High yield and ultrafast sources of electrically triggered entangled-photon pairs based on strain-tunable quantum dots

Abstract

Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10(-2)). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications.

Figure 1. Strain-tunable entangled-light-emitting diode.

(a) Sketch of the diode structure. Different from previous works, the PMN-PT top surface has (011) orientation, which imposes large anisotropic strain fields with well-defined orientation onto the overlying ELED. (b) EL from a single QD in an ST-ELED versus electric field F_p applied to the PMN-PT actuator.

Figure 2. Strain-induced change of fine structure splitting and exciton polarization angle.

(a,b) Representative variation of s and the polarization direction θ of the high-energy component of the exciton as a function of F_p for five QDs. The insets show sketches of biexciton cascade and the orientation of the exciton polarization. (c–g) s₀ and θ₀ for the five studied QDs at F_p=0 kV cm⁻¹. In the polar plot 0° corresponds to the [110] axis and 90° to the [1-10] crystal axis of the GaAs nanomembrane.

Figure 3. ST-ELED as source of polarization entangled photons.

(a) Co-polarized (blue) correlation and cross-polarized (red) correlation counts (G⁽²⁾(τ)) for a QD in an ST-ELED excited with electrical pulses with 185.2 MHz repetition rate, measured in the rectilinear, diagonal and circular bases. Representative density matrix : (b) real part and (c) imaginary part, which are reconstructed with 16 coincidence counts integrated in a 1.8-ns temporal window centred at 0 delay time.

Figure 4. Statistical investigation of the minimum FSS and dependence of the entanglement on the value of FSS.

(a) Histogram of the distribution of the minimum FSS (s_min) tuned by the externally induced strain fields in the ST-ELED device and the right y axis corresponds to the histogram probability. The inset is a scatter plot of s_min as a function of the X emission energy and s_min shows no energy dependence. (b) Fidelity (f⁺) as a function of s dynamically tuned by the anisotropic strain fields and the solid line is Lorentzian fit with a full width at half maximum of 3.3±0.2 μeV. The dashed line indicates the classical value of 0.5 and the error bars are defined as the s.d.

Figure 5. Polarization correlation results from the ST-ELED under electrically pulsed injection at repetition rate of 400 MHz.

(a) Normalized correlation functions for co- and cross-polarized XX and X photons in HV, DA and RL bases. (b,c) Degree of correlation C in given basis, in which correlation in HV and DA bases (C>0) and anti-correlation (C<0) in RL basis are obtained without temporal gate (Δτ=2.5 ns) and with a temporal gate width Δτ=0.8 ns centred at 0 delay time, respectively.