Peter Lodahl
Quantum dots embedded in photonic nanostructures have in recent years proven to be a very powerful solid-state platform for quantum optics experiments. The combination of near-unity radiative coupling of a single quantum dot to a photonic mode and the ability to eliminate decoherence processes imply that an unprecedented light-matter interface can be obtained. As a result, high-cooperativity photon-emitter quantum interfaces can be constructed opening a path-way to deterministic photonic quantum gates for quantum-information processing applications. In the present manuscript, I review current state-of-the-art on quantum dot devices and their applications for quantum technology. The overarching long-term goal of the research field is to construct photonic quantum networks where remote entanglement can be distributed over long distances by photons.
P. Lodahl, A. P. Mosk, A. Lagendijk
We predict a new spatial quantum correlation in light propagating through a multiple scattering random medium. The correlation depends on the quantum state of the light illuminating the medium, is infinite range, and dominates over classical mesoscopic intensity correlations. The spatial quantum correlation is revealed in the quantum fluctuations of the total transmission or reflection through the sample and should be readily observable experimentally.
P. Lodahl, A. Lagendijk
Oct 14, 2004·quant-ph·PDF We present an experimental study of the propagation of quantum noise in a multiple scattering random medium. Both static and dynamic scattering measurements are performed: the total transmission of noise is related to the mean free path for scattering, while the noise frequency correlation function determines the diffusion constant. The quantum noise observables are found to scale markedly differently with scattering parameters compared to classical noise observables. The measurements are explained with a full quantum model of multiple scattering.
P. Lodahl
Jun 30, 2005·quant-ph·PDF We investigate frequency correlations in multiple scattered light that are present in the quantum fluctuations. The memory effect for quantum and classical noise is compared, and found to have markedly different frequency scaling, which was confirmed in a recent experiment. Furthermore, novel mesoscopic correlations are predicted that depend on the photon statistics of the incoming light.
Xiao-Liu Chu, Vasiliki Angelopoulou, Peter Lodahl, Nir Rotenberg
Coherent interactions between quantum emitters in tailored photonic structures is a fundamental building block for future quantum technologies, but remains challenging to observe in complex solid-state environments, where the role of decoherence must be considered. Here, we investigate the optical interaction between two quantum emitters mediated by one-dimensional waveguides in a realistic solid-state environment, focusing on the creation, population and detection of a sub-radiant state, in the presence of dephasing. We show that as dephasing increases, the signatures of sub-radiance quickly vanish in intensity measurements yet remain pronounced in photon correlation measurements, particularly when the two emitters are pumped separately so as to populate the sub-radiant state efficiently. The applied Green's tensor approach is used to model a photonic crystal waveguide, including the dependence on the spatial position of the integrated emitter. The work lays out a route to the experimental realization of sub-radiant states in nanophotonic waveguides containing solid-state emitters.
Xiao-Liu Chu, Camille Papon, Nikolai Bart, Andreas D. Wieck, Arne Ludwig, Leonardo Midolo, Nir Rotenberg, Peter Lodahl
Efficient light-matter interaction at the single-photon level is of fundamental importance in emerging photonic quantum technology. A fundamental challenge is addressing multiple quantum emitters at once, as intrinsic inhomogeneities of solid-state platforms require individual tuning of each emitter. We present the realization of two semiconductor quantum dot emitters that are efficiently coupled to a photonic-crystal waveguide and individually controllable by applying a local electric Stark field. We present resonant transmission and fluorescence spectra in order to probe the coupling of the two emitters to the waveguide. We exploit the single-photon stream from one quantum dot to perform spectroscopy on the second quantum dot positioned 16$μ$m away in the waveguide. Furthermore, power-dependent resonant transmission measurements reveals signatures of coherent coupling between the emitters. Our work provides a scalable route to realizing multi-emitter collective coupling, which has inherently been missing for solid-state deterministic photon emitters.
