We propose an experimentally feasible scheme for generating entangled terahertz photon pairs in topological insulator quantum dots (TIQDs). We demonstrate theoretically that in generic TIQDs: 1) the fine structure splitting, which is the obstacle to produce entangled photons in conventional semiconductor quantum dots, is inherently absent for one-dimensional massless excitons due to the time-reversal symmetry; 2) the selection rules obey winding number conservation instead of the conventional angular momentum conservation between edge states with a linear dispersion. With these two advantages, the entanglement of the emitted photons during the cascade in our scheme is robust against unavoidable disorders and irregular shapes of the TIQDs.
Generating and detecting radiation in the technologically relevant range of the so-called terahertz gap ($0.1 - 10$ THz) is challenging because of a lack of efficient sources and detectors. Quantum dots in carbon nanotubes have shown great potential to build sensitive terahertz detectors usually based on photon-assisted tunnelling. A recently reported mechanism combining resonant quantum dot transitions and tunnelling barriers asymmetries results in a narrow linewidth photocurrent response with a large signal-to-noise ratio under weak THz radiation. That device was sensitive to one frequency, …
We investigate room temperature lasing of terahertz quantum cascade lasers using quantum dot chains as active material suitable for wireless communication and imaging technologies. Bandstructure calculations for such extended systems of coupled quantum dots are made possible by a novel 'linear combination of quantum dot orbitals'--method, based on single quantum dot wavefunctions. Our results demonstrate strong vertical-emission of coupled quantum dots, reduced phonon coupling and in-plane scattering, enabling room-temperature lasing with significantly reduced threshold current densities.
Time evolution of initially prepared entangled state in the system of coupled quantum dots has been analyzed by means of two different theoretical approaches: equations of motion for the all orders localized electron correlation functions, considering interference effects, and kinetic equations for the pseudo-particle occupation numbers with constraint on the possible physical states. Results obtained by means of different approaches were carefully analyzed and compared with each other. Revealed direct link between concurrence (degree of entanglement) and quantum dots pair correlation function…
We analyze the potential of the $c$-plane InGaN/GaN quantum dots for polarization entangled photon emission by means of an atomistic many-body framework. Special attention is paid to the impact of random alloy fluctuations on the excitonic fine structure and the excitonic binding energy. Our calculations show that $c$-plane InGaN/GaN quantum dots are ideal candidates for high temperature entangled photon emission as long as the underlying $C_{3v}$-symmetry is preserved. However, when assuming random alloy fluctuations in the dot, our atomistic calculations reveal that while the large excitonic…
We theoretically model the electronic dynamics of a coupled quantum dot pair in a static electric field. We then investigate the possibility of polarization-entangled photon emission from the radiative cascade of the molecular biexciton state. Through numerical simulations, we analyze the dependence of entanglement fidelity on temperature and electric field, as well as tunnel coupling. We establish a regime of direct-indirect exciton detunings for which coupled quantum dots are superior to single dots for entangled photon generation, yielding near-unit fidelity over a larger range of exchange …
Continuous and concerted development of colloidal quantum-dot light-emitting diodes over the past two decades has established them as a bedrock technology for the next generation of displays. However, a fundamental issue that limits the performance of these devices is the quenching of photoluminescence due to excess charges from conductive charge transport layers. Although device designs have leveraged various workarounds, doing so often comes at the cost of limiting efficient charge injection. Here we demonstrate that high-field terahertz (THz) pulses can dramatically brighten quenched QDs on…
More than 80 years passed since the first publication on entangled quantum states. In this period of time the concept of spookily interacting quantum states became an emerging field of science. After various experiments proving the existence of such non-classical states, visionary ideas were put forward to exploit entanglement in quantum information science and technology. These novel concepts have not yet come out of the experimental stage, mostly because of the lack of suitable, deterministic sources of entangled quantum states. Among many systems under investigation, semiconductor quantum d…
A source of single photons and quantum entangled photon pairs is a key element in quantum information networks. Here, we demonstrate the electrically driven generation of quantum entangled pairs using a naturally symmetric GaAs quantum dot grown by droplet epitaxy. Coincidence histograms obtained at a temperature of 10 K reveal the generation of quantum entangled pairs that have a fidelity to the Bell pairs of 0.71 +- 0.015, much beyond the classical limit. The quantum nature of the emitted pairs is conserved at temperatures of up to ~65 K, and is essentially limited by the charge carrier conf…
The scalability of quantum dot based non-classical light sources relies on the control over their dissimilar emission energies. Electric fields offer a promising route to tune the quantum dot emission energy through the quantum-confined Stark effect. However, electric fields have been mostly used for tuning the energy of single-photon emission from quantum dots, while electrical control over the energy of entangled-photon emission, which is crucial for building a solid-state quantum repeater using indistinguishable entangled photons, has not been realized yet. Here, we present a method to achi…
