Quantum Nanophotonic Materials, Devices, and Systems
On-demand generation of entangled photons in the telecom C-band
Katharina D. Zeuner, Klaus D. Jöns, Lucas Schweickert, Carl Reuterskiöld-Hedlund, Carlos Nuñez Lobato, Thomas Lettner, Kai Wang, Samuel Gyger, Eva Schöll, Stephan Steinhauer, Mattias Hammar, Val Zwiller
Fiber-based quantum networks require on-demand sources of entangled photons in the telecom C-band for long distance information transfer. Historically, the field of in-fiber entanglement distribution has been dominated by photons provided via spontaneous processes. In recent years, semiconductor quantum dots have emerged as strong competitors in terms of generating single and entangled photons due to their promise of deterministic qubit generation in the NIR wavelength region. Here, we show the on-demand generation of polarization entangled photons in the telecom C-band based on InAs/GaAs quantum dots grown via metal-organic vapor-phase epitaxy. By employing a robust phonon-assisted two-photon excitation scheme, we are able to generate pairs of entangled photons with a concurrence of 91.4 ± 3.8 % and a maximum fidelity to the Bell state Φ+ of 95.2 ± 1.1 %.
Fiber-based quantum networks require on-demand sources of entangled photons in the telecom C-band for long distance information transfer. Historically, the field of in-fiber entanglement distribution has been dominated by photons provided via spontaneous processes. In recent years, semiconductor quantum dots have emerged as strong competitors in terms of generating single and entangled photons due to their promise of deterministic qubit generation in the NIR wavelength region. Here, we show the on-demand generation of polarization entangled photons in the telecom C-band based on InAs/GaAs quantum dots grown via metal-organic vapor-phase epitaxy. By employing a robust phonon-assisted two-photon excitation scheme, we are able to generate pairs of entangled photons with a concurrence of 91.4 ± 3.8 % and a maximum fidelity to the Bell state Φ+ of 95.2 ± 1.1 %.
On-demand sources of entangled photons for the transmission of quantum information in the telecom C-band are required to realize fiber-based quantum networks. So far, non-deterministic sources of quantum states of light were used for long distance entanglement distribution in this lowest loss wavelength range. However, they are fundamentally limited in either efficiency or security due to their Poissonian emission statistics. Here, we show on-demand generation of entangled photon pairs in the telecom C-band by an InAs/GaAs semiconductor quantum dot. Using a robust phonon-assisted excitation scheme we measure a concurrence of 91.4% and a fidelity of 95.2% to Φ+. On-demand generation of polarization entangled photons will enable secure quantum communication in fiber-based networks. Furthermore, applying this excitation scheme to several remote quantum dots tuned into resonance will enable first on-demand entanglement distribution over large distances for scalable real-life quantum applications.
High Resolution Image Download MS PowerPoint Slide Entangled photons are an integral part in quantum optics experiments and a key resource in quantum imaging, quantum communication, and photonic quantum information processing. Making this resource available on-demand has been an ongoing scientific challenge with enormous progress in recent years. Of particular interest is the potential to transmit quantum information over long distances, making photons the only reliable flying qubit. Entangled photons at the telecom C-band could be directly launched into single-mode optical fibers, enabling worldwide quantum communication via existing telecommunication infrastructure. However, the on-demand generation of entangled photons at this desired wavelength window has been elusive. Here, we show a photon pair generation efficiency of 69.9 ± 3.6% in the telecom C-band by an InAs/GaAs semiconductor quantum dot on a metamorphic buffer layer. Using a robust phonon-assisted two-photon excitation scheme we measure a maximum concurrence of 91.4 ± 3.8% and a peak fidelity to the Φ + state of 95.2 ± 1.1%, verifying on-demand generation of strongly entangled photon pairs and marking an important milestone for interfacing quantum light sources with our classical fiber networks.
High Resolution Image Download MS PowerPoint Slide Entangled photon pairs at telecom wavelengths are essential for quantum communication, distributed computing, and quantum-enhanced sensing. The telecom O-band offers low chromatic dispersion and fiber loss, which is ideal for long-distance networks. Site-controlled nanowire quantum dots have emerged as a promising platform for generating single and entangled photons, offering high extraction efficiency and scalability. However, their operation has largely been restricted to the visible and first near-infrared (NIR-I) windows. Here, we demonstrate a bright source of entangled photon pairs in the telecom O-band based on site-controlled nanowire quantum dots. We measure a fine-structure splitting of 4.6 μeV, confirming suitability for high-fidelity polarization entanglement. Quantum-state tomography of the biexciton–exciton cascade reveals a maximum fidelity of 85.8 ± 1.1% to the Φ + Bell state and a maximum concurrence of 75.1 ± 2.1%. This work establishes nanowire quantum dots as viable entangled photon sources at telecom, advancing scalable quantum technologies for fiber-based networks.
