To enhance the spatial utility of typical two-port Hadamard gate, we propose a novel single-channel scheme through frequency conversion in Λ-atom-mediated single-photon Raman scattering process in chiral quantum nanophotonics. We demonstrate faithful and efficient gate operations, and quantitatively analyze gate performance. Moreover, by manipulating photon-emitter coupling and frequency detuning, it is confirmed that an arbitrary unitary single-qubit operations are achieved in the presented configuration, including most representative single-qubit Hadamard, X, Z, S, and T gates. Due to the advent of directional emission techniques, the chiral condition is readily experimentally feasible. In addition, we further propose an alternative N-type atom architecture to perform Hadamard operations that are enabled by hyperfine structure in the strong-coupling regime.
Atom coherence in the cooperative interaction between the atoms and a single photon creates ultrafast spontaneous emission and ultrastrong intensity peaks, namely single-photon superradiance, which has attracted considerable research interest in the recent years. As the investigation for such a single-photon superradiance usually involves only quantum emitters, in this paper we present the cooperative atom-photon interaction in a system including whispering gallery mode resonators, which are one of the most essential components in nanophotonic devices. Here we both analytically and computationally show that the separated atoms on a resonator can obtain cooperative interaction, manifesting superradiant coupling strength, which results in the ultrafast spontaneous emission and ultrastrong intensity peaks. The conditions of such single-photon superradiance are called whispering gallery mode superradiance conditions. Furthermore, the atoms are proved to have cooperative interaction on a cascade of resonators by a renormalization approach.
To resolve the intrinsic trade-off between the deterministic nature and scalability of controlled phase gate implementation in the linear optics regime, we propose a novel deterministic two-photon controlled phase gate scheme in chiral quantum nanophotonics. The essential ingredient here is that, a non-linear π-phase shift is imprinted during the photonic molecule generations. On one hand, the gate operates in a deterministic way without the assistance of probabilistic ancilla qubit measurement. On the other hand, the gate implementation is of low complexity to be highly scalable. To date, the chiral coupling is readily underpinned by the advent of directional emission technique. Potential implementation platforms include QD, superconducting qubit, Rydberg atom, or N-V center that is coupled to a PhC waveguide, transmission line, or optical fiber.
Photonic Molecule, also called Photonic Dimer, is a quantum bound state of two photons. A photonic bound state has a specific entanglement of a Lorentzian anti-correlation in frequency space and two photons are in proximity due to its binding nature.Such signatures of a photonic molecule illuminates a potential tool that increases the two-photon microscopy efficiency to orders of magnitude higher. Here we numerically and analytically demonstrate the two-photon excitation efficiency between photonic molecules, long uncorrelated light pulses and ultrashort light pulses. The high excitation efficiency of a photonic molecule enables a saturation of fluorophores, such that the linear dependence of two-photon excitation crosssection does not necessarily hold. Also, we exhibits two possible methods to obtain the photonic molecules, as a fundamental possibility for a continuous photonic molecule source.
We study computationally the 3-photon molecule generation through coherent scattering process in nonlinear quantum nanophotonics. Specifically, the molecule signature is confirmed with an imprinted π conditional phase shift by examining the wave function in both real- and frequency-space representation, and correlation functions g(3) and g(2). Moreover, we show that the correlation metrics for the three- and two-photon Fock state scattering also apply to a weak-coherent optical input, which describe well the recent experimental results in ultra-cold atomic gas. Our work opens up a new research direction of computational study for correlated three-photon scattering and transport processes. Generations of 3-photon molecule may tremendously enhance the three-photon fluorescence microscopy efficiency and facilitate the realization of deterministic quantum logic gates.
In a waveguide-QED system, under certain condition, the spontaneous emission rate of an atom cloud with a single excitation can be enhanced. Single-photon superradiance refers to the case when the enhancement attains its maximum. We show that an atom cloud exhibiting single-photon superradiance can be described by an effective two-level system. We also adopt a real space numerical approach to validate the understanding of single-photon superradiance using such an effective mapping picture. We further numerically investigate the spontaneous emission of superradiant state and dark state.
We present a computational study of two-photon scattering process in an atom-ring resonator-waveguide QED system. By properly manipulating the operating frequency of incoming photons, we show that two-photon bound state and photon antibunching statistics are generated through resonator-mediated atom-photon interactions. Numerically, we find that mild backscattering and dissipation enhance the quality of generated photonic correlations. In addition, we also report the quantum photonic halo effect and the dissipation-induced photonic correlation transition phenomenon.
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