A research team has demonstrated quantum enhancement in a real X-ray machine, thereby achieving the goal of elimination of background noise for precision detection. The relationship between photon pairs on quantum scales can be used to generate sharp, high-resolution images compared to classical optics. This field is called quantum imaging and has huge potential since optical light can be used to show objects that cannot be seen normally like bones and organs. Quantum correlation describes several relationships between photon pairs, among which entanglement is one and it is used in optical quantum imaging.
The technical challenges of generating entangled photons in X-ray wavelength are greater than optical light, so the team used a different approach. They used a method called quantum illumination to minimize background noise. Using parametric down-conversion (PDC), the researchers split a high energy photon into two low energy photons, signal photon, and idler photon. Researchers mentioned that the application of X-Ray PDC as a source of ghost imaging has been demonstrated recently. In previous publications, the photon statistics were not measured with any experimental evidence to date, which is generated by X-Ray PDC. Similarly, the observations of quantum enhancement sensitivity were not reported at X-ray wavelengths. The work appears in Physical Review X.
The X-Ray PDC was achieved with the help of a diamond crystal. The non-linear structure of crystal splits X-Ray photons into signal and idler beams, each having half the energy of the pump beam. The team scaled up power by using SPring-8 synchrotron in Japan. They shot a 22 KeV beam of X-rays at their crystal, splitting into two beams, carrying the energy of 11 KeV. The signal beam is sent towards the object which has to be imaged. Here, it is a small metal piece with three slits and a detector on the other side. The idler beam is directly sent to another detector so that each beam hits its respective detector at the same place and time.
The researchers then compared the detections. They found 100 correlated photons per point in the image and 10,000 background photons. Researchers could match each idler to the signal and could trace back the photons which came from the beam, thereby eliminating the noise. They later compared the images to the images developed using non-correlated photons. The correlated photons produced a sharper image.
Quantum X-ray imaging could have many uses outside current X-ray technology with a benefit of lower X-ray radiation required for imaging. This means that samples which are easily damaged by X-Rays could be imaged along with the samples with lower temperature requirement. As quantum X-Ray requires particle accelerator, there are no medical applications currently. The researchers say that they have demonstrated the ability to utilize the strong time-energy correlations of photon pairs for quantum-enhanced photodetection. The procedure they have presented possesses great potential for improving the performances of X-ray measurements.
Journal Reference: Physical Review X.