Vittorio Peano

Topological quantum fluctuations and travelling wave amplifiers

  1. Vittorio Peano,
  2. Martin Houde,
  3. Florian Marquardt,
  4. and Aashish A. Clerk
It is now well-established that photonic systems can exhibit topological energy bands; similar to their electronic counterparts, this leads to the formation of chiral edge modes which
can be used to transmit light in a manner that is protected against back-scattering. Most topological photonic states are completely analogous to their electronic counterpart, as they are based on single-particle physics: the topological invariants and edge states are identical in both the bosonic and fermionic case. Here, we describe a new kind of topological photonic state which has no electronic analogue. In our system, a non-zero topological invariant guarantees the presence of a parametrically-unstable chiral edge mode in a system with boundaries, even though there are no bulk-mode instabilities. We show that by stabilizing these unstable edge modes via coupling waveguides, one realizes a topologically protected, quantum-limited travelling-wave parametric amplifier. The device is protected against both internal losses and back-scattering; the latter feature is in stark contrast to standard travelling wave amplifiers. We show that the unstable edge mode also naturally serves as a topologically-protected source for non-classical squeezed light.
arxiv pdf

Emission spectrum of the driven nonlinear oscillator

  1. Stephan André,
  2. Lingzhen Guo,
  3. Vittorio Peano,
  4. Michael Marthaler,
  5. and Gerd Schön
Motivated by recent „circuit QED“ experiments we investigate the noise properties of coherently driven nonlinear resonators. By using Josephson junctions in superconducting
circuits, strong nonlinearities can be engineered, which lead to the appearance of pronounced effects already for a low number of photons in the resonator. Based on a master equation approach we determine the emission spectrum and observe for typical circuit QED parameters, in addition to the primary Raman-type peaks, second-order peaks. These peaks describe higher harmonics in the slow noise-induced fluctuations of the oscillation amplitude of the resonator and provide a clear signature of the nonlinear nature of the system.
arxiv pdf