Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots

Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots Hamidreza Siampour, Savvas Germanis, Xuchao Chen, René Dost, Dominic J. Hallett, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5938986/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract We report on an integrated semiconductor chip where a single quantum dot (QD) is excited in-plane via a photonic-crystal waveguide through its nearest p-shell optical transition. The chirality of the waveguide mode is exploited to achieve both directional absorption and directional emission, resulting in a substantial enhancement in directional contrast, as measured for the Zeeman components of the waveguide-coupled QD. This remote excitation scheme enables high directionality ( \(\:\ge\:0.95\) ) across ~ 56% of the waveguide area, with significant overlap with the Purcell-enhanced region, where the electric field intensity profile is near its peak. In contrast, local excitation methods using an out-of-plane excitation beam focused directly over the area of the QD achieve only ~ 25% overlap. This enhancement increases the likelihood of locating Purcell-enhanced QDs in regions that support high directionality, enabling the experimental demonstration of a six-fold enhancement in the decay rate of a QD with > 90% directionality. The remote p-shell excitation protocol establishes a new benchmark for waveguide quantum optics in terms of the combination of Purcell enhancement and high directionality, thereby paving the way for on-chip excitation of spin-based solid-state quantum technologies in regimes of high β-factor. Physical sciences/Optics and photonics Physical sciences/Physics/Electronics, photonics and device physics/Photonic devices Physical sciences/Optics and photonics/Optical materials and structures/Quantum dots Physical sciences/Physics/Optical physics/Single photons and quantum effects Physical sciences/Physics/Optical physics/Slow light Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The rapid evolution of photonic quantum technologies is driven by potential breakthroughs in quantum computing, communication, and sensing. 1 – 3 Central to this progress is the development of chip-scale quantum optical circuits that seamlessly integrate the excitation, manipulation, and detection of single photons. 4 – 8 A key component of this integration is on-chip excitation, where quantum emitters are excited via waveguide modes rather than using an off-chip laser. This technique is essential for implementing precise quantum operations, miniaturising devices, and enabling more compact quantum technologies. 5 , 9 For instance, recent advancements in quantum sensing and light guiding, such as the use of fluorescent nanodiamond-doped polyvinyl alcohol (PVA) fibres, demonstrate promising applications in on-chip excitation. 10 This method offers several advantages, including reduced optical crosstalk, minimised local heating, the ability to excite multiple emitters using a single mode, and access to emitters in hard-to-reach regions of a photonic device. Additionally, this technique can be extended to chiral quantum systems, where engineering and preserving the polarization and flow of light within the waveguide allows information stored in polarized states to be transmitted unidirectionally. 11 A key parameter for waveguide quantum optics is the β-factor, which quantifies the probability that an emitted or scattered photon is coupled to the waveguide mode. Values of the β-factor close to unity are required to observe strong quantum-optical effects such as single-photon nonlinearities, and the high-β regime acquires additional interest when the quantum emitter is positioned at a chiral point of the waveguide. 11 For such a chirally-coupled quantum emitter, a spin-dependent phase shift of π can be imparted to a photon propagating in a specific direction, and this can be exploited to develop quantum spin-networks. 12 There have been numerous observations of chiral emission from quantum emitters in a variety of nano-photonic systems 13 – 20 , and in a recent paper we demonstrated a notable combination of chiral emission with a high Purcell factor, and hence β-factor. 21 However, the demonstration of directional absorption associated with the chirality of the waveguide modes has received far less attention, with all previous studies restricted to nanobeam waveguides in regimes of only moderate β-factor. 9 , 22 , 23 The in-plane excitation geometry permits efficient spin pumping via a remote laser of arbitrary polarization 9 , and establishes protocols for spin-dependent dot-to-dot interactions in a chip-based geometry. This capability is crucial for developing spin-based quantum computing architectures and advancing quantum communication technologies. Furthermore, it enables the interaction of quantum spin states from two or more QDs within photonic devices, mediated through photons, which is essential for the implementation of spin cluster states. 12 , 24 , 25 In this work, we push the boundaries of in-plane excitation by exploiting the chirality of slow-light waveguide modes to initialise and manipulate exciton spins in the high β-factor regime. We employ a remote excitation method that significantly enhances the directional contrast under a linearly-polarized pump. Specifically, we demonstrate that, when combined with glide-plane photonic crystal waveguides, in-plane p-shell excitation enables the efficient initialisation of circularly polarized spin states, leading to enhanced directionality of the emitted photons. These photons are coupled to the right- or left-circularly polarized propagating waveguide mode, depending on their polarization. This approach not only improves the directionality of emitter-waveguide interactions but also facilitates the coherent manipulation and readout of quantum information encoded in these spins. Remote Excitation Method Figure 1 illustrates the device layout and working principle. The device consists of a glide-plane photonic-crystal waveguide containing quantum dots with in- and out-couplers at opposite ends, as illustrated in Fig. 1 a. The quantum dots are located within a p-i-n diode as shown in Fig. 1 b to enable exciton tuning via the quantum-confined Stark effect. This tunability is particularly important for photonic-crystal waveguides in which slow-light enhancement is only achieved at specific wavelengths. On application of a strong external magnetic field in Faraday geometry, the QD exciton states are circularly polarized, with the Zeeman components having opposite helicities. If the quantum dot is located at a chiral point of the waveguide, the modes are circularly polarized (see inset to Fig. 1 a), with the helicity depending on the direction of propagation. Hence photons with opposite circular polarizations generated by exciton recombination propagate to either left or right according to their helicity. The Zeeman lines are therefore observed with differing intensities at the out-couplers, with their intensity ratio depending on the relative populations of the exciton spin states and on the chirality of the waveguide. Figures 1 c and 1 d contrasts two possible methods to excite the quantum dot, namely local and remote . For local excitation, the pump laser is focused directly onto the QD, as shown in Fig. 1 c. This is the method employed in the great majority of previous studies, 13 – 15 , 21 and the intensity ratio of the Zeeman components is assumed to be determined by the chirality of the waveguide mode at the position where the QD is located. For this assumption to be correct, it is necessary that the populations of the σ + and σ − polarized exciton spin states should be identical. The assumption is valid for the case of resonant or near-resonant pumping with a linearly-polarized or unpolarized laser, and for non-resonant pumping with any polarization if there is no spin memory. Figure 1 d illustrates the contrasting case of the remote excitation scheme, where the laser is focussed on one of the grating couplers at the end of the device and the quantum dot is excited via photons propagating within the waveguide. In this case, a quantum dot at a chiral point will be driven by a circularly-polarized field irrespective of the polarization of the pump laser, with the helicity of the circular field depending on the direction of propagation. In our experiment, the laser is tuned to the p-shell of the QD, and initialises the spin of the p-shell exciton states depending on the helicity of the waveguide mode. The p-shell photogenerated carriers relax non-radiatively to form s-shell excitons, preserving the spin memory of their initial state. 