Yong Meng Sua

Quantum Parametric Mode Sorting: Beating the Time-Frequency Filtering

Selective detection of signal over noise is essential to measurement and signal processing. Time-frequency filtering has been the standard approach for the optimal detection of non-stationary signals. However, there is a fundamental tradeoff between the signal detection efficiency and the amount of undesirable noise detected simultaneously, which restricts its uses under weak signal yet strong noise conditions. Here, we demonstrate quantum parametric mode sorting based on nonlinear optics at the edge of phase matching to improve the tradeoff. By tailoring the nonlinear process in a commercial lithium-niobate waveguide through optical arbitrary waveform generation, we demonstrate highly selective detection of picosecond signals overlapping temporally and spectrally but in orthogonal time-frequency modes as well as against broadband noise, with performance well exceeding the theoretical limit of the optimized time-frequency filtering. We also verify that our device does not introduce any significant quantum noise to the detected signal and demonstrate faithful detection of pico-second single photons. Together, these results point to unexplored opportunities in measurement and signal processing under challenging conditions, such as photon-starving quantum applications.

Direct Generation and Detection of Quantum Correlated Photons with 3.2 um Wavelength Spacing

Quantum correlated, highly non-degenerate photons can be used to synthesize disparate quantum nodes and link quantum processing over incompatible wavelengths, thereby constructing heterogeneous quantum systems for otherwise unattainable superior performance. Existing techniques for correlated photons have been concentrated in the visible and near-IR domains, with the photon pairs residing within one micron. Here, we demonstrate direct generation and detection of high-purity photon pairs at room temperature with 3.2 um wavelength spacing, one at 780u2009nm to match the rubidium D2 line, and the other at 3950u2009nm that falls in a transparent, low-scattering optical window for free space applications. The pairs are created via spontaneous parametric downconversion in a lithium niobate waveguide with specially designed geometry and periodic poling. The 780u2009nm photons are measured with a silicon avalanche photodiode, and the 3950u2009nm photons are measured with an upconversion photon detector using a similar waveguide, which attains 34% internal conversion efficiency. Quantum correlation measurement yields a high coincidence-to-accidental ratio of 54, which indicates the strong correlation with the extremely non-degenerate photon pairs. Our system bridges existing quantum technology to the challenging mid-IR regime, where unprecedented applications are expected in quantum metrology and sensing, quantum communications, medical diagnostics, and so on.

Observation of Quantum Zeno Blockade on Chip.

Overlapping in an optical medium with nonlinear susceptibilities, lightwaves can interact, changing each other’s phase, wavelength, waveform shape, or other properties. Such nonlinear optical phenomena, discovered over a half-century ago, have led to a breadth of important applications. Applied to quantum-mechanical signals, however, these phenomena face fundamental challenges that arise from the multimodal nature of the interaction between the electromagnetic fields, such as phase noises and spontaneous Raman scattering. The quantum Zeno blockade allows strong interaction between lightwaves without physical overlap between them, thus offering a viable solution for the aforementioned challenges, as indicated in recent bulk-optics experiments. Here, we report on the observation of quantum Zeno blockade on chip, where a lightwave is modulated by another in a distinct “interaction-free” manner. For quantum applications, we also verify its operations on single-photon signals. Our results promise a scalable platform for overcoming several longstanding challenges in applied nonlinear and quantum optics, enabling manipulation and interaction of quantum signals without decoherence.

Quantum Airy photons

With exotic propagation properties, optical Airy beams have been well studied for innovative applications in communications, biomedical imaging, micromachining, and so on. Here we extend those studies to the quantum domain, creating quantum correlated photons in finite-energy Airy transverse modes via spontaneous parametric down conversion and sub-sequential spatial light modulation. Through two-photon coincidence measurements, we verify their Airy spatial wavefunctions, propagation along a parabolic trajectory, and that the spatial modulation does not introduce any observable degradation of quantum correlation between the photons. These results suggest the feasibility of using spatially structured photons for practically advantageous quantum applications.

Observation of quantum Zeno blockade on chip

Quantum Zeno blockade offers a distinct approach to signal manipulation and logic operations in a counterintuitive “interaction-free” implementation. Previous experimental studies have used nonlinear waveguides and optical cavities, both in bulk-optics settings. We report the observation of quantum Zeno blockade in a chip-integrable platform, whose results point to all-optical information processing on a single photon level.

On-Chip Demonstration of Interaction-free Quantum Switching

Quantum Zeno blockade allows all-optical switching in a counterintuitive “interaction-free” manner. Using a lithium-niobate microdisk cavity nanofabricated on chip, we have observed phase matched sum-frequency generation and interaction-free switching between optical pulses in two tightly confined whispering-gallery modes. We have also verified that our device is suitable for nonlinear operations in a single-photon regime. Our results point to a scalable, chip-integrated platform for nonlinear optics extendable to the quantum regime.