Researchers led by Dr. Olga Kocharovskaya, a distinguished professor at Texas A&M University, have successfully demonstrated a novel way to store and release X-ray pulses at the single photon level, achieving quantum memory in the notoriously difficult hard X-ray range. This breakthrough was made possible by using Doppler-shifted nuclear resonant absorbers to form a nuclear frequency comb. The team’s findings, published in Science Advances, open up new possibilities for future X-ray quantum technologies.
The research, performed at the German Electron Synchrotron (DESY) and the European Synchrotron Radiation Facility, was led by Dr. Ralf Röhlsberger of the Helmholtz Institute Jena. The team’s work builds upon earlier theoretical proposals by Kocharovskaya’s group, which suggested using nuclear rather than atomic ensembles to achieve longer memory times. This approach could lead to the development of long-lived broad-band compact solid-state quantum memories.
Achieving Quantum Memory in the Hard X-Ray Range
Quantum memory is a crucial element in quantum networks, enabling the storage and retrieval of quantum information. However, processing light signals is far more complex compared to working with common electronic signals. An international team of researchers, including Dr. Olga Kocharovskaya from Texas A&M University, has demonstrated a novel way of storing and releasing X-ray pulses at the single photon level, achieving quantum memory in the hard X-ray range.
The team’s work, led by Professor Dr. Ralf Röhlsberger, utilized Doppler-shifted nuclear resonant absorbers to form a nuclear frequency comb, enabling the storage and retrieval of X-ray photons with high fidelity. This achievement is a significant milestone in the development of quantum technologies, as it allows for the manipulation of X-ray photons at the single-photon level.
The concept of quantum memory is based on the idea of storing quantum information in a physical system, such as atoms or nuclei, and retrieving it later. Several protocols for quantum memories have been established, but they are limited to optical photons and atomic ensembles. Using nuclear rather than atomic ensembles delivers much longer memory times achievable even at high solid-state densities and room temperature.
The Nuclear Frequency Comb Protocol
The idea behind the team’s new protocol is based on the Doppler frequency shift caused by the motion of a set of moving nuclear absorbers. A short pulse with a spectrum matching the comb absorbed by such a set of nuclear targets will be re-emitted with a delay determined by the inverse Doppler shift as a result of constructive interference between different spectral components.
In their experiment, the team used one stationary and six synchronously moving absorbers that formed a seven-teeth frequency comb. The nuclear coherence lifetime is the limiting factor that determines the maximum storage time for this type of quantum memory. Using longer-lived isomers than the iron 57 isotope chosen for their current study would result in a longer memory time.
Potential Applications and Future Directions
The team’s research highlights the potential for extending optical quantum technologies to the short wavelength range, which is intrinsically less “noisy” due to averaging of fluctuations over a large number of high-frequency oscillations. The next steps planned by the team include on-demand release of the stored photon wave packets, which could lead to the realization of entanglement between different hard X-ray photons — the main resource for quantum information processing.
Dr. Kocharovskaya notes that the challenging possibilities are intriguing and that she and her collaborators look forward to continuing to explore the potential of their tunable, robust, and highly versatile platform to advance the field of quantum optics at X-ray energies in the near future.
Research Impact and Funding
Kocharovskaya’s research was supported in part by the National Science Foundation (Grant No. PHY-2012194 “Quantum Optics with Ultra-Narrow Gamma Resonances”). The achievement of quantum memory in the hard X-ray range has significant implications for the development of quantum technologies, and it is a testament to the importance of fundamental research in advancing our understanding of the physical world.
As one of the world’s leading research institutions, Texas A&M University is at the forefront in making significant contributions to scholarship and discovery, including in science and technology. The university’s research creates new knowledge that provides basic, fundamental, and applied contributions resulting, in many cases, in economic benefits to the state, nation, and world.
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