• Filtering multiphoton emission from state-of the-art cavity quantum electrodynamics

      Sanchez Munoz, Carlos; Laussy, Fabrice P.; Valle, Elena del; Tejedor, Carlos; Gonzalez-Tudela, Alejandro (OSA, 2018-01-08)
      Engineering multiphoton states is an outstanding challenge with applications in multiple fields such as quantum metrology, quantum lithography, or even biological sensing. State-of-the-art methods to obtain them rely on post-selection, multi-level systems, or Rydberg atomic ensembles. Recently, it was shown that a strongly driven two-level system interacting with a detuned cavity mode can be engineered to continuously emit 𝑛-photon states. In the present work, we show that spectral filtering of its emission relaxes considerably the requirements on the system parameters even to the more accessible bad-cavity situation, opening up the possibility of implementing this protocol in a much wider landscape of different platforms. This improvement is based on a key observation: in the imperfect case where only a certain fraction of emission is composed of 𝑛-photon states, these have a well-defined energy separated from the rest of the signal, which allows one to reveal and purify multiphoton emission just by frequency filtering. We demonstrate these results by obtaining analytical expressions for the relevant figures of merit of multiphoton emission, such as the 𝑛-photon coupling rate between cavity and emitter, the fraction of light emitted as 𝑛-photon states, and 𝑛-photon emission rates. This allows us to make a systematic study of such figures of merit as a function of the system parameters and demonstrate the viability of the protocol in several relevant types of cavity quantum electrodynamics setups, where we take into account the impact of their respective experimental limitations.
    • Impact of detuning and dephasing on a laser-corrected subnatural-linewidth single-photon source

      López Carreño, Juan Camilo; Zubizarreta Casalengua, E.; Laussy, Fabrice P.; Valle, Elena del (IOP Publishing, 2019-01-08)
      The elastic scattering peak of a resonantly driven two-level system has been argued to provide narrow-linewidth antibunched photons. Although independent measurements of spectral width on the one hand and antibunching, on the other hand, do seem to show that this is the case, a joint measurement reveals that only one or the other of these attributes can be realised in the direct emission. We discuss a scheme which interferes the emission with a laser to produce simultaneously single photons of subnatural linewidth. In particular, we consider the effect of dephasing and of the detuning between the driving laser and/or the detector with the emitter. We find that our scheme brings such considerable improvement as compared to the standard schemes as to make it the best single-photon source in terms of all-order multi-photon suppression by several orders of magnitudes. While the scheme is particularly fragile to dephasing, its superiority holds even for subnatural-linewidth emission down to a third of the radiative lifetime.
    • Quasichiral interactions between quantum emitters at the nanoscale

      Downing, Charles; López Carreño, Juan Camilo; Laussy, Fabrice P.; Valle, Elena del; Fernández-Domínguez, Antonio (American Physical Society, 2019-02-07)
      We present a combined classical and quantum electrodynamics description of the coupling between two circularly polarized quantum emitters held above a metal surface supporting surface plasmons. Depending on their position and their natural frequency, the emitter-emitter interactions evolve from being reciprocal to nonreciprocal, which makes the system a highly tunable platform for chiral coupling at the nanoscale. By relaxing the stringent material and geometrical constraints for chirality, we explore the interplay between coherent and dissipative coupling mechanisms in the system. Thus, we reveal a quasichiral regime in which its quantum optical properties are governed by its subradiant state, giving rise to extremely sharp spectral features and strong photon correlations.