Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2102.00283 · AIP Advances

Demonstration and modeling of time-bin entangled photons from a quantum dot in a nanowire

Philipp Aumann, Maximilian Prilmüller, Florian Kappe, Laurin Ostermann, Dan Dalacu, Philip J. Poole, Helmut Ritsch, Wolfgang Lechner, Gregor Weihs

Published May 1, 2022• 17 citations
arXivHTMLPDF

Abstract

Resonant excitation of the biexciton state in an InAsP quantum dot by a phase-coherent pair of picosecond pulses allows preparing time-bin entangled pairs of photons via the biexciton–exciton cascade. We show that this scheme can be implemented for a dot embedded in an InP nanowire. The underlying physical mechanisms can be represented and quantitatively analyzed by an effective three-level open system master equation. Simulation parameters including decay and intensity dependent dephasing rates are extracted from experimental data, which in turn let us predict the resulting entanglement and optimal operating conditions.

DOI
10.1063/5.0081874

Related papers

Towards On-demand Generation of Entangled Photons with Quantum Dots

Arash Ahmadi

The biexciton-exciton cascade in quantum dots (QDs) yields entangled photon pairs, and recent developments in engineering photonic structures around the dot for efficient light extraction and proper control of the fine-structure splitting, has led to significant breakthroughs in achieving an ideal entangled photon source -- exhibiting properties such as high extraction efficiency, low multi-photon emission and high entanglement fidelity. This thesis presents our development in enhancing the performance of entangled photon generation of QDs towards near-unity efficiency and fidelity. We study InAsP quantum dots in photonic nanowires for efficient light extraction and to reveal the effect of a quantum dot with high nuclear spin on the entanglement fidelity. \n \nRevealing the ultimate limit of entanglement in QDs is still a challenge, and it is generally believed that a sample made of atoms possessing high nuclear spins exhibits limited entanglement due to the dephasing caused by spin-spin interactions. Moreover, it is assumed that the fine-structure splitting of QDs degrades the entanglement fidelity, as it introduces a which-path information in the biexciton-exciton cascade. We have performed two-photon state tomography on InAsP QDs in InP nanowires, comprising of nuclear spin 9/2, and have realized that such a source is capable of generating entangled photon pairs with negligible dephasing during the emission lifetime, with a peak concurrence C = 77% and a count-weighted average concurrence 62%. This result was obtained by comparing the outcome of our measurements with a theoretical model that assumes no dephasing, however, takes into account the details of the detection system, i.e., dark-count rates and timing resolution, as well as, specific features of the QD, e.g., emission lifetime, fine-structure splitting, multi-photon emission probability, etc. Proper engineering of tapered nanowires allows for extraction of the emitted photons with high efficiency, which makes it possible to perform a complete two-photon state tomography and monitoring the evolution of the exciton state, as well as, the entanglement fidelity of the photon-pair, during the emission lifetime. This enabled us to reveal the effect of an imperfect detection system, as well as, multi-photon emission in recording low values for entanglement fidelity. Moreover, our calculations show that proper analysis of the time-energy uncertainty relation provides the necessary means to measure a high entanglement fidelity even in the presence of fine-structure splitting; since, a detection system with high timing resolution can overlook the which-path information, as the uncertainty in measuring the energy of the photons will be larger than the fine-structure splitting. Therefore, realizing near-unity entanglement fidelity using QDs is merely a technical challenge, i.e., resonant excitation of the QD, in order to suppress multi-photon emission, and use of a detection system with low timing jitter and dark-count rates. \n \nAs a next step to achieve this goal, we have performed the resonant two-photon excitation scheme for the first time on a QD in a photonic nanowire, which resulted in an enhancement of the performance of our source. We managed to improve the single-photon purity of the source, g^(2)(0), by two orders of magnitude; moreover, analysis of the emission spectrum reveals that this scheme increases the pair-production efficiency to values above 93% for the biexciton-exciton cascade. Taking the efficiency of our experimental setup into consideration, the results indicate an approximately eight-fold enhancement of the pair-extraction efficiency as compared to the quasi-resonant excitation scheme (12.55% vs. 1.6%). Based on these results, two-photon state tomography on our source, under resonant two-photon excitation and performed by a detection system with high timing resolution and low dark-count rates, yields near-unity entanglement fidelity. By considering the enhancement in pair-extraction efficiency that we obtained, QDs in photonic nanowires can surpass the performance of spontaneous parametric down conversion sources in terms of entanglement fidelity and pair-extraction efficiency. \n \nEven though we have shown a finite fine-structure splitting does not degrade the entanglement fidelity in QDs, for various application in quantum information removing the fine-structure splitting is beneficial. Therefore, we have proposed a universal all-optical approach for removing the fine-structure splitting. In this scheme, the energy of the photons are shifted by using a pair of quarter-wave plates and fast-rotating half-wave plates after they have been emitted; and as a result, the energy difference between the two decay paths in the biexciton-exciton cascade is erased. This method is applicable to any QD source and can be easily implemented using the currently available technology; moreover, no further sample processing will be required in order to achieve zero fine-structure splitting.

