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arXiv:2212.07701 · Physical Review A

Steady-state subradiance manipulated by the two-atom decay

Qian Bin, Xin‐You Lü

Published Dec 5, 2022• 6 citations
arXivHTMLPDF

Abstract

We investigate theoretically the collective radiance characteristics of an atomic ensemble with the simultaneous decay of two atoms. We show that the two-atom decay can significantly suppress the steady-state collective radiance of the atoms, expanding the region of subradiance. In the steady-state subradiance regime, the system is in an entangled state, and the mean populations of the system in the excited state and ground state of the atoms are almost equal. The processes of the two-atom decay can be demonstrated by the population distribution of the system state on the Dicke ladder. Moreover, we show the correlation property of the emitted light from the atomic ensemble, where the correlation function is rewritten in the presence of the two-atom decay. We find that the emitted photons of steady state only show bunching in the case of two-atom decay. This work broadens the realm of collective radiance, with potential applications for quantum information processing.

DOI
10.1103/physreva.106.063701

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We investigate theoretically the collective radiance characteristics of an atomic ensemble with the simultaneous decay of two atoms. We show that the two-atom decay can significantly suppress the steady-state collective radiance of the atoms, expanding the region of subradiance. In the steady-state subradiance regime, the system is in an entangled state, and the mean populations of the system in the excited state and ground state of the atoms are almost equal. The processes of the two-atom decay can be demonstrated by the population distribution of the system state on the Dicke ladder. Moreover, we show the correlation property of the emitted light from the atomic ensemble, where the correlation function is rewritten in the presence of the two-atom decay. We find that the emitted photons of steady state only show bunching in the case of two-atom decay. This work broadens the realm of collective radiance, with potential applications for quantum information processing.
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Quantum Optics An excited atom will naturally decay to the ground state, with the exciting and emitted photons forming the basis for the optical protocols in quantum communication and computation. Within an ensemble of atoms, this emission process can proceed constructively, resulting in faster ensemble decay in an effect known as superradiance. In contrast to the superradiant process, Ferioli et al. report subradiance in an ensemble of excited rubidium atoms, where collective behavior between the decaying atoms proceeds destructively, thereby extending the lifetime of the excited atom ensemble in what can be described as a dark state. Engineering such dark states could provide a route to storing light. The reduced linewidth could also be useful in metrology applications. Phys. Rev. X 11 , 021031 (2021).
We study numerically the slow (subradiant) decay of the fluorescence of motionless atoms after a weak pulsed excitation. We show that, in the linear-optics regime and for an excitation detuned by several natural linewidths, the slow decay rate can be dominated by close pairs of atoms (dimers) forming superradiant and subradiant states. However, for a large-enough resonant optical depth and at later time, the dynamics is dominated by collective many-body effects. In this regime, we study the polarization and the spectrum of the emitted light, as well as the spatial distribution of excitation inside the sample, as a function of time during the decay dynamics. The behavior of these observables is consistent with what would be expected for radiation trapping of nearly resonant light. This finding sheds light on subradiance in dilute samples by providing an interpretation based on the light behavior of the system (multiple scattering) which is complementary to the more commonly used picture of the collective atomic Dicke state.
We investigate the collective interaction of a multi-atom three-level ladder system with an environmental incoherent reservoir. The exact solution of the master equation that describes such a system of atoms emitting distinguishable or indistinguishable photons on interaction with an incoherent reservoir is obtained. The quantum decay interference effects have no influences over steady-state distribution of population among the energy levels. However, the photon statistics of the collectively emitted photons are different in this case. In particular, the normalized second-order photon correlation function shows a minimum in its value for the photons generated on lower atomic transition in a system with orthogonal dipoles. The minimum is due to the steady-state amplified spontaneous emission by the incoherent applied fields.
We investigate the collective interaction of a multi-atom three-level ladder system with an environmental incoherent reservoir. The exact solution of the master equation that describes such a system of atoms emitting distinguishable or indistinguishable photons on interaction with an incoherent reservoir is obtained. The quantum decay interference effects have no influences over steady-state distribution of population among the energy levels. However, the photon statistics of the collectively emitted photons are different in this case. In particular, the normalized second-order photon correlation function shows a minimum in its value for the photons generated on lower atomic transition in a system with orthogonal dipoles. The minimum is due to the steady-state amplified spontaneous emission by the incoherent applied fields.
Spontaneous emission of atoms in free space is modified by the presence of other atoms in close vicinity inducing collective super- and subradiance. For two nearby atoms with a single decay channel the entangled antisymmetric superposition state of the two single excited states will not decay spontaneously. No such excited two-atom dark state exists, if the excited state has two independent optical decay channels of different frequencies or polarizations. However, we show that for an excited atomic state with N-1 independent spontaneous decay channels one can find a highly entangled N-particle dark state, which completely decouples from the vacuum radiation field. It does not decay spontaneously, nor will it absorb resonant laser light. Mathematically, we see that this state is the only such state orthogonal to the subspace spanned by the atomic ground states. Moreover, by means of generic numerical examples we demonstrate that the subradiant behavior largely survives at finite atomic distances including dipole-dipole interactions.