@article{13227,
  abstract     = {Currently available quantum processors are dominated by noise, which severely limits their applicability and motivates the search for new physical qubit encodings. In this work, we introduce the inductively shunted transmon, a weakly flux-tunable superconducting qubit that offers charge offset protection for all levels and a 20-fold reduction in flux dispersion compared to the state-of-the-art resulting in a constant coherence over a full flux quantum. The parabolic confinement provided by the inductive shunt as well as the linearity of the geometric superinductor facilitates a high-power readout that resolves quantum jumps with a fidelity and QND-ness of >90% and without the need for a Josephson parametric amplifier. Moreover, the device reveals quantum tunneling physics between the two prepared fluxon ground states with a measured average decay time of up to 3.5 h. In the future, fast time-domain control of the transition matrix elements could offer a new path forward to also achieve full qubit control in the decay-protected fluxon basis.},
  author       = {Hassani, Farid and Peruzzo, Matilda and Kapoor, Lucky and Trioni, Andrea and Zemlicka, Martin and Fink, Johannes M},
  issn         = {2041-1723},
  journal      = {Nature Communications},
  publisher    = {Springer Nature},
  title        = {{Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours}},
  doi          = {10.1038/s41467-023-39656-2},
  volume       = {14},
  year         = {2023},
}

@article{9928,
  abstract     = {There are two elementary superconducting qubit types that derive directly from the quantum harmonic oscillator. In one, the inductor is replaced by a nonlinear Josephson junction to realize the widely used charge qubits with a compact phase variable and a discrete charge wave function. In the other, the junction is added in parallel, which gives rise to an extended phase variable, continuous wave functions, and a rich energy-level structure due to the loop topology. While the corresponding rf superconducting quantum interference device Hamiltonian was introduced as a quadratic quasi-one-dimensional potential approximation to describe the fluxonium qubit implemented with long Josephson-junction arrays, in this work we implement it directly using a linear superinductor formed by a single uninterrupted aluminum wire. We present a large variety of qubits, all stemming from the same circuit but with drastically different characteristic energy scales. This includes flux and fluxonium qubits but also the recently introduced quasicharge qubit with strongly enhanced zero-point phase fluctuations and a heavily suppressed flux dispersion. The use of a geometric inductor results in high reproducibility of the inductive energy as guaranteed by top-down lithography—a key ingredient for intrinsically protected superconducting qubits.},
  author       = {Peruzzo, Matilda and Hassani, Farid and Szep, Gregory and Trioni, Andrea and Redchenko, Elena and Zemlicka, Martin and Fink, Johannes M},
  issn         = {2691-3399},
  journal      = {PRX Quantum},
  keywords     = {quantum physics, mesoscale and nanoscale physics},
  number       = {4},
  pages        = {040341},
  publisher    = {American Physical Society},
  title        = {{Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction}},
  doi          = {10.1103/PRXQuantum.2.040341},
  volume       = {2},
  year         = {2021},
}

@article{8038,
  abstract     = {Microelectromechanical systems and integrated photonics provide the basis for many reliable and compact circuit elements in modern communication systems. Electro-opto-mechanical devices are currently one of the leading approaches to realize ultra-sensitive, low-loss transducers for an emerging quantum information technology. Here we present an on-chip microwave frequency converter based on a planar aluminum on silicon nitride platform that is compatible with slot-mode coupled photonic crystal cavities. We show efficient frequency conversion between two propagating microwave modes mediated by the radiation pressure interaction with a metalized dielectric nanobeam oscillator. We achieve bidirectional coherent conversion with a total device efficiency of up to ~60%, a dynamic range of 2 × 10^9 photons/s and an instantaneous bandwidth of up to 1.7 kHz. A high fidelity quantum state transfer would be possible if the drive dependent output noise of currently ~14 photons s^−1 Hz^−1 is further reduced. Such a silicon nitride based transducer is in situ reconfigurable and could be used for on-chip classical and quantum signal routing and filtering, both for microwave and hybrid microwave-optical applications.},
  author       = {Fink, Johannes M and Kalaee, M. and Norte, R. and Pitanti, A. and Painter, O.},
  issn         = {20589565},
  journal      = {Quantum Science and Technology},
  number       = {3},
  publisher    = {IOP Publishing},
  title        = {{Efficient microwave frequency conversion mediated by a photonics compatible silicon nitride nanobeam oscillator}},
  doi          = {10.1088/2058-9565/ab8dce},
  volume       = {5},
  year         = {2020},
}