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EP-4075110-B1 - QUANTUM ABSORPTION SPECTROSCOPY SYSTEM AND QUANTUM ABSORPTION SPECTROSCOPY METHOD

EP4075110B1EP 4075110 B1EP4075110 B1EP 4075110B1EP-4075110-B1

Inventors

  • TAKEUCHI, SHIGEKI
  • OKAMOTO, RYO
  • MUKAI, Yu

Dates

Publication Date
20260506
Application Date
20201204

Claims (14)

  1. A quantum absorption spectroscopy system (100, 100A, 200, 300, 300A, 300B, 400, 400A) comprising: a light source (1) configured to emit pump light; a quantum optical system (201, 203, 204, 205) including: a nonlinear optical element (23, 7) that generates a quantum entangled photon pair of a signal photon and an idler photon by irradiation with the pump light; and a phase converter (25, 250) that changes a phase of one photon of the signal photon and the idler photon, and configured to cause quantum interference between a plurality of physical processes in which the quantum entangled photon pair is generated; a photodetector (31, 32) configured to output a quantum interference signal corresponding to a number of detected signal photons when the phase of the one photon is changed by the phase converter (25, 250) in a state where a sample (SP) is disposed on an optical path of the idler photon; and a processor (41) configured to calculate an absorption spectroscopy characteristic of the sample (SP) by performing Fourier transform on the quantum interference signal, characterized in that : the processor calculates a complex transmittance spectrum of the sample (SP) based on a ratio between a Fourier spectrum and a reference Fourier spectrum, the Fourier spectrum obtained by performing Fourier transform on the quantum interference signal in a state where the sample (SP) is disposed on the optical path of the idler photon, the reference Fourier spectrum obtained by performing Fourier transform on the quantum interference signal in a state where the sample (SP) is not disposed on the optical path of the idler photon, and obtains an absolute value of a transmittance of the sample and a phase difference due to the sample from the complex transmittance spectrum.
  2. The quantum absorption spectroscopy system (100, 100A, 200, 300, 300A, 300B, 400, 400A) according to claim 1, wherein the processor (41) calculates an absorption spectrum of the sample (SP) by squaring an absolute value of the complex transmittance spectrum of the sample.
  3. The quantum absorption spectroscopy system (100, 100A, 200, 300, 300A, 300B, 400, 400A) according to claim 1 or 2, wherein the processor (41) calculates the absorption spectroscopy characteristic of the sample (SP) by performing Fourier transform on the quantum interference signal, the quantum interference signal acquired without wavelength sweep of the quantum entangled photon pair and without the signal photon being wavelength-resolved in the quantum optical system (201, 203, 204, 205).
  4. The quantum absorption spectroscopy system (200) according to any one of claims 1 to 3, wherein the nonlinear optical element (7) is a chirp-type or fan-type quasi-phase-matched element.
  5. The quantum absorption spectroscopy system (200) according to any one of claims 1 to 3, wherein the nonlinear optical element (7) is a quasi-phase-matched element including a nonlinear optical crystal (72), the quasi-phase-matched element (7) is configured such that a wavelength of an idler photon group including the idler photon is distributed over a wide wavelength range determined according to a material and a poling period of the nonlinear optical crystal (72) when the quantum entangled photon pair occurs a plurality of times.
  6. The quantum absorption spectroscopy system (200) according to claim 5, wherein the material of the nonlinear optical crystal (72) contains lithium niobate, the poling period of the nonlinear optical crystal (72) is defined such that the idler photon group includes a plurality of photons having wavelengths different from each other in a wavelength range of 0.4 µm to 5.2 µm.
  7. The quantum absorption spectroscopy system (200) according to claim 5, wherein the material of the nonlinear optical crystal (72) contains gallium phosphide, the poling period of the nonlinear optical crystal (72) is defined such that the idler photon group includes a plurality of photons having wavelengths different from each other in a wavelength range of 0.7 µm to 12 µm.
  8. The quantum absorption spectroscopy system (200) according to claim 5, wherein the material of the nonlinear optical crystal (72) contains gallium arsenide, the poling period of the nonlinear optical crystal (72) is defined such that the idler photon group includes a plurality of photons having wavelengths different from each other in a wavelength range of 1 µm to 18 µm.
  9. The quantum absorption spectroscopy system (200) according to claim 5, wherein the material of the nonlinear optical crystal (72) contains lithium tantalate, the poling period of the nonlinear optical crystal (72) is defined such that the idler photon group includes a plurality of photons having wavelengths different from each other in a wavelength range of 0.3 µm to 5.5 µm.
  10. The quantum absorption spectroscopy system (200) according to claim 5, wherein the material of the nonlinear optical crystal (72) contains zinc selenide, the poling period of the nonlinear optical crystal (72) is defined such that the idler photon group includes a plurality of photons having wavelengths different from each other in a wavelength range of 0.4 µm to 22 µm.
  11. The quantum absorption spectroscopy system (400A) according to any one of claims 1 to 10, wherein the quantum optical system (205) further includes a total reflection measuring device (8) that performs total reflection measurement of the sample.
  12. The quantum absorption spectroscopy system (400) according to any one of claims 1 to 11, wherein the phase converter (25, 250, 28, 280) includes a first moving mirror (28) that is movable along a propagation direction of the signal photon, and a second moving mirror (25) that is movable along a propagation direction of the idler photon, the quantum absorption spectroscopy system further includes a controller (4), the controller (4) selectively moves one mirror of the first and the second moving mirrors (28, 25).
  13. The quantum absorption spectroscopy system (100, 100A, 200, 300, 300A, 300B, 400, 400A) according to any one of claims 1 to 3, wherein the nonlinear optical element (23, 7) generates the idler photon in an ultraviolet range, the processor (41) calculates an ultraviolet absorption spectroscopy characteristic of the sample.
  14. A quantum absorption spectroscopy method comprising: generating a quantum entangled photon pair of a signal photon and an idler photon by irradiating a nonlinear optical element (23, 7) with pump light in a quantum optical system (201, 203, 204, 205) that causes quantum interference between a plurality of physical processes in which the quantum entangled photon pair is generated; acquiring a quantum interference signal corresponding to a number of detected photons by detecting the signal photon with a photodetector (31, 32) when a phase of one photon of the signal photon and the idler photon is changed by a phase converter (25, 250) in a state where a sample is disposed on an optical path of the idler photon; and calculating an absorption spectroscopy characteristic of the sample (SP) by performing Fourier transform on the quantum interference signal, characterized in that : the calculating the absorption spectroscopy characteristic includes calculating complex transmittance spectrum of the sample (SP) based on a ratio between a Fourier spectrum and a reference Fourier spectrum, the Fourier spectrum obtained by performing Fourier transform on the quantum interference signal in a state where the sample (SP) is disposed on the optical path of the idler photon, the reference Fourier spectrum obtained by performing Fourier transform on the quantum interference signal in a state where the sample (SP) is not disposed on the optical path of the idler photon, and in that the method further includes obtaining an absolute value of a transmittance of the sample and a phase difference due to the sample from the complex transmittance spectrum.

