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Highlights • Thermal effect of the biphotons generated from M TiO X O 4 is thoroughly investigated. • The thermal effect is the key to precisely control the quantum state. • The maximal spectral purity of biphotons is insensitive to temperature shift. • The HOM interference patterns are very sensitive to temperature shift. • The research results are useful for quantum interference and spectroscopy. Abstract We theoretically and numerically investigate the temperature-dependent properties of the biphotons generated from four isomorphs of periodically poled KTiOPO 4 (PPKTP): i.e., PPRTP, PPKTA, PPRTA and PPCTA. It is discovered that the first type of group-velocity-matched (GVM) wavelength is decreased by 6.4, 1.2, 8.9, 25.6 and 6.3 nm, while the phase-matched wavelength is decreased by 4.4, −0.4, −1.2, 29.1 and 59.5 nm for PPKTP, PPRTP, PPKTA, PPRTA and PPCTA, respectively, when the temperature is increased from 20 °C to 120 °C. Although the maximal spectral purity of the heralded single photons is not changed at different temperature, the Hong-Ou-Mandel (HOM) interference shows different patterns due to a shift of the joint spectral amplitude. These thermal effects are very important for precise control of the quantum state for the future applications in quantum information processing, for example, in quantum interference or spectroscopy. [ABSTRACT FROM AUTHOR]

In spontaneous parametric down conversion (SPDC) based quantum information processing (QIP) experiments, there is a tradeoff between the coincidence count rates (i.e. the pumping power of the SPDC), which limits the rate of the protocol, and the visibility of the quantum interference, which limits the quality of the protocol. This tradeoff is mainly caused by the multi-photon pair emissions from the SPDCs. In theory, the problem is how to model the experiments without truncating these multi-photon emissions while including practical imperfections.In this paper, we establish a method to theoretically simulate SPDC-based QIPs which fully incorporates the effect of multi-photon emissions and various practical imperfections. The key ingredient in our method is the application of the characteristic function formalism which has been used in continuous variable QIPs. We apply our method to three examples, the Hong–Ou–Mandel interference and the Einstein–Podolsky–Rosen interference experiments, and the concatenated entanglement swapping protocol. For the first two examples, we show that our theoretical results quantitatively agree with the recent experimental results. Also we provide the closed expressions for these interference visibilities with the full multi-photon components and various imperfections. For the last example, we provide the general theoretical form of the concatenated entanglement swapping protocol in our method and show the numerical results up to five concatenations. Our method requires only a small computational resource (a few minutes by a commercially available computer), which was not possible in the previous theoretical approach. Our method will have applications in a wide range of SPDC-based QIP protocols with high accuracy and a reasonable computational resource. [ABSTRACT FROM AUTHOR]

A modified Hong–Ou–Mandel (HOM) interference reveals that the two-photon interference phenomenon can be explained only by the concept of a two-photon wave packet rather than a single-photon one. However, the temporal interferogram in the modified HOM interferometer becomes flat in some cases so that no useful information can be extracted from time-domain measurement. Here, we theoretically explore such temporal interferogram from the frequency domain and obtain the spectrally resolved interference with high visibility. The result represents a modulation of the joint spectral intensity along both the frequency sum and the frequency difference directions. This is quite different from the cases of the spectrally resolved HOM interference and N00N state interference where the modulations happened only in one direction. Moreover, we have shown that such modulations have a potential application in the generation and characterization of high-dimensional frequency entanglement. • Spectrally resolved interference with high visibility in the modified HOM interferometer can be obtained even if the temporal visibility is zero. • Joint spectral intensity can be modulated by the time delay along both the frequency sum and the frequency difference directions. • High-dimensional frequency entanglement can be generated by adjusting the time delay and can be characterized directly using the two-side dips appeared in temporal interferogram. • The research results could facilitate further development of spectrally resolved multi-photon interference and its applications in quantum information science. [ABSTRACT FROM AUTHOR]