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Time-bin entangled photon pairs from quantum dots embedded in a self-aligned cavity

Laia Ginés, Carlo Pepe, Gonzales, Junior, Niels Gregersen, Sven Höfling, Christian Schneider, Ana Predojević

Published Feb 1, 2021• 12 citations
OpenAlex

Abstract

We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.

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Time-bin entangled photon pairs from quantum dots embedded in a self-aligned cavity

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We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.

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Deterministic sources of entangled photon pairs and indistinguishable photons are expected to play a key role in photonic quantum technologies. Semiconductor quantum dots are promising candidates due to their on-demand emission and compatibility with nanophotonic structures. However, current implementations face trade-offs between extraction efficiency, Purcell enhancement, as well as charge noise that causes blinking and degrades indistinguishability. Here we demonstrate a tunable nano-optoelectronic device based on a quantum dot embedded in a p-i-n diode circular-Bragg-grating-resonator and featuring extraction efficiencies up to 0.55(6) and Purcell-factor of $\sim$8. The device generates wavelength-tunable entangled photon pairs with suppressed blinking and raw (corrected) concurrence > 0.89 (0.91) over a range of 1.6 nm. The very same source also emits single, nearly Fourier-limited and highly indistinguishable photons with raw (corrected) $\mathcal{V}_{\text{HOM}}$ = 0.951(4) (0.988(6)). These results demonstrate a viable platform for semiconductor quantum photonics.

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Generation of entangled photon pairs from quantum dots in self-aligned broadband cavities

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The quick development of quantum technologies and quantum communication demands a continuous search for more efficient and with higher performance quantum sources and devices. In particular, quantum dots are firmly established sources of single photon emitters and entangled photon pairs, with entanglement of photons emitted by a single quantum dot probed in polarization[1], time-bin[2] and hyperentanglement[3]. Although spontaneous parametric down conversion sources (SPDC) are widely used as entangled photon sources with the highest values of entanglement[4], are being reached by quantum dot devices[5]. With similar quality as SPDC sources, QDs however stand out as sources with sub-Poissonian statistics, essential for safe quantum communication. Still, most of the quantum dots devices exhibit low extraction efficiencies. Attempts to maximize the extraction efficiency involve sophisticated engineered photonic systems[6,7]. Furthermore, the accurate alignment of the quantum dot-cavity system is crucial for an effective quantum dotcavity coupling and hence an emission enhancement into free space[8]. All of this implies the need of intricated nanofabrication processes. Here we present a simple, scalable photonic device that grants efficient creation of entangled photon pairs from InAs quantum dots. The device, spontaneously formed during the growth process, is based on pairs of bottom/top distributed bragg reflectors (DBRs). A propagating deformation in the DBRs, leads to the formation of self-aligned dimples on top of the QDs, resulting in a self-aligned quantum-dot cavity system[9]. Therefore, costly and complex deterministic nanofabrication techniques are not required. In this work, the device performance was characterized, showing experimental collection efficiencies of 0.17, with theoretically pair extraction efficiencies above 0.45. Furthermore, a Purcell enhancement up to 1.7 was obtained. Finally, the device potential to generate time-bin entangled photons was investigated performing state tomography measurements. The subsequent reconstruction of the density matrix yields a concurrence of 0.70(10) and a fidelity of 0.84(5).

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A bright source of on-demand entangled photons is needed for quantum networks. A single quantum dot in a site-selected nanowire waveguide is a promising candidate for realizing such sources. However, such sources are associated with poor single-photon indistinguishability, limiting their applicability in quantum networks. A common approach for enhancing the single-photon indistinguishability in quantum dot-based entangled photon sources is to implement a broadband optical cavity. Achieving a high-Purcell cavity while retaining the advantages of the nanowire, such as directional emission, a broad operational bandwidth, and high light extraction efficiency, has been a significant challenge. Here, we propose a nanowire cavity based on quasi-bound states in the continuum formed by the strong coupling of two resonant optical modes. We numerically predict this design to support a cavity mode with 4 nm bandwidth and a Purcell enhancement of $\sim$17. This cavity mode enables a directional far-field emission profile (88% overlap with a Gaussian) with a light extraction efficiency of $\sim$74%. Our solution opens up a route for generating entangled photon pairs with enhanced extraction efficiency and single-photon indistinguishability for the practical realization of quantum networks.

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We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity of the two photon state by reducing spin induced phase shift during the radiative cascade.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Dec 4, 2010•1 citation

Generation of time-bin entangled photon pairs using a quantum-dot cavity system

Pradyumna K. Pathak, Stephen Hughes

We present a scheme to realize a deterministic solid state source of time-bin entangled photon pairs using cavity-assisted stimulated Raman adiabatic passage (STIRAP) in a single quantum dot. The quantum dot is embedded inside a semiconductor cavity, and the interaction of a coherent superposition of two temporally separated input pulses and the cavity mode leads to a two-photon Raman transition, which produces a time-bin entangled photon pair through the biexciton-exciton cascade. We show that the entanglement of the generated state can be measured using triple coincidence detection, and the degree of entanglement is quantified as the visibility of the interference. We also discuss the effect of pure dephasing on entanglement of the generated photon pair. Pronounced interference visibility values of greater than $1/\sqrt{2}$ are demonstrated in triple coincidence measurement using experimentally achievable parameters, thus demonstrating that the generated photons are suitable for applications with Bell's inequality violation and quantum cryptography.