26 – 28 The s-shell excitons recombine radiatively emitting circularly polarized photons into the waveguide. The photons of different helicities then propagate in opposite directions according to the chirality at the QD’s position. The chief difference between the two excitation methods is that the chirality of the waveguide enters twice into the intensity ratio of the Zeeman components for the remote excitation method. First, the initial populations of the σ + and σ − excitons are determined by the helical pumping at the chiral point, and hence are not the same. Second, the directional emission of the opposite spin states is again determined by the chirality. These two effects combine to produce a much stronger directional contrast between the Zeeman components for remote excitation compared to local, where the chirality only affects the results at the second stage. The successful observation of enhanced directionality for remote excitation thus establishes the effectiveness of the chiral spin-pumping method, and hence demonstrates the validity of photon-mediated spin-spin interaction in chip-based photonic circuits. Numerical Simulations Figure 2 a presents the simulated chirality map of the glide-plane photonic crystal waveguide used in the device’s slow-light region. The map employs the Stokes parameters, \(\:{S}_{3}\:=-2Im\left({E}_{x}\:{E}_{y}^{*}\:\:\right)\) and \(\:{S}_{0}=I\) , to visualise the degree of circular polarization normalised by light intensity, represented as \(\:{C}_{l}={S}_{3}/{S}_{0}\) . Here I is the intensity, and E x and E y are the electric field components within the sample plane. The subscript l indicates that this is the chirality measured using the local excitation method according to the position of the quantum emitter. The map shows strong chirality, with \(\:{C}_{l}\ge\:0.95\) in certain regions (solid black contour), enabling efficient coupling between exciton spins and the waveguide modes, thus facilitating controlled spin initialisation and manipulation. The waveguide's band structure reveals two bands (Fig. 2 b), with the simulated Purcell factor shown near the crossing point \(\:(\text{i}.\text{e}.\:\:\text{k}\text{a}/{\pi\:}=0.44\) ), where the slow-light effect is most pronounced. The spatial dependence of the chirality and the Purcell factor demonstrate that regions of strong chirality and high Purcell factor coincide. Restricting chirality to \(\:{C}_{l}\ge\:0.95\) (solid black contour), the overlap region covers more than 25% of the waveguide area, and includes areas with a predicted Purcell factor exceeding 20. The helicity of the waveguide mode in the photonic-crystal line defect allows for the selective excitation of QD spins via remote excitation followed by directional absorption (Fig. 1 d), as opposed to local excitation (Fig. 1 c). When an incident photon propagating within the waveguide drives a QD dipole transition, the polarization of the local electric field is transferred to the exciton, resulting in the quantum state \(\:\mid\:{\psi\:}_{s}⟩={\alpha\:}_{n}\mid\:\uparrow\:⟩+{\beta\:}_{n}\mid\:\downarrow\:⟩,\) where \(\:\alpha\:\) and \(\:\beta\:\) are normalised coefficients that satisfy \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}+\mid\:{\beta\:}_{n}{\mid\:}^{2}=1\) . If \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}\ne\:\mid\:{\beta\:}_{n}{\mid\:}^{2}\) , the imbalance in the population of the two Zeeman states significantly affects the measured directional contrast, as the polarization-dependent absorption is followed by directional emission, and both processes depend on \(\:{C}_{l}\) . By contrast, for local excitation with linear polarization or in conditions where there is no spin memory, it follows that \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}=\mid\:{\beta\:}_{n}{\mid\:}^{2}\) , and the directionality just depends on the value of \(\:{C}_{l}\) for the emission process. Consequently, the directional contrast observed under in-plane remote excitation differs from that observed under local excitation with a linearly polarized pump. To further analyse this effect, we derive a conversion formula that quantitatively relates the directionality observed through local excitation to that achieved under remote excitation. This relationship holds under the assumptions of the circular dipole approximation, spin-preserving scattering, and weak excitation. Specifically, consider a QD located where the intensity ratio between the Zeeman components via local excitation is \(\:x\::1\) . The directional contrast in this scenario is given by: $$\:{C}_{l}\:=(x-1\:)/(x+1\:)$$ 1 . If we assume that the populations of the σ + and σ − polarized exciton spin states are identical under local excitation (i.e. \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}=\mid\:{\beta\:}_{n}{\mid\:}^{2}\) ), then \(\:{C}_{l}\) will be equal to the value of \(\:{S}_{3}/{S}_{0}\) at the position of the quantum dot. This assumption is valid for a linearly polarized pump. It will also be valid for any pump polarization under conditions where the spin memory is lost after excitation. Under remote excitation, electron-hole pairs are generated with the exciton spin populations reflecting the polarization of the local electric field. In the ideal case of 100% spin fidelity, quantum spin information in the form of photon directionality is fully transferred to the polarization of excitons, with \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}\text{}:\text{}\mid\:{\beta\:}_{n}{\mid\:}^{2}=x\::1\) , or vice versa, depending on the direction of propagation. The excitons then emit with a relative intensity of \(\:x\::1\) . This spin-selective, directional excitation (absorption), followed by another directional emission process, results in a squared intensity ratio of \(\:{x}^{2}\::1\) for the emitted photons. Consequently, the effective directional contrast under remote excitation, which reflects the combined effects of both directional absorption and directional emission, is given by: $$\:{D}_{r}\:=({x}^{2}-1\:)/({x}^{2}+1\:)$$ 2 . By substituting \(\:x\:=(1+{C}_{l})/(1-{C}_{l})\) , we obtain the following expression: $$\:{D}_{r}\:=2{C}_{l}\:/(1+{C}_{l}^{2}\:)$$ 3 . This relationship reveals that the directional contrast under remote excitation depends on the initial contrast \(\:{C}_{l}\) ​ but exhibits a non-linear enhancement for moderate values of \(\:{C}_{l}\) , as illustrated in Fig. 2 d. This suggests that a modest directionality observed under direct excitation using a linearly polarized pump can yield a substantial increase in effective directional contrast for measurements with remote excitation. For example, if \(\:{C}_{l}=0.5\) (corresponding to an intensity ratio of \(\:3\::1\) ), the resulting effective directional contrast will reach \(\:{D}_{r}=0.8\) – a significant improvement. Additionally, remote excitation can expand the effective area of directionality for waveguide-based photonic devices. In particular, the area with over 95% effective directional contrast increases from 25–56% in our glide-plane waveguide devices under remote excitation (dashed black contour in Fig. 2 a). This represents more than a twofold expansion of the highly directional region compared to local excitation, and the expanded region encompasses areas with strong Purcell enhancement exceeding 20 (solid black contour in Fig. 2 c). Our remote excitation technique takes advantage of the helicity of the slow-light waveguide mode, enabling the combination of higher Purcell factors and near-unity directional contrast. This balance underscores the potential of remote excitation in optimising chiral photonic systems for waveguide quantum optics. Experimental Results In the experiment, the sample is housed in a liquid helium cryostat surrounded by superconducting coils, enabling magneto-photoluminescence studies under an applied magnetic field along the sample axis (see setup in Supplementary, Figure S1 ). For quasi-resonant excitation, the laser is tuned to energies just above the exciton state, specifically targeting the QD’s p-shell. As shown in the photoluminescence (PL) excitation spectrum in Figure S2, the p-shell is located at ~ 896 nm, approximately 20.7 meV (14 nm) above the exciton emission