Quantum Parametric Mode Sorting: Beating the Time-Frequency Filtering

Abstract

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.

Modal phase matched lithium niobate nanocircuits for integrated nonlinear photonics

“…This can be an important feature for all-optical classical or quantum information processing on-chip. 34,35…”

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

“…The immediate future work is to adopt the quantum optical arbitrary waveform technique 35 for both photon pair generation and upconversion detection, which will potentially improve the coincidence-to-accidental coincidence ratio by >20 times (to over 1000) while further suppressing background noise photons. The same technique can be used to create high-dimensional entanglement, which will further increase the robustness of the quantum free space applications against even some of the most challenging atmospheric conditions.…”

“…This rather narrow phase matching bandwidth intrinsically filters out background photons outside the idler band. Even for those in-band noise photons, further rejection is attainable by using broadband, mode-shaped upconversion pump pulses approach the phase matching limit 35 . This is especially advantageous for quantum applications in the mid-IR regime where substantial background noise exists, such as from the blackbody radiation.…”

Tailoring nonlinear processes for quantum optics with pulsed temporal-mode encodings

“…Applying their waveform generation and numerical optimisation to this situation, they were able to demonstrate efficiencies above 75% for a four-dimensional Hermite-Gaussian alphabet with separabilities above 65% and as high as 87% for picosecondscale Gaussian pulses [98]. These results have been extended to novel mode-selective pulse-shaping schemes based on over-conversion in SFG [107] and demonstrations of mode-selective upconversion with efficiencies and selectivities high enough to outperform time-frequency filtering for signal isolation [108].…”