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Influence of impurity on the rate of single photon superradiance and photon transport in disordered N qubit chain
摘要： We investigate the rate of superradiant emission for a number of artificial atoms (qubits) embedded in a one-dimensional open waveguide. More specifically, we study the 1D (N+1)- qubit chain where N qubits are identical with respect to their excitation frequency Ω but have different rates of spontaneous emission Γn, and a single impurity qubit which is different from N qubits by its excitation frequency ΩP and the rate of spontaneous emission ΓP . We performed exact diagonalization of Hamiltonian and showed that the system has two hybridized collective states one of which accumulates the widths of all qubits. The energy spectrum of these states and corresponding probabilities are investigated as a function of the frequency detuning between the impurity and other qubits in a chain. It is shown that the inclusion of the impurity qubit alters the resonance widths of the system if the total width overlaps the frequency detuning between qubits and the impurity. In this case the resonance widths experience a significant repulsion. The photon transmission through disordered N- qubit chain with the impurity qubit is also considered. It is shown that a single photon transport through this system is described by a simple expression which predicts for specific photon frequency the existence of a complete transmission peak and transparency window between frequencies Ω and ΩP .
关键词： superradiance,impurity,photon transport,qubit chain,non-Hermitian Hamiltonian
更新于2025-09-23 15:23:52
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Single-photon limit of dispersive readout of a qubit with a photodetector
摘要： We study the dispersive readout of a qubit in the ultimate limit of a single-photon probe. The use of a single-photon probe avoids the errors due to nonorthogonality of coherent states. A photodetector is used in the scheme we consider. The dynamics of the system is studied using the Heisenberg-Langevin equations. We treat the counter-rotating terms in the Hamiltonian perturbatively, which leads to the Bloch-Siegert shift in the resonator frequency. It is shown how the shift can improve the readout. The theory of photon transport through the qubit and the resonator it couples to is provided while taking the effect of the counter-rotating terms into account. To calculate the readout contrast, we use two approaches. The first one neglects the qubit relaxation and allows us to derive a compact expression for the contrast. Also, we obtain simple estimates for the system parameters to maximize the contrast. The second approach accounts for the qubit relaxation, which allows us to further improve the contrast. We demonstrate that for a readout time of 1 μs, a contrast of more than 75% can be achieved for an ideal detector and single-photon source.
关键词： Heisenberg-Langevin equations,qubit,dispersive readout,photon transport,Bloch-Siegert shift,readout contrast,photodetector,single-photon probe
更新于2025-09-23 15:21:01
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The spectral signature of cloud spatial structure in shortwave irradiance
摘要： We found that cloud spatial structure manifests itself as spectral signature in shortwave irradiance fields – specifically in transmittance and net horizontal photon transport in the visible and near-ultraviolet wavelength range. In this paper, we demonstrate this through radiative transfer calculations with cloud imagery from a field experiment, and show that such three-dimensional effects may occur on scales up to 60 kilometers. Neglecting net horizontal photon transport leads to a transmittance bias on the order of ±12-19% even at the relatively coarse spatial resolution of 20 kilometers, and of more than ±50% for 1 kilometer. This poses a problem for radiative energy budget estimates from space because the bias for any pixel depends on its spatial context in a non-trivial way. The key for solving this problem may lie in the spectral dimension, since we found a robust correlation between the magnitude of net horizontal photon transport (H) and its spectral dependence (slope). It is scale-invariant and holds for the entire pixel population of a domain. This was at first surprising given the large degree of spatial inhomogeneity, but seems to be valid for any cloud field. We prove that the underlying physical mechanism for this phenomenon is molecular scattering in conjunction with cloud inhomogeneity. On this basis, we developed a simple parameterization through a single parameter ??, which quantifies the characteristic spectral signature of spatial heterogeneities. In a companion paper, we will show that it is accompanied by spectral radiance perturbations, which can be detected from multi-spectral imagers and may be translated into bias reductions for cloud radiative effect estimates in the future.
关键词： cloud spatial structure,molecular scattering,shortwave irradiance,spectral signature,radiative transfer,cloud radiative effect,horizontal photon transport
更新于2025-09-04 15:30:14