Quantum Phase Imaging System

Updated 20 November 2025

Quantum phase imaging systems are advanced optical platforms that use quantum light and metasurfaces to recover phase or phase gradients from transparent samples.
They integrate SPDC-based photon generation with dual-metasurface architectures to perform all-optical, calibration-driven phase gradient extraction with no mechanical scanning.
Experimental benchmarks show high sensitivity with resolutions around 60 μm and 88% fidelity, enabling applications in biomedical microscopy and on-chip optical metrology.

Quantum phase imaging systems are designed to recover phase, phase gradients, or full quantitative phase distributions of transparent or weakly absorbing samples by harnessing quantum optical resources, engineered nanophotonic elements, or computationally optimized diffractive architectures. These systems achieve high phase sensitivity, low-light operation, and enhanced information extraction per photon, enabling precise, compact, and robust imaging platforms across a wide range of scientific domains.

1. System Architectures: Metasurface-Enabled Quantum Phase Imaging

Recent advancements integrate metasurface photonics with quantum light generation and detection, producing highly compact quantum phase imaging systems. A representative realization employs a cascaded dual-metasurface architecture on a planar substrate: a LiNbO₃ metasurface patterned for enhanced spontaneous parametric down-conversion (SPDC) serves as the entangled photon-pair source, while a Si metasurface performs phase gradient extraction by implementing a nearly linear optical transfer function (OTF). The SPDC metasurface is engineered for guided-mode-resonance–enhanced χ² nonlinearity (Q_{LN} ≈ 500) with angular dispersion, and generates spatially anti-correlated photon pairs in the z–axis and narrowly correlated pairs in the y–axis. The Si metasurface, operating in a leaky-wave GMR regime (Q_{Si} ≈ 20), provides a linear k_z transfer function (H(k_z) ≈ a k_z + b), effectively acting as a spatial differentiator.

The measurement protocol leverages spatial quantum correlations for ghost imaging along one axis and all-optical scanning by pump wavelength tuning along the other, enabling simultaneous phase gradient mapping in two dimensions with no mechanical motion. The architecture eliminates interferometric complexity, bulk optics, and scanning stages, achieving high integration and alignment-free operation (Ren et al., 13 Nov 2025).

2. Quantum Theory and Optical Transfer Functions

Photon generation in these systems is governed by the undepleted-pump SPDC Hamiltonian: $\hat H_{\rm SPDC} = \varepsilon_0 \int d^3r\,\chi^{(2)}(\mathbf r)\, E_p(\mathbf r,t)\, \hat E_s^{(-)}(\mathbf r,t)\, \hat E_i^{(-)}(\mathbf r,t) + \mathrm{h.c.}$ with phase-matching conditions $\omega_p=\omega_s+\omega_i$ and $\mathbf k_p=\mathbf k_s+\mathbf k_i+\mathbf G$ . The engineered SPDC emission, under metasurface-induced dispersion, produces joint two-photon amplitudes with sharp momentum anti-correlation ( $\delta(k_z^s + k_z^i)$ )—exploited in quantum ghost imaging and quantum microscopy protocols.

For phase extraction, a single-photon passing through a Si metasurface with transfer function $H(k_z) = a\,k_z + b$ receives a spatially resolved amplitude proportional to the local phase gradient: $C_N(z_N) \propto \frac{a^2}{4\sigma_z^2} + \bigl(a\,\phi'(z_N)-b\bigr)^2.$ This direct encoding of the phase derivative $\phi'(z)$ enables detection of both magnitude and sign of the phase gradient without ambiguity or the need for a global reference, providing robustness in practical scenarios (Ren et al., 13 Nov 2025).

3. Measurement Protocols and Reconstruction

Quantum phase imaging systems employ multiple measurement protocols, often leveraging entangled photon correlations for signal extraction. In the metasurface system, phase-gradient information is recovered by:

Acquiring coincidence maps $C(z,\lambda_c)$ for different spatial pixels (z) and pump wavelengths (corresponding to y-pixels).
Correcting raw counts by the measured Gaussian collection envelope ( $G(z;\lambda_c)$ ).
Applying a nonlinear calibration transform to extract the local phase gradient $\phi'(z)$ from coincidence-encoded intensities.