line at 910 nm. We measured the PL of the exciton emission line under p-shell excitation, while applying an external magnetic field of 3T in the Faraday geometry. For the local excitation scheme (Fig. 1 c), where the pump laser is focused directly on the QD1, the PL spectra (Fig. 3 a) exhibit relatively weak directionality. In contrast, under the remote excitation scheme (Fig. 1 d), where the QD1 is excited via waveguide modes, the PL spectra (Fig. 3 b) show a significantly enhanced directional contrast. This enhancement is attributed to stronger spin-selective pumping of the QD via the waveguide mode, driven by directional absorption and, in turn, directional coupling of the QD emission within the glide-plane photonic-crystal devices. In Fig. 2 d, we present data from a study of four QDs coupled into the glide-plane waveguide, represented by coloured points. The graph compares the directionality for remote excitation and local excitation, with the prediction of Eq. ( 3 ) for \(\:{D}_{r}\) shown by the solid line. The dashed line shows the case where there is no enhancement under remote excitation, i.e. \(\:{{D}_{r}=C}_{l}\) . For all QDs shown in this graph, excitation conditions were carefully selected to ensure p-shell excitation above the QD ground states. Black circular points correspond to the values from QD1, the primary QD studied in this report. The labels L and R indicate the two out-couplers where the PL was collected. The variation between points arises from chiral asymmetry, commonly observed in these devices due to waveguide disorder and multiple scattering processes affecting the propagating mode (see e.g. ref. 13). Red, blue, and orange square points represent PL measurements from QDs in other devices with the same chiral design parameters. These QDs, embedded within the glide-plane photonic-crystal waveguide, exhibit relatively low chiral behaviour under local excitation. In all cases, the directional contrast increases under remote excitation. It is striking that the enhancement is close to, or sometimes larger, than that predicted by Eq. ( 3 ), which confirms that the spin memory under p-shell excitation is close to 100%. For the results that exceed Eq. ( 3 ), it could be the case there is some ellipticity in the pump laser, which could result in \(\:\mid\:{\alpha\:}_{n}{\mid\:}^{2}\ne\:\mid\:{\beta\:}_{n}{\mid\:}^{2}\) even for local excitation, and hence affect the experimental values of \(\:{C}_{l}\) . Figures 4a and 4b present time-resolved PL measurements to assess the decay rate enhancement in the slow-light waveguide for the same QD1 as in Fig. 3 . In our experiments, electrical and magnetic field tuning were generally employed to achieve a red or blue shift, resulting from either or both the quantum confined Stark effect and Zeeman energy. Specifically, for QD1, electrical field tuning was applied at zero magnetic field to induce a red shift and align the QD's wavelength as closely as possible with the centre of the slow-light band of the photonic-crystal waveguide (Supplementary Figure S4). Figure 4a shows the time-resolved PL at a wavelength of 910.4 nm, where the emission is the fastest. In addition, Fig. 4b presents the variation in lifetime with emission wavelength as the electric field is increased and red-shift tuning is applied. It demonstrates a reduction in decay time within the slow-light band as the emission wavelength approaches the centre of the band, followed by an increase in decay time as the wavelength moves beyond the centre, returning to larger values. The single exponential fit in Fig. 4a indicates a lifetime of approximately 200 ps, corresponding to a six-fold decay rate enhancement compared to the ensemble lifetime of 1.2 ns for the dots in the wafer. This results in an estimated Purcell factor of 6 for the chirally-coupled QD1, achieving a significant combination of high directional contrast (> 90%) and Purcell factor in a QD, and demonstrating spin pumping of the QD1 in the slow light region of glide-plane waveguides where the estimated β-factor, calculated using FDTD simulations, is 97%. Figure 4c shows the results of a Hanbury Brown and Twist (HBT) measurement under continuous-wave (CW) excitation at the p-shell resonance for the same QD1 as in Fig. 3 . The clear anti-bunching behaviour at zerotime delay ( \(\:{g}^{2}\:\left(0\right)\sim0.06)\:\) without background subtraction demonstrates its excellent performance as a chirally-coupled single-photon source in the high-β-factor regime. The HBT results under pulsed excitation are shown in the Supplement (Figure S3). Discussion and Conclusions By demonstrating enhanced directional contrast through remote excitation and combining it with Purcell enhancement, we introduce a novel mechanism for improving chiral light-matter interactions in nanophotonic platforms in the high-β regime that is required for waveguide quantum optics. The process of spin-photon coupling plays a critical role, that is, the transfer of photon polarization to the exciton spin, followed by its recombination and subsequent re-emission. The method only works when the exciton spin is preserved during relaxation, as any decoherence processes would lower the final chiral response, which is why we use p-shell excitation. In our work we have focussed on exciton spins, but the method can easily be adapted for spin pumping of electrons and holes in charged quantum dots, opening up new possibilities for spin-based quantum networks and quantum information processing systems. Our investigation demonstrates the potential of remote excitation techniques combined with photonic-crystal waveguides to significantly enhance spin initialisation and directional coupling of QDs. By leveraging the chirality of waveguide modes in the slow-light regime, we have expanded the region of high directionality, theoretically achieving directionality exceeding 95% and a Purcell enhancement greater than 20. The simulations highlight a substantial improvement when using remote excitation, with approximately 56% of the waveguide area having \(\:\ge\:95\%\) directionality – compared to only around 25% achieved with local excitation methods. Furthermore, our experimental measurements demonstrate a six-fold enhancement in the emission decay rate of a coupled QD with 90% directional contrast under remote excitation, which corresponds to a β-factor of ~97%, as calculated using FDTD simulations. This advancement enables improved control of quantum states and facilitates the integration of such systems into chip-scale quantum optical circuits. This work provides a foundation for future research to optimise chiral quantum emitter interactions within photonic circuits, an important step toward functional quantum devices. Methods Photoluminescence Measurements : Measurements were performed in a helium bath cryostat (supplementary Figure S1 ) at T = 4K equipped with a superconducting magnet (0–5 Tesla). The sample was mounted in a socket giving access to electrical control of the PIN devices. The sample holder apparatus was fixed on a X-Y-Z piezo-stage, ensuring stable positioning of the sample. The optical access of the sample was through a confocal scanning microscope set-up. A CW tunable laser (Toptica single-mode laser DL Pro) was used for PL excitation and P-shell excitation experiments, while a femtosecond pulsed Ti:Sapphire laser (Spectra-Physics Tsunami, Newport) with an 80 MHz repetition rate was used for lifetime and PL correlation experiments. Both lasers were fibre-coupled. On the collection path, an ultranarrow bandpass filter with a full width at half maximum (FWHM) of less than 0.55 nm (935.4–0.45 OD5 Ultra Narrow Bandpass Filter, Alluxa) was angle-tuned with respect to the emission line of the QD under study, effectively filtering out unwanted emission lines and the quasi-resonant p-shell excitation laser from the QD signal. PL Spectra were recorded by a liquid nitrogen-cooled charge-coupled device (CCD) camera after being dispersed through a 0.75 Acton Pro monochromator. Time resolved PL measurements were implemented by using a superconducting nanowire fast single-photon detectors (SNSPD - Single Quantum Eos), while the laser pulse repetition rate was detected by a photodiode. The pulses from the SNSPD and the photodiode were analysed using a time-correlated photon counting card (Becker and Hickl SPC-130-EM). Simulation: Numerical calculations were performed using the commercial software package Lumerical FDTD Solutions and the open-source Python package Legume (see details in the Supplementary section, Section 3). Declarations Data Availability The data that support the findings of this study are available from the authors. Acknowledgements This work was funded by the Engineering and Physical Sciences Research Council (EPSRC) UK Programme Grants EP/V026496/1. H.S. acknowledges support from the UKRI Strength in Places Fund programme, Smart Nano NI, and technical assistance from Shelby Hanna in creating Figure 1. 