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Quantum Sensing and Nano Electronics and Photonics

Remote fiber sensing by quantum spectroscopy using frequency entangled photons via a real-world fiber network

Masahiro Ishizeki, Tomoya Okita, Akifumi Asahara, Ryōsuke Shimizu, Kaoru Minoshima

Published Jan 23, 2025• 0 citations
Publisher

Abstract

Quantum optics has attracted significant interest owing to its potential for novel applications in fields such as computing, communication, and sensing. With advancements in single photon generation and detection in the telecom band, quantum remote applications utilizing the nonlocality of entangled photon pairs are becoming increasingly viable. In this study, we demonstrate quantum remote spectroscopy by transmitting frequency entangled photons through a real-world fiber network. In the experiment, entangled photon pairs in the telecom band (photon 1 and photon 2) were generated via spontaneous parametric down-conversion in a type-II PPMgSLT crystal using a mode-locked Ti:Sapphire laser (76MHz repetition rate, 792nm center wavelength). The photon pairs were separated with a fiber polarization beam splitter. Photon 1 was transmitted through a 2.6-km real-world fiber network and programmable spectral filter, serving as the sample under investigation. Both photons were detected using superconducting single photon detectors (SSPDs). Quantum frequency correlation, termed joint spectral intensity (JSI), was obtained as a two-dimensional histogram utilizing coincidence counting and time-stretch methods. The spectrum of photon 2, which did not transmit fiber network and spectral filter, was obtained by projecting the JSI. Although photon 1 interact with the fiber network and programmable filter, the spectrum of photon 2 exhibited strong agreement with the reference spectrum defined by programmable filter. Finally, one photon of the pair was transmitted over a 2.6km real-world fiber network with a fiber sensor. Using quantum frequency correlation, the spectral information of the fiber sensor was deduced remotely from the spectrum of the counter part of the photon, which did not directly interact with the sensor. This demonstrated the feasibility of remote spectroscopic sensing using frequency entanglement via a real-world fiber network. The findings pave the way for practical quantum remote spectroscopy, obviating the need for sophisticated spectroscopic equipment at the remote site.