Description

TECHNICAL FIELD The present disclosure relates to a quantum absorption spectroscopy system and a quantum absorption spectroscopy method. BACKGROUND ART Generally, in an infrared absorption spectroscopy method, a sample is irradiated with infrared light. A change in intensity of infrared light associated with absorption by a sample is acquired as the infrared absorption spectrum of the sample. In particular, Fourier transform infrared spectroscopy (FTIR) is widely used to specify a molecular structure (the type of functional group, or a three-dimensional structure or the like) in fields such as chemistry, biology, and pharmacy. CITATION LIST PATENT LITERATURE PTL 1: U.S. Patent No. 10,648,908 NON PATENT LITERATURE NPL 1:Anna Paterova, Hongzhi Yang, Chengwu An, Dmitry Kalashnikov and Leonid Krivitsky, "Measurement of infrared optical constants with visible photons", New Journal of Physics 20(2018)043015NPL 2: Masayuki Okano, Hwan Hong Lim, Ryo Okamoto, Norihiko Nishizawa, Sunao Kurimura and Shigeki Takeuchi, "0.54 µm resolution two-photon interference with dispersion cancellation for quantum optical coherence tomography", Scientific Reports volume 5, Article number: 18042 (2015)NPL3: Chiara Lindner et al., "Fourier transform infrared spectroscopy with visible light", arxiv.org, 1 November 2019, DOI: 10.1364/OE.382351, URL: https://arxiv.org/ pdf/1909.06864v2.pdf SUMMARY OF INVENTION TECHNICAL PROBLEM In recent years, in the fields of quantum technology such as quantum metrology, quantum communication, and quantum computing, research for achieving a new function using a "quantum entangled" photon pair in which two photons have a quantum mechanical correlation has been advanced. Hereinafter, such a photon pair is also referred to as a "quantum entangled photon pair". The present inventors have focused on the application of the quantum entangled photon pair to a spectroscopy system and a spectroscopy method. The inventors have found that a spectral wavelength range can be expanded by performing appropriate arithmetic processing to a detection signal from a photodetector. The present disclosure has been made to solve such a problem, and an object of the present disclosure is to provide technology allowing spectroscopy in a wide wavelength range in a spectroscopy system or a spectroscopy method (quantum absorption spectroscopy system or quantum absorption spectroscopy method) in which a quantum entangled photon pair is applied. The article NPL3 discloses that an infrared spectrum can be inferred from a Fourier analysis of interferograms measured with a nonlinear Michelson interferometer. The magnitude of the transmittance is calculated. SOLUTION TO PROBLEM The invention is defined by the quantum absorption spectroscopy system of claim 1 and by the corresponding method of claim 14. (1) A quantum absorption spectroscopy system according to a first aspect of the present disclosure includes a light source, a quantum optical system, a photodetector, and a processor. The light source emits pump light. The quantum optical system includes a nonlinear optical element that generates a quantum entangled photon pair of a signal photon and an idler photon by irradiation with the pump light, and a phase converter that changes a phase of one photon of the signal photon and the idler photon. The quantum optical system causes quantum interference between a plurality of physical processes in which the quantum entangled photon pair is generated. The photodetector outputs a quantum interference signal corresponding to a number of detected signal photons when the phase of the one photon is changed by the phase converter in a state where a sample is disposed on an optical path of the idler photon. The processor calculates an absorption spectroscopy characteristic of the sample by performing Fourier transform on the quantum interference signal.(2) In the invention, the processor calculates a Fourier spectrum by performing Fourier transform on the quantum interference signal in a state where the sample is disposed on the optical path of the idler photon, and further calculate a reference Fourier spectrum by performing Fourier transform on the quantum interference signal in a state where the sample is not disposed on the optical path of the idler photon. The processor calculates a complex transmittance spectrum of the sample based on a ratio between the Fourier spectrum and the reference Fourier spectrum.(3) In an embodiment, the processor may calculate an absorption spectrum of the sample by squaring an absolute value of the complex transmittance spectrum of the sample.(4) In an embodiment, the processor may calculate the absorption spectroscopy characteristic of the sample by performing Fourier transform on the quantum interference signal, the quantum interference signal acquired without wavelength sweep of the quantum entangled photon pair and without the signal photon being wavelength-resolved in the quantum optical system.(5) In an e