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ENTANGLEMENT BETWEEN TWO SINGLE-PHOTON SOURCES DUE TO A BEAM SPLITTER

Juan Camilo López Carreño, Herbert Vinck-Posada

Published Jan 1, 2014• 0 citations
OpenAlex

Abstract

We consider a quantum dot of frequency w_s embedded in a semiconductor microcavity interacting with an electromagnetic mode of frequency w_a. The cavity is subject to a pumping laser of power W and frequency w_L, and to dissipative mechanisms such as photonic and excitonic relaxation, at rates g_a and g_s, respectively. The power and frequency of the laser is set so that the cavity-dot system reaches a stationary state, in which it emits single photons. Taking two of this single-photon emitters as the input for a semi transparent beam splitter, we consider the entanglement of the two output states in the low excitation regime using the Peres criteria. Thus, we study the dependence of the entanglement with the photonic and excitonic relaxation rates.

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We consider a quantum dot of frequency w_s embedded in a semiconductor microcavity interacting with an electromagnetic mode of frequency w_a. The cavity is subject to a pumping laser of power W and frequency w_L, and to dissipative mechanisms such as photonic and excitonic relaxation, at rates g_a and g_s, respectively. The power and frequency of the laser is set so that the cavity-dot system reaches a stationary state, in which it emits single photons. Taking two of this single-photon emitters as the input for a semi transparent beam splitter, we consider the entanglement of the two output states in the low excitation regime using the Peres criteria. Thus, we study the dependence of the entanglement with the photonic and excitonic relaxation rates.
We consider a quantum dot of frequency w_s embedded in a semiconductor microcavity interacting with an electromagnetic mode of frequency w_a. The cavity is subject to a pumping laser of power W and frequency w_L, and to dissipative mechanisms such as photonic and excitonic relaxation, at rates g_a and g_s, respectively. The power and frequency of the laser is set so that the cavity-dot system reaches a stationary state, in which it emits single photons. Taking two of this single-photon emitters as the input for a semi transparent beam splitter, we consider the entanglement of the two output states in the low excitation regime using the Peres criteria. Thus, we study the dependence of the entanglement with the photonic and excitonic relaxation rates.
We study the photon emission from a quantum dot embedded in a microcavity. Incoherent pumping of its excitons and biexciton provokes the emission of leaky and cavity modes. By solving a master equation we obtain the correlation functions required to compute the spectrum and the relative efficiency among the emission of pairs and single photons. A quantum regime appears for low pumping and large rate of emission. By means of a post-selection process, a two beams experiment with different linear polarizations could be performed producing a large polarization entanglement visibility precisely in the quantum regime.
We propose cooperative two-photon lasing in two quantum dots coupled to a single-mode photonic crystal cavity. We consider both quantum dots are driven either incoherently or coherently using an external pump. We incorporate exciton-phonon coupling using polaron transformed master equation. Using quantum laser theory, single- and multiphoton excess emission rates (difference between emission and absorption) into cavity mode are investigated. The single- and two-photon excess emission rates contribute to cavity photons, predominantly. Varying the pump strength can lead to single-photon excess emission rate change from negative to positive, and thus, by appropriately selecting pump strength, single-photon excess emission rate can be made negligible.
A deterministic "on demand" source of single photons is a basic building block for linear quantum computation \cite{linear}, quantum cryptography \cite{crypto}, quantum teleportation \cite{teleport}, and quantum networks \cite{network}. In all these applications, quantum interference between two single-photon pulses on a symmetric beam splitter has been exploited \cite{review}, which imposes stringent requirement for the implemented single photons to be indistinguishable in all degrees of freedom, including their frequencies, spectral widths, pulse shapes, and polarizations. To generate single photons one requires a pumping mechanism to excite a "two-level emitter" and an efficient channeling of the subsequently emitted photons. The efficiency of the source can be enhanced by coupling the emitter to the waveguide \cite{manga} or a microcavity mode \cite{cklaw}. However, hitherto the solid-state single photon sources realized by using a quantum dot coupled with a microcavity rely on incoherent pumping of excitons, which leads to problems with timing jitter \cite{kiraz}, leading to a trade off between efficiency and indistinguishability. Here we introduce a means to realize a highly efficient solid state source of indistinguishable single photons using cavity-assisted adiabatic Raman passage in a single quantum dot - cavity system. We demonstrate pulse-triggered single photons with 100% efficiency and >90>90>90% indistinguishability using currently available experimental parameters.
Semiconductor quantum dots are among the best sources of on-demand entangled photon pairs. The degree of entanglement, however, is generally limited by the fine structure splitting of exciton states. In this paper, we theoretically investigate the generation of polarization-entangled photon pairs under two-photon excitation and cavity-assisted two-photon emission, both in the weak and strong cavity coupling regimes. We demonstrate and clarify that cavity coupling together with an excitation pulse reduces the degree of entanglement in three different ways. First, in a strong coupling regime, the cavity introduces the unequal ac-Stark shift of horizontally and vertically polarized exciton states, which results in the effective splitting of exciton states. Second, it induces the cross-coupling between the exciton states even in the weak coupling regime, causing the creation of unfavorable two-photon states. Finally, higher excited states of the cavity modes also contribute to the reduction of entanglement. Therefore, in the setting considered here, cavity coupling, which is generally required for the efficient collection of emitted photons, degrades the entanglement both in weak and strong coupling regimes.