Academic Year 2025

• Unidirectional Transport Effect in non-Hermitian Non-reciprocal System: A General NEGF Approach
  • Sumit Kumar Jana (Indian Institute of Technology Hyderabad)
    
  • 2025/04/21 16:00 --
    
  • Conference Room K202, Main Building, Yukawa Institute, Kyoto U.
    
  • The emergence of dissipation and noises in quantum systems poses a major technological challenge. As an alternative, we focus on designing quantum systems that utilize dissipation and noise advantageously for the same purpose. We developed a non-Hermitian Hamiltonian with frequency-dependent non-reciprocal hopping analogous to the Hatano-Nelson model, by integrating out bath degrees of freedom in the microscopical lattice bath model. Our framework presents a novel feature of frequency-dependent unidirectional transport phenomena beyond the Markovian regime, also we uncover the emergence of skin effect at a specific frequency. We study the transport phenomena by employing the non-equilibrium Green’s function technique. These findings provide a new perspective on leveraging dissipation to achieve controlled directional transport in quantum systems.
    
• Constructing an interface equation, in or out of equilibrium
  • Lila Sarfati (Université Paris Cité)
    
  • 2025/04/16 16:00 --
    
  • Conference Room K202, Main Building, Yukawa Institute, Kyoto U.
    
  • Abstract: Given a mesoscopic description where a field admits two stationary solutions, we are interested in the interface separating the two states. In most cases, the dynamics of this interface is described by the Edwards-Wilkinson (EW) equation. However in the presence of additional symmetries or conservation laws, the description departs from the EW one, as already understood in the 1980's (Langer and Turski, Kawasaki and Ohta). Because obtaining the interface dynamics is technically challenging, several authors (Bray et al, Fausti et al) have introduced a mathematical shortcut yielding results consistent with the correct behavior in several standard models. In this presentation, I will review the existing literature and I will show not only that such shortcuts have unphysical features, but also that a fully systematic method, built on procedures developed by Kawasaki and Ohta and Bausch et al, can be implemented. This method is applied in and out of equilibrium, both to linear order and beyond.
    
• Measurement Induced Gain and Lasing
  • Apan Dinda (Indian Institute of Technology Hyderabad)
    
  • 2025/04/09 16:00 --
    
  • Conference Room K206, Main Building, Yukawa Institute, Kyoto U.
    
  • Abstract: We discuss a framework based on the measurement and feedback protocol where the feedback energy is stored inside the cavity interacting with a single qubit via Jaynes-Cummings coupling. We include cavity loss as a repeated interaction model with an imaginary qubit. This can be thought to model a detector. In this setting, we find that the gain from the feedback can take the cavity to the lasing regime, with Poissonian photon distribution. This nonlinear behavior is well captured within our repeated interaction scheme. On taking the continuous limit, one obtains a Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation, which, however, is unable to explain long time Poissonian photon distribution. We further analyze the nature of the light in the cavity using Glauber's coherence function and Wigner Quasi-probability distribution.