Quantum dot spin valves are characterized by exchange fields which induce spin precession and generate current spin resonances even in absence of spin splitting. Analogous effects have been studied in double quantum dots, in which the orbital degree of freedom, the pseudospin, replaces the spin in the valve configuration. We generalize, now, this setup to allow for arbitrary spin and orbital polarization of the leads, thus obtaining an even richer variety of current resonances, stemming from the precession dynamics of entangled spin and pseudospin. We observe for both vectors a delicate interp…
We theoretically study the generation of quantum correlations in a hybrid system composed by two interacting semiconductor quantum dots mediated by a metal nanoparticle and coupled to an external laser field. Interactions present in the hybrid system are treated using a semiclassical approximation except for the direct dipole-dipole interaction. We report the entanglement of formation, which gives information about entanglement quantum correlations, for continuous wave and pulsed driving applied fields. We have found that for proper values of the physical and geometrical parameters of the hybr…
We present a novel "linear combination of atomic orbitals"-type of approximation, enabling accurate electronic structure calculations for systems of up to 20 or more electronically coupled quantum dots. Using realistic single quantum dot wavefunctions as basis to expand the eigenstates of the heterostructure, our method shows excellent agreement with full 8-band $\boldsymbol{k}\cdot\boldsymbol{p}$ calculations, exemplarily chosen for our benchmarking comparison, with an orders of magnitude reduction in computational time. We show that, in order to correctly predict the electronic properties of…
State-of-the-art quantum key distribution systems are based on the BB84 protocol and single photons generated by lasers. These implementations suffer from range limitations and security loopholes, which require expensive adaptation. The use of polarization entangled photon pairs substantially alleviates the security threads while allowing for basically arbitrary transmission distances when embedded in quantum repeater schemes. Semiconductor quantum dots are capable of emitting highly entangled photon pairs with ultra-low multi-pair emission probability even at maximum brightness. Here we repor…
Entangled photon pairs are essential for many applications in quantum technologies. Recent theoretical studies demonstrated that different types of entangled Bell states can be created in a constantly driven four-level quantum emitter-cavity system. Unlike other candidates for the realization of the four-level emitter, semiconductor quantum dots unavoidably interact with their environment, resulting in carrier-phonon interactions. Surprisingly, phonons change the entanglement of emitted photon pairs in a qualitative way, already at low temperatures on the order of 4 K. While one type of Bell s…
Ultrafast pump-probe technique is a powerful tool to understand and manipulate properties of materials for designing novel quantum devices. An intense, single cycle terahertz pulse can change the intrinsic properties of semiconductor quantum dots to have different luminescence. In a hybrid system of plasmon and exciton, the coherence and coupling between these two degrees of freedom play an important role on their optical properties. Therefore, we consider a terahertz pump optical probe experiment in the hybrid systems where the terahertz pump pulse couples to the exciton degrees of freedom on…
We study the luminescence dynamics of telecom wavelength InAs quantum dots grown on InP(111)A by droplet epitaxy. The use of the ternary alloy InAlGaAs as a barrier material leads to photon emission in the 1.55 $μ$m telecom C-band. The luminescence decay is well described in terms of the theoretical interband transition strength without the impact of nonradiative recombination. The intensity autocorrelation function shows clear anti-bunching photon statistics. The results suggest that our quantum dots are useful for constructing a practical source of single photons and quantum entangled photon…
We introduce a high-temperature droplet epitaxy procedure, based on the control of the arsenization dynamics of nanoscale droplets of liquid Ga on GaAs(111)A surfaces. The use of high temperatures for the self-assembly of droplet epitaxy quantum dots solves major issues related to material defects, introduced during the droplet epitaxy fabrication process, which limited its use for single and entangled photon sources for quantum photonics applications. We identify the region in the parameter space which allows quantum dots to self-assemble with the desired emission wavelength and highly symmet…
We show unusual cooperative two-photon resonance between two-modes of field inside a photonic crystal cavity. The two-photon resonance occurs when two off resonant quantum dots emit one photon in each cavity mode and de-excite simultaneously. In the presence of phonon coupling the conditions for two-photon resonance change significantly. Using such two-photon two-mode interaction we propose to generate entangled state of two qutrits. The basis of a qutrit are formed by the state of the cavity mode containing $0$, $1$ and $2$ photons. We also discuss effect of phonon coupling on negativity of t…
Graphene is an ideal material for hot-electron bolometers, due to its low heat capacity and weak electron-phonon coupling. Nanostructuring graphene with quantum dot constrictions yields detectors with extraordinarily high intrinsic responsivity, higher than 1x10^9 V/W at 3K. The sensing mechanism is bolometric in nature: the quantum confinement gap causes a strong dependence of the electrical resistance on the electron temperature. Here we show that this quantum confinement gap does not impose a limitation on the photon energy for light detection and these quantum dot bolometers work in a very…
