Two-photon quantum interference and entanglement at 2.1 μm

Abstract

Quantum-enhanced optical systems operating within the 2 μm spectral region have the potential to revolutionise emerging applications in communications, sensing and metrology. However, to date, sources of entangled photons have been realised mainly in the near-infrared 700-1550 nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting-nanowire single-photon detectors, we demonstrate two-photon interference and polarisation-entangled photon pairs at 2090 nm, i.e. in the mid-infrared and significantly beyond existing technology. These results open the 2 μm window for the development of optical quantum technologies such as quantum key distribution in nextgeneration mid-infrared fibre communications systems and novel Earth-to-satellite communications that exploits reduced atmospheric scattering in a spectral region with a reduced solar background.

Quantum Fourier-Transform Infrared Spectroscopy for Complex Transmittance Measurements

“…The detection bandwidth can be significantly improved, combined with a broadband photon-pair source [37,38]. The operating wavelength of QFTIR spectroscopy could be extended to the mid-and far-infrared regions by choosing a suitable nonlinear crystal as the photon-pair source [39][40][41][42]. Our method can be applied to a variety of quantum spectroscopy systems, such as those based on a Mach-Zehnder nonlinear interferometer, with minor modifications, and is also applicable for infrared hyperspectral imaging [43].…”

Investigation of 1064-nm Pumped Type II SPDC in Potassium Niobate for Generation of High Spectral Purity Photon Pairs

“…The generation and detection of nonclassical light of about 2 µm has good potential in an emerging field of high-sensitivity metrology, especially in gravitational wave detection [1][2][3]. Such long wavelengths can reduce quantum noise and scattering losses in interferometric gravitational wave detectors such as the laser interferometer gravitational wave observatory (LIGO)-Voyager [4].…”

“…Mansell et al utilized a combination of a second-harmonic generator and an optical parametric oscillator with two pieces of periodically poled potassium titanyl phosphates (PPKTPs) to generate nonclassical squeezed states of light [1]. Prabhakar et al demonstrated twophoton quantum interference and entanglement at 2.1 µm using Type 0 spontaneous parametric down-conversion (SPDC) in a magnesium oxide-doped periodically poled lithium niobate (MgO:PPLN) [3]. In future studies, the basic requirements of the platform for generating photon pairs in the 2-µm spectral range can be listed as follows: (1) SPDC using the frequency-degenerate Type II extended phase matching (EPM) is desirable for the generation of high spectral purity photon pairs.…”

“…The wavelength of the photon pairs generated via the SPDC pumped by the Nd:YAG laser is 2128 nm, which is within the high transparency range in the atmospheric absorption spectrum [5]. (3) The larger the nonlinearity of the crystal used for SPDC, the higher the SPDC efficiency. The SPDC efficiency is proportional to the square of the effective nonlinear optic coefficient for the given EPM condition [13].…”

Generalized Photon Added and Subtracted f‐Deformed Displaced Fock States

“…The nonclassical states of light, known as any optical field with a nonpositive Glauber–Sudarshan P distribution function, represent useful applications ranging from quantum metrology [ 1 ] to quantum teleportation, [ 2 ] quantum communications and cryptography, [ 3 ] quantum interference and entanglement, [ 4 ] and quantum information processing. [ 5 ] With respect to these applications in modern technology, the question whether a quantum state of light is nonclassical, that is, a state with no classical analogue, has attracted great attention.…”