Enhanced two-photon emission from a dressed biexciton

Radiative two-photon cascades from biexcitons in semiconductor quantum dots under resonant two-photon excitation are promising candidates for the generation of photon pairs. In this work, we propose a scheme to obtain two-photon emission that allows us to operate under very intense driving fields. This approach relies on the Purcell enhancement of two-photon virtual transitions between states of the biexciton dressed by the laser. The richness provided by the biexcitonic level structure allows to reach a variety of regimes, from antibunched and bunched photon pairs with polarization orthogonal to the driving field, to polarization entangled two-photon emission. This provides evidence that the general paradigm of two-photon emission from a ladder of dressed states can find interesting, particular implementations in a variety of systems.Radiative two-photon cascades from biexcitons in semiconductor quantum dots under resonant two-photon excitation are promising candidates for the generation of photon pairs. In this work, we propose a scheme to obtain two-photon emission that allows us to operate under very intense driving fields. This approach relies on the Purcell enhancement of two-photon virtual transitions between states of the biexciton dressed by the laser. The richness provided by the biexcitonic level structure allows to reach a variety of regimes, from antibunched and bunched photon pairs with polarization orthogonal to the driving field, to polarization entangled two-photon emission. This provides evidence that the general paradigm of two-photon emission from a ladder of dressed states can find interesting, particular implementations in a variety of systems.

arXiv:1506.05050New Journal of PhysicsDec 16, 201570 citations

Two-photon physics with quantum-dot biexcitons

Stefan Schumacher, A. Zrenner

Emitters based on semiconductor quantum dots are promising sources for both single photons and pairs of polarization-entangled photons. Typically, single photons are generated through a photon emission event bringing the electronic system from a single-exciton state back to the ground state. In the case of entangled photons two photons are generated through a cascaded emission from the biexciton to either one of the single-exciton states and then back to the ground state. Alternatively, emission of two photons can also be achieved through a higher-order two-photon process bringing the quantum dot directly from the biexciton state (through a virtual intermediate state) back to the ground state. Here we discuss in particular how this two-photon process can lead to certain conceptual advantages in both the generation of polarization-entangled photon pairs and generation of single photons.Emitters based on semiconductor quantum dots are promising sources for both single photons and pairs of polarization-entangled photons. Typically, single photons are generated through a photon emission event bringing the electronic system from a single-exciton state back to the ground state. In the case of entangled photons two photons are generated through a cascaded emission from the biexciton to either one of the single-exciton states and then back to the ground state. Alternatively, emission of two photons can also be achieved through a higher-order two-photon process bringing the quantum dot directly from the biexciton state (through a virtual intermediate state) back to the ground state. Here we discuss in particular how this two-photon process can lead to certain conceptual advantages in both the generation of polarization-entangled photon pairs and generation of single photons.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEMar 14, 20130 citations

Cavity-enhanced simultaneous dressing of quantum dot exciton and biexciton states

Fabian Hargart, Markus A. Müller, Kaushik Roy‐Choudhury +6 more

We demonstrate the simultaneous dressing of both vacuum-to-exciton and exciton-to-biexciton transitions of a single semiconductor quantum dot in a high-Q micropillar cavity, using photoluminescence spectroscopy. Resonant two-photon excitation of the biexciton is achieved by spectrally tuning the quantum dot emission with respect to the cavity mode. The cavity couples to both transitions and amplifies the Rabi frequency of the likewise resonant continuous wave laser, driving the transitions. We observe strong-field splitting of the emission lines, which depend on the driving Rabi field amplitude and the cavity-laser detuning. A dressed state theory of a driven 4-level atom correctly predicts the distinct spectral transitions observed in the emission spectrum, and a detailed description of the emission spectra is further provided through a polaron master equation approach which accounts for cavity coupling and acoustic phonon interactions of the semiconductor medium.We demonstrate the simultaneous dressing of both vacuum-to-exciton and exciton-to-biexciton transitions of a single semiconductor quantum dot in a high-Q micropillar cavity, using photoluminescence spectroscopy. Resonant two-photon excitation of the biexciton is achieved by spectrally tuning the quantum dot emission with respect to the cavity mode. The cavity couples to both transitions and amplifies the Rabi frequency of the likewise resonant continuous wave laser, driving the transitions. We observe strong-field splitting of the emission lines, which depend on the driving Rabi field amplitude and the cavity-laser detuning. A dressed state theory of a driven 4-level atom correctly predicts the distinct spectral transitions observed in the emission spectrum, and a detailed description of the emission spectra is further provided through a polaron master equation approach which accounts for cavity coupling and acoustic phonon interactions of the semiconductor medium.