The spatial resolution is fundamentally limited by the bandwidth of the transfer function ( $\delta z_{\min}\approx 1/(2\Delta k_z)$ ), which in practice yields pixel sizes on the order of 60–350 μm. Isotropic features or multidimensional gradients are recovered by combining anti-correlated detection (ghost imaging) and wavelength multiplexing (all-optical scanning). No mechanical scanning or external phase plate modulation is required (Ren et al., 13 Nov 2025).

4. Experimental Demonstration and Performance Benchmarks

Proof-of-concept experiments demonstrate phase gradient imaging of complex objects (e.g., T- and S-shaped phase patterns) with maximum local gradients of 25 rad/mm. Reconstruction fidelity, measured as mode-overlap, reaches 88% for a 6×3-pixel system, limited primarily by metasurface Q-factors and collection efficiency. Data are accumulated under shot-noise-limited statistics with typical acquisition times of 1 h per object.

Key performance metrics include:

Maximum resolvable phase gradient: 25 rad/mm
Spatial resolution (z-axis): δz ≈ 60 μm (with σ_z=87 μm, Δz=350 μm)
Reconstructed fidelity: 88% (mode-overlap)
Detection protocol: zero-mechanical scanning, all-optical wavelength tuning (Ren et al., 13 Nov 2025)

A summary of system-level parameters appears below.

Component	Key Parameters	Function
LiNbO₃ metasurface	Q_{LN} ≈ 500, Δλ_s+i≈3nm	SPDC photon-pair generation
Si metasurface	Q_{Si} ≈ 20, Δk_z≈8 rad/mm, H(k_z)=a k_z+b	Phase-gradient filtering
Coincidence detection	0.42 ns window, 6z×3y	Joint phase-gradient mapping

Quantum phase imaging extends beyond metasurface systems to include non-interferometric transport-of-intensity approaches using SPDC (Ortolano et al., 2023, Paniate et al., 9 Jun 2025), Fourier ptychographic imaging with heralded photons (Aidukas et al., 2019), quantum ghost imaging protocols (Sephton et al., 2022, Asban et al., 2019), and on-chip diffractive QPI architectures (Li et al., 2023, Mengu et al., 2022, Shen et al., 16 Mar 2024). The metasurface-enabled method uniquely combines:

Planar, chip-scale integration of both SPDC generation and phase-gradient detection.
Direct optical differentiation for phase-gradient extraction via appropriately engineered OTFs, contrasted to iterative or interferometric digital phase-retrieval methods.
All-optical, calibration-based inversion with minimal data acquisition overhead, compared to multi-step phase-shifting or complex multi-illumination protocols.

These properties position the metasurface system as a distinct and viable platform for portable, high-throughput, and application-specific quantum phase imaging (Ren et al., 13 Nov 2025).

6. Limitations and Prospects for Enhancement

Resolution and dynamic range are fundamentally constrained by fabrication-imposed quality factors (Q_{LN}, Q_{Si}) and metasurface aperture. Increasing Q_{Si} extends the linear range of the phase-differentiating OTF, allowing larger gradient dynamic range; increasing Q_{LN} would narrow photon bandwidths, enabling finer spectral resolution and more y-pixels. Pump beam shaping, multiplexed channel architectures, and larger metasurfaces are proposed as future directions.

Limitations include the current trade-off between resolution and photon bandwidth, limited multi-pixel implementation scale, and fixed phase-gradient sensitivity determined by metasurface design. However, the planar architecture is inherently compatible with on-chip integration, wavelength scaling (telecom to visible and mid-IR), and parallel operation (Ren et al., 13 Nov 2025).

7. Applications and Outlook

Quantum phase imaging systems based on metasurfaces are suited for scenarios requiring quantitative, low-light-level mapping of transparent or weakly scattering samples. Notable application areas include:

Biomedical microscopy for label-free imaging of transparent cell monolayers, interfaces, or live tissues.
Compact, alignment-free noninvasive LiDAR for phase-tracking and biosensing.
On-chip integration for optical metrology, microfluidics, and chip-based photonic platforms.

The demonstrated platform establishes a template for future advances in portable quantum imaging, leveraging the unique interplay of engineered quantum correlations and nanophotonic functionality (Ren et al., 13 Nov 2025).