Quantum-inspired interferometry with chirped laser pulses

Abstract

Interference is a defining feature of both quantum and classical theories of light, enabling the most precise measurements of a wide range of physical quantities including length 1 and time 2 . Quantum metrology exploits fundamental differences between these theories for new measurement techniques and enhanced precision 3,4 . Advantages stem from several phenomena associated with quantum interferometers, including non-local interference 5,6 , phase-insensitive interference 7 , phase super-resolution and super-sensitivity 8-10 , and automatic dispersion cancellation 6,11,12 . However, quantum interferometers require entangled states that are in practice difficult to create, manipulate and detect, especially compared with robust, intense classical states. In the present work, we report an interferometer based on chirped femtosecond laser pulses and classical nonlinear optics showing all of the metrological advantages of the quantum Hong-Ou-Mandel interferometer 7 , but with 10 million times more signal. Our work emphasizes the importance of delineating truly quantum effects from those with classical analogues 10,13,14 , and shows how insights gained from quantum mechanics can inspire novel classical technologies.Arguably the best known example of quantum interference was demonstrated by Hong, Ou and Mandel 7 (HOM); their interferometer is depicted in Fig. 1a. HOM interference is central to optical quantum technologies, including quantum teleportation 15 and linear-optical quantum computing 16 . Several characteristics distinguish HOM from classical interference, such as Michelson's or Young's. The HOM signal stems from pairs of interfering photons and is manifest as a dip in the rate of coincident photon detections spanning the coherence length of the light, as opposed to classical wavelength fringes. It is therefore inherently robust against path-length fluctuations. If the photons are entangled, the visibility and width of the HOM interferogram are insensitive to loss 17 and dispersion 11 . Furthermore, HOM interferometers achieve higher resolution than classical interferometers using the same bandwidth 18,19 . These features are ideal for precision optical path measurements of dispersive and lossy materials, implemented by placing the sample in one interferometer arm and measuring the delay required to restore interference. A quantum version of optical coherence tomography 20 was proposed and demonstrated 18,19 to harness these advantages.Recently, two proposals 21,22 and one experimental demonstration 23 have described classical systems showing automatic dispersion cancellation. Drawbacks to these techniques include reliance on unavailable technology 21 or significant postprocessing 22,23 . The experimentally demonstrated technique requires wavelength path stability; the interference visibility falls precipitously with loss and is limited to 50% of that possible with the HOM effect. Alternatively, background-free autocorrelation of transform-limited pulses, recently used for optical coherence tomography 24 , s...

Generation of broadband spontaneous parametric fluorescence using multiple bulk nonlinear crystals

“…The second harmonic generation from broadband anti-correlated frequencies have recently been demonstrated by classical laser pulses for optical coherence tomography [28,29].…”

Matter correlations induced by coupling to quantum light

“…(22). However, even if the two-photon state is separable, (ω a ,ω b ) = 1 (ω a ) 2 (ω b ), we obtain…”

“…Our results suggest that classical light cannot induce nonclassical correlations in the matter system, but this remains to be proved. Most importantly, it will be necessary to identify signatures of classical frequency correlations of light [22] on the created matter density matrices, and whether they can create matrices with nonzero quantum discord. Furthermore, introducing interactions between the atoms opens up the possibility to discuss the entanglement of delocalized quasiparticles, since the excitations can be regarded as interacting bosons [53][54][55].…”

“…Quantum spectroscopy offers increased signal strength at low photon fluxes [10][11][12], new control parameters to disentangle complex spectra [13][14][15][16], the control of exciton distributions [17][18][19][20], and the suppression of exciton transport [21] thanks to the unusual combination of high temporal and spectral resolution. However, whether all of these effects are genuine quantum effects in the sense that they may not be mimicked-at least in principle-by properly shaped pulses with classical correlations [22][23][24] remains an open topic. Besides, the interpretation of nonlinear experiments on photosynthetic complexes has ignited a vivid debate about the possible role of quantum coherences in the biological function of these systems [25][26][27].…”

The second-order interference between laser and thermal light

“…The second-order interference of light has been studied with photons emitted by different kinds of sources, such as entangled photon pair source [3], two independent single-photon sources [4][5][6], laser and single-photon source [7], laser and entangled photon pair source [8], two lasers [9][10][11], two thermal sources [12][13][14][15][16][17], etc. Many interesting results were obtained from those studies.…”