Room-temperature THz photon detection via nonlinear upconversion with 2% full-system efficiency

TL;DR

This paper demonstrates a novel room-temperature THz photon detector using nonlinear upconversion in an organic crystal, achieving 2% efficiency and enabling quantum-level THz measurements in ambient conditions.

Contribution

The authors introduce a highly efficient, room-temperature THz detection method based on nonlinear upconversion in BNA crystals, surpassing previous low-temperature or less efficient techniques.

Findings

Achieved 2% overall detection efficiency for THz photons.

Detected pulses with fewer than 0.04 photons on average at unity signal-to-noise ratio.

Converted more than 75% of THz photons to near-infrared photons in BNA.

Abstract

Sensitive detection of terahertz (THz) radiation is fundamental to progress in spectroscopy, advanced wireless communication, and the realization of emerging quantum technologies. However, the intrinsically low photon energies in the THz range combined with thermal background radiation tend to constrain detector performance when operating at ambient temperatures. Here, we demonstrate efficient room-temperature THz detection based on nonlinear upconversion in the organic crystal N-benzyl-2-methyl-4-nitroaniline (BNA) to resolve frequencies from 1 to 7.5 THz. The system encompassing spectral filters and a single-photon counter achieves an overall detection efficiency of 2% for sum-frequency generated photons. This enables the detection of a train of 50 000 terahertz pulses carrying, on average, fewer than 0.04 photons per pulse, with a signal-to-noise ratio of unity. At a higher flux, when ~60 photons per pulse impinge on the BNA crystal, the per-pulse detection probability reaches 50%. After accounting for loss mechanisms in the setup, the nonlinear THz-to-near-infrared conversion efficiency in BNA exceeds 75%. These results demonstrate the feasibility of quantum experiments relying on single-photon-level THz detection via upconversion in nonlinear crystals in ambient conditions.