Efficient demultiplexed single-photon source with a quantum dot coupled to a nanophotonic waveguide

Abstract

Planar nanostructures allow near-ideal extraction of emission from a quantum emitter embedded within, thereby realizing deterministic single-photon sources. Such a source can be transformed into M single-photon sources by implementing active temporal-to-spatial mode demultiplexing. We report on the realization of such a demultiplexed source based on a quantum dot embedded in a nanophotonic waveguide. Efficient outcoupling (> 60%) from the waveguide into a single mode optical fiber is obtained with high-efficiency grating couplers. As a proof-of-concept, active demultiplexing into M = 4 spatial channels is demonstrated by the use of electro-optic modulators with an end-to-end efficiency of > 81% into single-mode fibers. Overall we demonstrate four-photon coincidence rates of > 1 Hz even under nonresonant excitation of the quantum dot. The main limitation of the current source is the residual population of other exciton transitions that corresponds to a finite preparation efficiency of the desired transition. We quantitatively extract a preparation efficiency of 15% using the second-order correlation function measurements. The experiment highlights the applicability of planar nanostructures as efficient multiphoton sources through temporal-to-spatial demultiplexing and lays out a clear path way of how to scale up towards demonstrating quantum advantages with the quantum dot sources.The recent advances in experimental quantum-information processing 1-5 and cryptography 6-8 highlight the necessity for efficient single-photon sources. Photons are robust carriers of quantum information and enable scalable quantum simulations. 9-11 These applications require efficient deterministic sources of multiple indistinguishable single photons. [12][13][14] The traditional approach to multiphoton generation is based on probabilistic parametric downconversion or four wave mixing sources. [15][16][17] The scaling up of the number of generated photons using such sources is limited by the low generation efficiency and the large amount of resources (detectors and optical switches) needed for heralding the photons. Over the last decade, fundamental and technological progress in the growth and control of semiconductor quantum dots has resulted in their applicability as near-ideal single-photon emitters. [18][19][20] Crucially, enhancing light-matter interaction through the fabrication of on-chip nanophotonic structures containing quantum dots has resulted in efficient deterministic and coherent single-photon sources. 21-25 However, the inhomogeneous broadening of the quantum dots poses a challenge in creating multiple identical sources.An alternative route towards high-brightness multi-photon generation is by implementing active temporal-to-spatial mode demultiplexing of the emitted single-photon train from a single quantum dot. 26,27 Recent experiments achieved high degree of indistinguishability (> 90%) over long timescales, 28 which enabled the temporal demultiplexing of a quantum dot in a micropillar cavity. 26 Planar nanostructures...

Scalable integrated single-photon source

“…We generate temporal strings of >100 single photons with pairwise photon indistinguishability exceeding 96%. Such a source coupled with an active temporal-to-spatial mode demultiplexer ( 14 , 27 ) will realize a paradigm shift for multiphoton experiments aimed at establishing photonic quantum advantage that requires more than 50 photons ( 22 , 28 ). In a recent breakthrough experiment, up to 20 photons were used in a boson sampling experiment ( 25 ); however, the photon indistinguishability was observed to decay over the 20-photon chain.…”

Advances in Silicon Quantum Photonics

“…1g). Ultra-low-loss delay lines are a critical component for (de)multiplexing technology [114], [115], [116]. Delay lines are discussed further in Sec.…”

Optimizing spontaneous parametric down-conversion sources for boson sampling

“…A major drawback of building an n-photon SPDC source is the probabilistic generation of the photon pairs, meaning that generating n photons simultaneously will take exponentially long. This resulted in doubt regarding the suitability of SPDC for multiphoton experiments as the brightness can only increase at the expense of an increased purity [12][13][14]. Scattershot boson sampling improves on this by enabling the generation of n photons in polynomial time using ∼n 2 sources in parallel [15].…”