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Widely tunable solid-state source of single-photons matching an atomic transition

Rubayet Al Maruf, Sreesh Venuturumilli, Divya Bharadwaj, Paul Anderson, Jiawei Qiu, Yujia Yuan, Mohd Zeeshan, Behrooz Semnani, Philip J. Poole, Dan Dalacu, Kevin J. Resch, Michael E. Reimer, Michal Bajcsy

Published Nov 28, 2023• 0 citations
Publisher

Abstract

Abstract Hybrid quantum technologies aim to combine diverse quantum systems, mirroring classical computers' integration of electronic, photonic, magnetic, and mechanical components. Quantum dots in semiconductor nanowires emit high-purity, deterministic single photons with high repetition, while atomic ensembles offer photon storage and strong optical nonlinearities controllable by single photons. To interface quantum dots with atomic ensembles successfully, precise optical frequency matching of these two platforms is crucial. We demonstrate a simple, precise, reversible, broad-range, and local method for controlling the emission frequency of individual quantum dots embedded in tapered semiconductor nanowires. We then interface the quantum dots with an atomic ensemble via single-photons matched to hyperfine transitions and slow-light regions of the cesium D1-line. Our approach allows linking atomic and solid-state quantum systems and can potentially also be applied to other types of nanowire-embedded solid-state emitters, as well as for creating devices based on multiple solid-state emitters tuned to produce indistinguishable photons.

