arXiv subjects

Teemu Loippo

Publications and source records attributed to Teemu Loippo.

4 recordsLinked to original sources

arXiv2026

Coherent control of thermal transport with pillar-based phononic crystals

Two-dimensional phononic crystals (PnCs) formed by a periodic array of holes in a suspended membrane have previously been used to coherently control thermal conductance at low temperatures by modifying the phonon dispersion, thereby altering the phonon group velocities and the density of states. Here, in contrast, we demonstrate that PnCs formed by a periodic array of Al pillars on an uncut \SiN membrane can also be used to achieve similar coherent control. We have measured and simulated the thermal conductance of four pillar-based PnCs with different lattice constants ranging from 0.3 to 5 $\mu$m at sub-Kelvin temperatures, showing a strong up to an order of magnitude reduction in thermal conductance compared to an unaltered membrane. For the larger lattice constants $> 1 $ $\mu$m, however, the experiments do not agree with the coherent theory simulations, which we interpret as a breakdown of coherence induced by increasingly effective diffusive scattering due to the roughness of the Al pillar surfaces.

cond-mat.mes-hall↗

arXiv2025

Optomechanical quantum bus for donor spins in silicon

Silicon is the foundation of current information technology, and a promising platform for future quantum information technology as silicon-based qubits exhibit some of the longest coherence times in solid-state. At the same time, silicon is the underlying material for advanced photonics activity, and photonics structures in silicon can be used to define optomechanical cavities where the vibrations of nanoscale mechanical resonators can be probed down to the quantum level with laser light. Here, we propose to bring all these developments together by coupling silicon donor spins into optomechanical structures. We show theoretically and numerically that this allows telecom wavelength optical readout of the spin-qubits and implementing high-fidelity entangling two-qubit gates between donor spins that are spatially separated by tens of micrometers. We present an optimized geometry of the proposed device and discuss with the help of numerical simulations the predicted performance of the proposed quantum bus. We analyze the optomechanical spin readout fidelity and find the optimal donor species for different coupling mechanisms.

quant-ph↗

arXiv2023

Strain effects in phosphorous bound exciton transitions in silicon

Donor spin states in silicon are a promising candidate for quantum information processing. One possible donor spin readout mechanism is the bound exciton transition that can be excited optically and creates an electrical signal when it decays. This transition has been extensively studied in bulk, but in order to scale towards localized spin readout, microfabricated structures are needed for detection. As these electrodes will inevitably cause strain in the silicon lattice, it will be crucial to understand how strain affects the exciton transitions. Here we study the phosphorous donor bound exciton transitions in silicon using hybrid electro-optical readout with microfabricated electrodes. We observe a significant zero-field splitting as well mixing of the hole states due to strain. We can model these effects assuming the known asymmetry of the hole g-factors and the Pikus-Bir Hamiltonian describing the strain. In addition, we describe the temperature, laser power and light polarization dependence of the transitions. Importantly, the hole-mixing should not prevent donor electron spin readout and using our measured parameters and numerical simulations we anticipate that hybrid spin readout in a silicon-on-insulator platform should be possible, allowing integration to silicon photonics platforms.

cond-mat.mes-hall↗

arXiv2021

The effects of ion implantation damage to photonic crystal optomechanical resonators in silicon

Optomechanical resonators were fabricated on a silicon-on-insulator (SOI) substrate that had been implanted with phosphorus donors. The resonators' mechanical and optical properties were then measured (at 6 kelvin and room temperature) before and after the substrate was annealed. All measured resonators survived the annealing and their mechanical linewidths decreased while their optical and mechanical frequencies increased. This is consistent with crystal lattice damage from the ion implantation causing the optical and mechanical properties to degrade and then subsequently being repaired by the annealing. We explain these effects qualitatively with changes in the silicon crystal lattice structure. We also report on some unexplained features in the pre-anneal samples. In addition, we report partial fabrication of optomechanical resonators with neon ion milling.

physics.optics↗