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Chirality in Quantum Computation with Spin Cluster Qubits. Physical Review Letters 93 , 120503 (2004). Pichler, H., Ramos, T., Daley, A.J. & Zoller, P. Quantum optics of chiral spin networks. Physical Review A 91 , 042116 (2015). Benny, Y. et al. Coherent Optical Writing and Reading of the Exciton Spin State in Single Quantum Dots. Physical Review Letters 106 , 040504 (2011). Benny, Y. et al. Two-photon photoluminescence excitation spectroscopy of single quantum dots. Physical Review B 84 , 075473 (2011). Benny, Y. et al. Excitation spectroscopy of single quantum dots at tunable positive, neutral, and negative charge states. Physical Review B 86 , 085306 (2012). 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5938986","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":413528631,"identity":"5e49deae-9fe2-4bcd-a48b-c6bcf60a08d1","order_by":0,"name":"Hamidreza Siampour","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIiWNgGAWjYLCChB82cvLsDUCWgQWRWh72pBkb9hwAaZEgTgfjA7bDiQ03EkBsIrSYt7c//JDAc9iYcebzqxt+FEgw8Ld3J+DVInPmQLJEgkW6HLt0TtnNHqDDJM6c3YBXi4REwgGJBB5rY8bZOWk3eIBaDCRyCWiRf9j8I4GNObHh5pm0m3+I0iLBzCaRwOYM9D77sdvE2cKTxmaRCA7kHLbbMgYSPIT9wn788c0f4Kg8/uzmmz82cvztvfi1IAEeAzBJrHIQYH9AiupRMApGwSgYQQAA1fZG/J/d0ioAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-8476-0207","institution":"Queen's University Belfast","correspondingAuthor":true,"prefix":"","firstName":"Hamidreza","middleName":"","lastName":"Siampour","suffix":""},{"id":413528632,"identity":"ebf6770f-7b7a-4317-bde1-926d99cc1a7e","order_by":1,"name":"Savvas Germanis","email":"","orcid":"https://orcid.org/0000-0003-1323-3666","institution":"University of Sheffield,","correspondingAuthor":false,"prefix":"","firstName":"Savvas","middleName":"","lastName":"Germanis","suffix":""},{"id":413528633,"identity":"936d26cc-ee38-415e-ae06-1fd81691d984","order_by":2,"name":"Xuchao Chen","email":"","orcid":"","institution":"University of Sheffield,","correspondingAuthor":false,"prefix":"","firstName":"Xuchao","middleName":"","lastName":"Chen","suffix":""},{"id":413528634,"identity":"ded3a3ee-f825-4c82-b7c5-84da4fb1fdc9","order_by":3,"name":"René Dost","email":"","orcid":"https://orcid.org/0000-0002-8578-0389","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"René","middleName":"","lastName":"Dost","suffix":""},{"id":413528635,"identity":"477e8f59-a5a2-4f33-ac82-f5bcec64f82a","order_by":4,"name":"Dominic J. Hallett","email":"","orcid":"","institution":"University of Sheffield,","correspondingAuthor":false,"prefix":"","firstName":"Dominic","middleName":"J.","lastName":"Hallett","suffix":""},{"id":413528636,"identity":"2010617a-3221-4c1d-a394-7de41464b421","order_by":5,"name":"Edmund Clarke","email":"","orcid":"https://orcid.org/0000-0002-8287-0282","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Edmund","middleName":"","lastName":"Clarke","suffix":""},{"id":413528637,"identity":"82648538-e5a4-46e6-8c5c-ba34f88f16a2","order_by":6,"name":"Pallavi K. Patil","email":"","orcid":"","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Pallavi","middleName":"K.","lastName":"Patil","suffix":""},{"id":413528638,"identity":"ea405b97-5e79-40ca-bd64-310c70fca5ee","order_by":7,"name":"Maurice Skolnick","email":"","orcid":"","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Maurice","middleName":"","lastName":"Skolnick","suffix":""},{"id":413528639,"identity":"06058cb1-99cd-4c6d-93c7-cc51ee638eca","order_by":8,"name":"Luke Wilson","email":"","orcid":"","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Luke","middleName":"","lastName":"Wilson","suffix":""},{"id":413528640,"identity":"5479a1cc-6bf1-4348-a589-f2b0ce028086","order_by":9,"name":"Mark Fox","email":"","orcid":"","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Mark","middleName":"","lastName":"Fox","suffix":""}],"badges":[],"createdAt":"2025-01-31 22:10:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5938986/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5938986/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":76102534,"identity":"4569be7e-eb10-4ae0-b9f0-4945dbe9ee46","added_by":"auto","created_at":"2025-02-12 10:31:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":722209,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the device layout and working principle. \u003cstrong\u003e(a)\u003c/strong\u003e A semiconductor chip where a pump laser, indicated by a green arrow, is coupled into a waveguide using a grating. The waveguide directs light towards a QD positioned within the chiral region of the waveguide. The helicity of the waveguide mode in the photonic-crystal line defect enables selective excitation of the QD spins. Once excited, photons emitted from the QD couple to the waveguide mode and propagate either to the left (red) or right (blue) along the waveguide, depending on their circular polarization. The inset shows the intensity profile and helicity (chirality) of the waveguide mode within the slow-light section of the photonic-crystal line defect. \u003cstrong\u003e(b)\u003c/strong\u003e Schematic of the p-i-n GaAs diode structure with embedded InGaAs QDs and electrical contacts (yellow) made to the p- and n-GaAs layers. (\u003cstrong\u003ec\u003c/strong\u003e) Schematic of the local excitation scheme, where the pump laser is focused directly onto the QD. \u003cstrong\u003e(d)\u003c/strong\u003e Schematic of the remote excitation scheme, where the QD is excited via waveguide modes.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/6bad3c55aca549bb93690d34.png"},{"id":76102538,"identity":"d5f4aea5-68c7-4cf5-937d-a0250a267f49","added_by":"auto","created_at":"2025-02-12 10:31:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":193741,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/9cb99ddcae92fe4d7b3683e0.png"},{"id":76102539,"identity":"a419f8c0-f327-4235-bc43-be12e709cbee","added_by":"auto","created_at":"2025-02-12 10:31:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":196185,"visible":true,"origin":"","legend":"\u003cp\u003ePL spectra of the exciton emission line under an external magnetic field of 3T in Faraday geometry where the field is applied along the sample growth axis. \u003cstrong\u003e(a)\u003c/strong\u003e PL spectra for local excitation and \u003cstrong\u003e(b)\u003c/strong\u003ecorresponding PL spectra for remote excitation. The comparison highlights the significant enhancement in the directional emission under remote excitation, demonstrating improved spin-selective interactions.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/b021a729eeca88fb07ed7197.png"},{"id":76103304,"identity":"be5d2e9d-0f47-46cd-af1d-2b6f26c43c04","added_by":"auto","created_at":"2025-02-12 10:39:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":289767,"visible":true,"origin":"","legend":"\u003cp\u003eEmission characteristics and single-photon verification of the QD. \u003cstrong\u003e(a)\u003c/strong\u003e Lifetime measurement of the QD at a wavelength of 910.4 nm, demonstrating a lifetime of approximately 200 ps and a six-fold enhancement in the decay rate compared to the ensemble lifetime of 1.2 ns. \u003cstrong\u003e(b)\u003c/strong\u003eWavelength dependence of the QD's lifetime and corresponding Purcell factor as the wavelength is tuned by electric field within the slow light region. It shows a decrease in decay time as the emission wavelength nears the center of the slow-light band, followed by an increase as the wavelength moves past the center.\u003cstrong\u003e (c)\u003c/strong\u003e The second-order correlation function was obtained through HBT correlation measurements on the exciton line under CW laser excitation, with a strong p-shell resonance detuned by ~20.7 meV from the exciton state (Supplementary Figure S2).