DOI
10.21203/rs.3.rs-3408644/v1

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Abstract Hybrid quantum technologies aim to combine diverse quantum systems, mirroring classical computers' integration of electronic, photonic, magnetic, and mechanical components. Quantum dots in semiconductor nanowires emit high-purity, deterministic single photons with high repetition, while atomic ensembles offer photon storage and strong optical nonlinearities controllable by single photons. To interface quantum dots with atomic ensembles successfully, precise optical frequency matching of these two platforms is crucial. We demonstrate a simple, precise, reversible, broad-range, and local method for controlling the emission frequency of individual quantum dots embedded in tapered semiconductor nanowires. We then interface the quantum dots with an atomic ensemble via single-photons matched to hyperfine transitions and slow-light regions of the cesium D1-line. Our approach allows linking atomic and solid-state quantum systems and can potentially also be applied to other types of nanowire-embedded solid-state emitters, as well as for creating devices based on multiple solid-state emitters tuned to produce indistinguishable photons.
Quantum dots embedded in semiconductor photonic nanowires (NW-QDs) can deterministically produce single-photons and entangled photon pairs at high repetition rates. These photons can be efficiently coupled from the photonic nanowire into free space or optical fibers thanks to the sharp tip of the nanowire, which provides impedance matching. However, precise control of the NW-QD emission frequency in a way that is reversible, does not degrade the properties of the emitted photons, and can be used independently for individual NW-QDs on the same chip has so far remained a challenge. Resolving this issue is crucial for applications when interfacing the photons with quantum systems that require MHz to sub-GHz precision, such as atomic ensembles acting as memories in a quantum network. Here, we demonstrate a reversible tuning method that can tune the emission frequency of a NW-QD by more than 300 GHz with sub-GHz precision. We achieve this through gas condensation that is then partially reversed with localized laser ablation. This process finely adjusts stress applied to the quantum dots, thereby tuning their emission frequency. We validate the precision and stability of this method by tuning the frequency of the emitted single-photons across an atomic resonance to probe its absorption and dispersion. We observed up to 80\% absorption of the single-photons from NW-QD in hot caesium vapour at the D1-line resonances and a 75-fold decrease in group velocity associated with the hyperfine transitions of the D1-line ground states. We observed no discernible effects in the second-order autocorrelation function, lifetime, or linewidth of the NW-QD emission for up to 300 GHz of tuning and we saw minimal effects on the fine structure splitting of the NW-QD when tuning up to 100 GHz.
High Resolution Image Download MS PowerPoint Slide Quantum dots embedded in semiconductor photonic nanowires (NW-QDs) can deterministically produce single-photons and entangled photon pairs at high repetition rates. These photons can be efficiently coupled from the photonic nanowire into free space or optical fibers thanks to the sharp tip of the nanowire, which provides impedance matching. However, precise control of the NW-QD emission frequency in a way that is reversible, does not degrade the properties of the emitted photons, and can be used independently for individual NW-QDs on the same chip has so far remained a challenge. Resolving this issue is crucial for applications when interfacing the photons with quantum systems that require MHz to sub-GHz precision, such as atomic ensembles acting as memories in a quantum network. Here, we demonstrate a reversible tuning method that can tune the emission frequency of a NW-QD by more than 300 GHz with sub-GHz precision. We achieve this through gas condensation that is then partially reversed with localized laser ablation. This process finely adjusts stress applied to the quantum dots, thereby tuning their emission frequency. We validate the precision and stability of this method by tuning the frequency of the emitted single-photons across an atomic resonance to probe its absorption and dispersion. We observed up to 80% absorption of the single-photons from NW-QD in hot cesium vapor at the D 1 -line resonances and a 75-fold decrease in group velocity associated with the hyperfine transitions of the D 1 -line ground states. We observed no discernible effects in the second-order autocorrelation function, lifetime, or linewidth of the NW-QD emission for up to 300 GHz of tuning and we saw minimal effects on the fine structure splitting of the NW-QD when tuning up to 100 GHz.
Abstract Hybrid quantum interfaces that combine the fast, deterministic single-photon emission of semiconductor quantum dots (QDs) with the long-lived quantum memories of atomic vapors represent a promising route towards scalable quantum networks and distributed quantum computing. However, the realization of such interfaces is fundamentally limited by the stringent spectral matching required between the narrow optical transitions of atomic systems and the intrinsically variable emission of QDs. Moreover, achieving bright QD emission requires integration into an efficient light-collecting structure. In this work, we present a systematic investigation of three tuning mechanisms for cavity-enhanced QDs embedded in micropillar cavities: thermal tuning, in situ laser processing, and nitrogen gas deposition. We experimentally evaluated the applicability of each method and characterized their tuning ranges and precisions. All three methods enable reliable and precise wavelength shifts, even for QDs in larger micropillars. These results provide practical strategies for achieving spectral resonance between QD emitters and atomic vapor lines, paving the way for tunable solid-state-atomic hybrid platforms for photon storage, synchronization, and interfacing in hybrid quantum systems.
We describe the development and applications of a single-photon source based on a quantum dot embedded in a semiconductor nanowire, which can be precision-tuned to emit ∼1ns long photons at wavelengths that match the transitions of caesium D1 line. We discuss interfacing such single-photon source with atomic ensembles and present our experimental results demonstrating a new method of tuning the emission of the quantum dot by condensing inert gas (N2) on the nanowire. Next, we describe how these single photons at ∼895nm can be efficiently converted to wavelength suitable for satellite QKD links (∼794 nm) and optical fiber links (∼1469 nm) using a laser-cooled atomic ensemble that is loaded and confined inside a hollow-core optical fiber. Lastly, we inroduce our proposal of integrating the semiconductor nanowire with a lensed fiber to create a compact single-photon source with improved photon-collection efficiency compared to conventional setups.
Scalable optical quantum technologies require interference between large numbers of indistinguishable single-photons emitted by independent sources. Semiconductor quantum dots are known to be excellent on-demand sources of single-photons. They show record efficiency when inserted into optical cavities to control their spontaneous emission and generate trains of near identical photons over microsecond timescales. However, generating perfectly identical photons from distant cavity-based sources has remained a long-standing challenge. It requires precise matching of the emission wavelengths and emission dynamics, while simultaneously minimizing spectral noise across all time scales for distant emitters in uncorrelated environments. Here, we report on the nanofabrication of a large number of quantum dot-cavity sources with ultra-low spectral noise and wavelength dispersion. The high source efficiency and the use of two tuning mechanisms enable precise optimization of the spectral overlap between distant sources. With this approach, we demonstrate a two-photon indistinguishability of 88±188\pm188±1 % between photons emitted from two distant sources. Remarkably, this value reaches the upper bound set by the intrinsic indistinguishability of photons emitted successively by each source. These results represent a key milestone for scaling photon-based quantum technologies.
Abstract Hybrid quantum systems play a crucial role in advancing scalable and versatile quantum networks as they combine the strengths of different quantum platforms. An important challenge for the development of hybrid quantum networks lies in interfacing heterogeneous quantum nodes and distributing entanglement among them. Single photons emitted from these dissimilar quantum nodes typically show distinct spectral and temporal properties. Therefore, they necessitate spectral filtering and temporal synchronization, which introduce significant photon losses and require additional resources. In this work, we successfully generate indistinguishable photons from two distinct quantum systems of a warm atomic ensemble and a solid-state quantum dot. Remarkably, quantum interference between dissimilar sources is achieved without additional spectral filtering and time synchronization, which enables autonomous quantum nodes for a hybrid quantum network. 133Cs atomic ensemble can efficiently generate heralded single photons at the wavelength of 917 nm of the 6P_(3/2)-6D_(5/2) transition, while the single photons emitted from an InAs/GaAs quantum dot can be tuned to match the 133Cs transition wavelength. Our dense warm atomic ensemble and cavity-coupled quantum dot can efficiently generate bright and resonant single photons at detection rates approaching MHz, respectively. More importantly, these single photons exhibit inherent spectral similarities not only in the wavelength but also in the spectral linewidth, achieving a high spectral overlap of 0.92. Such intrinsic compatibility between dissimilar quantum sources is essential to leverage the advantages of different quantum platforms, paving the way toward a large-scale and functional hybrid quantum network.