[Paper Review] Witnessing the survival of time-energy entanglement through biological tissue and scattering media

Daniel J. Lum, Michael D. Mazurek+8 more|arXiv (Cornell University)|Feb 25, 2021

Quantum Information and Cryptography67 references16 citations

TL;DR

This study demonstrates that time-energy entangled photons from spontaneous parametric down-conversion can retain nonlocal quantum correlations after propagating through thick biological tissues, including skim milk (up to 1.556 mm), 2% milk (286 μm), and chicken breast (235 μm), with interference contrast exceeding 90%, indicating robust survival of entanglement in turbid, scattering media relevant to biological imaging applications.

ABSTRACT

We demonstrate the preservation of time-energy entanglement of near-IR photons through thick biological media ($\leq$1.55 mm) and tissue ($\leq$ 235 $\mu$m) at room temperature. Using a Franson-type interferometer, we demonstrate interferometric contrast of over 0.9 in skim milk, 2% milk, and chicken tissue. This work supports the many proposed opportunities for nonclassical light in biological imaging and analyses from sub-shot noise measurements to entanglement-enhanced fluorescence imaging, clearly indicating that the entanglement characteristics of photons can be maintained even after propagation through thick, turbid biological samples.

Motivation & Objective

• .
• To investigate whether time-energy entanglement can survive propagation through thick, scattering biological tissues at room temperature.
• To demonstrate that nonclassical correlations in time and energy remain viable for quantum-enhanced biological imaging despite strong scattering and absorption.
• To validate the use of a compact, stable Franson interferometer for witnessing entanglement in complex biological media without active phase stabilization.

Proposed method

• .
• A modified 'hugging' Franson interferometer with polarizing beamsplitters and waveplates was used to measure non-local interference in coincidence counts.
• Photons were generated via type-I spontaneous parametric down-conversion (SPDC) and coupled into single-mode fibers to minimize spatial-mode mismatch.
• Interference contrast was measured by varying the optical path length in one arm using half-wave plates and monitoring coincidence rates across phase settings.
• Polarizers were used before detectors to erase path information, enabling observation of quantum interference without which-path knowledge.
• The system was operated without active phase stabilization, relying on mechanical stability and a compact folded design to maintain coherence.

Experimental results

Research questions

• RQ1 .
• RQ2 Can time-energy entanglement survive propagation through biological tissues thicker than 100 μm?
• RQ3 What is the maximum depth of biological tissue through which time-energy entanglement can be preserved?
• RQ4 How does scattering and absorption in biological media affect the visibility of non-local interference in time-energy entangled photons?
• RQ5 Can a compact, un-stabilized Franson interferometer reliably witness entanglement in turbid biological samples?

Key findings

• .
• Interference contrast exceeding 90% was observed in skim milk up to 1.556 mm thickness, confirming survival of time-energy entanglement.
• In 2% milk, entanglement survived up to 286 μm with interference contrast above 90%.
• In chicken breast tissue, time-energy entanglement persisted through samples up to 235 μm thick, with visibility exceeding 90%.
• The measured interference contrast significantly exceeded the 70.7% threshold required to violate a CHSH-Bell inequality, confirming nonclassical correlations.
• The results indicate that time-energy entanglement is robust against scattering and absorption in biological media, supporting its use in quantum-enhanced fluorescence imaging and sensing.