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/dcd1cce5dff15159ff4f8fbe.png"},{"id":83894874,"identity":"0b052503-7ecc-4ffe-bd31-7a775456f9f3","added_by":"auto","created_at":"2025-06-04 08:39:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2165791,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/6e6aa8cb-c109-4895-89e5-89b08f1dda0d.pdf"},{"id":76102537,"identity":"8fe25e3d-e89c-4514-b840-5f9004a2ab65","added_by":"auto","created_at":"2025-02-12 10:31:01","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":392088,"visible":true,"origin":"","legend":"Supplementary Materials","description":"","filename":"Supplementarysubmitted.docx","url":"https://assets-eu.researchsquare.com/files/rs-5938986/v1/5d9ef2a013617dcfc014a603.docx"}],"financialInterests":"There is no conflict of interest","formattedTitle":"Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe rapid evolution of photonic quantum technologies is driven by potential breakthroughs in quantum computing, communication, and sensing.\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Central to this progress is the development of chip-scale quantum optical circuits that seamlessly integrate the excitation, manipulation, and detection of single photons.\u003csup\u003e\u003cspan additionalcitationids=\"CR5 CR6 CR7\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e A key component of this integration is on-chip excitation, where quantum emitters are excited via waveguide modes rather than using an off-chip laser. This technique is essential for implementing precise quantum operations, miniaturising devices, and enabling more compact quantum technologies.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e For instance, recent advancements in quantum sensing and light guiding, such as the use of fluorescent nanodiamond-doped polyvinyl alcohol (PVA) fibres, demonstrate promising applications in on-chip excitation.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e This method offers several advantages, including reduced optical crosstalk, minimised local heating, the ability to excite multiple emitters using a single mode, and access to emitters in hard-to-reach regions of a photonic device. Additionally, this technique can be extended to chiral quantum systems, where engineering and preserving the polarization and flow of light within the waveguide allows information stored in polarized states to be transmitted unidirectionally.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eA key parameter for waveguide quantum optics is the β-factor, which quantifies the probability that an emitted or scattered photon is coupled to the waveguide mode. Values of the β-factor close to unity are required to observe strong quantum-optical effects such as single-photon nonlinearities, and the high-β regime acquires additional interest when the quantum emitter is positioned at a chiral point of the waveguide.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e For such a chirally-coupled quantum emitter, a spin-dependent phase shift of π can be imparted to a photon propagating in a specific direction, and this can be exploited to develop quantum spin-networks.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e There have been numerous observations of chiral emission from quantum emitters in a variety of nano-photonic systems\u003csup\u003e\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17 CR18 CR19\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, and in a recent paper we demonstrated a notable combination of chiral emission with a high Purcell factor, and hence β-factor.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e However, the demonstration of directional absorption associated with the chirality of the waveguide modes has received far less attention, with all previous studies restricted to nanobeam waveguides in regimes of only moderate β-factor.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e The in-plane excitation geometry permits efficient spin pumping via a remote laser of arbitrary polarization\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, and establishes protocols for spin-dependent dot-to-dot interactions in a chip-based geometry. This capability is crucial for developing spin-based quantum computing architectures and advancing quantum communication technologies. Furthermore, it enables the interaction of quantum spin states from two or more QDs within photonic devices, mediated through photons, which is essential for the implementation of spin cluster states.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn this work, we push the boundaries of in-plane excitation by exploiting the chirality of slow-light waveguide modes to initialise and manipulate exciton spins in the high β-factor regime. We employ a remote excitation method that significantly enhances the directional contrast under a linearly-polarized pump. Specifically, we demonstrate that, when combined with glide-plane photonic crystal waveguides, in-plane p-shell excitation enables the efficient initialisation of circularly polarized spin states, leading to enhanced directionality of the emitted photons. These photons are coupled to the right- or left-circularly polarized propagating waveguide mode, depending on their polarization. This approach not only improves the directionality of emitter-waveguide interactions but also facilitates the coherent manipulation and readout of quantum information encoded in these spins.\u003c/p\u003e\n\u003ch3\u003eRemote Excitation Method\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the device layout and working principle. The device consists of a glide-plane photonic-crystal waveguide containing quantum dots with in- and out-couplers at opposite ends, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The quantum dots are located within a p-i-n diode as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb to enable exciton tuning via the quantum-confined Stark effect. This tunability is particularly important for photonic-crystal waveguides in which slow-light enhancement is only achieved at specific wavelengths. On application of a strong external magnetic field in Faraday geometry, the QD exciton states are circularly polarized, with the Zeeman components having opposite helicities. If the quantum dot is located at a chiral point of the waveguide, the modes are circularly polarized (see inset to Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), with the helicity depending on the direction of propagation. Hence photons with opposite circular polarizations generated by exciton recombination propagate to either left or right according to their helicity. The Zeeman lines are therefore observed with differing intensities at the out-couplers, with their intensity ratio depending on the relative populations of the exciton spin states and on the chirality of the waveguide.\u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed contrasts two possible methods to excite the quantum dot, namely \u003cem\u003elocal\u003c/em\u003e and \u003cem\u003eremote\u003c/em\u003e. For local excitation, the pump laser is focused directly onto the QD, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. This is the method employed in the great majority of previous studies,\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e and the intensity ratio of the Zeeman components is assumed to be determined by the chirality of the waveguide mode at the position where the QD is located. For this assumption to be correct, it is necessary that the populations of the σ\u003csup\u003e+\u003c/sup\u003e and σ\u003csup\u003e\u0026minus;\u003c/sup\u003e polarized exciton spin states should be identical. The assumption is valid for the case of resonant or near-resonant pumping with a linearly-polarized or unpolarized laser, and for non-resonant pumping with any polarization if there is no spin memory.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed illustrates the contrasting case of the remote excitation scheme, where the laser is focussed on one of the grating couplers at the end of the device and the quantum dot is excited via photons propagating within the waveguide. In this case, a quantum dot at a chiral point will be driven by a circularly-polarized field irrespective of the polarization of the pump laser, with the helicity of the circular field depending on the direction of propagation. In our experiment, the laser is tuned to the p-shell of the QD, and initialises the spin of the p-shell exciton states depending on the helicity of the waveguide mode. The p-shell photogenerated carriers relax non-radiatively to form s-shell excitons, preserving the spin memory of their initial state.