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arXiv:quant-ph/0306154 · Physical Review A

Spectroscopy by frequency-entangled photon pairs

Atsushi Yabushita, Takayoshi Kobayashi

Published Jan 14, 2004• 136 citations
arXivHTMLPDF

Abstract

Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.

DOI
10.1103/physreva.69.013806

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Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.
Classical time-resolved optical spectroscopy experiments are performed using sequences of ultrashort light pulses, with photon fluxes incident on the sample which are many orders of magnitude higher than real-world conditions corresponding to sunlight illumination. Here we overcome this paradigm by exploiting quantum correlations to perform time-resolved spectroscopy with entangled photons. Starting from spontaneous parametric down-conversion driven by a continuous-wave laser, we exploit the temporal entanglement between randomly generated signal/idler pairs to obtain temporal resolution, and their spectral entanglement to select the excitation frequency. We also add spectral resolution in detection, using a Fourier transform approach which employs a common-path interferometer. We demonstrate the potential of our entangled-photon streak camera by resolving, at the single-photon level, excitation energy transfer cascades from LH2 to LH1 in the photosynthetic membrane and disentangling the lifetimes of two dyes in a mixture. We show that time-resolved spectroscopy with quantum light can be performed without compromising measurement time, recording a fluorescence time trace in less than a minute even for samples with low quantum yield, which can be reduced to sub-second times with acceptable signal-to-noise ratio. Our results provide a new approach to ultrafast optical spectroscopy, where experiments are performed under conditions comparable to real-world sunlight illumination.
Abstract We report an experimental implementation of linear absorption spectroscopy using a fiber source of frequency-correlated photon pairs. The object under study is illuminated by a signal beam of a photon pair entangled in frequency. Due to the tight correlation of entangled photons, the absorption spectrum of the object can be measured from the idler beam, counting coincidences in both channels. The main advantages of ghost optics are analyzed, including significant noise reduction due to detecting only paired coincidences and cutting off all single background photons, as well as the potential sensitivity of studying samples, which is especially important when working with biological objects.
Quantum light is a key resource for promoting quantum technology. One such class of technology aims to improve the precision of optical measurements using engineered quantum states of light. In this study, we investigate transmission measurement of frequency-entangled broadband photon pairs generated via parametric down-conversion with a monochromatic laser. It is observed that state-to-state dynamics in the system under study are temporally resolved by adjusting the path difference between the entangled twin beams when the entanglement time is sufficiently short. The non-classical photon correlation enables time-resolved spectroscopy with monochromatic pumping. It is further demonstrated that the signal corresponds to the spectral information along anti-diagonal lines of, for example, two-dimensional Fourier-transformed photon-echo spectra. This correspondence inspires us to anticipate that more elaborately engineered photon states would broaden the availability of quantum light spectroscopy.
It has been known for some time that correlated detection of pairs of photons generated by parametric down-conversion can eliminate several sources of error that occur in single-beam measurements. In the correlated photon measurements, the down-converted photons are separated into two beams with one photon of a pair in each beam. The absolute detection efficiency of a detector in one beam can be determined from the count rate of a detector in the other beam and the coincidence rate for the two detectors. These ideas can be used to measure the optical absorbance of a sample placed in front of one of the detectors. Errors due to stray light and dark counts are substantially reduced and fluctuations in pump intensity largely eliminated.
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.
Broadband photon-pairs from a parametric down-conversion (PDC) source are essential for quantum optics experiments in the context of spectroscopy, quantum optical coherence tomography and entangled two-photon absorption [1]–[2]. Entangled two-photon absorption benefits from the ultra-short correlation time of a highly time-frequency entangled photon-pair which increases the absorption cross-section while in spectroscopy, broad spectral coverage in the mid-infrared allows one to enter the regime of life science applications.