arXiv:1509.03861Physical review. B./Physical review. BMar 14, 201670 citations

Antibunched entangled photon pair emission via two-photon excitation in a four-level quantum dot within an optical cavity

Zhenglu Duan, Cuicui Li, Yongkang Shao +1 more

Entangled photon pairs are a crucial resource in quantum information processing. However, common sources of entangled photon pairs, such as generation by spontaneous parametric down-conversion, impose a Poisson distribution on the pairs, limiting their applicability to quantum information processing. Therefore, generating entangled photon pairs exhibiting a sub-Poisson distribution (i.e., entangled photon bundle) would be crucial/an important advancement in the current research context. Recently, it has been proposed that antibunched photon pairs can be generated using pulsed excitation of quantum dots based on photon blockade. In this work we propose a scheme to generate entangled photon pairs with strong antibunching properties via continuous driving. Under two-photon resonant continuous pumping, a quantum dot is first excited to a biexciton state and then emits a pair of entangled photons into a two-mode cavity. Owing to the strong coupling between the quantum dot and optical modes of the cavity, at most one pair of left-/right-polarized photons exists at a time in the cavity. Specifically, the antibunching effect, average photon number, and entanglement of the left- or right-polarized photons can be resonantly enhanced when the coupling strengths between the exciton (biexciton) transition and cavity modes are equal. Moreover, our results show that the binding energy of the biexciton substantially affects the antibunching effect, average photon number, and entanglement of the left-/right-polarized photons. With suitable parameters, we can realize photon pairs with strong antibunching, a large average photon number, and deep entanglement. Hence, the studied quantum dot-cavity system is a promising source of antibunched entangled photon pairs.Entangled photon pairs are a crucial resource in quantum information processing. However, common sources of entangled photon pairs, such as generation by spontaneous parametric down-conversion, impose a Poisson distribution on the pairs, limiting their applicability to quantum information processing. Therefore, generating entangled photon pairs exhibiting a sub-Poisson distribution (i.e., entangled photon bundle) would be crucial/an important advancement in the current research context. Recently, it has been proposed that antibunched photon pairs can be generated using pulsed excitation of quantum dots based on photon blockade. In this work we propose a scheme to generate entangled photon pairs with strong antibunching properties via continuous driving. Under two-photon resonant continuous pumping, a quantum dot is first excited to a biexciton state and then emits a pair of entangled photons into a two-mode cavity. Owing to the strong coupling between the quantum dot and optical modes of the cavity, at most one pair of left-/right-polarized photons exists at a time in the cavity. Specifically, the antibunching effect, average photon number, and entanglement of the left- or right-polarized photons can be resonantly enhanced when the coupling strengths between the exciton (biexciton) transition and cavity modes are equal. Moreover, our results show that the binding energy of the biexciton substantially affects the antibunching effect, average photon number, and entanglement of the left-/right-polarized photons. With suitable parameters, we can realize photon pairs with strong antibunching, a large average photon number, and deep entanglement. Hence, the studied quantum dot-cavity system is a promising source of antibunched entangled photon pairs.