\u003csup\u003e\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e The s-shell excitons recombine radiatively emitting circularly polarized photons into the waveguide. The photons of different helicities then propagate in opposite directions according to the chirality at the QD\u0026rsquo;s position.\u003c/p\u003e \u003cp\u003eThe chief difference between the two excitation methods is that the chirality of the waveguide enters twice into the intensity ratio of the Zeeman components for the remote excitation method. First, the initial populations of the σ\u003csup\u003e+\u003c/sup\u003e and σ\u003csup\u003e\u0026minus;\u003c/sup\u003e excitons are determined by the helical pumping at the chiral point, and hence are not the same. Second, the directional emission of the opposite spin states is again determined by the chirality. These two effects combine to produce a much stronger directional contrast between the Zeeman components for remote excitation compared to local, where the chirality only affects the results at the second stage. The successful observation of enhanced directionality for remote excitation thus establishes the effectiveness of the chiral spin-pumping method, and hence demonstrates the validity of photon-mediated spin-spin interaction in chip-based photonic circuits.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eNumerical Simulations\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea presents the simulated chirality map of the glide-plane photonic crystal waveguide used in the device\u0026rsquo;s slow-light region. The map employs the Stokes parameters, \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{S}_{3}\\:=-2Im\\left({E}_{x}\\:{E}_{y}^{*}\\:\\:\\right)\\)\u003c/span\u003e \u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{S}_{0}=I\\)\u003c/span\u003e\u003c/span\u003e, to visualise the degree of circular polarization normalised by light intensity, represented as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}={S}_{3}/{S}_{0}\\)\u003c/span\u003e\u003c/span\u003e. Here \u003cem\u003eI\u003c/em\u003e is the intensity, and \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003e are the electric field components within the sample plane. The subscript \u003cem\u003el\u003c/em\u003e indicates that this is the chirality measured using the local excitation method according to the position of the quantum emitter. The map shows strong chirality, with \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\ge\\:0.95\\)\u003c/span\u003e\u003c/span\u003e in certain regions (solid black contour), enabling efficient coupling between exciton spins and the waveguide modes, thus facilitating controlled spin initialisation and manipulation. The waveguide's band structure reveals two bands (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), with the simulated Purcell factor shown near the crossing point \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:(\\text{i}.\\text{e}.\\:\\:\\text{k}\\text{a}/{\\pi\\:}=0.44\\)\u003c/span\u003e\u003c/span\u003e), where the slow-light effect is most pronounced. The spatial dependence of the chirality and the Purcell factor demonstrate that regions of strong chirality and high Purcell factor coincide. Restricting chirality to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\ge\\:0.95\\)\u003c/span\u003e\u003c/span\u003e (solid black contour), the overlap region covers more than 25% of the waveguide area, and includes areas with a predicted Purcell factor exceeding 20.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe helicity of the waveguide mode in the photonic-crystal line defect allows for the selective excitation of QD spins via remote excitation followed by directional absorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed), as opposed to local excitation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). When an incident photon propagating within the waveguide drives a QD dipole transition, the polarization of the local electric field is transferred to the exciton, resulting in the quantum state \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\psi\\:}_{s}⟩={\\alpha\\:}_{n}\\mid\\:\\uparrow\\:⟩+{\\beta\\:}_{n}\\mid\\:\\downarrow\\:⟩,\\)\u003c/span\u003e\u003c/span\u003e where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\alpha\\:\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e are normalised coefficients that satisfy \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}+\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}=1\\)\u003c/span\u003e\u003c/span\u003e. If \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}\\ne\\:\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}\\)\u003c/span\u003e\u003c/span\u003e, the imbalance in the population of the two Zeeman states significantly affects the measured directional contrast, as the polarization-dependent absorption is followed by directional emission, and both processes depend on \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e. By contrast, for local excitation with linear polarization or in conditions where there is no spin memory, it follows that \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}=\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}\\)\u003c/span\u003e\u003c/span\u003e, and the directionality just depends on the value of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e for the emission process. Consequently, the directional contrast observed under in-plane remote excitation differs from that observed under local excitation with a linearly polarized pump.\u003c/p\u003e \u003cp\u003eTo further analyse this effect, we derive a conversion formula that quantitatively relates the directionality observed through local excitation to that achieved under remote excitation. This relationship holds under the assumptions of the circular dipole approximation, spin-preserving scattering, and weak excitation. Specifically, consider a QD located where the intensity ratio between the Zeeman components via local excitation is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x\\::1\\)\u003c/span\u003e\u003c/span\u003e. The directional contrast in this scenario is given by:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{C}_{l}\\:=(x-1\\:)/(x+1\\:)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e.\u003c/p\u003e \u003cp\u003eIf we assume that the populations of the σ\u003csup\u003e+\u003c/sup\u003e and σ\u003csup\u003e\u0026minus;\u003c/sup\u003e polarized exciton spin states are identical under local excitation (i.e. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}=\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}\\)\u003c/span\u003e\u003c/span\u003e), then \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e will be equal to the value of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{S}_{3}/{S}_{0}\\)\u003c/span\u003e\u003c/span\u003e at the position of the quantum dot. This assumption is valid for a linearly polarized pump. It will also be valid for any pump polarization under conditions where the spin memory is lost after excitation.\u003c/p\u003e \u003cp\u003eUnder remote excitation, electron-hole pairs are generated with the exciton spin populations reflecting the polarization of the local electric field. In the ideal case of 100% spin fidelity, quantum spin information in the form of photon directionality is fully transferred to the polarization of excitons, with \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}\\text{}:\\text{}\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}=x\\::1\\)\u003c/span\u003e\u003c/span\u003e, or vice versa, depending on the direction of propagation. The excitons then emit with a relative intensity of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x\\::1\\)\u003c/span\u003e\u003c/span\u003e. This spin-selective, directional excitation (absorption), followed by another directional emission process, results in a squared intensity ratio of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{x}^{2}\\::1\\)\u003c/span\u003e\u003c/span\u003e for the emitted photons. Consequently, the effective directional contrast under remote excitation, which reflects the combined effects of both directional absorption and directional emission, is given by:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{D}_{r}\\:=({x}^{2}-1\\:)/({x}^{2}+1\\:)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e.