CMOS-compatible Kerr microcombs have drawn substantial interest as mass-manufacturable, compact alternatives to bulk frequency combs. This could enable 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 due to the ∼THz repetition rates typically required for octave-spanning comb generation. Additionally, it is challenging to spectrally engineer a microcomb system to align a comb mode with an atomic clock transition with 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 a ∼235 MHz output frequency. In addition to enabling measurement of the comb repetition rates, this scheme brings the freedom to pick comb lines from either or both of the combs. We exploit this flexibility to shift an ultra-high-frequency (∼100 GHz) carrier-envelope offset beat down to frequencies where detection is possible and to place 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^+. Moreover, we introduce a novel scheme which suppresses frequency noise arising from interferometric phase fluctuations in our dual-comb system and reduces the frequency instability down to our measurement limit. Our dual-comb system can potentially combine with an integrated ion trap toward future chip-scale optical atomic clocks.

We introduce what we believe to be novel spectral light detection and ranging (LiDAR) architectures that enable ultra-compact systems by a transition from spectral signal processing in space (gratings) to processing in time. The architectures leverage temporal dispersion and the unique spectro-temporal waveforms produced from the cascaded Raman scattering generated in the (H-2) filled hollow core fiber. The characterized Raman source yields as many as six Raman orders from 1.06-1.70 mu m; their unique spectro-temporal waveforms are measured. System performance simulations based on measured Raman waveforms show that high accuracy measurement of range and reflectivity are possible with proper selection of signal-to-noise ratio and detector bandwidth. Materials classification analysis based on the system performance analysis shows that near-optimal classification is feasible with time domain processing.

We present a multispectral LiDAR source based on stimulated Raman scattering in a pressurized oxygen-filled antiresonant fiber. The 1.064 $\mu m$ laser, two generated vibrational Stokes orders, and surrounding rotational orders are contained in and spectrally fill the SWIR atmospheric transmission windows.

We use the Vernier dual-comb method to separately detect and stabilize the ~ THz rep rate and ~100 GHz carrier envelope offset frequency of an octave spanning Kerr comb - both outside the bandwidth of conventional electronics.

Wavelength conversion afforded by stimulated Raman scattering within a hollow core fiber is potentially useful for multispectral light detection and ranging (LiDAR). Herein, we make use of the ideal 1550 cm−1 vibrational Raman shift of an antiresonant fiber filled with gaseous oxygen so that the first and second Raman orders as well as the transmitted pump are all located in separate atmospheric transmission windows. To the best of our knowledge, this is the first report of stimulated Raman scattering in an oxygen-filled fiber. The host of closely spaced rotational stimulated Raman scattering (SRS) lines (12 cm−1) accompanying the transmitted pump and vibrational Raman orders form continuum bands allowing for much greater spectral coverage of the atmospheric transmission windows. The temporal profiles of the Raman orders can be separated without the use of a grating to potentially achieve a multi-band LiDAR.

We use the Vernier dual-comb scheme to stabilize two octave-spanning Kerr microcombs with similar to THz repetition rate realized in a CMOS-compatible silicon nitride platform.

We demonstrate microcomb-based frequency division from a narrow-linewidth 871nm laser to a radio-frequency clock output. We introduce a noise suppression scheme to mitigate the fiber interferometric noise experienced by the system.

Leveraging the Vernier dual-comb method, we self-reference a THz octave¬spanning microcomb with f CEO ~100 GHz - normally too high for typical detection equip¬ment - and translate the stability of an RF reference to optical frequencies.

We demonstrate an architecture for dualmicrocomb-based readout of an optical clock. Microcombs frequency-divide a compact narrow-linewidth laser, capable of being frequency-doubled to within a few GHz of a 171 Yb + clock transition, to an RF output.

Electronic analog to digital converters (ADCs) are running up against the well-known bit depth versus bandwidth trade off. Towards this end, radio frequency (RF) photonic-enhanced ADCs have been the subject of interest for some time. Optical frequency comb technology has been used as a workhorse underlying many of these architectures. Unfortunately, such designs must generally grapple with size, weight, and power (SWaP) concerns, as well as frequency ambiguity issues which threaten to obscure critical spectral information of detected RF signals. In this work, we address these concerns via an RF photonic downconverter with potential for easy integration and field deployment by leveraging a novel, to the best of our knowledge, hybrid microcomb/electro-optic comb design.

We demonstrate a novel Vernier dual-comb based method for the detection and division of a microcomb's carrier envelope offset frequency that is beyond the bandwidth of typical commercial detection electronics.

