An Integrated CMOS-Compatible Photonic Platform for Room-Temperature Rydberg Electromagnetically Induced Transparency in Rubidium Vapor via Counter-Propagating Stark-Chirped Rapid Adiabatic Passage and Quasiperiodic Control
Deterministic quantum state control at ambient temperature remains a central challenge for scalable photonic quantum technologies. Thermal rubidium vapor cells offer a cryogenic-free platform for light-matter interaction, but Doppler broadening, collision-induced dephasing, and transit-time effects limit coherent state transfer. We present a CMOS-compatible photonic architecture for studying room-temperature Rydberg electromagnetically induced transparency (EIT) in rubidium vapor, combining integrated on-chip pulse generation, counter-propagating beam geometry, and Stark-Chirped Rapid Adiabatic Passage (SCRAP). The platform integrates an on-chip silicon nitride pulse-generation stage, dual-wavelength optical addressing at 780 nm and 480 nm, a heated rubidium vapor microcell near 140°C, and a quasiperiodic Fibonacci control layer. We model the atomic response with a three-level ladder Hamiltonian and confirm numerically that the EIT transparency window scales as Ωc²/Γe, consistent with analytic theory. Thermal averaging over the Maxwell-Boltzmann velocity distribution confirms that counter-propagating excitation reduces residual Doppler-induced absorption relative to a co-propagating geometry. Fibonacci-modulated control fields are shown to possess substantially broader spectral content than periodic modulation, supporting their use as a candidate noise-avoidance strategy; this is presented as a spectral-shaping hypothesis, not as established topological protection. Numerical scans of SCRAP-assisted Rydberg transfer under realistic Rabi frequencies do not yet show a clear efficiency advantage over resonant excitation, and this is reported as an open problem for parameter optimization. We do not claim a demonstrated two-qubit logic gate; multi-atom blockade dynamics and gate fidelity benchmarking are identified explicitly as future work.
Deterministic quantum state control at ambient temperature remains a central challenge for scalable photonic quantum technologies. Thermal rubidium vapor cells offer a cryogenic-free platform for light-matter interaction, but Doppler broadening, collision-induced dephasing, and transit-time effects limit coherent state transfer. We present a CMOS-compatible photonic architecture for studying room-temperature Rydberg electromagnetically induced transparency (EIT) in rubidium vapor, combining integrated on-chip pulse generation, counter-propagating beam geometry, and Stark-Chirped Rapid Adiabatic Passage (SCRAP). The platform integrates an on-chip silicon nitride pulse-generation stage, dual-wavelength optical addressing at 780 nm and 480 nm, a heated rubidium vapor microcell near 140°C, and a quasiperiodic Fibonacci control layer. We model the atomic response with a three-level ladder Hamiltonian and confirm numerically that the EIT transparency window scales as Ωc²/Γe, consistent with analytic theory. Thermal averaging over the Maxwell-Boltzmann velocity distribution confirms that counter-propagating excitation reduces residual Doppler-induced absorption relative to a co-propagating geometry. Fibonacci-modulated control fields are shown to possess substantially broader spectral content than periodic modulation, supporting their use as a candidate noise-avoidance strategy; this is presented as a spectral-shaping hypothesis, not as established topological protection. Numerical scans of SCRAP-assisted Rydberg transfer under realistic Rabi frequencies do not yet show a clear efficiency advantage over resonant excitation, and this is reported as an open problem for parameter optimization. We do not claim a demonstrated two-qubit logic gate; multi-atom blockade dynamics and gate fidelity benchmarking are identified explicitly as future work.
Paper I established a single-atom baseline for room-temperature Rydberg electromagnetically induced transparency (EIT) in thermal rubidium vapor and reported two unresolved numerical questions: whether genuine counter-intuitive pulse ordering improves Stark-chirped rapid adiabatic passage (SCRAP)-assisted transfer, and whether Fibonacci-modulated control improves coherence beyond merely broadening the drive spectrum. We address both directly. Using the same three- level ladder Hamiltonian, decay rates, and 10 ns pulse window as the prior preprint, we find that counter-intuitive ordering within the fixed window degrades transfer efficiency to near zero (0.02%) rather than improving it, and we diagnose the failure as a short-window boundary-condition problem rather than a failure of the STIRAP mechanism itself. We then model a stored |1⟩–|3⟩coherence subject to Ornstein–Uhlenbeck dephasing noise and compare periodic and Fibonacci-timed π-phase- flip sequences using direct time-domain Monte Carlo simulation. In the regime where the noise correlation time matches the inter-pulse spacing, Fibonacci timing yields a 2.4×coherence advantage over periodic decoupling (0.0266 vs. 0.0110), while periodic decoupling outperforms Fibonacci in the quasi-static noise limit (0.964 vs. 0.785). We report both the negative and positive results transparently, without tuning parameters to force a preferred outcome.
