All Publications

  • Parametric longitudinal coupling between a high-impedance superconducting resonator and a semiconductor quantum dot singlet-triplet spin qubit NATURE COMMUNICATIONS Bottcher, C. L., Harvey, S. P., Fallahi, S., Gardner, G. C., Manfra, M. J., Vool, U., Bartlett, S. D., Yacoby, A. 2022; 13 (1): 4773


    Coupling qubits to a superconducting resonator provides a mechanism to enable long-distance entangling operations in a quantum computer based on spins in semiconducting materials. Here, we demonstrate a controllable spin-photon coupling based on a longitudinal interaction between a spin qubit and a resonator. We show that coupling a singlet-triplet qubit to a high-impedance superconducting resonator can produce the desired longitudinal coupling when the qubit is driven near the resonator's frequency. We measure the energy splitting of the qubit as a function of the drive amplitude and frequency of a microwave signal applied near the resonator antinode, revealing pronounced effects close to the resonator frequency due to longitudinal coupling. By tuning the amplitude of the drive, we reach a regime with longitudinal coupling exceeding 1 MHz. This mechanism for qubit-resonator coupling represents a stepping stone towards producing high-fidelity two-qubit gates mediated by a superconducting resonator.

    View details for DOI 10.1038/s41467-022-32236-w

    View details for Web of Science ID 000840984400031

    View details for PubMedID 35970821

    View details for PubMedCentralID PMC9378792

  • Nickelate Superconductivity without Rare-Earth Magnetism: (La,Sr)NiO2. Advanced materials (Deerfield Beach, Fla.) Osada, M., Wang, B. Y., Goodge, B. H., Harvey, S. P., Lee, K., Li, D., Kourkoutis, L. F., Hwang, H. Y. 2021: e2104083


    The occurrence of unconventional superconductivity in cuprates has long motivated the search for manifestations in other layered transition metal oxides. Recently, superconductivity is found in infinite-layer nickelate (Nd,Sr)NiO2 and (Pr,Sr)NiO2 thin films, formed by topotactic reduction from the perovskite precursor phase. A topic of much current interest is whether rare-earth moments are essential for superconductivity in this system. In this study, it is found that with significant materials optimization, substantial portions of the La1- x Srx NiO2 phase diagram can enter the regime of coherent low-temperature transport (x= 0.14 - 0.20), with subsequent superconducting transitions and a maximum onset of 9 K at x= 0.20. Additionally, the unexpected indication of a superconducting ground state in undoped LaNiO2 is observed, which likely reflects the self-doped nature of the electronic structure. Combining the results of (La/Pr/Nd)1- x Srx NiO2 reveals a generalized superconducting dome, characterized by systematic shifts in the unit cell volume and in the relative electron-hole populations across the lanthanides.

    View details for DOI 10.1002/adma.202104083

    View details for PubMedID 34536042

  • High-energy quasiparticle injection into mesoscopic superconductors. Nature nanotechnology Alegria, L. D., Bottcher, C. G., Saydjari, A. K., Pierce, A. T., Lee, S. H., Harvey, S. P., Vool, U., Yacoby, A. 2021


    At non-zero temperatures, superconductors contain excitations known as Bogoliubov quasiparticles (QPs). The mesoscopic dynamics of QPs inform the design of quantum information processors, among other devices. Knowledge of these dynamics stems from experiments in which QPs are injected in a controlled fashion, typically at energies comparable to the pairing energy1-5. Here we perform tunnel spectroscopy of a mesoscopic superconductor under high electric fields. We observe QP injection due to field-emitted electrons with 106 times the pairing energy, an unexplored regime of QP dynamics. Upon application of a gate voltage, the QP injection decreases the critical current and, at sufficiently high electric field, a field-emission current (<0.1nA in our device) switches the mesoscopic superconductor into the normal state, consistent with earlier observations6. We expect that high-energy injection will be useful for developing QP-tolerant quantum information processors, will allow rapid control of resonator quality factors and will enable the design of electric-field-controlled superconducting devices with new functionality.

    View details for DOI 10.1038/s41565-020-00834-8

    View details for PubMedID 33462428

  • Isotropic Pauli-limited superconductivity in the infinite-layer nickelate Nd0.775Sr0.225NiO2 NATURE PHYSICS Wang, B., Li, D., Goodge, B. H., Lee, K., Osada, M., Harvey, S. P., Kourkoutis, L. F., Beasley, M. R., Hwang, H. Y. 2021
  • Superconducting Dome in Nd_{1-x}Sr_{x}NiO_{2} Infinite Layer Films. Physical review letters Li, D., Wang, B. Y., Lee, K., Harvey, S. P., Osada, M., Goodge, B. H., Kourkoutis, L. F., Hwang, H. Y. 2020; 125 (2): 027001


    We report the phase diagram of Nd_{1-x}Sr_{x}NiO_{2} infinite layer thin films grown on SrTiO_{3}. A superconducting dome spanning 0.125

    View details for DOI 10.1103/PhysRevLett.125.027001

    View details for PubMedID 32701320

  • Superconducting Dome in Nd1-xSrxNiO2 Infinite Layer Films PHYSICAL REVIEW LETTERS Li, D., Wang, B., Lee, K., Harvey, S. P., Osada, M., Goodge, B. H., Kourkoutis, L. F., Hwang, H. Y. 2020; 125 (2)