Periodic Reporting for period 3 - QUANtIC (Quantum Nanowire Integrated Photonic Circuits)
Période du rapport: 2022-01-01 au 2023-06-30
Future applications in on-chip data processing, communication, storage and metrology are destined to exploit photonics as a key enabling technology due to the outstanding high-speed and low-noise properties of photons. One of the most promising visions is, thereby, the on-chip integration of light sources onto platforms of waveguide-based classical and quantum circuits and the ability to transduce and manipulate classical and non-classical (quantum) states of light. Silicon (Si) or silicon-on-insulator (SOI) based photonic circuitry is probably the best platform to realize such optical links, however, an outstanding challenge in developing such next-generation photonic and quantum technologies is to realize deterministic and high-efficiency active light sources coupled to integrated Si- or SOI-based photonic circuitry.
One of the most promising candidates for implementing highly efficient emitters and quantum light sources are nanostructured III-V semiconductors. In particular, light sources incorporated in the form of III-V semiconductor nanowires (NW) are emerging as very promising platform due to many extraordinary properties: (i) NWs are natural dielectric resonator cavities providing intrinsically a gain medium for emission of coherent photons while simultaneously acting as optical waveguide, (ii) they can be integrated in a highly deterministic, position-controlled fashion onto Si with very small foot-print while maintaining high structural integrity, (iii) the 1D-structure offers exceptionally high light extraction efficiency and emission directionality from embedded quantum emitters, and (iv) the optical properties can be tuned by strong electronic quantum confinement phenomena.
The objective of this action is to combine the unprecedented features of semiconductor NWs and realize first demonstrations of high-performance classical and non-classical light sources monolithically integrated onto photonic/quantum circuits for on-chip communication and metrology. The ultimate vision of this scalable technology is to enable solid-state optical networks at the emitter-waveguide, emitter-emitter, and emitter-environment interface, where NW-based emitters can be exploited for signal manipulation, distribution, switching and sensing down to the few-photon limit.
One of the most promising candidates for implementing highly efficient emitters and quantum light sources are nanostructured III-V semiconductors. In particular, light sources incorporated in the form of III-V semiconductor nanowires (NW) are emerging as very promising platform due to many extraordinary properties: (i) NWs are natural dielectric resonator cavities providing intrinsically a gain medium for emission of coherent photons while simultaneously acting as optical waveguide, (ii) they can be integrated in a highly deterministic, position-controlled fashion onto Si with very small foot-print while maintaining high structural integrity, (iii) the 1D-structure offers exceptionally high light extraction efficiency and emission directionality from embedded quantum emitters, and (iv) the optical properties can be tuned by strong electronic quantum confinement phenomena.
The objective of this action is to combine the unprecedented features of semiconductor NWs and realize first demonstrations of high-performance classical and non-classical light sources monolithically integrated onto photonic/quantum circuits for on-chip communication and metrology. The ultimate vision of this scalable technology is to enable solid-state optical networks at the emitter-waveguide, emitter-emitter, and emitter-environment interface, where NW-based emitters can be exploited for signal manipulation, distribution, switching and sensing down to the few-photon limit.
So far, progress was made on several objectives related to the design and monolithic integration of advanced light sources using quantum NW-heterostructures on Si and SOI platform. First milestones were achieved on identifying suitable NW gain materials and optimizing the coupling efficiency of NW-lasers to SOI-waveguides (WG) at telecom wavelengths. For example, we established best-practice III-V NW materials with optically efficient resonator structures emitting near the telecom O-band (1.3 µm). Using advanced GaAs-InAlGaAs core-shell NW quantum well (QW) structures that incorporated specific strain-compensating layers, large built-in compressive strains were alleviated and optically pumped lasing operation with very low threshold achieved up to room-temperature. We also made intense efforts to integrate such NW-QW lasers deterministically onto Si-ridge WG, and demonstrated first successful nanofabrication of under-cut NW-lasers in the unique vertical-cavity geometry. The experimental work was also supported by systematic modelling efforts to set up guidelines for efficient coupling of light emission from vertical-cavity NW lasers to Si-ridge WG. Hereby, we found that under optimized geometries and proper bottom-mirror design, indeed, large coupling efficiencies > 50% can be achieved. To further obtain understanding of the intrinsic lasing dynamics of the NWs, ultrafast pump-probe spectroscopy methods were developed to probe the microscopic mechanisms for high-frequency (>250 GHz) intensity oscillations in the lasing evolution. We recognized that self-induced electron-hole plasma temperature oscillations govern the observed behavior, which will provide interesting new approaches for ultrafast intensity and phase modulation of chip-integrated NW-lasers.
