Saleha Fatema

We demonstrate high-fidelity, tunable, and ultrafine-resolution frequency beamsplitters using a quantum frequency processor based on an integrated pulse shaper with six spectral channels and off-chip electro-optic phase modulators. Near-ideal Hadamard gate performance is achieved, with fidelity F >0.9995 and modified success probability P ~>0.9621 maintained across frequency spacings from 2–5 GHz and down to as few as four spectral pulse shaper channels. The system’s support of frequency spacings as narrow as 2 GHz significantly surpasses prior bulk demonstrations and enables arbitrary splitting ratios via spectral phase or modulation index control, the latter offering a path toward fast reconfigurability. These results establish a scalable and resource-efficient platform for integrated frequency-bin quantum photonics, opening new directions in quantum information processing—including densely parallel single-qubit operations and multidimensional gate implementations.

Phase-coherent radio-frequency (RF)-to-optical links provide highly frequency-stable optical signals, critical for ultrafast and high-precision metrology. Optical frequency combs generated from mode-locked lasers can achieve this with exceptional accuracy, but face limitations in size, power consumption, and scalability. Microcombs generated from an integrated photonic chip offer a compact, mass-manufacturable alternative with the advantage of achieving the octave-spanning bandwidth, essential for self-referencing. Yet, this is accompanied by comb line spacing outside the bandwidth of conventional electronics. Here, we utilize two ∼1THz microcombs in a Vernier configuration to stabilize their optical frequencies to a common RF reference, establishing a phase-coherent RF-to-optical link for programmable optical frequency synthesis. Importantly, the divided repetition rates extracted from the Vernier scheme enable electronic control and reconfigurability of the comb grid through electro-optic modulation. We demonstrate reduced comb grids of ∼ 10 GHz, facilitating static laser frequency calibration with kHz-resolution and dynamic-tracking. The fully stabilized, octave-spanning dual-comb system can be widely used in applications requiring stable optical frequency sources and high-precision metrology. *Saleha Fatema & Kaiyi Wu contributed equally to this work.

Kerr microcombs have drawn substantial interest as mass-manufacturable, compact alternatives to bulk frequency combs. This could enable the deployment of many comb-reliant applications previously confined to laboratories. Particularly enticing is the prospect of microcombs performing optical frequency division in compact optical atomic clocks. Unfortunately, it is difficult to meet the self-referencing requirement of microcombs in these systems owing to the approximately terahertz repetition rates typically required for octave-spanning comb generation. In addition, it is challenging to spectrally engineer a microcomb system to align a comb mode with an atomic clock transition with a sufficient signal-to-noise ratio. Here we adopt a Vernier dual-microcomb scheme for optical frequency division of a stabilized ultranarrow-linewidth continuous-wave laser at 871 nm to an ~235 MHz output frequency. This scheme enables shifting an ultrahigh-frequency (~100 GHz) carrier-envelope offset beat down to frequencies where detection is possible and simultaneously placing a comb line close to the 871 nm laser—tuned so that, if frequency doubled, it would fall close to the clock transition in ¹⁷¹Yb⁺. Our dual-comb system can potentially combine with an integrated ion trap towards future chip-scale optical atomic clocks.

Optical pulse shaping stands as a formidable technique in ultrafast optics, radio-frequency photonics, and quantum communications. While existing systems rely on bulk optics or integrated platforms with planar waveguide sections for spatial dispersion, they face limitations in achieving finer (few- or sub-GHz) spectrum control. These methods either demand considerable space or suffer from pronounced phase errors and optical losses when assembled to achieve fine resolution. Addressing these challenges, we present a foundry-fabricated six-channel silicon photonic shaper using microresonator filter banks with inline phase control and high spectral resolution. Leveraging existing comb-based spectroscopic techniques, we devise a system to mitigate thermal crosstalk and enable the versatile use of our on-chip shaper. Our results demonstrate the shaper’s ability to phase-compensate six comb lines at tunable channel spacings of 3, 4, and 5 GHz. Specifically, at a 3 GHz channel spacing, we showcase the generation of arbitrary waveforms in the time domain. This scalable design and control scheme holds promise in meeting future demands for high-precision spectral shaping capabilities.

We showcase a fully on-chip CMOS-fabricated silicon photonic integrated circuit employing a bidirectionally pumped microring and polarization splitter-rotators tailored for the generation of broadband (>9 THz), high-fidelity (90–98%) polarization-entangled photons. Spanning the optical C+L-band and producing over 116 frequency-bin pairs on a 38.4-GHz-spaced grid, this source is ideal for flex-grid wavelength-multiplexed entanglement distribution in multiuser networks.

In this work, we describe a procedure for synthesizing racetrack resonators with large quality factors and apply it to realize a multi-channel wavelength-selective switch (WSS) on a silicon photonic chip. We first determine the contribution of each component primitive to propagation loss in a racetrack resonator and use this data to develop a model for the frequency response of arbitrary order, coupled-racetrack channel dropping filters. We design second-order racetrack filters based on this model and cascade multiple such filters to form a 1×7 WSS. We find good agreement between our model and device performance with second-order racetrack that have ≈ 1 dB of drop-port loss, ≈ 2 GHz FWHM linewidth, and low optical crosstalk due to the quick filter roll-off of ≈ 5.3 dB $/$ GHz. Using a control algorithm, we show three-channel operation of our WSS with a channel spacing of only 10 GHz. Owing to the high quality factor and quick roll-off of our filter design, adjacent channel crosstalk is measured to be < $-$ 25 dB for channels spaced on a 10 GHz grid. As a further demonstration, we use five of seven WSS channels to perform a demultiplexing operation on both an 8 GHz and a 10 GHz grid. These results suggest that a low-loss WSS with fine channel resolution can be realized in a scalable manner using the silicon photonics platform.

We achieve a broadband near-zero dispersion in a thin silicon nitride waveguide array at near-infrared utilizing the multiple mode couplings. Different orders of modes are coupled at four different wavelengths, generating eight zero dispersion wavelengths (ZDWs). The broadband near-zero dispersion profile within 90 ps/nm/km is achieved, spanning over the spectral range of 1350 - 1900 nm. Using the dispersion engineered waveguide array, an octave-spanning supercontinuum is numerically generated with a pump of 100 fs and 200 pJ. The concept of using multiple mode couplings to obtain broadband near-zero dispersion can be applied to other spectral regimes and material platforms as well, by engineering the structural parameters to shift the positions of the ZDWs.