\u003c/p\u003e \u003cp\u003eBy substituting \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x\\:=(1+{C}_{l})/(1-{C}_{l})\\)\u003c/span\u003e\u003c/span\u003e, we obtain the following expression:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{D}_{r}\\:=2{C}_{l}\\:/(1+{C}_{l}^{2}\\:)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e.\u003c/p\u003e \u003cp\u003eThis relationship reveals that the directional contrast under remote excitation depends on the initial contrast \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e​ but exhibits a non-linear enhancement for moderate values of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. This suggests that a modest directionality observed under direct excitation using a linearly polarized pump can yield a substantial increase in effective directional contrast for measurements with remote excitation.\u003c/p\u003e \u003cp\u003eFor example, if \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}=0.5\\)\u003c/span\u003e\u003c/span\u003e (corresponding to an intensity ratio of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:3\\::1\\)\u003c/span\u003e\u003c/span\u003e), the resulting effective directional contrast will reach \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{D}_{r}=0.8\\)\u003c/span\u003e\u003c/span\u003e \u0026ndash; a significant improvement. Additionally, remote excitation can expand the effective area of directionality for waveguide-based photonic devices. In particular, the area with over 95% effective directional contrast increases from 25\u0026ndash;56% in our glide-plane waveguide devices under remote excitation (dashed black contour in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). This represents more than a twofold expansion of the highly directional region compared to local excitation, and the expanded region encompasses areas with strong Purcell enhancement exceeding 20 (solid black contour in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Our remote excitation technique takes advantage of the helicity of the slow-light waveguide mode, enabling the combination of higher Purcell factors and near-unity directional contrast. This balance underscores the potential of remote excitation in optimising chiral photonic systems for waveguide quantum optics.\u003c/p\u003e \u003c/div\u003e"},{"header":"Experimental Results","content":"\u003cp\u003eIn the experiment, the sample is housed in a liquid helium cryostat surrounded by superconducting coils, enabling magneto-photoluminescence studies under an applied magnetic field along the sample axis (see setup in Supplementary, Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). For quasi-resonant excitation, the laser is tuned to energies just above the exciton state, specifically targeting the QD\u0026rsquo;s p-shell. As shown in the photoluminescence (PL) excitation spectrum in Figure S2, the p-shell is located at ~\u0026thinsp;896 nm, approximately 20.7 meV (14 nm) above the exciton emission line at 910 nm.\u003c/p\u003e\n\u003cp\u003eWe measured the PL of the exciton emission line under p-shell excitation, while applying an external magnetic field of 3T in the Faraday geometry. For the local excitation scheme (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec), where the pump laser is focused directly on the QD1, the PL spectra (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea) exhibit relatively weak directionality. In contrast, under the remote excitation scheme (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed), where the QD1 is excited via waveguide modes, the PL spectra (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) show a significantly enhanced directional contrast. This enhancement is attributed to stronger spin-selective pumping of the QD via the waveguide mode, driven by directional absorption and, in turn, directional coupling of the QD emission within the glide-plane photonic-crystal devices.\u003c/p\u003e\n\u003cp\u003eIn Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed, we present data from a study of four QDs coupled into the glide-plane waveguide, represented by coloured points. The graph compares the directionality for remote excitation and local excitation, with the prediction of Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{D}_{r}\\)\u003c/span\u003e\u003c/span\u003e shown by the solid line. The dashed line shows the case where there is no enhancement under remote excitation, i.e. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{D}_{r}=C}_{l}\\)\u003c/span\u003e\u003c/span\u003e. For all QDs shown in this graph, excitation conditions were carefully selected to ensure p-shell excitation above the QD ground states. Black circular points correspond to the values from QD1, the primary QD studied in this report. The labels \u003cem\u003eL\u003c/em\u003e and \u003cem\u003eR\u003c/em\u003e indicate the two out-couplers where the PL was collected. The variation between points arises from chiral asymmetry, commonly observed in these devices due to waveguide disorder and multiple scattering processes affecting the propagating mode (see e.g. ref. 13). Red, blue, and orange square points represent PL measurements from QDs in other devices with the same chiral design parameters. These QDs, embedded within the glide-plane photonic-crystal waveguide, exhibit relatively low chiral behaviour under local excitation. In all cases, the directional contrast increases under remote excitation. It is striking that the enhancement is close to, or sometimes larger, than that predicted by Eq. (\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), which confirms that the spin memory under p-shell excitation is close to 100%. For the results that exceed Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), it could be the case there is some ellipticity in the pump laser, which could result in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mid\\:{\\alpha\\:}_{n}{\\mid\\:}^{2}\\ne\\:\\mid\\:{\\beta\\:}_{n}{\\mid\\:}^{2}\\)\u003c/span\u003e\u003c/span\u003eeven for local excitation, and hence affect the experimental values of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{l}\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eFigures 4a and 4b present time-resolved PL measurements to assess the decay rate enhancement in the slow-light waveguide for the same QD1 as in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. In our experiments, electrical and magnetic field tuning were generally employed to achieve a red or blue shift, resulting from either or both the quantum confined Stark effect and Zeeman energy. Specifically, for QD1, electrical field tuning was applied at zero magnetic field to induce a red shift and align the QD\u0026apos;s wavelength as closely as possible with the centre of the slow-light band of the photonic-crystal waveguide (Supplementary Figure S4). Figure 4a shows the time-resolved PL at a wavelength of 910.4 nm, where the emission is the fastest. In addition, Fig. 4b presents the variation in lifetime with emission wavelength as the electric field is increased and red-shift tuning is applied. It demonstrates a reduction in decay time within the slow-light band as the emission wavelength approaches the centre of the band, followed by an increase in decay time as the wavelength moves beyond the centre, returning to larger values. The single exponential fit in Fig. 4a indicates a lifetime of approximately 200 ps, corresponding to a six-fold decay rate enhancement compared to the ensemble lifetime of 1.2 ns for the dots in the wafer. This results in an estimated Purcell factor of 6 for the chirally-coupled QD1, achieving a significant combination of high directional contrast (\u0026gt;\u0026thinsp;90%) and Purcell factor in a QD, and demonstrating spin pumping of the QD1 in the slow light region of glide-plane waveguides where the estimated \u0026beta;-factor, calculated using FDTD simulations, is 97%.\u003c/p\u003e\u003cp\u003eFigure 4c shows the results of a Hanbury Brown and Twist (HBT) measurement under continuous-wave (CW) excitation at the p-shell resonance for the same QD1 as in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The clear anti-bunching behaviour at zerotime delay (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{g}^{2}\\:\\left(0\\right)\\sim0.06)\\:\\)\u003c/span\u003e\u003c/span\u003e without background subtraction demonstrates its excellent performance as a chirally-coupled single-photon source in the high-\u0026beta;-factor regime. The HBT results under pulsed excitation are shown in the Supplement (Figure S3).