Scientists were astounded to observe electromagnetic transmission time reflections.

 

(a) Conventional spatial reflections: A person sees their face when they look into a mirror, or when they speak the echo comes back in the same order. (b) Time reflections: The person sees their back when they look into a mirror, and they see themselves in different colors. They hear their echoes in a reversed order, similar to a rewound tape. (c) Illustration of the experimental platform used to realize time reflections. A control signal (in green) is used to uniformly activate a set of switches distributed along a metal stripline. Upon closing/opening the switches, the electromagnetic impedance of this tailored metamaterial is abruptly decreased/increased, causing a broadband forward-propagating signal (in blue) to be partially time-reflected, (in red) with all its frequencies converted. (Adapted from Nature Physics) CREDIT Andrea Alu

Researchers from the CUNY Graduate Center's Advanced Science Research Center (CUNY ASRC) describe a ground-breaking experiment in which they were able to see time reflections of electromagnetic impulses in a specially designed metamaterial.

In a switched transmission-line metamaterial, whose effective capacitance is changed abruptly and uniformly by a synchronized array of switches, they witnessed photonic time reflection and related broadband frequency translation.

 

The reflection is in the glass. When we look in a reflection, we are accustomed to seeing our own faces. Electromagnetic light waves bounce off the mirror surface to create the reflected images, which is a common occurrence known as spatial reflection.

Researchers have conjectured about the possibility of seeing temporal reflections, also known as time reflections, a distinct kind of wave reflection, for more than 60 years. Unlike spatial reflections, which take place when light or sound waves come into contact with a boundary like a mirror or a wall at a specific location in space, time reflections happen when the entire medium through which the wave is flowing suddenly and abruptly changes its properties over all of space. During such an occurrence, a wave component is time-reversed, changing its frequency.

Electromagnetic swells have noway before endured this circumstance. The main cause of this dearth of evidence is the difficulty in changing a material's optic characteristics snappily enough to beget time reflections.

" This has been instigative to see because of how long ago this counterintuitive miracle was prognosticated, and how different time- reflected swells bear compared to space- reflected bones ," said Andrea Alù, launching director of the CUNY ASRC Photonics Initiative and distinguished professor of drugs at The City University of New York Graduate Center and the paper's corresponding author.

" We realised the conditions to alter the material's parcels in time suddenly and with a large discrepancy using a sophisticated metamaterial design."

The results of the study were presented in a paper published in the Journal of the American Chemical Society in the year 2000. As a consequence, the final part of the signal is reflected first, producing an odd echo. As a result, your image would be inverted in a time mirror, displaying your back rather than your face. This remark would sound similar to how a tape is wound up if it were to be heard acoustically.

Engineered metamaterials were used in this exercise. They constructed a printed board, meandering strip of metal, about 6 meters long, with a dense array of electrical switches linked to reservoir capacitors, and they pumped broadband signals into it.

The simultaneous actuation of all switches caused an abrupt and uniform doubling of the impedance along the line. This abrupt and important change in electromagnetic properties generated a temporal interface, and the measured signals accurately carried a time-reversed replica of the entering signals.

The experiment effectively reversed time and changed the frequency of broadband electromagnetic waves, demonstrating the feasibility of a time interface. The most extreme wave control is made possible by these two methods, which add new degrees of freedom. The achievement might pave the way for novel wireless messaging applications and the development of portable, low-power wave-based computers.

Electromagnetic time crystals and time metamaterials are made feasible with the aid of the recently created metamaterial platform. When coupled with specialized spatial interfaces, the finding might create new avenues for photonic technologies as well as new ways to improve and control wave-matter interactions.

Reference: Moussa, H., Xu, G., Yin, S. et al. Observation of temporal reflection and broadband frequency translation at photonic time interfaces. Nat. Phys. (2023). DOI: 10.1038/s41567-023-01975-y