Jeppe Johansen, Brian Julsgaard, Søren Stobbe, Jørn M. Hvam, Peter Lodahl
The spin-flip rate that couples dark and bright excitons in self-assembled quantum dots is obtained from time-resolved spontaneous emission measurements in a modified local density of optical states. Employing this technique, we can separate effects due to non-radiative recombination and unambiguously record the spin-flip rate. The dependence of the spin-flip rate on emission energy is compared in detail to a recent model from the literature, where the spin flip is due to the combined action of short-range exchange interaction and acoustic phonons. We furthermore observe a surprising enhancement of the spin-flip rate close to a semiconductor-air interface, which illustrates the important role of interfaces for quantum dot based nanophotonic structures. Our work is an important step towards a full understanding of the complex dynamics of quantum dots in nanophotonic structures, such as photonic crystals, and dark excitons are potentially useful for long-lived coherent storage applications.
Yuntian Chen, Torben Roland Nielsen, Niels Gregersen, Peter Lodahl, Jesper Mork
We develop a self-consistent finite element method to study spontaneous emission at nanoscale proximity of plasmonic waveguides. In the model, it is assumed that only one guided mode is dominatingly excited by the quantum emitter. With such one dominating mode assumption, the cross section of the plasmonic waveguide can be arbitrary. We apply our numerical method to calculate the coupling of a quantum emitter to a cylindrical nanowire and a rectangular waveguide, and compare the cylindrical nanowire to previous work valid in quasistatic approximation. The fraction of the energy coupled to the plasmonic mode can be calculated exactly, which can be used to determine the single optical plasmon generation efficiency for a quantum emitter. For a gold nanowire we observe agreement with the quasistatic approximation for radii below 20 nm, but for larger radii the total decay rate is up to 10 times larger. For the rectangular waveguide we estimate an optimized value for the spontaneous emission factor βof up to 80%.
Johannes Borregaard, Hannes Pichler, Tim Schöder, Mikhail D. Lukin, Peter Lodahl, Anders S. Sørensen
Jul 11, 2019·quant-ph·PDF We propose a novel one-way quantum repeater architecture based on photonic tree-cluster states. Encoding a qubit in a photonic tree-cluster protects the information from transmission loss and enables long-range quantum communication through a chain of repeater stations. As opposed to conventional approaches that are limited by the two-way communication time, the overall transmission rate of the current quantum repeater protocol is determined by the local processing time enabling very high communication rates. We further show that such a repeater can be constructed with as little as two stationary qubits and one quantum emitter per repeater station, which significantly increases the experimental feasibility. We discuss potential implementations with diamond defect centers and semiconductor quantum dots efficiently coupled to photonic nanostructures and outline how such systems may be integrated into repeater stations.
Xiaoyan Zhou, Ravitej Uppu, Zhe Liu, Camille Papon, Rudiger Schott, Andreas D. Wieck, Arne Ludwig, Peter Lodahl, Leonardo Midolo
Semiconductor quantum dots in photonic integrated circuits enable scaling quantum-information processing to many single photons and quantum-optical gates. On-chip spectral filters are essential to achieve high-purity and coherent photon emission from quantum dots embedded in waveguides, without resorting to free-space optics. Such spectral filters should be tunable, to compensate for the inhomogeneous spectral distribution of the quantum dots transitions. Here, we report an on-chip filter monolithically integrated with quantum dots, that uses nanomechanical motion for tuning its resonant wavelength over 10 nm, enabling operation at cryogenic temperatures and avoiding cross-talk with the emitter. We demonstrate single-photon emission from a quantum dot under non-resonant excitation by employing only the on-chip filter. These results are key for the development of fully-integrated de-multiplexing, multi-path photon encoding schemes, and multi-emitter circuits.