Recent developments in Kerr microcombs may pave the way to a future with fully stabilized ultralow size, weight, and power consumption (SWaP) frequency combs. Nevertheless, Kerr microcombs are still hindered by a bandwidth/repetition rate trade-off. That is, the octave bandwidth needed for self-referencing is typically realized only with ∼THz repetition rates beyond the range of standard commercial photodetectors. The carrier envelope offset frequency is often likewise too high for detection. Dual-comb techniques for the measurement of THz repetition rates have made exciting progress, but the f CEO detection problem remains largely unaddressed. In this work, utilizing a Vernier dual-comb configuration, we demonstrate simultaneous detection of the electronically divided repetition rate and f CEO carrier envelope offset frequency of an octave-spanning microcomb. This, in turn, could help usher optical atomic clocks, low-noise microwave generators, and optical frequency synthesizers into various real-world applications.

We demonstrate the use of a dual comb photonic system for downconversion and disambiguation of RF signals ranging from 4.3 GHz to 17.3 GHz. Our system has future potential for miniaturization, a key for deployment in real-world applications.

Owing in large part to the advent of integrated biphoton frequency combs (BFCs), recent years have witnessed increased attention to quantum information processing in the frequency domain for its inherent high dimensionality and entanglement compatible with fiber-optic networks. Quantum state tomography (QST) of such states, however, has required complex and precise engineering of active frequency mixing operations, which are difficult to scale. To address these limitations, we propose a novel solution that employs a pulse shaper and electro-optic phase modulator (EOM) to perform random operations instead of mixing in a prescribed manner. We successfully verify the entanglement and reconstruct the full density matrix of BFCs generated from an on-chip Si$_{3}$N$_{4}$ microring resonator(MRR) in up to an $8\times8$-dimensional two-qudit Hilbert space, the highest dimension to date for frequency bins. More generally, our employed Bayesian statistical model can be tailored to a variety of quantum systems with restricted measurement capabilities, forming an opportunistic tomographic framework that utilizes all available data in an optimal way.

We demonstrate a Bell state analyzer that operates directly on frequency mismatch. Based on electro-optic modulators and Fourier-transform pulse shapers, our quantum frequency processor design implements interleaved Hadamard gates in discrete frequency modes. Experimental tests on entangled-photon inputs reveal fidelities of ∼ 98 % for discriminating between the | Ψ + ⟩ and | Ψ − ⟩ frequency-bin Bell states. Our approach resolves the tension between wavelength-multiplexed state transport and high-fidelity Bell state measurements, which typically require spectral indistinguishability.

We generate all four frequency-bin Bell states via single and dual spectral-line pumping of spontaneous parametric down-conversion and demonstrate their sensitivity to the sum and difference of entangled-photon delays using spectral interferometry.

We report the experimental generation of all four frequency-bin Bell states in a single versatile setup via successive pumping of spontaneous parametric down-conversion with single and dual spectral lines. Our scheme utilizes intensity modulation to control the pump configuration and offers turn-key generation of any desired Bell state using only off-the-shelf telecommunication equipment. We employ Bayesian inference to reconstruct the density matrices of the generated Bell states, finding fidelities ≥97% for all cases. Additionally, we demonstrate the sensitivity of the frequency-bin Bell states to common-mode and differential-mode temporal delays traversed by the photons comprising the state-presenting the potential for either enhanced resolution or nonlocal sensing enabled by our complete Bell basis synthesizer.

Suparna Seshadri, Navin Lingaraju, Hsuan-Hao Lu, Poolad Imany, 3 Daniel E. Leaird, and Andrew M. Weiner School of Electrical and Computer Engineering and Purdue Quantum Science and Engineering Institute, Purdue University, West Lafayette, Indiana 47907, USA National Institute of Standards and Technology, Boulder, CO 80305, USA Department of Physics, University of Colorado, Boulder, CO 80309,USA (Dated: February 25, 2022)

Timing and positioning measurements are key requisites for essential quantum network operations such as Bell state measurement. Conventional time-of-flight measurements using single-photon detectors are often limited by detection timing jitter. In this work, we demonstrate a nonlocal scheme to measure changes in relative link latencies with subpicosecond resolution by using tight timing correlation of broadband time-energy entangled photons. Our sensing scheme relies on spectral interference achieved via phase modulation, followed by filtering and biphoton coincidence measurements, and is resilient to microsecond-scale mismatch between the optical link traversed by the biphotons. Our experiments demonstrate a precision of +/-0.04 ps in measurements of nonlocal delay changes and +/-0.7{\deg} in measurements of radio-frequency phase changes. Furthermore, we complement our technique with time-tag information from single-photon detectors in the same setup to present unambiguous sensing of delay changes. The proposed technique can be implemented using off-the-shelf telecom equipment thus rendering it adaptable to practical quantum network infrastructure.

We utilize the Vernier effect to partially stabilize a pair of high repetition rate, octave-spanning Kerr solitons in silicon nitride microrings fabricated on the same wafer.