Project #: 22-160 | Year 1 of 3
Gary Walker,a Ryan Martin,a Daniel Champion,a Ryan Camachob
aNevada National Security Site (NNSS)-Remote Sensing Laboratory; bBrigham Young University (BYU)
This project is investigating the use of quantum-correlated x-rays (QCX) for enhanced interrogation of enclosed targets. Efforts have focused on developing Hong-Ou-Mandel (HOM) metrology using x-rays, with preparatory work at near-infrared wavelengths, followed by demonstration of entangled x-rays in the coming year.
There is a long‐standing need within the response community to be able to determine the internal characteristics of an enclosed target. Traditional x‐ray techniques provide standoff capability to image the interior of the target and its contents. However, other key attributes can only be determined using methods that require physical contact with the enclosure or contents, which may not be allowable or possible. This project has explored the benefits that the use of QCX may provide, including perhaps non-contact measurement of these key attributes, as well as potential for enhanced imaging. Team members included personnel from the NNSS and subject matter experts from BYU. Efforts began with literature research and discussion to determine the theoretical benefits and to identify avenues for research. Initial discussion focused on three approaches: ghost imaging, quantum plenoptic imaging, and HOM metrology. Ghost imaging was considered to have a poor cost-to-benefit ratio, while quantum plenoptic imaging would be prohibitively difficult using current technology. Conversely, HOM metrology was considered challenging but feasible, and the potential benefits made it worth pursuing. In an HOM interferometer, correlated photons are sent along separate paths, as shown in figure 1a. If the photons arrive at the beam splitter in phase, they will exit from the same port of the splitter and will thus go to a single detector. However, if they are out of phase, they will exit opposite ports and will thus be seen by both detectors. For 10-keV x-ray photons, coincidence measurements between the detectors are predicted to detect a phase difference of less than 10-18 seconds, as shown in figure 1b. This ultra-fine resolution may allow stand-off measurement of key target attributes that are currently available only through physical contact.
Because the BYU team has quantum expertise and experience with quantum optics, the HOM interferometer build took place at BYU. It was built for near-infrared wavelengths as a steppingstone towards building an x-ray interferometer in years two and three. By repurposing equipment already on hand, the build advanced quickly, generating down-converted photons at 710 nm by early May. Necessary equipment was also purchased, including a dual-polarization down-conversion crystal, a spatial light modulator, and a single-photon camera to enable 2D HOM measurements. BYU students also wrote code to simulate the overall process, and NNSS personnel evaluated the code, made improvements to the simulated uncertainty, and laid groundwork for a photon count input parameter. In parallel, the team prepared and submitted a proposal for beam time at the Advanced Photon Source (APS) at Argonne, as well as an FY 2023 SDRD proposal. The APS proposal was accepted, and beam time is scheduled for December 2022. The SDRD proposal was also accepted, but with limited funding, pending the demonstration of entangled x-ray photons. Due to manpower, budget, and schedule constraints, work on the infrared HOM interferometer has been postponed in order to prepare for beam time at the APS, where the primary goal will be to demonstrate the production of entangled x-ray photons.
This project has identified HOM metrology as a promising approach to using QCX for enhanced x-ray interrogation. Good progress was made towards building a near-infrared HOM interferometer, and the BYU team estimates they are 70% of the way to generating the HOM dip seen in Figure 1b. Further work on this interferometer has been postponed, and efforts are now focused on preparing for APS beam time. Efforts there will progress in four stages. The first will be to generate entangled photons at 10 keV. Subsequent stages will be to align the interferometer, count the entangled pair rate, and measure the x-ray HOM dip.
The use of QCX for x-ray interrogation may have the potential for non-contact measurement of key attributes of an enclosed target. This would represent a significant and valuable advancement beyond current methods. QCX may also provide enhanced imaging capability. Note, however, that this study is a proof of principle. The HOM interferometer is feasible but difficult at 10 keV, while 100 keV x-rays are necessary for practical use.
Publications, Technology Abstracts, Presentations/Posters
Pending results from APS beam time and later from the near-infrared HOM interferometer.
This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy. DOE/NV/03624–1598.