Nils Hauff, Stephen Hughes, Hanna Le Jeannic, Peter Lodahl, Nir Rotenberg
On-chip chiral quantum light-matter interfaces, which support directional interactions, provide a promising platform for efficient spin-photon coupling, non-reciprocal photonic elements, and quantum logic architectures. We present full-wave three-dimensional calculations to quantify the performance of conventional and topological photonic crystal waveguides as chiral emitter-photon interfaces. Specifically, the ability of these structures to support and enhance directional interactions while suppressing subsequent backscattering losses is quantified. Broken symmetry waveguides, such as the non-topological glide-plane waveguide and topological bearded interface waveguide are found to act as efficient chiral interfaces, with the topological waveguide modes allowing for operation at significantly higher Purcell enhancement factors. Finally, although all structures suffer from backscattering losses due to fabrication imperfections, these are found to be smaller at high enhancement factors for the topological waveguide. These reduced losses occur because the optical mode is pushed away from the air-dielectric interfaces where scattering occurs, and not because of any topological protection. These results are important to the understanding of light-matter interactions in topological photonic crystals and to the design of efficient, on-chip chiral quantum devices.
Freja T. Østfeldt, Eva M. González-Ruiz, Nils Hauff, Ying Wang, Andreas D. Wieck, Arne Ludwig, Rüdiger Schott, Leonardo Midolo, Anders S. Sørensen, Ravitej Uppu, Peter Lodahl
Entanglement is the fuel of advanced quantum technology. It is for instance consumed in measurement-based quantum computing and allows loss-tolerant encoding of quantum information. In photonics, entanglement has traditionally been generated probabilistically, requiring massive multiplexing for scaling up to many photons. An alternative approach utilizes quantum emitters in nanophotonic devices for deterministic generation of single photons, which an be extended to two- and multi-photon generation on demand. The proposed polarization-entanglement sources are, however, incompatible with spatial dual-rail qubit encoding, which is preferred in photonic quantum computing realized in scalable integrated photonic circuits. Here we propose and experimentally realize an on-demand source of dual-rail photon pairs using a quantum dot in a planar nanophotonic waveguide. The source exploits the cascaded decay of a biexciton state and chiral light-matter coupling to achieve deterministic generation of spatial dual-rail Bell pairs with the amount of entanglement determined by the chirality. The operational principle can readily be extended to multi-photon entanglement generation, and such sources may be interfaced with advanced photonic-integrated circuits, e.g., for efficient preparation of entanglement resource states for photonic quantum computing.
Martin Hayhurst Appel, Alexey Tiranov, Simon Pabst, Ming Lai Chan, Christian Starup, Ying Wang, Leonardo Midolo, Konstantin Tiurev, Sven Scholz, Andreas D. Wieck, Arne Ludwig, Anders Søndberg Sørensen, Peter Lodahl
Nov 24, 2021·quant-ph·PDF Deterministic sources of multi-photon entanglement are highly attractive for quantum information processing but are challenging to realize experimentally. In this paper, we demonstrate a route towards a scaleable source of time-bin encoded Greenberger-Horne-Zeilinger and linear cluster states from a solid-state quantum dot embedded in a nanophotonic crystal waveguide. By utilizing a self-stabilizing double-pass interferometer, we measure a spin-photon Bell state with $(67.8\pm0.4)\%$ fidelity and devise steps for significant further improvements. By employing strict resonant excitation, we demonstrate a photon indistinguishability of $(95.7\pm0.8)\%$, which is conducive to fusion of multiple cluster states for scaling up the technology and producing more general graph states.
Petru Tighineanu, Mads Lykke Andersen, Anders Søndberg Sørensen, Søren Stobbe, Peter Lodahl
The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this paper we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.
Pedro David García, Peter Lodahl
Nanophotonics focuses on the control of light and the interaction with matter by the aid of intricate nanostructures. Typically, a photonic nanostructure is carefully designed for a specific application and any imperfections may reduce its performance, i.e., a thorough investigation of the role of unavoidable fabrication imperfections is essential for any application. However, another approach to nanophotonic applications exists where fabrication disorder is used to induce functionalities by enhancing light-matter interaction. Disorder leads to multiple scattering of light, which is the realm of statistical optics where light propagation requires a statistical description. We review here the recent progress on disordered photonic nanostructures and the potential implications for quantum photonics devices.
