The authors fabricate a fluxonium circuit using a granular aluminium nanoconstriction to replace the conventional superconductor–insulator–superconductor tunnel junction. Their characterization suggests that this approach will be a useful element in the superconducting qubit toolkit.
Granular aluminium nanojunction fluxonium qubitMesoscopic Josephson junctions, consisting of overlapping superconducting electrodes separated by a nanometre-thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits. Here we show that in a fluxonium qubit, the role of the Josephson junction can also be played by a lithographically defined, self-structured granular aluminium nanojunction: a superconductor–insulator–superconductor Josephson junction obtained in a single-layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from that of a standard fluxonium. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large granular aluminium nanojunction charging energy in the range of tens of gigahertz, comparable to its Josephson energy. We measure coherence times in the microsecond range and we observe spontaneous jumps of the value of the Josephson energy on timescales from milliseconds to days, which offers a powerful diagnostics tool for microscopic defects in superconducting materials.
The gralmonium, a single-layer grAl fluxonium circuit.
D. Rieger, S. Günzler, M. Spiecker, P. Paluch, P. Winkel, L. Hahn, J. K. Hohmann, A. Bacher, W. Wernsdorfer & I. M. Pop
doi: 10.1038/s41563-022-01417-9 | |
Both bosonic and fermionic collective states can emerge in two-dimensional semiconductor lattices, and mixing these species can further expand the landscape of quantum phases. Here, the authors report Bose–Fermi mixtures of neutral and charged excitons and the emergence of dual-density waves in an electrostatic lattice in a GaAs bilayer.
Dual-density waves with neutral and charged dipolar excitons of GaAs bilayersStrongly correlated quantum particles in lattice potentials are the building blocks for a wide variety of quantum insulators—for instance, Mott phases and density waves breaking lattice symmetry. Such collective states are accessible to bosonic and fermionic systems. To expand further the spectrum of accessible quantum matter phases, mixing both species is theoretically appealing because density order then competes with phase separation. Here we manipulate such a Bose–Fermi mixture by confining neutral (boson-like) and charged (fermion-like) dipolar excitons in an artificial square lattice of a GaAs bilayer. At unitary lattice filling, strong inter- and intraspecies interactions stabilize insulating phases when the fraction of charged excitons is around (1/3, 1/2, 2/3). We evidence that dual Bose–Fermi density waves are then realized, with species ordered in alternating stripes. Our observations highlight that dipolar excitons allow for controlled implementations of Bose–Fermi Hubbard models extended by off-site interactions.
Neutral and charged excitons’ Bose–Fermi mixture.
Camille Lagoin, Stephan Suffit, Kirk Baldwin, Loren Pfeiffer & François Dubin
doi: 10.1038/s41563-022-01409-9 | |
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