The field of quantum physics has long grappled with the challenge of efficiently synchronizing individual and independently generated photons. Such synchronization would have significant implications for quantum information processing, particularly in regards to the interactions between multiple photons. Researchers at the Weizmann Institute of Science have recently made progress in this area, using an atomic quantum memory operating at room temperature to synchronize single photons. This groundbreaking study, published in Physical Review Letters, has the potential to open up new avenues of research for multi-photon states and their application in quantum information processing.
The idea for this project came about several years ago when the research group of Ian Walmsley, in collaboration with the current group, demonstrated an atomic quantum memory with an inverted atomic-level scheme. This inverted scheme, known as fast ladder memory (FLAME), is fast and noise-free, making it ideal for synchronizing single photons. As most quantum sources used in research thus far are probabilistic and not suitable for generating multi-photon states at a reasonable rate, the researchers set out to explore the possibility of using an atomic quantum memory to store and release probabilistically generated photons on demand to generate a multi-photon state.
To achieve their objective of synchronizing single photons using an independent room-temperature atomic quantum memory, the researchers had to make several improvements to the memory and build a single-photon source that could efficiently interface with the memory. They also developed suitable control electronics for the experiment. The FLAME memory used in this study has an inverted atomic-level scheme, known as a ladder scheme, which is both fast and noise-free. Additionally, the small wavelength mismatch of the signal and control light-field transitions in rubidium atoms enables a relatively long memory lifetime compared to other ladder schemes. The photons used in the experiment were generated using the same atomic-level structure as the memory, ensuring efficient coupling of the photons with the memory.
The FLAME memory scheme used by the researchers proved to be highly successful in synchronizing individual photons at a high rate. They achieved an end-to-end efficiency of 25% and a final antibunching of 0.023 for the synchronized photons. The antibunching value indicates the “singleness” of the photons, with perfect single photons having a value of 0. The noise-free operation of the memory in this experiment contributed to the near-perfect singleness of the synchronized photons. The synchronization rate achieved by the researchers was more than 1,000 times better than previous demonstrations using photons compatible with atomic systems. This breakthrough opens up new opportunities for studying interactions between multi-photon states and atoms, such as deterministic two-photon entangling gates. Quantum information processing and quantum optics systems stand to benefit greatly from these findings.
The researchers at the Weizmann Institute of Science are currently pursuing two main paths for future research. The first is to achieve strong photon-photon interactions with rubidium atoms, similar to the system used for synchronization. This would allow them to demonstrate a deterministic entangling gate between synchronized single photons. These gates are critical for photonic quantum computation, as they reduce resource overhead compared to current methods. To date, such gates have only been demonstrated with cold atoms setups, limiting the scalability of these systems. In addition, the researchers are working on further developing their FLAME memory to enable it to store a photonic qubit, which would allow them to perform quantum computations using photons. This development holds promise for advancing the field of quantum computing and expanding the capabilities of quantum information processing systems.
The synchronization of independent photons in quantum physics has long been a challenge, but researchers at the Weizmann Institute of Science have made significant progress in this area. Through their use of an atomic quantum memory operating at room temperature and their improvements to the memory system, they were able to synchronize single photons at an impressive rate. This breakthrough has important implications for quantum information processing and the study of multi-photon states. Future research aims to achieve strong photon-photon interactions and expand the capabilities of the FLAME memory system. Ultimately, this research has the potential to revolutionize the field of quantum physics and pave the way for new advancements in quantum computing.
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