Researchers propose a new method to generate light source by using entangled pho

Entanglement is a strange phenomenon in quantum physics. No matter how far the distance between two particles is, there is an internal connection. When one measurement is made, another measurement is immediately given. Researchers at Purdue University have proposed a new and non-traditional method to generate a special light source composed of entangled photons. On September 6, 2022, they published their findings in Physical Review Research.

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The team proposed a method to generate entangled photons where there is no extreme ultraviolet (XUV) wavelength. Their work provides a roadmap for how to generate these entangled photons, and uses them to track the dynamics of electrons in molecules and materials. The time scale is extremely short, in attoseconds.

Dr. Niranjan Shivaram, Assistant Professor of Physics and Astronomy, said: "The entangled photons in our work are guaranteed to reach a given position in a very short time, as long as they travel the same distance. The correlation of their arrival time makes them very useful in measuring ultrafast events. The attosecond metrology is an important application, which can promote the measurement limit of the shortest time scale phenomenon. This kind of entangled photon source can also be used in quantum imaging and spectroscopy. In these fields, entangled photons have been proven Ming can enhance the ability to obtain information, but it is now the wavelength of XUV or even X-ray. "

Schematic diagram of the generation and absorption of entangled photons in a spherical cavity. The emitting and absorbing atoms are located at the two focal points of the sphere. Photon is reflected by the boundary of the cavity and propagates along an equal length path to the absorber. The shape of the cavity will affect the rate of the process through geometric factors.

The authors of this paper, entitled Attosecond entangled photons from two-photon decay of metastable atoms: A source for attosecond experiments and beyond, are all from the Department of Physics and Astronomy of Purdue University, and cooperate with the Purdue Institute of Quantum Science and Engineering (PQSEI). They are Dr. Yimeng Wang, a doctoral candidate in experimental ultrafast spectroscopy, Siddhant Pandey, a distinguished professor of physics and astronomy Albert Overhauser, Dr. Chris H. Greene and Dr. Shivaram, who just graduated from Purdue University.

"The Department of Physics and Astronomy of Purdue University has a powerful atomic, molecular and optical (AMO) physics project, which brings together experts from various branches of AMO." Shivaram said. "Chris Greene's expertise in theoretical atomic physics, coupled with Niranjan's background in the relatively young field of experimental attosecond science, contributed to this cooperative project. Although many universities have AMO programs, Purdue University's AMO program is unique because it has experts in multiple branches of AMO science."

Fig. 3 The photon correlation function is a function of the time difference t2 − t1, which indicates that the correlation time is about 200 attoseconds.

Each researcher has played an important role in this ongoing study. Greene initially proposed the idea of using the photons emitted by helium atoms as entangled photon sources. Shivaram suggested applying them to attosecond science and proposed an experimental scheme. Wang and Greene subsequently developed a theoretical framework for calculating the emission of entangled photons from helium atoms, while Pandey and Shivaram estimated the emission/absorption rate of entangled photons and worked out the details of the proposed attosecond experimental scheme.

The publication of this book marks the beginning of Shivaram and Greene's research. In this article, the author puts forward this idea and the theoretical aspects of the experiment. Shivaram and Greene plan to continue to cooperate on experiments and further theoretical ideas. Shivaram's ultrafast Quantum Dynamics Group is currently building a device to prove some of these ideas through experiments. He said that he hoped that other researchers of second science could also begin to study these ideas. The joint efforts of many research groups can further increase the impact of this work. Finally, they hope to reduce the time scale of entangled photons to zeepto seconds, or 10-21 seconds.

(a) Entangled two-photons are generated in XUV by two-photon decay of 1s2s1S0 state excited by four photon excitation using a broadband 240 nm laser. (b) Using a high photon flux helium lamp and a 2059 nm coupled laser, the 1s2s state is excited sequentially in two steps through the 1s2p state. (c) The waste technology in 1s2s state is filled with multiphoton pump pulse and Stark shift pulse, which realizes rapid adiabatic passage and ionization suppression through LICS (LICS not shown). (a) The estimated two-photon generation rate for each scheme is also shown in - (c). (d) An experimental scheme is proposed to generate XUV entangled photons and use them in the attosecond pumped probe photoionization experiment. (e) An attosecond pump probe photoionization scheme using entangled two-photons in molecules.

In order to understand time, one must understand that electrons play a fundamental role in determining the behavior of atoms, molecules and solid materials. The time scale of electron motion is usually in femtosecond and atto second scales. According to Shivaram, it is important to understand the dynamics of electrons and track their movements on these ultra short time scales.

"The goal in the field of ultrafast science is to make such electronic 'films', and then use light to control the behavior of these electrons, so as to design chemical reactions, manufacture materials with new properties, and manufacture molecular scale devices." He said, "This is the most basic light matter interaction, and there are many possibilities for discovery. One zepto second is 10-21 seconds. One thousand zepto seconds is an atto second. Researchers are only now beginning to explore the phenomenon of zeep seconds, although it is impossible to achieve experimentally due to the lack of zeep second laser pulses. Our unique method is to use entangled photons instead of photons in the laser pulses, which allows us to reach the zepto second energy level. This will require large The amount of experimental effort is likely to be achieved in five years. "

Source: Attosecond entangled photons from two-photon decay of metastable atoms: A source for attosecond experiments and beyond, Physical Review Research (2022). DOI: 10.1103/PhysRevResearch.4.L032038