•Jan 17, 2020•0 citations

Coherence and degree of time-bin entanglement from quantum dots

Tobias Huber, Laurin Ostermann, Maximilian Prilmüller +4 more

We report a study on coherence of excitation of single quantum dots. We address the coherent excitation of biexcitons, the process that is indispensable for deterministic photon pair generation in quantum dots. Based on theoretical modeling we optimized the duration of the excitation pulse in our experiment to minimize the laser-induced dephasing and increase the biexciton-to-background single-exciton occupation probability. An additional effect of this approach is a high degree of time-bin entanglement with a concurrence of up to 0.78(6) and a 0.88(3) overlap with a maximally entangled state.

arXiv:1506.02429•Physical review. B./Physical review. B•May 12, 2016•37 citations

Single quantum dots as photon pair emitters

Ana Predojević, Tobias Huber, Miroslav Ježek +5 more

Summary form only given. A realization of time-bin entanglement obtained from quantum dots would join the strength of long distance transmission that characterizes this type of entanglement with the single photon state purity of the quantum dot emission. Compared with polarization entanglement from quantum dots this scheme does not require elimination of the fine structure splitting responsible for partial distinguishability of the quantum dot cascades [1].Here, we present our results on coherent and resonant excitation of quantum dots, creation of photon pairs, scattering free emission and measurement of the high purity of the emitted photons [2, 3]. In addition, we will show our measurements of the generated time-bin entanglement. To excite a single quantum dot we performed two-photon resonant excitation of the biexciton state. Here, we exploited the biexciton binding energy in order to use the laser light which was not resonant to any photon emitted from the quantum dot (Fig. 1a). Our measurements were performed on a single self-assembled InAs/GaAs quantum dot. We confirmed the resonant nature of the excitation by observing Rabi oscillations (Fig. 1b). Additionally, we performed Ramsey interference measurement and determined the coherence time of the ground-biexciton state superposition. These measurements show that we can coherently transfer the phase of the excitation laser onto the quantum dot system, a necessary requirement to obtain time-bin entanglement.To test the statistics of the emitted state we measured the auto-correlation of the emitted photons (Fig. 3c). Here, the auto-correlation parameter at zero delay was measured to be 0.012(1) without and 0.0073(8) with background subtraction. In addition, we performed a measurement to characterize the state emitted from a quantum dot using a witness-based criterion described in [4]. With this measurement we experimentally confirmed that the resonantly excited quantum dot emits a non-Gaussian state of light (Fig. 1d). This measurement is the first of this nature ever performed on a semiconductor single photon emitter.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•May 1, 2013•0 citations

Generation of C-band entangled photon pairs by biexciton-exciton cascade from symmetric InAs/InP quantum dots

