New photonic nanocavities open up new fields of optical confinement

In a significant leap in quantum nanophotonics, a team of European and Israeli physicists introduced a new type of polarized cavity and redefined the limits of light confinement. This groundbreaking work was detailed in a study published yesterday in Natural Materials, showcasing an unconventional photon confinement method that overcomes the traditional limitations of nanophotonics.

For a long time, physicists have been searching for ways to force photons into increasingly smaller volumes. The natural length scale of photons is wavelength, and when photons are forced into cavities much smaller than the wavelength, they actually become more "concentrated". This concentration enhances the interaction with electrons and amplifies the quantum process inside the cavity. However, despite significant success in limiting light to deep sub wavelength volumes, dissipation effects remain a major obstacle. The photons in the nanocavity are absorbed very quickly, much faster than the wavelength, which limits the applicability of the nanocavity in some of the most exciting quantum applications.

The research team led by Professor Frank Koppens from ICFO in Barcelona, Spain, has addressed this challenge by creating nanocavities with unparalleled sub wavelength volume and extended lifetime combinations. These nanocavities, with dimensions smaller than 100x100nm2 in area, are only 3nm thin, limiting the duration of light much longer. The key lies in the use of hyperbolic phonon polaritons, which are unique electromagnetic excitations that occur in two-dimensional materials that form cavities.

Unlike previous studies on cavities based on phonon polaritons, this work utilizes a new indirect constraint mechanism. The nanocavity is made by drilling nanoscale holes on a gold substrate, and has the extremely high accuracy of a helium focused ion beam microscope. After drilling, hexagonal boron nitride is transferred to its top. HBN supports electromagnetic excitation called hyperbolic photon polaritons, which are similar to ordinary light but can be confined to very small volumes. When polaritons pass above the metal edge, they are strongly reflected by the metal, which limits them. Therefore, this method avoids directly shaping hBN while maintaining its original mass, thereby achieving highly restricted and long-lived photons in the cavity.

This discovery began with a chance observation during the use of near-field optical microscopy to scan 2D material structures in another project. Near field microscopy allows for excitation and measurement of polaritons in the mid infrared range of the spectrum, and researchers have noticed that these polaritons reflect abnormally strongly from the edges of the metal. This unexpected observation sparked deeper research, enabling a unique constraint mechanism and its relationship with the formation of nanorays.

However, the team was very surprised when producing and measuring cavities. "Experimental measurements are usually worse than theory suggests, but in this case, we find that the performance of the experiment is better than optimistic simplified theoretical predictions," said Dr. Hanan Herzig Sheinfux from the Department of Physics at the University of Bayland, the first author. This unexpected success has opened the door to new applications and advancements in quantum photonics, breaking through what we consider possible boundaries.

Dr. Herzig Sheinfux conducted this study with Professor Koppens during his postdoctoral studies at ICFO. He plans to use these cavities to observe previously thought impossible quantum effects and further investigate the interesting and counterintuitive physics of hyperbolic phonon polariton behavior.

Source: Laser Net