J.-R. Souquet

Fock-state stabilization and emission in superconducting circuits using dc-biased Josephson junctions

  1. J.-R. Souquet,
  2. and A. A. Clerk
In this article we propose a protocol to autonomously stabilize a Fock state within a circuit QED architecture that doesn’t recourse to any ac-drive nor pulse. This protocol is
realized with a microwave cavity driven by a Josephson junction and coupled to quantum engineered reservoir. It relies on two important ingredients. First, a high-impedance resonator to enable photon-dependent driving used as the cavity. Such device has recently been implemented in circuit QED platforms and removes the need for periodic driving. Second, on an auxiliary, low-quality factor cavity used as a engineered environment. Its damping rate must be scaled with respect to the Josephson energy and the main cavity quality factor in order to stabilize a quantum state. A second protocol, based on the same platform, is used to produce a flying qubit.
arxiv pdf

Photon-assisted tunneling with non-classical light

  1. J.-R. Souquet,
  2. M. J. Woolley,
  3. Julien Gabelli,
  4. Pascal Simon,
  5. and Aashish A. Clerk
Among the most exciting recent advances in the field of superconducting quantum circuits is the ability to coherently couple microwave photons in low-loss cavities to quantum electronic
conductors (e.g.~semiconductor quantum dots or carbon nanotubes). These hybrid quantum systems hold great promise for quantum information processing applications; even more strikingly, they enable exploration of completely new physical regimes. Here we study theoretically the new physics emerging when a quantum electronic conductor is exposed to non-classical microwaves (e.g.~squeezed states, Fock states). We study this interplay in the experimentally-relevant situation where a superconducting microwave cavity is coupled to a conductor in the tunneling regime. We find the quantum conductor acts as a non-trivial probe of the microwave state; in particular, the emission and absorption of photons by the conductor is characterized by a non-positive definite quasi-probability distribution. This negativity has a direct influence on the conductance of the conductor.
arxiv pdf