Anna Musiał, Maja Wasiluk, Katarzyna Roszak +6 more

Hereby, we study the generation of pairs of polarization-entangled photons at telecom C-band by biexciton-exciton cascade from non-resonantly excited epitaxial InAs/InP quantum dots (QDs). It is realized without external tuning of the fine structure splitting (FSS), which does not exceed 10 $μ$eV in as-grown nanostructures, due to their high in-plane symmetry. Excitonic complexes are identified by means of excitation power-dependent and polarization-resolved magneto)microphotoluminescence. Their origin from different carrier configurations confined in the same QD is confirmed by time correlations of emitted photons. Experimental results are supported by 8-band kp calculations, followed by the configuration interaction method to include excitonic effects. This comparison reveals the structure of higher energy states, allowing for the reconstruction of the QD structural parameters. To verify and quantify the entanglement, we perform quantum state tomography and reconstruct the two-photon density matrix. Its diagonalization allows a detailed analysis of the entangled state and reveals an unfavourable interplay between phase accumulation and decoherence, pointing to a clear route for boosting entanglement by using a XX resonant, pulsed excitation scheme and shortening the radiative lifetimes.

arXiv:2509.24500•Sep 29, 2025•0 citations

Entangled Photon Pair Generator Via Biexciton–Exciton Cascade in Semiconductor Quantum Dots and its Simulation

Simon Sekavčnik, Paul R. Kohl, Janis Nötzel

ABSTRACT The generation of entangled photon pairs is highly useful for many types of quantum technologies. In this work an entangled photon pair generator that utilizes the biexciton–exciton cascade in semiconductor quantum dots is described on a physical, mathematical, and software level. The system is implemented and simulated as a self‐contained component in a framework for bigger quantum optical experiments. Thus, it is a description to further the holistic understanding of the system for interdisciplinary audiences in a hopefully simple yet sufficient manner. It is described from the condensed matter physics fundamentals, over the most important quantum optical properties, to a mathematical description of the used model, and finally a software description and simulation, making it an executable description of such a system. We provide a compact description in the Kraus operator formalism to seamlessly incorporate such an entangled photon pair generator simulation component into bigger simulations consisting of multiple components at a reasonable computational cost. The simulation accommodates a wide range of parameter regimes and makes it possible to simulate many different excitation strategies. This includes resonant two‐photon excitation, adiabatic rapid passage chirped excitation, and dichromatic pulsed excitation.

arXiv:2510.09262•Advanced Quantum Technologies•Apr 1, 2026•3 citations

Coherent generation of time-bin entangled photon pairs using the biexciton cascade and cavity-assisted piecewise adiabatic passage

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 piecewise adiabatic passage in a single quantum dot. The quantum dot is embedded inside a semiconductor microcavity, and the interaction of a coherent superposition of two temporally separated input pulses and the cavity mode leads to a piecewise adiabatic passage, 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 we quantify the degree of entanglement through the visibility of the interference. We also discuss the influence of pure dephasing on the entanglement of the generated photon pair. Pronounced interference visibility values of greater than $1/\sqrt{2}$ are predicted in triple coincidence measurement using experimentally achievable parameters, demonstrating that the generated photons could be suitable for applications such as Bell's inequality violation and quantum cryptography.

