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Quantum Sensing and Nano Electronics and Photonics

An integrated entangled photons source for mid-infrared ghost spectroscopy

Matteo Sanna, Davide Rizzotti, Stefano Signorini, Lorenzo Pavesi

Published Mar 4, 2022• 2 citations
Publisher

Abstract

In this work, we investigate the application of intermodal spontaneous four wave mixing (SFWM) to ghost spectroscopy in the mid-infrared (MIR) spectral region. This technique is of great interest for MIR sensing, being able to overcome the limitations faced by MIR detectors in terms of background noise and dark counts. Through intermodal SFWM in a Silicon-On-Insulator (SOI) waveguide, two temporally correlated photons are generated: using a standard C-band pump, the idler photon is in the near-infrared (NIR) and the signal photon is in the MIR. The integrated source, with a coincidence to accidental ratio (CAR) of 114 ± 4, is used to demonstrate that, in situations of environmental noise, ghost spectroscopy yields advantages with respect to the traditional absorption spectroscopy. The time-energy entanglement of the photon pairs is used to enhance the visibility of the measurement against noisy background conditions and to increase the spectral resolution in the MIR by spectral filtering the NIR photons. Modeling and experimental data support these improvements.

DOI
10.1117/12.2608514

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In this work, we investigate the application of intermodal spontaneous four wave mixing (SFWM) to ghost spectroscopy in the mid-infrared (MIR) spectral region. This technique is of great interest for MIR sensing, being able to overcome the limitations faced by MIR detectors in terms of background noise and dark counts. Through intermodal SFWM in a Silicon-On-Insulator (SOI) waveguide, two temporally correlated photons are generated: using a standard C-band pump, the idler photon is in the near-infrared (NIR) and the signal photon is in the MIR. The integrated source, with a coincidence to accidental ratio (CAR) of 114 ± 4, is used to demonstrate that, in situations of environmental noise, ghost spectroscopy yields advantages with respect to the traditional absorption spectroscopy. The time-energy entanglement of the photon pairs is used to enhance the visibility of the measurement against noisy background conditions and to increase the spectral resolution in the MIR by spectral filtering the NIR photons. Modeling and experimental data support these improvements.
Sources of quantum correlated photons pairs bridging the 3um-4um Mid-infrared (MIR) band and Telecom/Near-Infrared/Visible band are of high importance for quantum technologies. Spontaneous Parametric Down Conversion is generally used for realizing such sources, but requires costly implementation platforms with reduced versatility. Here, we explore the potentialities of Spontaneous Four-Wave Mixing (SFWM) in all-solid Silicon On Insulator (SOI) waveguides thanks to an experimentally validated model and propose designs ensuring the production of correlated photon pairs bridging the 3um-4um Mid-infrared band and Telecom C-band. Choosing a pump with a wavelength in the range 2100nm-2210nm and a pulse duration of 5ps, we quantitatively performed simulations targeting a probability of photon pair generation per pulse of 0.05, and we found realistic conditions of utilization (2cm-length straight waveguides, intra-modal Four Wave Mixing with the fundamental TE00 mode) with a pump peak power in between 9.2mW and 32mW. A first design (wCOM) reaches a signal wavelength as high as 3.905um, which is situated in an atmospheric transparency window, while maintaining an idler in the Telecom C-band, making it of high interest for atmospheric Quantum Key Distribution. Two other designs wCH4 and wNO2 aim precise CH4 and NO2 gas sensing with a signal wavelength of 3265nm and 3461nm respectively. In terms of signal/idler wavelength separation, wCOM attains the value of 2364nm which is well above the current record of ~1125nm obtained in quantum regime with SFWM in all-solid SOI waveguides.
Abstract A ghost spectroscopy measurement with an entangled photon source is demonstrated. The transmission spectrum at the 2 m absorption peak of gaseous carbon dioxide (CO 2 ) is measured in a highly noisy environment. Despite the noise, a high sensitivity is obtained, a value that is larger than the one found for a classical spectroscopy measurement performed in the same conditions. The probe photons are time‐energy correlated photon pairs generated through intermodal spontaneous four‐wave mixing in a silicon waveguide. This observation opens the way to low‐cost on‐chip MIR sensors insensitive to environmental noise.