Optics ExpressJul 1, 20251 citation

High-quality single photons from cavity-enhanced biexciton-to-exciton transition

Nils Heinisch, Francesco Salusti, Mark R. Hogg +7 more

Resonant laser excitation of a two-level system with subsequent single-photon emission can be used to generate single photons with high indistinguishability or Hong-Ou-Mandel (HOM) visibility. However, spectral overlap between excitation laser and emitted photons generally poses significant challenges. Furthermore, emitter re-excitation intrinsically limits achievable single-photon purity. Established solutions mitigate these issues at significant cost to source efficiency and with increased source complexity. This motivates the use of few-level systems with spectral separation of excitation and emission pathways. One option is a three-level cascade. However, without targeted lifetime engineering of emitting states, the cascade naturally limits achievable photon indistinguishability. Here we study a semiconductor quantum dot with resonant and selective cavity-enhancement of biexciton-to-exciton transition. Following resonant two-photon excitation of the biexciton state, we collect the emitted single photon with the cavity. This approach circumvents emitter re-excitation and naturally introduces spectral separation of excitation laser and emitted single photon. Supported by first experimental results, we demonstrate theoretically that with selective Purcell enhancement, the observed quality quantifiers of single-photon emission (purity, equivalently $g^{(2)}(0)$ , and HOM visibility $\mathcal{V}$ , equivalently indistinguishability) are competitive with respect to high-quality deterministic quantum-dot single-photon sources. This is already achieved without systematic optimization or targeted system engineering, which firmly places the reported approach as a viable route to the next generation of highest-quality quantum-dot based deterministic single-photon sources.Resonant laser excitation of a two-level system with subsequent single-photon emission can be used to generate single photons with high indistinguishability or Hong-Ou-Mandel (HOM) visibility. However, spectral overlap between excitation laser and emitted photons generally poses significant challenges. Furthermore, emitter re-excitation intrinsically limits achievable single-photon purity. Established solutions mitigate these issues at significant cost to source efficiency and with increased source complexity. This motivates the use of few-level systems with spectral separation of excitation and emission pathways. One option is a three-level cascade. However, without targeted lifetime engineering of emitting states, the cascade naturally limits achievable photon indistinguishability. Here we study a semiconductor quantum dot with resonant and selective cavity-enhancement of biexciton-to-exciton transition. Following resonant two-photon excitation of the biexciton state, we collect the emitted single photon with the cavity. This approach circumvents emitter re-excitation and naturally introduces spectral separation of excitation laser and emitted single photon. Supported by first experimental results, we demonstrate theoretically that with selective Purcell enhancement, the observed quality quantifiers of single-photon emission (purity, equivalently $g^{(2)}(0)$, and HOM visibility $\mathcal{V}$, equivalently indistinguishability) are competitive with respect to high-quality deterministic quantum-dot single-photon sources. This is already achieved without systematic optimization or targeted system engineering, which firmly places the reported approach as a viable route to the next generation of highest-quality quantum-dot based deterministic single-photon sources.

quant-pharXiv:2602.18153Physical Review AppliedFeb 23, 20261 citation

Polarization-entangled twin photons from two-photon quantum-dot emission

Dirk Heinze, A. Zrenner, Stefan Schumacher

Semiconductor quantum dots are promising sources for polarization-entangled photons. As an alternative to the usual cascaded biexciton-exciton emission, direct two-photon emission from the biexciton can be used. With a high-quality optical resonator tuned to half the biexciton energy, a large proportion of the photons can be steered into the two-photon emission channel. In this case the degree of polarization entanglement is inherently insensitive to the exciton fine-structure splitting. In the present work we analyze the biexciton emission with particular emphasis on the influence of coupling of the quantum-dot cavity system to its environment. Especially for a high-quality cavity, the coupling to the surrounding semiconductor material can open up additional phonon-assisted decay channels. Our analysis demonstrates that with the cavity tuned to half the biexciton energy, the potentially detrimental influence of the phonons on the polarization entanglement is strongly suppressed---high degrees of entanglement can still be achieved. We further discuss spectral properties and statistics of the emitted twin photons.Semiconductor quantum dots are promising sources for polarization-entangled photons. As an alternative to the usual cascaded biexciton-exciton emission, direct two-photon emission from the biexciton can be used. With a high-quality optical resonator tuned to half the biexciton energy, a large proportion of the photons can be steered into the two-photon emission channel. In this case the degree of polarization entanglement is inherently insensitive to the exciton fine-structure splitting. In the present work we analyze the biexciton emission with particular emphasis on the influence of coupling of the quantum-dot cavity system to its environment. Especially for a high-quality cavity, the coupling to the surrounding semiconductor material can open up additional phonon-assisted decay channels. Our analysis demonstrates that with the cavity tuned to half the biexciton energy, the potentially detrimental influence of the phonons on the polarization entanglement is strongly suppressed---high degrees of entanglement can still be achieved. We further discuss spectral properties and statistics of the emitted twin photons.

arXiv:1611.04328Physical review. B./Physical review. BJun 9, 201734 citations

g^{(2)}(0)

, and HOM visibility

\mathcal{V}

, equivalently indistinguishability) are competitive with respect to high-quality deterministic quantum-dot single-photon sources. This is already achieved without systematic optimization or targeted system engineering, which firmly places the reported approach as a viable route to the next generation of highest-quality quantum-dot based deterministic single-photon sources.