Finally, with respect to objectives focusing on non-classical (quantum) light sources integrated onto quantum photonic integrated circuits (QPIC), we proposed new NW-based architectures that embed single quantum dots (QD) as ideal sources for high-brightness single photons, a key ingredient for quantum technological applications in secure data communication and distributed quantum computing. In particular, we demonstrated through numerical simulations how the architecture needs to be tuned for efficient light coupling and propagation of single photons into a SOI-based QPIC. We found that by placing the QD emitter close to the SOI-based WG, peak power coupling efficiencies of up to > 80% can be realized.
Finally, with respect to objectives focusing on non-classical (quantum) light sources integrated onto quantum photonic integrated circuits (QPIC), we proposed new NW-based architectures that embed single quantum dots (QD) as ideal sources for high-brightness single photons, a key ingredient for quantum technological applications in secure data communication and distributed quantum computing. In particular, we demonstrated through numerical simulations how the architecture needs to be tuned for efficient light coupling and propagation of single photons into a SOI-based QPIC. We found that by placing the QD emitter close to the SOI-based WG, peak power coupling efficiencies of up to > 80% can be realized.
The photonic circuit integrated NW-lasers are new on-chip Fabry-Perot type nanolaser sources, which are unique due to their small sub-µm2 footprint, single mode character, high spontaneous emission coupling factors and site-selective integration capabilities. As such they are predestined as energy-efficient nanolaser sources with high-density integration potentials, going beyond the state-of-the-art of other types of nanolaser sources. Ongoing work currently aims to explore their ultimate intrinsic performance limits, in terms of cavity size, dielectric environment and the tuning of active gain media, which involves also developments towards mid-IR nanolasers (> 2 µm). In this regard, non-dielectric NW-lasers, such as metal-clad NW lasers are also considered for potential performance enhancements, since they are expected to host much larger modal overlap with the gain medium at comparatively small size. A further yet outstanding step forward is the experimental realization of a single vertical-cavity NW-laser and the verification of efficient in-coupling into SOI photonic WG at the relevant telecom-wavelength and mid-IR bands. Hereby, efforts are directed to fabricate improved undercut-cavity NW-lasers capable of high mode reflectivity, low-threshold lasing, and efficient in-coupling.
Likewise, for vertical-cavity NW-QD emitters coupled to QPIC, we aim to demonstrate experimentally the efficient coupling of deterministic, high-brightness single photons to SOI-based WGs for on-chip quantum communication, as proposed in our numerical simulation studies. Thanks to the excellent scalability of position-control of NW-WG cavities on QPIC this will allow the realization of multi-photon Boson sampling experiments from on-chip QDs. Such on-chip QPIC NW-QD sources will further offer exceptional platform to create spin networks with charged QDs at nodes for on-chip communication via photons, exploiting the transfer of spin information via circular photon states. Here, a central goal is to harness the unique spin-orbit interactions in sub-wavelength QPIC to control the spatial degree of freedom of light and tune intensity distributions and propagation paths of single photons within IQPCs. Thereby, the QD-in-NW-cavity platform will provide a uniquely deterministic approach to study such chiral-light-matter interactions for future spin-based quantum networks, where coupling and photon exchange effects from multiple on-chip QDs will be exploited.
Likewise, for vertical-cavity NW-QD emitters coupled to QPIC, we aim to demonstrate experimentally the efficient coupling of deterministic, high-brightness single photons to SOI-based WGs for on-chip quantum communication, as proposed in our numerical simulation studies. Thanks to the excellent scalability of position-control of NW-WG cavities on QPIC this will allow the realization of multi-photon Boson sampling experiments from on-chip QDs. Such on-chip QPIC NW-QD sources will further offer exceptional platform to create spin networks with charged QDs at nodes for on-chip communication via photons, exploiting the transfer of spin information via circular photon states. Here, a central goal is to harness the unique spin-orbit interactions in sub-wavelength QPIC to control the spatial degree of freedom of light and tune intensity distributions and propagation paths of single photons within IQPCs. Thereby, the QD-in-NW-cavity platform will provide a uniquely deterministic approach to study such chiral-light-matter interactions for future spin-based quantum networks, where coupling and photon exchange effects from multiple on-chip QDs will be exploited.