Ian Yang

In-situ tunable interaction with an invertible sign between a fluxonium and a post cavity

  1. Desislava G. Atanasova,
  2. Ian Yang,
  3. Teresa Hönigl-Decrinis,
  4. Daria Gusenkova,
  5. Ioan M. Pop,
  6. and Gerhard Kirchmair
Quantum computation with bosonic modes presents a powerful paradigm for harnessing the principles of quantum mechanics to perform complex information processing tasks. In constructing
a bosonic qubit with superconducting circuits, nonlinearity is typically introduced to a cavity mode through an ancillary two-level qubit. However, the ancilla’s spurious heating has impeded progress towards fully fault-tolerant bosonic qubits. The ability to in-situ decouple the ancilla when not in use would be beneficial but has not been realized yet. This work presents a novel architecture for quantum information processing, comprising a 3D post cavity coupled to a fluxonium ancilla via a readout resonator. This system’s intricate energy level structure results in a complex landscape of interactions whose sign can be tuned in situ by the magnetic field threading the fluxonium loop. Our results could significantly advance the lifetime and controllability of bosonic qubits.
arxiv pdf

Hot Schrödinger Cat States

  1. Ian Yang,
  2. Thomas Agrenius,
  3. Vasilisa Usova,
  4. Oriol Romero-Isart,
  5. and Gerhard Kirchmair
The observation of quantum phenomena often necessitates sufficiently pure states, a requirement that can be challenging to achieve. In this study, our goal is to prepare a non-classical
state originating from a mixed state, utilizing dynamics that preserve the initial low purity of the state. We generate a quantum superposition of displaced thermal states within a microwave cavity using only unitary interactions with a transmon qubit. We measure the Wigner functions of these „hot“ Schrödinger cat states for an initial purity as low as 0.06. This corresponds to a cavity mode temperature of up to 1.8 Kelvin, sixty times hotter than the cavity’s physical environment. Our realization of highly mixed quantum superposition states could be implemented with other continuous-variable systems e.g. nanomechanical oscillators, for which ground-state cooling remains challenging.
arxiv pdf