Many quantum communication schemes require sources of single, indistinguishable and entangled photon pairs with high brightness. Semiconductor quantum dots (QDs) hold great promise to meet these requirements offering the additional key advantage of the possibility of shifting the emission wavelength to the telecom C-band (centered around 1550 nm). This wavelength range is especially sought-after for fiber-based applications due to the global absorption minimum in standard glass fibers which maximizes the attainable communication distance.
Many quantum communication schemes require sources of single, indistinguishable and entangled photon pairs with high brightness. Semiconductor quantum dots (QDs) hold great promise to meet these requirements offering the additional key advantage of the possibility of shifting the emission wavelength to the telecom C-band (centered around 1550 nm). This wavelength range is especially sought-after for fiber-based applications due to the global absorption minimum in standard glass fibers which maximizes the attainable communication distance.
An emission wavelength around 1550 nm (telecom C-band) is highly appealing for nonclassical light sources, among others, due to the absorption minimum in standard glass fibers. In particular, semiconductor quantum dots at this wavelength promise to provide the outstanding results achieved with this emitter type in the near-infrared spectral region. Here, we study resonance fluorescence from InAs/GaAs quantum dots emitting in the telecom C-band under continuous wave and pulsed excitation. For the prior case, the quantum dot is excited in the strong driving regime and the characteristic Mollow triplet is observed allowing to draw conclusions on the nature and quantitative influence of different decoherence mechanisms on the emission. Furthermore, under pulsed excitation, highly pure single-photon emission (g(2)(0)=0.023 ± 0.019) is demonstrated and a measurement of the photon indistinguishability (VTPI=0.144 ± 0.015; full width at half maximum of the time window for post-selection of (305 ± 33)ps with an associated maximally attainable value VTPI,p=0.955) is presented. In the process of making the emission properties of telecom quantum dots comparable to their well-established counterparts emitting in the near-infrared spectral region, these results represent a benchmark and provide valuable information for future optimization of sample structures.
In the field of quantum communication and quantum cryptography, the need for bright non-classical light sources remains a key requirement. Semiconductor quantum dots (QDs) have proven to be excellent candidates also being able to emit single-photons in the much sought after telecom bands. To overcome the high refractive index contrast between the semiconductor matrix and air, a main approach is to use cavity quantum electrodynamics (cQED). In this regard, circular Bragg gratings have achieved excellent results in the NIR regime [1] [2] . Using the existing fiber network, especially single-photons in the telecom O-band are favorable not only because of zero wave-packet dispersion but also for wavelength division multiplexing with classical communication signals in the telecom C-band.
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.
The implementation of fiber-based long-range quantum communication requires tunable sources of single photons at the telecom C-band. Stable and easy-to-implement wavelength-tunability of individual sources is crucial to (i) bring remote sources into resonance, (ii) define a wavelength standard, and (iii) ensure scalability to operate a quantum repeater. So far, the most promising sources for true, telecom single photons are semiconductor quantum dots, due to their ability to deterministically and reliably emit single and entangled photons. However, the required wavelength-tunability is hard to attain. Here, we show a stable wavelength-tunable quantum light source by integrating strain-released InAs quantum dots on piezoelectric substrates. We present triggered single-photon emission at 1.55 μm with a multi-photon emission probability as low as 0.097, as well as photon pair emission from the radiative biexciton–exciton cascade. We achieve a tuning range of 0.25 nm which will allow us to spectrally overlap remote quantum dots or tuning distant quantum dots into resonance with quantum memories. This opens up realistic avenues for the implementation of photonic quantum information processing applications at telecom wavelengths.
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.
High Resolution Image Download MS PowerPoint Slide Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, which are useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550 nm is ideal. The direct generation of QD-photons in this spectral range 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.