Abstract
Due to their frequency scaling and long-term coherence, frequency combs at the single-photon level can provide a fascinating platform for developments in quantum technology. Here we demonstrate frequency comb single-photon interferometry in an unheralded manner. We are able to induce coherence by erasing the which-way information of path-entangled photon pairs. The photon pairs are prepared using a dual parametric down-conversion pumped by a highly stable frequency comb laser and an ultra-narrow seed laser. This is conducted at the extremely low-conversion efficiency regime. The unique feature of our quantum interferometer is that the induced one-photon interference of the path-encoded single photons (signal), with multiple frequency components, is observed with a unit visibility without heralding conjugate photons (idler). We demonstrate that quantum information and frequency comb technology can be combined to realize quantum information platforms. We expect this will contribute to the application of quantum information and optical measurements beyond the classical limit.
Highlights
Due to their frequency scaling and long-term coherence, frequency combs at the singlephoton level can provide a fascinating platform for developments in quantum technology
Experimental schemes based on pathentangled photons use the induced quantum coherence of single photons generated from two spontaneous parametric down-conversion (SPDC) crystals, where the induced coherence resulted from erasing the which-path information of their conjugate photons[53]
Interferometry involves two stimulated parametric down-conversions (StPDCs), where the secondharmonic generation (SHG) comb is used as a pump and an additional ultra-narrow linewidth (1 Hz) CW laser at an idler wavelength of 1542 nm is used as a seed beam stimulating multiple frequency comb components at the signal wavelength
Summary
Due to their frequency scaling and long-term coherence, frequency combs at the singlephoton level can provide a fascinating platform for developments in quantum technology. By placing an optical material on the idler pathway, the degree of path-indistinguishability for the generated idler photons, which depends on the amplitude and phase change of the transmitted idler field, can be controlled, and the visibility of the interference fringe of the conjugate signal photons can be modulated in an unheralded way This method utilizing the signal-idler quantum entanglement enables material properties to be measured separately from probing the material via idler photon–matter interaction. We demonstrate experimentally and explain theoretically that, by combining the frequency comb technology and the quantum optical measurement method with undetected photons, frequency comb single-photon interferometry (FC-SPI) is feasible This shows that the quantum interference of signal single-photon frequency combs can be produced by erasing the which-path information of idler photons by making the idler single-photon-added states indistinguishable. Because the quantum state of FC-SPI has high dimensionality with multiple frequency comb components, we believe that the present work paves the way for single-photon interferometry to be applicable to quantum information science, and quantum metrology through quantum spectroscopy and imaging experiments
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