In this work, we demonstrate - for the first time, to the best of our knowledge - electromagnetically induced transparency (EIT) on a fully integrated, chip-scale platform based on nanoscale tapered suspended waveguides surrounded by hot rubidium vapour. We further show that these waveguides enable the excitation of rubidium atoms to Rydberg states, and implement an electric readout scheme to detect these atoms by their ionisation currents. The fabrication workflow for standard ridge waveguides made of silicon nitride (Si3N4) is optimised, leading to significantly improved optical quality. Building on this, different techniques for locally suspending photonic structures out of Si3N4 are developed, allowing us to retain the waveguide interconnects between the structures on a conventional SiO2 layer for full chip integration. The use of a sacrificial silicon layer proves to be advantageous for suspending resonator structures, as this method does not change the optical properties of the device, as opposed to other established suspension methods. With these fabrication techniques, high quality suspended tapered waveguides are realised. Spectroscopy measurements on the D2 transition of rubidium confirm that the Doppler and transit time broadening are significantly reduced compared to standard ridge waveguides, owing to the extended evanescent field of the tapered geometry. After this, EIT is demonstrated on the tapered waveguides using a three level ladder scheme, benefiting from the longer atomic interaction times enabled by the extended evanescent field. The experimental results are compared to numerical simulations, showing good agreement. Finally, the excitation to Rydberg levels in the evanescent field of the tapered waveguide is investigated. An electrically contacted vapour cell is designed to detect the current from excited Rydberg atoms, ionised through collisions with ground-state atoms or perturber gases in the cell. Clear Rydberg signals are observed and compared with simulations modelling excitation and ionisation in the confined geometry of the evanescent field. The results indicate that the excitation can indeed occur within the guided mode and that the corresponding ionisation currents are of the same order of magnitude as those measured experimentally. However, strong scattering of the guided light is also observed at the transitions to the underetched regions, suggesting that a fraction of the Rydberg excitation may originate from this scattered light rather than from the evanescent field alone. Further investigations are ongoing at the time of writing to quantify this contribution.
Controlling the optical response of a medium through suitably tuned coherent electromagnetic fields is highly relevant in a number of potential applications, from all-optical modulators to optical storage devices. In particular, electromagnetically induced transparency (EIT) is an established phenomenon in which destructive quantum interference creates a transparency window over a narrow spectral range around an absorption line, which, in turn, allows to slow and ultimately stop light due to the anomalous refractive index dispersion. Here we report on the observation of a new form of both induced transparency and amplification of a weak probe beam in a strongly driven silicon photonic crystal resonator at room temperature. The effect is based on the oscillating temperature field induced in a nonlinear optical cavity, and it reproduces many of the key features of EIT while being independent of either atomic or mechanical resonances. Such thermo-optically induced transparency will allow a versatile implementation of EIT-analogs in an integrated photonic platform, at almost arbitrary wavelength of interest, room temperature and in a practical, low cost, and scalable system.
Abstract We study the steady optical responses of a cold atomic ensemble driven into the three-level ladder configuration involving a Rydberg state at finite temperatures. By improving the superatom model with thermal movement included, we calculate relevant atomic coherence effects and find that the residual Doppler broadening at the mK–K temperatures will weaken the nonclassical properties of transmitted probe photons. Furthermore, propagation directions of the probe and coupling fields have a great influence on various properties related to electromagnetically induced transparency. That is, the residual Doppler effect is more destructive to relevant atomic coherence effects in the co-propagation case but can be partially eliminated in the counter-propagation case.
One of the critical elements in the realization of the quantum internet are deterministic two-photon gates. This CZ photonic gate also completes a set of universal gates for all-optical quantum information processing. This article discusses an approach to realize a high fidelity CZ photonic gate by storing both control and target photons within an atomic ensemble using non-Rydberg electromagnetically induced transparency (EIT) followed by a fast, single-step Rydberg excitation with global lasers. The proposed scheme operates by relative intensity modulation of two lasers used in Rydberg excitation. Circumventing the conventional π-gap-π schemes, the proposed operation features continuous laser protection of the Rydberg atoms from the environment noise. The complete spatial overlap of stored photons inside the blockade radius optimizes the optical depth and simplifies the experiment. The coherent operation here is performed in the region that was dissipative in the previous Rydberg EIT schemes. Encountering the main imperfection sources, i.e., the spontaneous emission of the Rydberg and intermediate levels, population rotation errors, Doppler broadening of the transition lines, storage/retrieval efficiency, and atomic thermal motion induced decoherence, this article concludes that with realistic experimental parameters 99.7% fidelity is achievable.
High-fidelity control of the thousands to millions of programmable qubits needed for utility-scale quantum computers presents a formidable challenge for control systems. In leading atomic systems, control is optical: UV-NIR beams must be fanned out over numerous spatial channels and modulated to implement gates. While photonic integrated circuits (PICs) offer a potentially scalable solution, they also need to simultaneously feature high-speed and high-extinction modulation, strong inter-channel isolation, and broad wavelength compatibility. Here, we introduce and experimentally validate a foundry-fabricated PIC platform that overcomes these limitations. Designed for Rubidium-87 neutral atom quantum computers, our 8-channel PICs, fabricated on a 200-mm wafer process, demonstrate an advanced combination of performance metrics. At the 795 nm single-qubit gate wavelength, we achieve a mean extinction ratio (ER) of 71.4 ± 1.1 dB, nearest-neighbor on-chip crosstalk of -68.0 ± 1.0 dB, and -50.8 ± 0.2 dB after parallel beam delivery in free-space. This high-performance operation extends to the 420 nm and 1013 nm wavelengths for two-qubit Rydberg gates, showing ERs of 42.4 dB (detector-limited) and 61.5 dB, respectively. The devices exhibit 10-90% rise times of 26 ± 7 ns, achieve dynamic switching to -60 dB levels within microsecond timescales, and show pulse stability errors at the 10−3 level. This work establishes a scalable platform for developing advanced large-scale optical control required in fault-tolerant quantum computers and other precision technologies.