Center for Relativistic Laser Science

FQMT17

We present our experimental progress for the first demonstration of high-resolution quantum spectroscopy experiment consisting of two type-0 SPDC (spontaneously pumped down converter) crystals pumped by a phase-locked optical frequency comb. Our quantum spectroscopy setup resembles that of the same quantum Mach-Zehnder interferometer of Zeilinger’s recent quantum imaging experiment [1], where the cw pump laser is replaced with the optical frequency comb in order to perform high-resolution quantum spectroscopy. The optical samples (Fabry-Perot interferometer or an atomic/molecular cell) is positioned within the path of the idler beams from the first SPDC crystal, and the transmitted idler photons from the optical sample are arranged into the second SPDC crystal and transmitted through it so that two idler photons, from the first and second SPDC crystals, becomes indistinguishable and reflected off the interferometer, making the two signal photons from the first and second SPDC crystals get path-entangled after the beam splitter. The spectrum of the signal photons can be analyzed by a high-resolution spectrometer in frequency domain or a fast single detector in time domain after Fourier transformed into the frequency domain.

A 250-MHz fiber optical frequency comb of 1 W optical power with 100 fs pulse-width at 1060 nm is frequency-doubled into 530 nm with the bandwidth of 3 nm by using a noncritically phase-matched LBO crystal. The type-0 MgO:PPLN SPDC crystals emit spectrally overlapped signal beams at 810 nm and idler beams at 1540 nm. Total power of 25 mW pump beam at 530 nm is split into two pump beams to pump the two SPDC crystals. In order to form a quantum Mach-Zehender interferometer, we overlapped not only the spatial mode of the Gaussian idler and signal beams, but also the path-length of the two idler and pump beams taking into account of the dispersion of the 100 fs pulses at two non-degenerate signal and idler wavelengths. As an optical sample for the proof-of-principle experiment of highresolution quantum spectroscopy, we used a 10 GHz Fabry-Perot collinear interferometer so that every 40 longitudinal modes of the frequency comb modes of the idler beam intensity is modulated in their transmitted spectrum and in turn their conjugate signal beam spectral intensity. The spectral intensity modulation of the signal beam is detected by a mode-resolved VIPA (virtually imaged phase array) and grating spectrometer.

This work was supported by IBS-R023-D1.

[1] G. B. Lemos, V. Borish, G. D. Cole, S. Ramelow, R. Lapkiewicz, and A. Zeilinger, Nature

512 (2014) 209.