, while the heralding arm’s polarization selection remains undefined. QWP, quarter-wave plate; HWP, half-wave plate; PBS, polarization beam splitter. (b) The heralding arm remotely manipulates the bright–dark phase contrast imaging modes. When the polarization basis vector of the heralded photon is projected to |H⟩ polarization, the image acquired by the intensified charge-coupled device (ICCD) camera in the imaging arm is a dark image; when the polarization basis vector of the heralding photon is projected to |V⟩ polarization, the image is a bright image.

Fig. 2. Characterization of experimental samples. (a) Phase distribution of the PO. Color-coded regions represent distinct phase shifts: yellow core (0), light pink first petal layer (π/5), dark pink second petal layer (2π/5), light green stems (3π/5), dark green leaves (4π/5), and blue background (π). All phase shifts are quantized in π/5 increments (see the Supplement 1, Sec. 2). (b) Schematic diagram of the metasurface. The metasurface has a size of 35 µm × 35 µm and a structural period of 350 nm, exhibiting a periodic arrangement of amorphous silicon pillars with dimensions of 190 nm in length, 110 nm in width, and 390 nm in height. (c) Top-view SEM image of the metasurface.

Fig. 3. Experimental setup and characterization of an entangled light source. (a) Experimental setup. A 390 nm pulsed ultraviolet laser was focused through a lens onto two sandwich-structured beta barium borate (BBO) crystals to generate entangled photon pairs. Each pair of entangled photons is indistinguishable after passing through the time-compensated and space-compensated crystals. The QHP combination is used to selectively detect heralding photons, which subsequently reach the SPAD trigger ICCD. The signal photons are modulated by the metasurface and then finally collected for imaging by the ICCD. The QHP combination comprised a QWP, an HWP, and a PBS. FC, fiber coupler; BPF, bandpass filter; YV, yttrium vanadate crystal (YVO4) for space compensation; LN, lithium niobate crystal (LiNbO3) for time compensation; PO, phase object. (b) Sinusoidal fit of the data when the HWP in the signal arm is fixed at 0° (red) and 22.5° (blue). (c) Real and imaginary parts of the density matrix of the quantum state.

Fig. 4. Imaging comparison between classical and quantum light sources. Under identical photon flux illumination conditions, phase contrast imaging using a quantum entangled source achieves high contrast compared to classical weak light sources, while high-contrast imaging can only be realized with the incorporation of metasurface modulation. (a) Bright phase contrast imaging with metasurface modulation under classical weak light illumination. (b) Bright phase contrast imaging without metasurface modulation under quantum light illumination. (c) Bright phase contrast imaging with metasurface modulation under quantum light illumination. (d) Dark phase contrast imaging without metasurface modulation under quantum light illumination. (e)–(h) Intensity maps at the white dashed lines in (a)–(d).

Fig. 5. Remote switching of quantum bright–dark phase contrast imaging functions. (a) Bright–dark phase contrast images of a low phase gradient sample. The number of acquisition frames is 1200 with an exposure time of 1 s per frame. (b) Quantum bright–dark phase contrast image of onion epidermis. The number of frames acquired is 3600. The horizontal axis represents the projected polarization state in the signal arm, while the vertical axis represents the projected polarization state in the heralding arm. The images displayed in the coordinate system show those acquired by the ICCD camera under different polarization states and processed to remove noise.