Physical Review B•Jun 3, 2011•18 citations
Resonant excitation of the biexciton state in an InAsP quantum dot by a phase-coherent pair of picosecond pulses allows preparing time-bin entangled pairs of photons via the biexciton–exciton cascade. We show that this scheme can be implemented for a dot embedded in an InP nanowire. The underlying physical mechanisms can be represented and quantitatively analyzed by an effective three-level open system master equation. Simulation parameters including decay and intensity dependent dephasing rates are extracted from experimental data, which in turn let us predict the resulting entanglement and optimal operating conditions.
The biexciton-exciton cascade in quantum dots (QDs) yields entangled photon pairs, and recent developments in engineering photonic structures around the dot for efficient light extraction and proper control of the fine-structure splitting, has led to significant breakthroughs in achieving an ideal entangled photon source -- exhibiting properties such as high extraction efficiency, low multi-photon emission and high entanglement fidelity. This thesis presents our development in enhancing the performance of entangled photon generation of QDs towards near-unity efficiency and fidelity. We study InAsP quantum dots in photonic nanowires for efficient light extraction and to reveal the effect of a quantum dot with high nuclear spin on the entanglement fidelity. \n \nRevealing the ultimate limit of entanglement in QDs is still a challenge, and it is generally believed that a sample made of atoms possessing high nuclear spins exhibits limited entanglement due to the dephasing caused by spin-spin interactions. Moreover, it is assumed that the fine-structure splitting of QDs degrades the entanglement fidelity, as it introduces a which-path information in the biexciton-exciton cascade. We have performed two-photon state tomography on InAsP QDs in InP nanowires, comprising of nuclear spin 9/2, and have realized that such a source is capable of generating entangled photon pairs with negligible dephasing during the emission lifetime, with a peak concurrence C = 77% and a count-weighted average concurrence 62%. This result was obtained by comparing the outcome of our measurements with a theoretical model that assumes no dephasing, however, takes into account the details of the detection system, i.e., dark-count rates and timing resolution, as well as, specific features of the QD, e.g., emission lifetime, fine-structure splitting, multi-photon emission probability, etc. Proper engineering of tapered nanowires allows for extraction of the emitted photons with high efficiency, which makes it possible to perform a complete two-photon state tomography and monitoring the evolution of the exciton state, as well as, the entanglement fidelity of the photon-pair, during the emission lifetime. This enabled us to reveal the effect of an imperfect detection system, as well as, multi-photon emission in recording low values for entanglement fidelity. Moreover, our calculations show that proper analysis of the time-energy uncertainty relation provides the necessary means to measure a high entanglement fidelity even in the presence of fine-structure splitting; since, a detection system with high timing resolution can overlook the which-path information, as the uncertainty in measuring the energy of the photons will be larger than the fine-structure splitting. Therefore, realizing near-unity entanglement fidelity using QDs is merely a technical challenge, i.e., resonant excitation of the QD, in order to suppress multi-photon emission, and use of a detection system with low timing jitter and dark-count rates. \n \nAs a next step to achieve this goal, we have performed the resonant two-photon excitation scheme for the first time on a QD in a photonic nanowire, which resulted in an enhancement of the performance of our source. We managed to improve the single-photon purity of the source, g^(2)(0), by two orders of magnitude; moreover, analysis of the emission spectrum reveals that this scheme increases the pair-production efficiency to values above 93% for the biexciton-exciton cascade. Taking the efficiency of our experimental setup into consideration, the results indicate an approximately eight-fold enhancement of the pair-extraction efficiency as compared to the quasi-resonant excitation scheme (12.55% vs. 1.6%). Based on these results, two-photon state tomography on our source, under resonant two-photon excitation and performed by a detection system with high timing resolution and low dark-count rates, yields near-unity entanglement fidelity. By considering the enhancement in pair-extraction efficiency that we obtained, QDs in photonic nanowires can surpass the performance of spontaneous parametric down conversion sources in terms of entanglement fidelity and pair-extraction efficiency. \n \nEven though we have shown a finite fine-structure splitting does not degrade the entanglement fidelity in QDs, for various application in quantum information removing the fine-structure splitting is beneficial. Therefore, we have proposed a universal all-optical approach for removing the fine-structure splitting. In this scheme, the energy of the photons are shifted by using a pair of quarter-wave plates and fast-rotating half-wave plates after they have been emitted; and as a result, the energy difference between the two decay paths in the biexciton-exciton cascade is erased. This method is applicable to any QD source and can be easily implemented using the currently available technology; moreover, no further sample processing will be required in order to achieve zero fine-structure splitting.
