Strain-Tunable GaAs Quantum Dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand

Abstract

We report on the observation of nearly maximally entangled photon pairs from semiconductor quantum dots, without resorting to postselection techniques. We use GaAs quantum dots integrated on a patterned piezoelectric actuator capable of suppressing the exciton fine structure splitting. By using a resonant two-photon excitation, we coherently drive the biexciton state and demonstrate experimentally that our device generates polarization-entangled photons with a fidelity of 0.978(5) and a concurrence of 0.97(1) taking into account the nonidealities stemming from the experimental setup. By combining fine-structure-dependent fidelity measurements and a theoretical model, we identify an exciton spin-scattering process as a possible residual decoherence mechanism. We suggest that this imperfection may be overcome using a modest Purcell enhancement so as to achieve fidelities >0.99, thus making quantum dots evenly matched with the best probabilistic entangled photon sources.

A solid-state source of strongly entangled photon pairs with high brightness and indistinguishability

“…The theoretically predicted entanglement fidelity of 0.92 can be reduced to 0.88 by using a much shorter spin scattering time (1 ns instead of 15 ns), which strongly indicates the existence of extra dephasing processes. Such extra dephasing processes have been also recently observed in a similar material system and is attributed to the interactions between the confined exciton and charge states 38 . In contrast to existing entangled sources with vanishing FSS, the pronounced Purcell effect in our work makes the high fidelity of entanglement possible for QDs with a comparatively large FSS.…”

“…Figure 2(a) presents the photoluminescence (PL) and white light reflectivity (1/R is shown, with R the reflectivity spectrum) of our device at 3.2 K, see the optical setup in S.I. V. Under a pulsed two-photon resonant excitation (TPE) scheme 16,20,21,38,39 , the intensities of the XX and X recombination are comparable, since TPE populates the XX state, which feeds the X state. The cavity mode, with a quality factor of ≈150, is clearly identified via the reflectivity measurement (see more details in S.I.…”

“…In contrast to existing entangled sources with vanishing FSS, the pronounced Purcell effect in our work makes the high fidelity of entanglement possible for QDs with a comparatively large FSS. A nearunity entanglement fidelity can be expected in the future by implementing GaAs QDs with very small FSS in CBR-HBRs or by eliminating the residual FSS with a strain-tunable CBR-HBR 38 (see strain-tunable CBR-HBR in the S.I. IX).…”

Dipolar interactions between localized interlayer excitons in van der Waals heterostructures

“…4a should be contrasted with that of intralayer biexciton where a finite e-h exchange splits the degeneracy of X ± X ∓ states to make them linearly polarized. As a result, the biexciton cascade of the intralayer exciton yields maximally polarization entangled pairs of photons but the time averaged fidelity of the entanglement is reduced due the e-h splitting [27,31]. Due to the absence of e-h exchange in interlayer excitons, localized interlayer biexcitons are ideal sources of maximally entangled photons.…”

Generation of Non‐Classical Light Using Semiconductor Quantum Dots

“…In the year 2000, it was proposed that QDs can be used as sources of entangled photon pairs which was for the first time experimentally demonstrated in 2006 and over recent years their potential as high‐quality sources has been established . An important milestone for the generation of entangled photon pairs was the development of two‐photon excitation of either in a resonant two‐photon process or via a detuned phonon‐mediated process which allows for an on‐demand generation with high efficiency .…”