arXiv:1010.1713•Oct 8, 2010•0 citations
We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.
We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.
Deterministic sources of entangled photon pairs and indistinguishable photons are expected to play a key role in photonic quantum technologies. Semiconductor quantum dots are promising candidates due to their on-demand emission and compatibility with nanophotonic structures. However, current implementations face trade-offs between extraction efficiency, Purcell enhancement, as well as charge noise that causes blinking and degrades indistinguishability. Here we demonstrate a tunable nano-optoelectronic device based on a quantum dot embedded in a p-i-n diode circular-Bragg-grating-resonator and featuring extraction efficiencies up to 0.55(6) and Purcell-factor of $\sim$8. The device generates wavelength-tunable entangled photon pairs with suppressed blinking and raw (corrected) concurrence > 0.89 (0.91) over a range of 1.6 nm. The very same source also emits single, nearly Fourier-limited and highly indistinguishable photons with raw (corrected) VHOM\mathcal{V}_{\text{HOM}}VHOM​ = 0.951(4) (0.988(6)). These results demonstrate a viable platform for semiconductor quantum photonics.
The quick development of quantum technologies and quantum communication demands a continuous search for more efficient and with higher performance quantum sources and devices. In particular, quantum dots are firmly established sources of single photon emitters and entangled photon pairs, with entanglement of photons emitted by a single quantum dot probed in polarization[1], time-bin[2] and hyperentanglement[3]. Although spontaneous parametric down conversion sources (SPDC) are widely used as entangled photon sources with the highest values of entanglement[4], are being reached by quantum dot devices[5]. With similar quality as SPDC sources, QDs however stand out as sources with sub-Poissonian statistics, essential for safe quantum communication. Still, most of the quantum dots devices exhibit low extraction efficiencies. Attempts to maximize the extraction efficiency involve sophisticated engineered photonic systems[6,7]. Furthermore, the accurate alignment of the quantum dot-cavity system is crucial for an effective quantum dotcavity coupling and hence an emission enhancement into free space[8]. All of this implies the need of intricated nanofabrication processes. Here we present a simple, scalable photonic device that grants efficient creation of entangled photon pairs from InAs quantum dots. The device, spontaneously formed during the growth process, is based on pairs of bottom/top distributed bragg reflectors (DBRs). A propagating deformation in the DBRs, leads to the formation of self-aligned dimples on top of the QDs, resulting in a self-aligned quantum-dot cavity system[9]. Therefore, costly and complex deterministic nanofabrication techniques are not required. In this work, the device performance was characterized, showing experimental collection efficiencies of 0.17, with theoretically pair extraction efficiencies above 0.45. Furthermore, a Purcell enhancement up to 1.7 was obtained. Finally, the device potential to generate time-bin entangled photons was investigated performing state tomography measurements. The subsequent reconstruction of the density matrix yields a concurrence of 0.70(10) and a fidelity of 0.84(5).
A bright source of on-demand entangled photons is needed for quantum networks. A single quantum dot in a site-selected nanowire waveguide is a promising candidate for realizing such sources. However, such sources are associated with poor single-photon indistinguishability, limiting their applicability in quantum networks. A common approach for enhancing the single-photon indistinguishability in quantum dot-based entangled photon sources is to implement a broadband optical cavity. Achieving a high-Purcell cavity while retaining the advantages of the nanowire, such as directional emission, a broad operational bandwidth, and high light extraction efficiency, has been a significant challenge. Here, we propose a nanowire cavity based on quasi-bound states in the continuum formed by the strong coupling of two resonant optical modes. We numerically predict this design to support a cavity mode with 4 nm bandwidth and a Purcell enhancement of $\sim$17. This cavity mode enables a directional far-field emission profile (88% overlap with a Gaussian) with a light extraction efficiency of $\sim$74%. Our solution opens up a route for generating entangled photon pairs with enhanced extraction efficiency and single-photon indistinguishability for the practical realization of quantum networks.
We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity of the two photon state by reducing spin induced phase shift during the radiative cascade.
We present a scheme to realize a deterministic solid state source of time-bin entangled photon pairs using cavity-assisted stimulated Raman adiabatic passage (STIRAP) in a single quantum dot. The quantum dot is embedded inside a semiconductor cavity, and the interaction of a coherent superposition of two temporally separated input pulses and the cavity mode leads to a two-photon Raman transition, which produces a time-bin entangled photon pair through the biexciton-exciton cascade. We show that the entanglement of the generated state can be measured using triple coincidence detection, and the degree of entanglement is quantified as the visibility of the interference. We also discuss the effect of pure dephasing on entanglement of the generated photon pair. Pronounced interference visibility values of greater than 1/21/\sqrt{2}1/2​ are demonstrated in triple coincidence measurement using experimentally achievable parameters, thus demonstrating that the generated photons are suitable for applications with Bell's inequality violation and quantum cryptography.