We report a study on coherence of excitation of single quantum dots. We address the coherent excitation of biexcitons, the process that is indispensable for deterministic photon pair generation in quantum dots. Based on theoretical modeling we optimized the duration of the excitation pulse in our experiment to minimize the laser-induced dephasing and increase the biexciton-to-background single-exciton occupation probability. An additional effect of this approach is a high degree of time-bin entanglement with a concurrence of up to 0.78(6) and a 0.88(3) overlap with a maximally entangled state.
Summary form only given. A realization of time-bin entanglement obtained from quantum dots would join the strength of long distance transmission that characterizes this type of entanglement with the single photon state purity of the quantum dot emission. Compared with polarization entanglement from quantum dots this scheme does not require elimination of the fine structure splitting responsible for partial distinguishability of the quantum dot cascades [1].Here, we present our results on coherent and resonant excitation of quantum dots, creation of photon pairs, scattering free emission and measurement of the high purity of the emitted photons [2, 3]. In addition, we will show our measurements of the generated time-bin entanglement. To excite a single quantum dot we performed two-photon resonant excitation of the biexciton state. Here, we exploited the biexciton binding energy in order to use the laser light which was not resonant to any photon emitted from the quantum dot (Fig. 1a). Our measurements were performed on a single self-assembled InAs/GaAs quantum dot. We confirmed the resonant nature of the excitation by observing Rabi oscillations (Fig. 1b). Additionally, we performed Ramsey interference measurement and determined the coherence time of the ground-biexciton state superposition. These measurements show that we can coherently transfer the phase of the excitation laser onto the quantum dot system, a necessary requirement to obtain time-bin entanglement.To test the statistics of the emitted state we measured the auto-correlation of the emitted photons (Fig. 3c). Here, the auto-correlation parameter at zero delay was measured to be 0.012(1) without and 0.0073(8) with background subtraction. In addition, we performed a measurement to characterize the state emitted from a quantum dot using a witness-based criterion described in [4]. With this measurement we experimentally confirmed that the resonantly excited quantum dot emits a non-Gaussian state of light (Fig. 1d). This measurement is the first of this nature ever performed on a semiconductor single photon emitter.
Hereby, we study the generation of pairs of polarization-entangled photons at telecom C-band by biexciton-exciton cascade from non-resonantly excited epitaxial InAs/InP quantum dots (QDs). It is realized without external tuning of the fine structure splitting (FSS), which does not exceed 10 μμμeV in as-grown nanostructures, due to their high in-plane symmetry. Excitonic complexes are identified by means of excitation power-dependent and polarization-resolved magneto)microphotoluminescence. Their origin from different carrier configurations confined in the same QD is confirmed by time correlations of emitted photons. Experimental results are supported by 8-band kp calculations, followed by the configuration interaction method to include excitonic effects. This comparison reveals the structure of higher energy states, allowing for the reconstruction of the QD structural parameters. To verify and quantify the entanglement, we perform quantum state tomography and reconstruct the two-photon density matrix. Its diagonalization allows a detailed analysis of the entangled state and reveals an unfavourable interplay between phase accumulation and decoherence, pointing to a clear route for boosting entanglement by using a XX resonant, pulsed excitation scheme and shortening the radiative lifetimes.
ABSTRACT The generation of entangled photon pairs is highly useful for many types of quantum technologies. In this work an entangled photon pair generator that utilizes the biexciton–exciton cascade in semiconductor quantum dots is described on a physical, mathematical, and software level. The system is implemented and simulated as a self‐contained component in a framework for bigger quantum optical experiments. Thus, it is a description to further the holistic understanding of the system for interdisciplinary audiences in a hopefully simple yet sufficient manner. It is described from the condensed matter physics fundamentals, over the most important quantum optical properties, to a mathematical description of the used model, and finally a software description and simulation, making it an executable description of such a system. We provide a compact description in the Kraus operator formalism to seamlessly incorporate such an entangled photon pair generator simulation component into bigger simulations consisting of multiple components at a reasonable computational cost. The simulation accommodates a wide range of parameter regimes and makes it possible to simulate many different excitation strategies. This includes resonant two‐photon excitation, adiabatic rapid passage chirped excitation, and dichromatic pulsed excitation.
We present a scheme to realize a deterministic solid-state source of time-bin entangled photon pairs using cavity-assisted piecewise adiabatic passage in a single quantum dot. The quantum dot is embedded inside a semiconductor microcavity, and the interaction of a coherent superposition of two temporally separated input pulses and the cavity mode leads to a piecewise adiabatic passage, 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 we quantify the degree of entanglement through the visibility of the interference. We also discuss the influence of pure dephasing on the entanglement of the generated photon pair. Pronounced interference visibility values of greater than 1/21/\sqrt{2}1/2​ are predicted in triple coincidence measurement using experimentally achievable parameters, demonstrating that the generated photons could be suitable for applications such as Bell's inequality violation and quantum cryptography.