Petru Tighineanu, Anders Søndberg Sørensen, Søren Stobbe, Peter Lodahl
We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. At the microscopic level the deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, where a strong variation of the multipolar moments across the emission spectrum of quantum dots is observed. Our work enriches the physical understanding of quantum dots and is of significance for the fields of nanophotonics, quantum photonics, and quantum-information science, where quantum dots are actively employed.
Gabija Kiršanskė, Petru Tighineanu, Raphaël S. Daveau, Javier Miguel-Sánchez, Peter Lodahl, Søren Stobbe
Indirect excitons in coupled quantum wells have long radiative lifetimes and form a cold quasi-two-dimensional population suitable for studying collective quantum effects. Here we report the observation of the exciton Mott transition from an insulating (excitons) to a conducting (ionized electron-hole pairs) phase, which occurs gradually as a function of carrier density and temperature. The transition is inferred from spectral and time-resolved photoluminescence measurements around a carrier density of $2\times10^{10} \mathrm{cm}^{-2}$ and temperatures of $12-16 \mathrm{K}$. An externally applied electric field is employed to tune the dynamics of the transition via the quantum-confined Stark effect. Our results provide evidence of a gradual nature of the exciton Mott transition.
Peter Lodahl, Sahand Mahmoodian, Søren Stobbe, Philipp Schneeweiss, Jürgen Volz, Arno Rauschenbeutel, Hannes Pichler, Peter Zoller
At the most fundamental level, the interaction between light and matter is manifested by the emission and absorption of single photons by single quantum emitters. Controlling light--matter interaction is the basis for diverse applications ranging from light technology to quantum--information processing. Many of these applications are nowadays based on photonic nanostructures strongly benefitting from their scalability and integrability. The confinement of light in such nanostructures imposes an inherent link between the local polarization and propagation direction of light. This leads to {\em chiral light--matter interaction}, i.e., the emission and absorption of photons depend on the propagation direction and local polarization of light as well as the polarization of the emitter transition. The burgeoning research field of {\em chiral quantum optics} offers fundamentally new functionalities and applications both for single emitters and ensembles thereof. For instance, a chiral light--matter interface enables the realization of integrated non--reciprocal single--photon devices and deterministic spin--photon interfaces. Moreover, engineering directional photonic reservoirs opens new avenues for constructing complex quantum circuits and networks, which may be applied to simulate a new class of quantum many--body systems.
Pedro David García, Søren Stobbe, Immo Söllner, Peter Lodahl
Complex dielectric media often appear opaque because light traveling through them is scattered multiple times. Although the light scattering is a random process, different paths through the medium can be correlated encoding information about the medium. Here, we present spectroscopic measurements of nonuniversal intensity correlations that emerge when embedding quantum emitters inside a disordered photonic crystal that is found to Anderson-localize light. The emitters probe in-situ the microscopic details of the medium, and imprint such near-field properties onto the far-field correlations. Our findings provide new ways of enhancing light-matter interaction for quantum electrodynamics and energy harvesting, and may find applications in subwavelength diffuse-wave spectroscopy for biophotonics.
Hanna Le Jeannic, Alexey Tiranov, Jacques Carolan, Tomás Ramos, Ying Wang, Martin H. Appel, Sven Scholz, Andreas D. Wieck, Arne Ludwig, Nir Rotenberg, Leonardo Midolo, Juan José García-Ripoll, Anders S. Sørensen, Peter Lodahl
Dec 13, 2021·quant-ph·PDF Single photons constitute a main platform in quantum science and technology: they carry quantum information over extended distances in the future quantum internet and can be manipulated in advanced photonic circuits enabling scalable photonic quantum computing. The main challenge in quantum photonics is how to generate advanced entangled resource states and efficient light-matter interfaces. Here we utilize the efficient and coherent coupling of a single quantum emitter to a nanophotonic waveguide for realizing quantum nonlinear interaction between single-photon wavepackets. This inherently multimode quantum system constitutes a new research frontier in quantum optics. We demonstrate control of a photon with another photon and experimentally unravel the dynamical response of two-photon interactions mediated by a quantum emitter, and show that the induced quantum correlations are controlled by the pulse duration. The work will open new avenues for tailoring complex photonic quantum resource states.