Caltech researchers have made a significant breakthrough in microscopy by using a strange phenomenon in quantum physics. By harnessing quantum entanglement, they have been able to double the resolution of light microscopes.
Quantum entanglement occurs when two particles become linked, so that the state of one particle affects the state of the other particle, regardless of their distance from each other. This baffling effect was famously dubbed “spooky action at a distance” by Albert Einstein, as it defied his theory of relativity.
The researchers have used entangled photons, known as biphotons, in their new microscopy technique called quantum microscopy by coincidence (QMC). Biphotons behave like a single particle with double the momentum of a single photon, resulting in a halving of their wavelength. As particles with larger momentum have smaller wavelengths, this enables the microscope to image smaller features and increases its resolution.
While there are other ways to reduce the wavelength of light used in a microscope, such as using green or purple light, the energy carried by shorter wavelengths of light can damage the objects being imaged, particularly living cells. This is where QMC comes in – by using entangled biphotons that carry the lower energy of longer-wavelength photons while having the shorter wavelength of higher-energy photons, the technique achieves the resolution of shorter-wavelength light without damaging the objects being imaged.
The QMC process involves shining laser light into a crystal that converts some photons into biphotons. This conversion is rare, occurring in only one in a million photons. The biphotons are then split into two discrete photons, one of which passes through the object being imaged (the signal photon) and the other does not (the idler photon). The signal photon carries the information used to build an image of the object on a computer, while the idler photon serves as a reference. The entangled biphotons remain entangled even when passing through the object and taking separate paths, resulting in higher-resolution images without damaging the object being imaged.
Although Wang’s lab was not the first to experiment with biphoton imaging, they were the first to create a functional system using this concept. Their success is attributed to the development of a rigorous theory and a more accurate method for measuring entanglement. They were able to achieve microscopic resolution and capture images of cells using this technology.
While it is theoretically possible to entangle any number of photons, adding more photons would increase the momentum of the resulting multiphoton while decreasing its wavelength even further. Wang believes that future research could lead to entanglement of more photons, but notes that each additional photon reduces the likelihood of successful entanglement even further. Currently, the probability of successful entanglement is only one in a million.
The paper detailing their work, titled “Quantum Microscopy of Cells at the Heisenberg Limit,” has been published in Nature Communications.