TPnCs_for_QIT · Tunable phononic crystals for quantum information technology

A phononic crystal (PnC) is an engineered metamaterial designed to control the propagation of mechanical waves (phonons). In PnCs, a periodic variation of material properties, e.g. stiffness, mass, or strain, gives rise to a phononic band structure, similar to the electronic band structure in solids. By adjusting the lattice parameters of the PnC, one can open a phononic band gap and engineer localised ‘defect modes’ with ultra-high mechanical quality factors (Qs), enabling state-of-the-art optomechanics and hybrid quantum systems (e.g. transduction or mechanical memory). While promising for quantum information technology (QIT), these systems are currently limited to fixed frequencies and lack dynamic control of Qs and coupling, constraining their utilisation and scalability.In this work, we will develop a dynamically tunable phononic platform based on a suspended silicon nitride membrane. This platform will allow us to realise analogues of fundamental solid-state physics phenomena for mechanical excitation, which we will harness for QIT. Specifically, through dynamic strain engineering, we will control the position and size of the phononic band gap – down to completely closing it. This change in hierarchy/topology in the band structure can be seen as the mechanical analogue to a metal-insulator transition (mMIT). Based on this we will realise a reconfigurable mechanical quantum memory (at 5 GHz; compatible with 1550 nm fibre optics) with an erase function capability.The successful completion of this project will significantly impact quantum optomechanics, introducing a new experimental ‘knob’ – comparable to gating in electronic systems. This will open the door for a large range of experiments and unlock the full potential of phonons for QIT. The researcher Jan N. Kirchhof is in a unique position to realise this project given his background in nanomechanics and phononics, which matches perfectly with the quantum optomechanics expertise of the host group at TUD.