Periodic Reporting for period 2 - PALANTIRI (Phase-sensitive Alteration of Light colorAtioN in quadri-parTIte gaRnet cavIty)
Periodo di rendicontazione: 2023-10-01 al 2024-09-30
Coherently converting information between the microwave frequencies used in wireless networks and quantum computers and the optical frequencies ideal for long-distance communications is a formidable technical challenge. This is because the phase information is fragile and weak, so the coherence between the microwave and optical signals is easily lost. The EU-funded PALANTIRI project aims to create an integrated solid-state device that performs an embedded coherent up-conversion from microwave to optical frequencies. The idea is to combine microwave photons, acoustic phonons, magnons and optical photons in a single low-loss opto-mechanical resonator to build a highly efficient converter capable of achieving a unity conversion rate.
In PALANTIRI, we propose a radically new approach to opto-mechanics by inserting a magnetic element that maintains high cooperativity both with the mechanical mode via magneto-elasticity and with the microwave antenna via contactless inductive coupling. The cost of the increased complexity is the gain of a substantial increase in the effective coupling strength: through magneto-elasticity and opto-mechanics we combine the best of both worlds, i.e. a much stronger coupling to microwaves compared to purely mechanical systems and to optical modes than the purely magnetic systems. This is made possible by recent advances in materials science that allow the fabrication of free-standing micron-sized disks of the ultra-high quality magnetic insulator yttrium iron garnet. The subsequent challenge is the implementation of this idea in the form of an on-chip integrated device. The scientific goal of PALANTIRI is to deliver a proof-of-principle on-chip analog coherent frequency converter with high efficiency within 42 months. The delivered phase-sensitive device will provide the breakthroughs needed to radically expand the connectivity capacity of a backhaul network, enabling high-speed Internet access for anyone, anywhere. It will also provide the fundamental building block for the quantum-capable Internet infrastructure of the future.
In PALANTIRI, we propose a radically new approach to opto-mechanics by inserting a magnetic element that maintains high cooperativity both with the mechanical mode via magneto-elasticity and with the microwave antenna via contactless inductive coupling. The cost of the increased complexity is the gain of a substantial increase in the effective coupling strength: through magneto-elasticity and opto-mechanics we combine the best of both worlds, i.e. a much stronger coupling to microwaves compared to purely mechanical systems and to optical modes than the purely magnetic systems. This is made possible by recent advances in materials science that allow the fabrication of free-standing micron-sized disks of the ultra-high quality magnetic insulator yttrium iron garnet. The subsequent challenge is the implementation of this idea in the form of an on-chip integrated device. The scientific goal of PALANTIRI is to deliver a proof-of-principle on-chip analog coherent frequency converter with high efficiency within 42 months. The delivered phase-sensitive device will provide the breakthroughs needed to radically expand the connectivity capacity of a backhaul network, enabling high-speed Internet access for anyone, anywhere. It will also provide the fundamental building block for the quantum-capable Internet infrastructure of the future.
The consortium has demonstrated its ability to build high quality suspended garnet structures. It has also begun to build the various spectrometers that will be needed to characterize the physical properties, both magnetic and elastic, of these suspended structures. It has also identified the spatio-temporal vector field pattern of the eigenmode with the most efficient quadripartite coupling. The highlights of the work performed are the achievement by the MLU node of high finesse YIG mushrooms and the patterning by ICN2 of suspended YIG rings. Magnetic resonance force microscopy at the CEA has allowed the measurement of the line width of magnetic resonance of a freestanding slab of YIG, while scanning local interformetry at the CNRS has allowed to map the spatio-temporal pattern of elastic deformations. The MPG has integrated this suspended YIG ring into an optical circuit. TUD and RWTH have identified the optimal process to increase the efficiency of the interconversion. An analytical framework for the optimization of the four cooperativities of the quadruple coupling was formulated.
During the second period, two new home-made experimental setups were built to measure the opto-mechanical coupling. The first is a dedicated Brillouin light scattering spectrometer operating inside an electromagnet. The second is a scanning interferometer to map the elastic deformation oscillating at microwave frequencies with a spatial resolution reaching the diffraction limit and a sensitivity of a few picometers. Both setups will allow a spectral and spatial characterization of the opto-mechanical mechanism.
During the second period, two new home-made experimental setups were built to measure the opto-mechanical coupling. The first is a dedicated Brillouin light scattering spectrometer operating inside an electromagnet. The second is a scanning interferometer to map the elastic deformation oscillating at microwave frequencies with a spatial resolution reaching the diffraction limit and a sensitivity of a few picometers. Both setups will allow a spectral and spatial characterization of the opto-mechanical mechanism.
Over the past period, we have achieved four key results. The first is that we have demonstrated our ability to fabricate low-loss suspended garnet cavities in which photons, phonons, and magnons can resonate. This advance is based on the development of new methods for growing and patterning single-crystal garnet thin films. The second is that we have demonstrated our ability to excite and detect spin-wave and elastic modes with large orbital angular momentum index. The method relies on the fact that in magnetic systems the spin-orbit interaction is controllable by the magnetic field and can be made very large. A third result is the discovery of a new mechanism to efficiently generate elastic waves with non-zero orbital angular momentum. The process relies on the scattering of the circular magnetization dynamics on an anisotropic magneto-elastic tensor. We found that the rotational order symmetry of this tensor can be transferred to the elastic wave index. A patent has been filed. A fourth result is the development of an efficient finite element simulation eigen-solver for both spin and elastic waves in axi-symmetric geometries. The solver uses rotational invariance to solve a 3D problem in 2D.