Frequency-correlated light offers a route to mid-infrared (MIR) spectroscopy without direct spectral detection in the MIR. Previous MIR ghost spectroscopy has mainly relied on low-gain spontaneous parametric down-conversion (SPDC) and photon-pair coincidence measurements, where the limited photon flux has restricted acquisition times to longer than one minute. Here, we demonstrate ghost infrared spectroscopy using bright twin beams generated by high-gain parametric down-conversion (PDC). High-gain PDC amplifies vacuum fluctuations, producing a different pair of frequency-correlated random spectra in each pump pulse. This pulse-resolved stochastic emission is naturally matched to time-stretch detection, which records the spectrum of the correlated near-infrared telecom signal for every pulse, while the MIR idler is measured by bucket detection. Consequently, each pump pulse yields one paired projection measurement comprising a spectrally resolved reference and the corresponding bucket value. We reconstruct the transmission spectrum of a structured optical filter and the molecular vibrational absorption spectrum of liquid benzene near 3.3 um with millisecond-scale acquisition, in good agreement with Fourier-transform infrared spectroscopy. This reduces the acquisition time by four to five orders of magnitude compared with previous MIR ghost spectroscopy demonstrations. These results transform ghost spectroscopy from coincidence-based photon counting to high-flux analog correlation spectroscopy, establishing a practical architecture for high-speed computational infrared spectroscopy driven by a narrowband semiconductor laser.
Mid-infrared (MIR) spectroscopy serves as a powerful tool for molecular structure identification and chemical composition analysis. However, conventional Fourier-transform infrared spectrometers (FTIR) demonstrate compromised signal-to-noise ratios (SNR) under low-light conditions, which severely limit their performance in high-sensitivity applications. Although MIR superconducting nanowire single-photon detectors (SNSPDs) offer high detection efficiency and low timing jitter, their performance is hindered by background dark counts caused by room-temperature blackbody radiation. In this work, we present a quantum-correlated absorption spectroscopy platform that combines MIR-SNSPDs with entangled photon pairs to overcome these limitations. Leveraging the intrinsic temporal and spectral correlations of the photon pairs, coincidence detection effectively distinguishes signal photons from dominant thermal noise, achieving a remarkable improvement of two orders of magnitude in SNR under ultralow pump power conditions. The system achieves a spectral coverage of 3350-3540 nm with a resolution of 3.7 cm -1 at 3.4 µm, operating at an ultralow illumination photon flux of 4.4 × 10 6 photons/s. Validation experiments using polystyrene and polyethylene samples successfully detected CH 2 vibrational modes, demonstrating the platform’s capability for ultrasensitive biochemical analysis and material characterization. By integrating quantum correlation with MIR-SNSPDs, this work establishes a new paradigm for high-performance MIR spectroscopy in low-light scenarios.
Mid-infrared integrated quantum photonics is a promising platform for applications in sensing and metrology. However, there are only a few examples of on-chip single-photon sources at these wavelengths. These have limited performances with respect to their C-band counterparts. In this work, we demonstrate a new approach to generate heralded single photons in the mid-infrared on a silicon chip. By using a standard C-band pump, the inter-modal spontaneous four-wave mixing enables the generation of the herald idler at 1259.7 nm and the heralded signal at 2015 nm. The idler photon is easily detected with a common infrared single-photon detector while the signal photon is upconverted to visible before its detection. In this way, we are able to operate a mid-infrared source without the need for mid-infrared detectors and laser sources. By measuring a heralded g(2) of 0.23 ± 0.08, we demonstrate the single-photon behavior of the source as well as the feasibility of multi-photon coincidence measurements beyond 2 μm with our setup. The source exhibits a high-intrinsic heralding efficiency of (59 ± 5)%, a maximum coincidence to accidental ratio of 40.4 ± 0.9, and a generation probability of 0.70±0.10W−2.
The emissions of two identical spontaneous parametric down-conversion (SPDC) sources pumped coherently, e.g. with the same beam (c.f. Fig. 1(a)), show interference in both, the signal and idler light. This phenomenon results from the indistinguishability of the photon pairs emitted by the identical sources [1]. If a medium between the two SPDC sources absorbs the idler light, the photon pairs from the first and second SPDC source become distinguishable and the interference contrast decreases for both, signal and idler light. By measuring the signal light spectrum in the visible or near-infrared (NIR) range and the corresponding interference contrast, we obtain the information about the idler light absorption of the analyte in the mid-infrared (MIR). Hereby, we enable spectroscopy in the MIR using a standard silicon detector, making detection easier and more efficient than using typical MIR detectors [2].