DOI
10.1117/12.3041068

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Quantum optics has attracted significant interest owing to its potential for novel applications in fields such as computing, communication, and sensing. With advancements in single photon generation and detection in the telecom band, quantum remote applications utilizing the nonlocality of entangled photon pairs are becoming increasingly viable. In this study, we demonstrate quantum remote spectroscopy by transmitting frequency entangled photons through a real-world fiber network. In the experiment, entangled photon pairs in the telecom band (photon 1 and photon 2) were generated via spontaneous parametric down-conversion in a type-II PPMgSLT crystal using a mode-locked Ti:Sapphire laser (76MHz repetition rate, 792nm center wavelength). The photon pairs were separated with a fiber polarization beam splitter. Photon 1 was transmitted through a 2.6-km real-world fiber network and programmable spectral filter, serving as the sample under investigation. Both photons were detected using superconducting single photon detectors (SSPDs). Quantum frequency correlation, termed joint spectral intensity (JSI), was obtained as a two-dimensional histogram utilizing coincidence counting and time-stretch methods. The spectrum of photon 2, which did not transmit fiber network and spectral filter, was obtained by projecting the JSI. Although photon 1 interact with the fiber network and programmable filter, the spectrum of photon 2 exhibited strong agreement with the reference spectrum defined by programmable filter. Finally, one photon of the pair was transmitted over a 2.6km real-world fiber network with a fiber sensor. Using quantum frequency correlation, the spectral information of the fiber sensor was deduced remotely from the spectrum of the counter part of the photon, which did not directly interact with the sensor. This demonstrated the feasibility of remote spectroscopic sensing using frequency entanglement via a real-world fiber network. The findings pave the way for practical quantum remote spectroscopy, obviating the need for sophisticated spectroscopic equipment at the remote site.
We demonstrate the suitability of fiber-generated entangled photon pairs for practical quantum communications in the telecom band by measuring their properties with superconducting single-photon detectors that produce negligible dark counts. The photon pairs are created in approximately 5-ps duration windows at 50 MHz rate while the detectors are operated in ungated free running mode. We obtain a coincidence to accidental-coincidence ratio >80 with raw photon-counting data, i.e., without making any post-measurement corrections. Using a previously demonstrated counter-propagating scheme we also produce polarization-entangled photon pairs at 50-MHz rate, which in coincidence detection directly yield two-photon interference with a fringe visibility >98%.
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This thesis describes work on single-photon pair creation, entanglement and entanglement measurement; single-photon spectral narrowing for atomic interaction; and single-photon detection and spectral analysis. The systems developed exploit the interactions of light beams in non-linear crystal materials. Greatly non-degenerate time-bin entangled photon pair sources are implemented based on the quantum process of spontaneous-parametric-down-conversion. The non-degenerate wavelengths correspond to an atomic transition (895 nm) and a telecommunications band (1310 nm). Interference-fringe-visibilities of over 78% are achieved, verifying entanglement. An efficient and low-noise single-photon up-conversion detector based on sum-frequency-generation is implemented. Photons at 1310 nm are converted to the visible region and efficiently detected using a visible single-photon detector. An overall detection efficiency of over 32% is achieved with a dark-count noise rate of 2500 s-1. The detector is further developed to achieve an inter-symbol-interference free detection rate at twice the limit of the type of visible detector used. The detector is adapted into an up-conversion spectrometer for wavelengths near 1310 nm. A sensitivity of -126 dBm is achieved, corresponding to photon fluxes of approximately 500 s-1. The up-conversion spectrometer is further adapted for correlated biphoton spectroscopy by incorporating a frequency entangled and time correlated source. In this scheme, the spectral function near 895 nm of a remote object can be reproduced by locally measuring the 1310 nm with the up-conversion spectrometer and monitoring the coincidence detection rates. To achieve linewidths feasible for atomic interaction, a very narrow linewidth non-degenerate single-photon pair source is implemented based on spontaneous-parametric-down-conversion embedded in a singly-resonant cavity which is locked to and resonating at the frequency corresponding to a target atomic transition. Linewidths as narrow as 28 MHz are achieved. The brightness of the source within the modes is increased by two-orders compared to the single-pass implementations.
The nonclassical light sources, such as frequency-time entangled photons, are anticipated to offer significant benefits for emerging quantum optical sensing or spectroscopic measurements and manifest on ultrafast time scales (sub-ps to fs). However, the constrained time resolution (ns to ps) of photon-counting detectors poses challenges in comprehensively characterizing their detailed properties on ultrafast time scales. Therefore, we present a novel asynchronous optical sampling (ASOPS) technique utilizing two-color optical frequency combs to demonstrate highly precise and sensitive ultrafast time-resolved cross-correlation measurements at the single-photon level. By employing photon counting statistics, this method successfully reconstructed the picosecond pulse width cross-correlation waveforms at extremely low power level (<1 photon per pulse), while effectively suppressing the residual temporal jitter between the two combs via optically triggered averaging using asynchronous optical sampling of combs. The use of repetition frequency stabilized distinct-wavelength pulses allowed for the effective suppression of strong background light from the pump through spectral filtering, achieving single-photon sensitivity. Subsequently, we parametrically down converted the frequency doubled light from the Er comb in the nonlinear ppKTP waveguide to generate quantum entangled photons at telecom band. A 9.04% Klyshko efficiency with a photon pair generation rate of 0.98 MHz/mW was obtained using heralding detection. Employing the established ASOPS technique to the generated photon pairs enabled the realization of ultrafast time-resolved and quantum mechanical correlation measurements. This paves the way for a versatile and comprehensive manipulation of quantum-entangled photon pairs in the time-domain, with potential applications in ultrafast optical quantum technology and ultrashort fluorescence measurements.
We present an all-optical method for synchronizing remote quantum network stations dedicated to the generation or the storage of photonic entanglement. We apply our method to the connection of two sources emitting pairs of photons at telecom wavelengths. Our experimental setup is based on a pulsed telecom fiber laser operating at 2.5 GHz that pumps, after frequency doubling, two nonlinear waveguide photon-pair sources. Our synchronization scheme is validated via the implementation of a two-photon interference experiment performed at the relay station, i.e. where the Bell state measurement takes place. We show a raw visibility greater than 90%, obtained in the 4-fold coincidence counts, for a separation distance of 100 km between the photon- pair sources. This result demonstrates the relevance of our approach.
Quantum spectroscopy with undetected photons (QSUP) utilizing the quantum entanglement of parametrically down-converted photons has emerged as a new spectroscopic platform. Here, we demonstrate a high-resolution and remote-measurement QSUP, where light-matter interactions and photon detections are performed in spectrally and spatially different regions. A dual-stimulated parametric down-conversion scheme with an optical frequency-comb pump and ultra-narrow coherent seed beam in an idler mode is used to generate path-entangled pairs of the undetected idler and measured frequency-comb signal photons. To demonstrate the frequency resolution of this scheme, a Fabry-Pérot cavity with a narrow bandwidth is used as a sample that modulates the distinguishability of one-photon-added coherent idler beams, which directly affects the interference fringe visibility of the entangled signal photons. We thus anticipate that the remote QSUP whose frequency resolution is determined by the linewidth of the coherent seed laser will enable the development of quantum spectroscopy featuring high resolution.