Increased Fidelity via Quantum Correlated X-Rays: IF via QCX

Project # 23-053 | Year 2 of 2

Gary Walker^a, Sean Sheehan^a, Hilary Tarvin^a, Joseph Wunschel^b, Richard Sandberg^b, Ryan Camacho^c

^aRemote Sensing Lab- Nellis (RSLN), ^bY-12 National Security Campus, ^cUniversity: BYU
_{This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy, the NNSA Office of Defense Programs, and supported by the Site-Directed Research and Development Program. DOE/NV/03624–1925.}

Abstract

This project investigated the use of quantum-correlated x-rays (QCX) for enhanced x-ray interrogation, and Hong-Ou-Mandel (HOM) metrology was identified as a promising approach. Measurements at the Advanced Photon Source (APS) have conclusively demonstrated the production of correlated x-ray photon pairs, but the project ended before an HOM interferometer could be built.

Background

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 QCX may provide.

Technical Approach

A feasibility study identified HOM metrology as a challenging but promising approach. An HOM interferometer using 10-keV photons has a predicted resolution less than 10^-18 seconds, which may allow stand-off measurement of key target attributes. Work began at Brigham Young University (BYU) to build an HOM interferometer at infrared wavelengths as a steppingstone to using x-rays, but it was postponed near the end of the first year at about 70% complete to prepare for beam time at the APS. The overarching goal for the second year, as requested by the Site-Directed Research and Development committee, was to demonstrate quantum-correlated x-rays. This would be done via spontaneous parametric down conversion (SPDC), which is a non-linear optical process in which a single photon can down convert into a pair of lower energy photons whose sum is the original. The efficiency of the process is extremely low, but it is highest near Bragg angles. For beam time at the APS, a single-crystal diamond was used with a beam energy of 22 keV to look for down converted photons at 11 keV. The Bragg angle for the desired 660 plane is θ_B = 42.094°, and the crystal was rotated past that by ~10 mdeg to 42.104°. A pair of Vortex single-photon detectors was positioned to look for the down converted pair. In preparation for beam time, BYU spearheaded efforts to gather or purchase the necessary equipment, while the Nevada National Security Sites (NNSS) team led efforts to estimate the observable rate of correlated pairs using published theoretical equations. These calculations proved to have little practical value, but the in-depth research and learning they required enabled the NNSS team to actively participate and contribute during beam time.

Results and Technical Accomplishments

The research study entailed two experimental campaigns at the APS. The first beam time, which occurred in December 2022, was a learning experience. Despite some geometry mistakes runtime totaled 21 hours, and a tentative signal was seen. Following beam time, the NNSS team developed in-depth analysis that showed a strong detection of correlated pairs, though the rate was low. During the April 2023 campaign, improvements to the experimental setup resulted in an unambiguous correlated signal at ~11 keV with a much higher rate. Improvements included a stepwise approach to ensure the correct geometry, an improved rotation stage, no lead shielding to reduce scattering peaks, and improved real-time analysis. The figure shows a clear peak centered at 0 ns, while no peak is seen for the background runs. The April runtime totaled 64 hours in a variety of configurations, with a signal of 4,001 coincident pairs against a background of 740.

Conclusions and Path Forward

This project has identified HOM metrology as a promising approach to using QCX for enhanced x-ray interrogation. Two week-long trips to the APS beamline have demonstrated QCX pairs. This was done with high confidence but low rate for the December beam time. Data collected during April showed unambiguous detection and a higher rate approaching what would be needed for HOM metrology. The project ended before this could be pursued further.

X-ray HOM metrology has the potential for non-contact measurement of key attributes of an enclosed target. Note, however, that this study is only proof of principle. Tremendous advancement in the generation of correlated x-ray pairs would be required for practical use.

Publications

• Title: Confirming X-ray parametric down conversion by time–energy correlation
  Journal / Conference: Results in Physics
  Year: 2023
  Author(s): N.J. Hartley, D. Hodge, T. Buckway, R. Camacho, P. Chow, E. Christie, A. Gleason, S. Glenzer, A. Halavanau, A.M. Hardy, C. Recker, S. Sheehan, S. Shwartz, H. Tarvin, M. Ware, J. Wunschel, Y. Xiao, R. Sandberg, G. Walker
  
• Title: Evidence of Parametrically Down-Converted Photon Pairs in the X-Ray Spectrum
  Journal / Conference: Optica Imaging Congress, Technical Digest Series (Optica Publishing Group, 2023), paper JW2A.40, August 2023
  Year: 2023
  Author(s): Abigail Mae Hardy, Nicholas J Hartley, Daniel Hodge, Sean Sheehan, Eric Christie, Taylor Buckway, David Allred, Michael Ware, Shiuh-hua Wood Chiang, Alex Halavanau, Hilary Tarvin, Joseph Wunschel, Yuming Xiao, Paul Chow, Arianna E Gleason, Ryan Camacho, Gary Walker, and Richard L. Sandberg
  

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