A quantum-enhanced wide-field phase imager

Abstract

Quantum techniques can be used to enhance the signal-to-noise ratio in optical imaging. Leveraging the latest advances in single-photon avalanche diode array cameras and multiphoton detection techniques, here, we introduce a supersensitive phase imager, which uses space-polarization hyperentanglement to operate over a large field of view without the need of scanning operation. We show quantum-enhanced imaging of birefringent and nonbirefringent phase samples over large areas, with sensitivity improvements over equivalent classical measurements carried out with equal number of photons. The potential applicability is demonstrated by imaging a biomedical protein microarray sample. Our technology is inherently scalable to high-resolution images and represents an essential step toward practical quantum-enhanced imaging.

Fig. 1.. Description of the experiment.

(A) Scheme of the entanglement-enhanced imaging setup. SI, Sagnac interferometer; PBS, polarizing beam splitter; HWP, half–wave plate; L, lenses; P, polarizer; DM, dicroic mirror; M, mirror; ϕ_b, birefringent sample (SLM); ϕ_nb, nonbirefringent sample; SP, Savart plate; dPBS, lateral displacement polarizing beam splitter; BPF, band-pass filter. (B) Detecting birefringent phase samples with the LIM. (C) Detecting nonbirefringent phase samples with the LIM. In (B) and (C), three example trajectories are shown through the LIM, dashed lines correspond to H, and dotted lines correspond to V polarized light. SP₁ is tilted using the pitch angle with respect to the optical axis.

Fig. 2.. Classical versus N00N state interference.

(A) Classical interference integrating across whole camera. Red crosses and blue circles correspond to 〈D∣ and 〈A∣ projections, respectively. (B) N00N state interference integrating across whole camera. (C) N00N state interference with a single fixed pixel. For (B) and (C), red crosses, blue circles, and green diamonds correspond to coincidence counts (Coinc.) from 〈DA∣, 〈DD∣, and 〈AA∣ projections, respectively. Solid lines are fitting curves. The doubled periodicity in (B) and (C) as compared to (A) is obtained by the tilting of SP₁ in the LIM, which induces a phase α in the classical state and 2α in the N00N state.

Fig. 3.. Retrieved phase images of a birefringent sample.

(A) Phase profile applied to SLM. (B) Classical phase image ${\widehat{\mathrm{\varphi }}}_{\text{Classical}}$. (C) Cross section of phase profile along the yellow dashed line in (B). (D) Entanglement-enhanced phase image ${\widehat{\mathrm{\varphi }}}_{\mathrm{N}00\mathrm{N}}$. (E) Cross section of phase profile along the yellow dashed line in (D). Black rectangles in (B) and (D) indicate the area used for LU calculations. The pixel-to-pixel noise is reduced in (D) and (E) compared to (B) and (C). The reduced edge contrast in (D) is due to the relatively large photon spatial correlation width, but can be addressed by engineering an entangled photon source with a tighter spatial correlation. Scale bars, 1 mm at sample plane.

Fig. 4.. Retrieved phase images of a nonbirefringent protein microarray sample.

(A) Reference phase image from high-intensity classical illumination. (B) Low-intensity (single-photon level) classical illumination phase image ${\widehat{\mathrm{\varphi }}}_{\text{Classical}}$. (C) Entanglement-enhanced phase image ${\widehat{\mathrm{\varphi }}}_{\mathrm{N}00\mathrm{N}}$. (D to F) Cross sections of phase profiles along the yellow dashed lines in (A) to (C). Black rectangles in (B) and (C) indicate the area used for LU calculations. All three experimental conditions show clear contrast between regions of high protein binding (circular spots) to regions with no binding (background). The entanglement-enhanced method (C) manifests less pixel-to-pixel noise than its classical counterpart (B) for an equal number of photons detected. Scale bars, 2 mm at sample plane.