Researchers at Caltech have demonstrated a quantum microscopy technique that achieves roughly four times the resolution of a classical light microscope. The work, led by Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, builds on the lab's 2023 demonstration of quantum microscopy by coincidence (QMC), which used entangled photon pairs to double resolution.
In the earlier QMC approach, entangled photon pairs called biphotons are split so that a signal photon passes through the sample while its entangled partner, the idler photon, travels a separate path. Because the pair behaves as a single particle with twice the momentum, each photon effectively images with half the wavelength, yielding a twofold resolution gain.
The new setup retains a single pass of the signal photon through the sample but routes the idler photon back through the same pair of lenses three times before detection. This is accomplished using a magnetic field and optical tools, including specialized beam splitters that control the polarization of light. The experimental results are described in a paper published in Science Advances.
When imaging a standard resolution target, the team measured an enhancement of about 1.8 times over classical imaging with the previous twofold configuration, while the new triple-pass configuration achieved roughly a fourfold improvement. Wang said the result enters a new physical regime, surpassing the widely assumed limit of a twofold gain from a single photon pair.
The technique uses much less intense light at the sample than conventional high-resolution methods, which can temporarily affect vision in retinal imaging or damage living tissue. The researchers say the low-light, high-resolution capability could eventually enable visualization of finer structures such as cell nuclei and mitochondria without harm.
Potential applications also include semiconductor inspection, where quality-control imaging sometimes uses longer wavelengths that limit resolution with classical optics. A fourfold improvement at the same wavelengths could substantially enhance defect detection in chips, according to Wang.
Wang noted that a full theoretical model explaining the resolution enhancement is still under development. He initially had difficulty convincing his lab to pursue the approach, which was based on a hunch from earlier theory. The lead authors of the paper are Xin Tong, Zhe He, and Yide Zhang, with support from Caltech's Center for Sensing to Intelligence, the Chan Zuckerberg Initiative DAF, the Silicon Valley Community Foundation, and the National Institutes of Health.
New Quantum Microscopy Trick Quadruples Microscope Resolution
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