Scalable Qauntum Interference from Indistinguishable Quantum Dots

Abstract

Quantum interference of indistinguishable photons is the foundation of photonic quantum technologies, yet scaling from a few to many identical quantum light sources remains a major challenge. In solid-state platforms, spatial and spectral inhomogeneity and resource-intensive architectures impede scaling. As a result, interference between remote, independent quantum emitters has been thus far limited to pairs. Here we introduce a wavefront-shaping approach that enables scalable interference from multiple indistinguishable quantum dots on the same chip. Using programmable spatial light modulators, we independently excite, collect, and route emission from spatially distinct, yet spectrally degenerate dots. Scaling from two to five indistinguishable emitters, we verify interference through cooperative-emission phenomena and Hong-Ou-Mandel two-photon interference, thereby establishing a route towards large-scale, programmable quantum photonic architectures.

Figures (5)

• Figure 1: Programmable wavefront shaping and measurement-induced cooperative emission. (a) Experimental schematic. An above-band CW laser is wavefront-shaped by a digital hologram implemented on an excitation spatial light modulator ($\rm{SLM_{exc}}$) to focus on selected positions on the quantum dot (QD) sample. The emission is routed by the collection SLM ($\rm{SLM_{coll}}$) and a lens (L) into a common mode using a single-mode fiber (SMF) located at the image plane of the sample and sent to a spectrometer or an HBT interferometer for measurement. Abbreviations: BS, beamsplitter. (b)Top row: Schematic sketch of emission from a single QD mapped to the SMF collection mode by a phase function implemented by a combination of $\mathrm{SLM}_{\mathrm{coll}}$ and a lens, yielding an HBT dip showing single-photon antibunching $g^{(2)}(0)=0$. Middle row: Emission from three spatially separated, spectrally distinct QDs is superposed at a single collection mode using a multiplexed hologram on $\mathrm{SLM}_{\mathrm{coll}}$. For $N=3$ mutually distinguishable, equal-brightness sources, $g^{(2)}(0)= 2/3$. Bottom row: Routing emission from three indistinguishable QDs to a common mode erases which-path information and, upon detection, produces a zero-delay bunching peak: $g^{(2)}(0)> 1$.
• Figure 2: Spatial mapping to identify spectrally degenerate QDs.(a) Spatially resolved PL scans are performed over a $\rm{15 \times 15 \, \mu m}$ area on the sample by rastering the excitation spot with $\mathrm{SLM}_{\mathrm{exc}}$ and routing emission with $\mathrm{SLM}_{\mathrm{coll}}$ into a SMF and spectrometer. The spatial map is analyzed by post-selecting slices of narrow wavelength ranges to identify degenerate QDs. The uppermost slice reveals five spectrally degenerate QDs, labeled A, B, C, D and E, within a $\rm{0.02 \ nm}$ wavelength window centered at $\rm{971.17 \ nm}$. (b) PL spectra of the $\rm{X^{1-}}$ transitions for QDs A--E. The blue curves are experimental data, the red curves Lorentzian fits for the selected QDs.
• Figure 3: Second-order correlation measurements of cooperative emission for QDs A and B at selected detuning ($\Delta$) values. At resonance ($\Delta = 0$) a zero-delay bunching peak is observed. As $\Delta$ increases, the central feature narrows and beat notes emerge at frequency $\Delta$, consistent with two-emitter quantum interference. Data points represent raw data and the curves are IRF-convolved fits to a two-emitter model.
• Figure 4: Second-order intensity correlations $g^{(2)}(\tau)$ for $N=2,3,4,5$ indistinguishable emitters routed into the SMF fundamental mode reveals zero-delay bunching peaks increasing with $N$: $g^{(2)}(0)=0.96\pm 0.027,\,1.28 \pm 0.028,\,1.43 \pm 0.025,\,1.52 \pm 0.029$ for $N=2,3,4,5$, respectively. Points: data; red curves: analytical fits.
• Figure 5: Pulsed HOM measurement on two QDs. (a) Conceptual sketch of the experiment. Two QDs are selected and the hologram on the SLM maps the distinct spatial modes with annihilation operators $a_1$ and $a_2$ onto superposition modes $b_1$ and $b_2$, such that $b_1= a_1+a_2$ and $b_2 = a_1-a_2$, which are collected by two separate cores of a multi-core fiber and directed to independent single photon detectors for corelation measurements. (b) HOM results for the two QDs in resonance (red) and out of resonance (blue). Theory fits are shown by solid lines. The results out of resonance are shifted by $1.5$ ns for visual clarity.