Quantum droplets reveal a new field of macroscopic complexity

Scientists have advanced this field by stabilizing exciton polaritons in semiconductor photonic gratings, achieving long-lived and optically configurable quantum fluids suitable for complex system simulations.

Researchers from Leicester CNR Nanotec and the School of Physics at the University of Warsaw used a new generation of semiconductor photonic gratings to optically customize the composite of quantum light droplets, which combine to form macroscopic coherent states. This study supports a new approach that uses optics to simulate and explore the interactions between artificial atoms in a highly reconfigurable manner. The research results have been published in the renowned journal Nature Physics.

Researchers often use condensed matter systems and photon technology to create microscale platforms that can simulate the complex dynamics of many interacting quantum particles in a more accessible environment. Some examples include optical lattices, superconducting arrays, and ultracold atomic ensembles in photonic crystals and waveguides. In 2006, a new platform emerged that showcased macroscopic coherent quantum fluids of excitons polaritons, exploring multi-body quantum phenomena through optical techniques.

When a semiconductor is placed between two mirrors, the internal electron excitation is strongly influenced by photons trapped between the mirrors. The new boson quantum particles generated from this are called exciton polaritons, which can undergo phase transitions under appropriate conditions, become non-equilibrium boson Einstein condensates, and form macroscopic quantum fluids or light droplets. The quantum fluid of polaritons has many significant properties, one of which is that they are optically configurable and readable, making it easy to measure polariton dynamics. That's why they are so advantageous for simulating multibody physics.

Polarized polariton condensate must be supplemented with particles using an external laser continuous optical pump, otherwise the condensate will dissipate within picoseconds. However, due to the repulsive force between particles, the greater the pumping force of the condensate, the more energy it has, causing particles to escape the condensate and subsequently decay spatial correlation. This is a fundamental issue for optical programmable polariton simulators. Scientists need to come up with a method to make condensate more stable and long-lasting, while still being optically pumped.

Scientists from Leicester CNR Nanotec and the School of Physics at the University of Warsaw have achieved this goal using a new generation of semiconductor photonic gratings. In their paper titled "Reconfigurable Quantum Fluid Molecules in Bound States of Continuum" published in Natural Physics, they injected new properties into polaritons using the sub wavelength properties of photon gratings. Firstly, polaritons can be driven to condense into an ultra long lifetime state called a bound state in a continuum. The charm of BIC lies in the fact that due to the mandatory protection of symmetry from the external continuum of photon modes, they are mostly non radiative. Secondly, due to the dispersion relationship from the grating, the polariton gains a negative effective mass. This means that the polarized polaritons of the pump cannot escape so easily through normal decay channels anymore. Now, researchers have polarized polariton fluids, which have a very long lifespan and can be safely restricted using only optical technology.

These mechanisms, combined together, enable Antonio Gianfrate and Danielle Sanvitto of Lecce CNR Nanotec to optically pump multiple polariton droplets, which can interact and hybridize into macroscopic complexes. They can use this new form of artificial atoms to customize and reversibly configure molecular arrangements and chains: condensation of negative mass BIC polaritons. The BIC characteristic provides a longer lifespan for polaritons, while the negative mass characteristic leads to their optical capture. These findings are supported by the BIC Dirac polariton theory developed between the University of Warsaw, the University of Siegen in Germany, and the University of Lyon in France.

The ultimate advantage of this platform is that artificial quantum composites can be fully optically programmed, but because they are not affected by continuum, they retain a very high lifespan. This may lead to a new adventure in optically programmable large-scale quantum fluids, defined by unprecedented coherent scales and stability, for structured nonlinear lasers and complex system simulations based on polaritons.

"In this artificially polarized Dirac system, there are still several interesting exploration methods. For example, the coupling mechanism between polariton droplets along the grating direction and perpendicular to the grating direction is very different. Along the waveguide, polaritons are actually negative mass particles tightly bound to the pump point. They are perpendicular to the waveguide and undergo ballistic transmission as positive mass particles. The combination of these two mechanisms opens a new window for studying the emergence behavior of synchronization and mode formation in structured polariton quantum fluids," said Helgi Sigur of the School of Physics at the University of Warsaw ð SSON concluded.

Source: Laser Net