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1. Deconvolving Contributions to Decoherence in Molecular Electron Spin Qubits: A Dynamic Ligand Field Approach

   https://doi.org/10.1002/chem.202100845  

   Mirzoyan, Ruben ; Kazmierczak, Nathanael_P ; Hadt, Ryan_G ( May 2021 , Chemistry – A European Journal)

   In the past decade, transition metal complexes have gained momentum as electron spin‐based quantum bit (qubit) candidates due to their synthetic tunability and long achievable coherence times. The decoherence of magnetic quantum states imposes a limit on the use of these qubits for quantum information technologies, such as quantum computing, sensing, and communication. With rapid recent development in the field of molecular quantum information science, a variety of chemical design principles for prolonging coherence in molecular transition metal qubits have been proposed. Here the spin‐spin, motional, and spin‐phonon regimes of decoherence are delineated, outlining design principles for each. It is shown how dynamic ligand field models can provide insights into the intramolecular vibrational contributions in the spin‐phonon decoherence regime. This minireview aims to inform the development of molecular quantum technologies tailored for different environments and conditions.

    

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2. Quantum communication with itinerant surface acoustic wave phonons

   https://doi.org/10.1038/s41534-021-00511-1  

   Dumur, É. ; Satzinger, K. J. ; Peairs, G. A. ; Chou, M. -H. ; Bienfait, A. ; Chang, H. -S. ; Conner, C. R. ; Grebel, J. ; Povey, R. G. ; Zhong, Y. P. ; et al ( December 2021 , npj Quantum Information)

   Surface acoustic waves are commonly used in classical electronics applications, and their use in quantum systems is beginning to be explored, as evidenced by recent experiments using acoustic Fabry–Pérot resonators. Here we explore their use for quantum communication, where we demonstrate a single-phonon surface acoustic wave transmission line, which links two physically separated qubit nodes. Each node comprises a microwave phonon transducer, an externally controlled superconducting variable coupler, and a superconducting qubit. Using this system, precisely shaped individual itinerant phonons are used to coherently transfer quantum information between the two physically distinct quantum nodes, enabling the high-fidelity node-to-node transfer of quantum states as well as the generation of a two-node Bell state. We further explore the dispersive interactions between an itinerant phonon emitted from one node and interacting with the superconducting qubit in the remote node. The observed interactions between the phonon and the remote qubit promise future quantum-optics-style experiments with itinerant phonons.

    

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3. Topological phonon-polariton funneling in midinfrared metasurfaces

   https://doi.org/10.1126/science.abj5488  

   Guddala, S. ; Komissarenko, F. ; Kiriushechkina, S. ; Vakulenko, A. ; Li, M. ; Menon, V. M. ; Alù, A. ; Khanikaev, A. B. ( October 2021 , Science)

   Topological photonics offers enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding of topological states of light. By combining the strong coupling between topological photons with phonons in hexagonal boron nitride (hBN), we demonstrate a platform to control and guide hybrid states of light and lattice vibrations. The observed topological edge states of phonon-polaritons are found to carry nonzero angular momentum locked to their propagation direction, which enables their robust transport. Thus, these topological quasiparticles enable the funneling of infrared phonons mediated by helical infrared photons along arbitrary pathways and across sharp bends, thereby offering opportunities for applications ranging from Raman and vibrational spectroscopy with structured phonon-polaritons to directional heat dissipation. 

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4. Phononic bath engineering of a superconducting qubit

   https://doi.org/10.1038/s41467-023-39682-0  

   Kitzman, J. M. ; Lane, J. R. ; Undershute, C. ; Harrington, P. M. ; Beysengulov, N. R. ; Mikolas, C. A. ; Murch, K. W. ; Pollanen, J. ( July 2023 , Nature Communications)

   Phonons, the ubiquitous quanta of vibrational energy, play a vital role in the performance of quantum technologies. Conversely, unintended coupling to phonons degrades qubit performance and can lead to correlated errors in superconducting qubit systems. Regardless of whether phonons play an enabling or deleterious role, they do not typically admit control over their spectral properties, nor the possibility of engineering their dissipation to be used as a resource. Here we show that coupling a superconducting qubit to a bath of piezoelectric surface acoustic wave phonons enables a novel platform for investigating open quantum systems. By shaping the loss spectrum of the qubit via the bath of lossy surface phonons, we demonstrate preparation and dynamical stabilization of superposition states through the combined effects of drive and dissipation. These experiments highlight the versatility of engineered phononic dissipation and advance the understanding of mechanical losses in superconducting qubit systems.

    

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5. Emergent interface vibrational structure of oxide superlattices

   https://doi.org/10.1038/s41586-021-04238-z  

   Hoglund, Eric R. ; Bao, De-Liang ; O’Hara, Andrew ; Makarem, Sara ; Piontkowski, Zachary T. ; Matson, Joseph R. ; Yadav, Ajay K. ; Haislmaier, Ryan C. ; Engel-Herbert, Roman ; Ihlefeld, Jon F. ; et al ( January 2022 , Nature)

   Abstract As the length scales of materials decrease, the heterogeneities associated with interfaces become almost as important as the surrounding materials. This has led to extensive studies of emergent electronic and magnetic interface properties in superlattices 1–9 . However, the interfacial vibrations that affect the phonon-mediated properties, such as thermal conductivity 10,11 , are measured using macroscopic techniques that lack spatial resolution. Although it is accepted that intrinsic phonons change near boundaries 12,13 , the physical mechanisms and length scales through which interfacial effects influence materials remain unclear. Here we demonstrate the localized vibrational response of interfaces in strontium titanate–calcium titanate superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy, density functional theory calculations and ultrafast optical spectroscopy. Structurally diffuse interfaces that bridge the bounding materials are observed and this local structure creates phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. Our results provide direct visualization of the progression of the local atomic structure and interface vibrations as they come to determine the vibrational response of an entire superlattice. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behaviour. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids with emergent infrared and thermal responses. 

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