\u003c/p\u003e"},{"header":"Discussion and Conclusions","content":"\u003cp\u003eBy demonstrating enhanced directional contrast through remote excitation and combining it with Purcell enhancement, we introduce a novel mechanism for improving chiral light-matter interactions in nanophotonic platforms in the high-β regime that is required for waveguide quantum optics. The process of spin-photon coupling plays a critical role, that is, the transfer of photon polarization to the exciton spin, followed by its recombination and subsequent re-emission. The method only works when the exciton spin is preserved during relaxation, as any decoherence processes would lower the final chiral response, which is why we use p-shell excitation. In our work we have focussed on exciton spins, but the method can easily be adapted for spin pumping of electrons and holes in charged quantum dots, opening up new possibilities for spin-based quantum networks and quantum information processing systems.\u003c/p\u003e \u003cp\u003eOur investigation demonstrates the potential of remote excitation techniques combined with photonic-crystal waveguides to significantly enhance spin initialisation and directional coupling of QDs. By leveraging the chirality of waveguide modes in the slow-light regime, we have expanded the region of high directionality, theoretically achieving directionality exceeding 95% and a Purcell enhancement greater than 20. The simulations highlight a substantial improvement when using remote excitation, with approximately 56% of the waveguide area having \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\ge\\:95\\%\\)\u003c/span\u003e\u003c/span\u003e directionality \u0026ndash; compared to only around 25% achieved with local excitation methods. Furthermore, our experimental measurements demonstrate a six-fold enhancement in the emission decay rate of a coupled QD with 90% directional contrast under remote excitation, which corresponds to a β-factor of ~97%, as calculated using FDTD simulations. This advancement enables improved control of quantum states and facilitates the integration of such systems into chip-scale quantum optical circuits. This work provides a foundation for future research to optimise chiral quantum emitter interactions within photonic circuits, an important step toward functional quantum devices.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cem\u003ePhotoluminescence Measurements\u003c/em\u003e: Measurements were performed in a helium bath cryostat (supplementary Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) at T\u0026thinsp;=\u0026thinsp;4K equipped with a superconducting magnet (0\u0026ndash;5 Tesla). The sample was mounted in a socket giving access to electrical control of the PIN devices. The sample holder apparatus was fixed on a X-Y-Z piezo-stage, ensuring stable positioning of the sample. The optical access of the sample was through a confocal scanning microscope set-up. A CW tunable laser (Toptica single-mode laser DL Pro) was used for PL excitation and P-shell excitation experiments, while a femtosecond pulsed Ti:Sapphire laser (Spectra-Physics Tsunami, Newport) with an 80 MHz repetition rate was used for lifetime and PL correlation experiments. Both lasers were fibre-coupled. On the collection path, an ultranarrow bandpass filter with a full width at half maximum (FWHM) of less than 0.55 nm (935.4\u0026ndash;0.45 OD5 Ultra Narrow Bandpass Filter, Alluxa) was angle-tuned with respect to the emission line of the QD under study, effectively filtering out unwanted emission lines and the quasi-resonant p-shell excitation laser from the QD signal. PL Spectra were recorded by a liquid nitrogen-cooled charge-coupled device (CCD) camera after being dispersed through a 0.75 Acton Pro monochromator. Time resolved PL measurements were implemented by using a superconducting nanowire fast single-photon detectors (SNSPD - Single Quantum Eos), while the laser pulse repetition rate was detected by a photodiode. The pulses from the SNSPD and the photodiode were analysed using a time-correlated photon counting card (Becker and Hickl SPC-130-EM).\u003c/p\u003e\u003cp\u003e\u003cem\u003eSimulation:\u0026nbsp;\u003c/em\u003eNumerical calculations were performed using the commercial software package \u003cem\u003eLumerical FDTD Solutions\u003c/em\u003e and the open-source Python package \u003cem\u003eLegume\u003c/em\u003e (see details in the Supplementary section, Section 3).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was funded by the Engineering and Physical Sciences Research Council (EPSRC) UK Programme Grants EP/V026496/1. H.S. acknowledges support from the UKRI Strength in Places Fund programme, Smart Nano NI, and technical assistance from Shelby Hanna in creating Figure 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.G. and X.C. performed the measurements. H.S. designed the photonic devices, and R.D. conducted the device fabrication. E.C. and P.K.P. grew the quantum dot wafer. X.C. contributed to the simulations. H.S. and A.M.F supervised the experiment. H.S. wrote the manuscript with input from S.G. and X.C. All authors discussed the results and commented on the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAwschalom, D.D., Hanson, R., Wrachtrup, J. \u0026amp; Zhou, B.B. Quantum technologies with optically interfaced solid-state spins. \u003cem\u003eNature Photonics\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 516-527 (2018).\u003c/li\u003e\n\u003cli\u003ePelucchi, E. et al. 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Excitation spectroscopy of single quantum dots at tunable positive, neutral, and negative charge states. \u003cem\u003ePhysical Review B\u003c/em\u003e\u003cstrong\u003e86\u003c/strong\u003e, 085306 (2012).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5938986/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5938986/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe report on an integrated semiconductor chip where a single quantum dot (QD) is excited in-plane via a photonic-crystal waveguide through its nearest p-shell optical transition. The chirality of the waveguide mode is exploited to achieve both directional absorption and directional emission, resulting in a substantial enhancement in directional contrast, as measured for the Zeeman components of the waveguide-coupled QD. This remote excitation scheme enables high directionality (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\ge\\:0.95\\)\u003c/span\u003e\u003c/span\u003e) across ~\u0026thinsp;56% of the waveguide area, with significant overlap with the Purcell-enhanced region, where the electric field intensity profile is near its peak. In contrast, local excitation methods using an out-of-plane excitation beam focused directly over the area of the QD achieve only ~\u0026thinsp;25% overlap. This enhancement increases the likelihood of locating Purcell-enhanced QDs in regions that support high directionality, enabling the experimental demonstration of a six-fold enhancement in the decay rate of a QD with \u0026gt;\u0026thinsp;90% directionality. The remote p-shell excitation protocol establishes a new benchmark for waveguide quantum optics in terms of the combination of Purcell enhancement and high directionality, thereby paving the way for on-chip excitation of spin-based solid-state quantum technologies in regimes of high β-factor.\u003c/p\u003e","manuscriptTitle":"Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-12 10:30:56","doi":"10.21203/rs.3.rs-5938986/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a92f2c1c-414b-4214-b2b8-8f5de24a3193","owner":[],"postedDate":"February 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":44092479,"name":"Physical sciences/Optics and photonics"},{"id":44092480,"name":"Physical sciences/Physics/Electronics, photonics and device physics/Photonic devices"},{"id":44092481,"name":"Physical sciences/Optics and photonics/Optical materials and structures/Quantum dots"},{"id":44092482,"name":"Physical sciences/Physics/Optical physics/Single photons and quantum effects"},{"id":44092483,"name":"Physical sciences/Physics/Optical physics/Slow light"}],"tags":[],"updatedAt":"2025-06-04T08:31:07+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-12 10:30:56","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5938986","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5938986","identity":"rs-5938986","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}