ABSTRACT Many protocols of future quantum networks rely on the availability of entangled qubits which enable links among remote nodes due to their unique properties. Therefore, the efficient generation of entangled photons constitutes a key goal toward the implementation of such quantum networks. However, currently available sources are bound by intrinsic limitations, as for instance probabilistic nature of emission. Deterministic quantum emitters pose a potential solution for this issue, however, the maturity of their device platforms still needs to be improved for truly on‐demand emission. While record efficiencies are currently found at near‐infrared wavelengths, sources at telecommunication wavelengths will likely be the ideal choice for quantum networks. That motivates the development of efficient sources of entangled photons in the telecom regime. This work addresses that challenge presenting a telecom C‐band source of polarization entangled photons based on semiconductor quantum dots incorporated in a planar cavity structure. In this way, triggered emission of entangled photon pairs with a coincidence rate of (biexciton/exciton fiber‐coupled single‐photon count rates of /) combined with values of / is achieved. Full quantum state tomography of the two‐photon state demonstrates simultaneously entanglement fidelities of up to to the Bell state.
Abstract Long-distance quantum communication and computation is based on the exchange of information via photons as flying qubits. In all foreseen implementations, from quantum relays and networks to remote quantum computing, the photons must be able to propagate over long distances, in silica fibers, with limited absorption and wave packet dispersion. When propagating into silica fibers, photons in the so-called telecom C-band (i.e. wavelength around 1550 nm) will experience the absolute minimum of absorption, together with a limited photon wave packet dispersion. This implies that losses of information will be minimized and additionally, the capability of the photons to quantum interfere (the so-called Hong–Ou–Mandel effect) will be negligibly affected. This motivated the search for efficient non-classical light sources in this wavelength range. In the present review, we discuss the approaches followed to red-shift the emission wavelength from the near-infrared (NIR) to telecom wavelengths. In particular, the use of metamorphic buffers (MMBs) enabled the use of highly developed InAs/GaAs systems, engineering the dots to emit single and entangled photons in the telecom C-band. The main advantage of this approach is set by the choice of the material system: being the same as state-of-the-art structures emitting in the NIR range, it opens the possibility of achieving comparable performances even at telecommunication wavelengths. Here we will discuss the current state-of-the-art in the generation of non-classical photons, comparing the properties and performances of MMB-based results with other competing quantum dot (QD) platforms. We report in particular that very low fine-structure splitting can be observed with conservative values, on average well below 10 μ eV. This allowed for the observation of post-selected entanglement fidelity higher than 0.6. Additionally, on-demand single-photon emission with g ( 0 ) 2 = 0.184 ± 0.002 was observed in addition to a very low emitter density of ≈ 10 7 cm − 2 and a decay time of τ ≈ 1.2 ns comparable to standard InAs QDs emitting in the NIR range. A final highlight on approaches to further improve the current device performances will also be reported.
Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550nm is ideal. The direct generation of QD-photons in this spectral range and with high quantum-optical quality, however, remained challenging. Here, we demonstrate the coherent on-demand generation of indistinguishable photons in the telecom C-band from single QD devices consisting of InAs/InP QD-mesa structures heterogeneously integrated with a metallic reflector on a silicon wafer. Using pulsed two-photon resonant excitation of the biexciton-exciton radiative cascade, we observe Rabi rotations up to pulse areas of 4π and a high single-photon purity in terms of g(2)(0)=0.005(1) and 0.015(1) for exciton and biexciton photons, respectively. Applying two independent experimental methods, based on fitting Rabi rotations in the emission intensity and performing photon cross-correlation measurements, we consistently obtain preparation fidelities at the π-pulse exceeding 80%. Finally, performing Hong-Ou-Mandel-type two-photon interference experiments we obtain a photon-indistinguishability of the full photon wave packet of up to 35(3)%, representing a significant advancement in the photon-indistinguishability of single photons emitted directly in the telecom C-band.