Researchers suggest a new way to generate a light source made of entangled photons

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Entanglement is a strange phenomenon in quantum physics where two particles are inherently connected regardless of the distance between them. When one is measured, the other is immediately a given. Purdue University researchers have proposed a new, unconventional approach to generate a special light source made up of entangled photons. On September 6, 2022, they published their findings in: Physical Assessment Exam.

The team proposed a method to generate entangled photons at extreme ultraviolet (XUV) wavelengths where no such source currently exists. Their work provides a roadmap on how to generate these entangled photons and use them to track the dynamics of electrons in molecules and materials on the incredibly short timescales of attoseconds.

“The entangled photons in our work are guaranteed to arrive at a given location within a very short duration of attoseconds, as long as they travel the same distance,” said Dr. Niranjan Shivaram, assistant professor of physics and astronomy. “This correlation in their arrival time makes them very useful to measure ultrafast events. An important application is in attosecond metrology to push the boundaries of measurement of the shortest timescale phenomena. This source of entangled photons can also be used in quantum imaging and spectroscopy, where Entangled photons have been shown to improve the ability to obtain information, but now at XUV and even X-ray wavelengths.”

The authors of the publication, titled “Attosecond Entangled Photons of Two-Photon Decay of Metastable Atoms: A Resource for Attosecond Experiments and Beyond,” are all from the Purdue University Department of Physics and Astronomy and are collaborating with the Purdue Quantum Science and Engineering Institute (PQSEI). They are Dr. Yimeng Wang, a recent graduate of Purdue University; Siddhant Pandey, Ph.D. candidate in experimental ultrafast spectroscopy; dr. Chris H. Greene, Albert Overhauser Distinguished Professor of Physics and Astronomy; and dr. Shivaram.

“Purdue’s Department of Physics and Astronomy has a strong atomic, molecular, and optical (AMO) physics program, which brings together experts in different areas of AMO,” said Shivaram. Chris Greene’s expert knowledge of theoretical atomic physics combined with Niranjan’s background in the relatively young field of experimental attosecond science led to this collaborative project. While many universities have AMO programs, Purdue’s AMO program is uniquely diverse as it has experts in multiple sub-fields of AMO -science.”

Each researcher played an important role in this ongoing investigation. Greene initially suggested the idea of ​​using photons emitted by helium atoms as a source of entangled photons and Shivaram suggested applications for science and proposed experimental schemes. Wang and Greene then developed the theoretical framework to calculate entangled photon emission from helium atoms, while Pandey and Shivaram estimated entangled photon emission/absorption rates and elaborated the details of the proposed attosecond experimental schemes.

The publication marks the beginning of this research for Shivaram and Greene. In this publication, the authors present the idea and elaborate the theoretical aspects of the experiment. Shivaram and Greene plan to continue working together on experimental and further theoretical ideas. Shivaram’s lab, the Ultrafast Quantum Dynamics Group, is currently building a device to experimentally demonstrate some of these ideas. According to Shivaram, the hope is that other researchers in attosecond science will start working on these ideas. A concerted effort by many research groups could further increase the impact of this work. Eventually they hope to get the timescale of entangled photons down to the zeptosecond, 10-21 seconds.

“Typically, experiments on attosecond timescales are performed using attosecond laser pulses as ‘flashes’ to ‘image’ the electrons. The current limits for these pulses are about 40 attoseconds. Our proposed idea of ​​using entangled photons would can decrease to a few attoseconds or zeptoseconds,” says Shivaram.

To understand the timing, one must understand that electrons play a fundamental role in determining the behavior of atoms, molecules and solid materials. The timescale of electron movement is typically in the femtosecond (one millionth of a billionth of a second-10-15 seconds) and attosecond (one billionth of a billionth of a second, or 10-18 seconds) scale. According to Shivaram, it is essential to understand the dynamics of electrons and track their movement on these ultra-short time scales.

“The goal of the field of ultrafast science is to make such ‘films’ of electrons and then use light to control the behavior of these electrons to develop chemical reactions, make materials with new properties, build molecular-scale devices. make, etc.” he says. “This is light-matter interaction at its most basic level, and the possibilities for discovery are many. A single zeptosecond is 10-21 seconds. A thousand zeptoseconds is an attosecond. Researchers are only now beginning to investigate zeptosecond phenomena, although it is experimentally out of reach due to a lack of zeptosecond laser pulses. Our unique approach to using entangled photons instead of photons in laser pulses could allow us to achieve the zeptosecond regime. This will require significant experimental effort and is likely to be possible within five years.”

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More information:
Yimeng Wang et al, Attosecond entangled photons from two-photon decay of metastable atoms: a source for attosecond experiments and beyond, Physical Assessment Exam (2022). DOI: 10.1103/PhysRevResearch.4.L032038

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