Researchers have developed a novel on-chip frequency beamsplitter with unprecedented control over quantum information carried by light. Chen-You Su, Kaiyi Wu, and Lucas M. Cohen, alongside Saleha Fatema, Navin B. Lingaraju et al. from Purdue University and The Johns Hopkins University Applied Physics Laboratory, demonstrate a device capable of splitting a single light beam into multiple frequency components with extremely high precision. This achievement represents a significant advance in integrated quantum photonics, exceeding the performance of previous technologies by supporting frequency spacings as narrow as 2GHz and enabling near-ideal Hadamard gate performance with a fidelity exceeding 0.9995. The resulting scalable platform promises to unlock new possibilities in quantum information processing, facilitating densely parallel operations and more complex quantum gate implementations.
High-fidelity integrated photonics enable scalable frequency-bin quantum computing with increased qubit numbers and coherence times
Scientists have engineered a new on-chip frequency beamsplitter achieving unprecedented control over individual photons and paving the way for more powerful quantum computers. This device, a quantum frequency processor, utilizes an integrated silicon pulse shaper with six spectral channels to manipulate the frequency of light with exceptional precision.
The research demonstrates high-fidelity, tunable, and ultrafine-resolution frequency beamsplitting, surpassing the capabilities of previous bulk optical systems and establishing a scalable platform for integrated frequency-bin quantum photonics. A near-ideal Hadamard gate performance was achieved, exhibiting a fidelity exceeding 0.9995 and a modified success probability greater than 0.9621 across frequency spacings ranging from 2 to 5GHz.
This breakthrough stems from the development of a compact, silicon-based pulse shaper that replaces bulky, traditional components. The system supports frequency spacings as narrow as 2GHz, representing a ninefold improvement in spectral resolution compared to existing tabletop implementations. This finer resolution not only increases the number of accessible frequency modes within a given bandwidth but also reduces the demands on waveform synthesis and modulation speeds.
Researchers validated the performance of the device through tunable Hadamard gates, consistently achieving high fidelity and success probability across the tested frequency range. The ability to finely control frequency spacing and splitting ratios, through spectral phase or modulation index control, opens new avenues for quantum information processing.
This includes the potential for densely parallel single-qubit operations and the implementation of multidimensional quantum gates. Tests utilising only four spectral channels further suggest the possibility of ultratight parallelization, enhancing computational efficiency. Overall, this work represents a significant step towards fully integrated, scalable quantum systems, bringing the promise of advanced frequency-encoded quantum technologies closer to realisation.
Integrated Pulse Shaping for High-Fidelity On-Chip Frequency Beamsplitters enables advanced photonic integrated circuits
A quantum frequency processor, incorporating an integrated pulse shaper with six spectral channels, served as the core of this work. Researchers fabricated this pulse shaper to create high-fidelity, tunable, and ultrafine-resolution on-chip frequency beamsplitters. Near-ideal Hadamard gate performance was achieved, demonstrating fidelity exceeding 0.9995 and a modified success probability greater than 0.9621.
These metrics were maintained across frequency spacings ranging from 2 to 5GHz, and crucially, with as few as four spectral channels utilized within the pulse shaper. The system supports frequency spacings as narrow as 2GHz, representing a significant advancement over previous bulk demonstrations. Arbitrary splitting ratios were implemented through precise control of spectral phase or modulation index.
To demonstrate this, the team experimentally varied the spectral phase parameter α, achieving configurations corresponding to α∈{π/3, π/2, 2π/3} in addition to the standard Hadamard configuration at α= π. Output spectra, obtained using single-frequency inputs, confirmed distinct splitting ratios, with quantitative comparisons between measured and theoretical values of reflectivity and transmissivity presented.
Beyond spectral phase control, a novel approach involved tuning the modulation index θ via adjustments to the RF drive power applied to electro-optic phase modulators. Experimental results were obtained for θ∈[0.5, 1.0], revealing qualitatively similar behaviour to phase control for θ 0.8283, the system exhibited frequency shifting behaviour, with mode-hopping probabilities exceeding mode-preserving probabilities.
Despite a reduction in success probability at higher θ values, this method provides a pathway for rapid frequency beamsplitter adjustments beyond 50/50 split ratios. The total insertion loss of the quantum frequency processor was measured at approximately 21 dB, comprising 15 dB from the on-chip pulse shaper and 3 dB per electro-optic phase modulator.
High-fidelity frequency manipulation using an integrated on-chip beamsplitter enables precise control of optical signals
Fidelity exceeding 0.9995 and a modified success probability greater than 0.9621 were achieved in a newly demonstrated on-chip frequency beamsplitter system. This quantum frequency processor utilizes an integrated pulse shaper with six spectral channels to enable high-fidelity, tunable, and ultrafine-resolution frequency manipulation.
The system consistently maintained this performance across frequency spacings ranging from 2 to 5GHz, utilizing as few as four spectral channels within the pulse shaper. Supporting frequency spacings as narrow as 2GHz represents a significant advancement beyond previous bulk demonstrations of similar systems.
Arbitrary splitting ratios are attainable through precise control of spectral phase or modulation index, offering flexibility in quantum state preparation and manipulation. This capability establishes a scalable and resource-efficient platform for integrated frequency-bin quantum photonics, paving the way for advanced quantum information processing techniques.
The research details a silicon-based integrated device occupying less than 1mm² which replaces traditional, bulky pulse shapers. Validation of the system’s performance was conducted through a tunable Hadamard gate, confirming consistent operation across the 2, 5GHz frequency range. This minimum spacing of 2GHz signifies a ninefold improvement in spectral resolution compared to prior tabletop implementations.
Further experiments with spectrally parsimonious gate configurations, utilizing only four frequency bins, suggest potential for ultratight parallelization of quantum operations. Demonstrations of splitting ratio control, achieved via both spectral phase tuning and modulation index adjustment of the electro-optic phase modulators, highlight the system’s versatility. Overall, the work presents a substantial step towards fully integrated, on-chip frequency-bin quantum state manipulation with enhanced resolution and scalability.
High fidelity frequency beamsplitters enable scalable quantum information processing with integrated photonic circuits
Scientists have created high-fidelity, tunable frequency beamsplitters on a chip using a quantum frequency processor and an integrated pulse shaper with six spectral channels. These beamsplitters achieve near-ideal Hadamard gate performance, maintaining a fidelity greater than 0.9995 and a success probability exceeding 0.9621 across frequency spacings from 2 to 5GHz, even when using as few as four spectral channels.
The system surpasses previous demonstrations by supporting frequency spacings as narrow as 2GHz and allows for arbitrary splitting ratios through spectral phase or modulation index control. These results demonstrate a scalable and resource-efficient platform for integrated frequency-bin quantum information processing, potentially enabling densely parallel single-qubit operations and multidimensional gate implementations.
The ultranarrow channel linewidths and tunable frequency spacings offer a significant improvement over existing quantum frequency processor implementations. The ability to precisely control optical frequency-bin states with few-GHz spacings suggests potential for future integration with quantum transduction technologies, bridging the spectral gap between solid-state qubits and optical photons suitable for long-distance communication.
The current system exhibits a total insertion loss of approximately 21 dB, primarily due to off-chip components and fiber-to-chip coupling, but the authors suggest that on-chip integration of electro-optic phase modulators and silicon-based light sources could substantially reduce this loss. Further development of pulse shapers with a greater number of spectral channels is also needed to realize high-dimensional quantum gates and parallel operations.
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🗞 High-resolution tunable frequency beamsplitter enabled by an integrated silicon pulse shaper
🧠ArXiv: https://arxiv.org/abs/2601.23028