Parametric downconversion with optimized spectral properties in nonlinear photonic crystals

We study the joint spectral properties of photon pairs generated by spontaneous parametric down-conversion in a one-dimensional nonlinear photonic crystal in a collinear, degenerate, type-II geometry. We show that the photonic crystal properties may be exploited to compensate for material dispersion and obtain photon pairs that are nearly factorable, in principle, for arbitrary materials and spectral regions, limited by the ability to fabricate the nonlinear crystal with the required periodic variation in the refractive indices for the ordinary and extraordinary waves.Comment: 9 pages, 6 figure

Generation of Fourier transform limited heralded single photons

In this paper we study the spectral (temporal) properties of heralded single photon wavepackets, triggered by the detection of an idler photon in the process of parametric downconversion. The generated single photons are studied within the framework of the chronocyclic Wigner function, from which the single photon spectral width and temporal duration can be computed. We derive specific conditions on the two-photon joint spectral amplitude which result in both pure and Fourier- transform limited heralded single photons. Likewise, we present specific source geometries which lead to the fulfilment of these conditions and show that one of these geometries leads, for a given pump bandwidth, to the temporally shortest possible heralded single photon wavepackets.Comment: 10 pages, 3 figure, PHYSICAL REVIEW A 75, 02381

Generation of two-photon states with arbitrary degree of entanglement via nonlinear crystal superlattices

We demonstrate a general method of engineering the joint quantum state of photon pairs produced in spontaneous parametric downconversion (PDC). The method makes use of a superlattice structure of nonlinear and linear materials, in conjunction with a broadband pump, to manipulate the group delays of the signal and idler photons relative to the pump pulse, and realizes a joint spectral amplitude with arbitrary degree of entanglement for the generated pairs. This method of group delay engineering has the potential of synthesizing a broad range of states including factorizable states crucial for quantum networking and states optimized for Hong-Ou-Mandel interferometry. Experimental results for the latter case are presented, illustrating the principles of this approach.Comment: 4 pages, 4 figures, accepted Phys. Rev. Let

Nonlocal Modulation of Entangled Photons

We consider ramifications of the use of high speed light modulators to questions of correlation and measurement of time-energy entangled photons. Using phase modulators, we find that temporal modulation of one photon of an entangled pair, as measured by correlation in the frequency domain, may be negated or enhanced by modulation of the second photon. Using amplitude modulators we describe a Fourier technique for measurement of biphoton wave functions with slow detectors

Shaping the waveform of entangled photons

We demonstrate experimentally the tunable control of the joint spectrum, i.e. waveform and degree of frequency correlations, of paired photons generated in spontaneous parametric downconversion. This control is mediated by the spatial shape of the pump beam in a type-I noncollinear configuration. We discuss the applicability of this technique to other sources of frequency entangled photons, such as electromagnetically induced Raman transitions.Comment: 5 Pages, 4 Figure

Experimental generation of complex noisy photonic entanglement

We present an experimental scheme based on spontaneous parametric down-conversion to produce multiple photon pairs in maximally entangled polarization states using an arrangement of two type-I nonlinear crystals. By introducing correlated polarization noise in the paths of the generated photons we prepare mixed entangled states whose properties illustrate fundamental results obtained recently in quantum information theory, in particular those concerning bound entanglement and privacy.Comment: 12 pages, 3 figure

On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion

We study the chronocyclic character, i.e. the joint temporal and spectral properties, of the single-photon constituents of photon pairs generated by spontaneous parametric down conversion. In particular we study how single photon properties, including purity and single-photon chirp, depend on photon pair properties, including the type of signal-idler spectral and correlations and the level of pump chirp.Comment: 13 pages, 6 figure

Heralded Generation of Ultrafast Single Photons in Pure Quantum States

We present an experimental demonstration of heralded single photons prepared in pure quantum states from a parametric downconversion source. It is shown that, through controlling the modal structure of the photon pair emission, one can generate pairs in factorable states and thence eliminate the need for spectral filters in multiple-source interference schemes. Indistinguishable heralded photons were generated in two independent spectrally engineered sources, and, by performing a Hong-Ou-Mandel interference between them without spectral filters at a raw visibility of 94.4%, their purity was measured to be over 95%.Comment: 5 pages, 4 figure

Efficient fiber coupling of down-conversion photon pairs

We develop and apply an effective analytic theory of a non-collinear, broadband type-I parametric down-conversion to study a coupling efficiency of the generated photon pairs into single mode optical fibers. We derive conditions necessary for highly efficient coupling for single and double type-I crystal producing polarization entangled states of light. We compare the obtained approximate analytic expressions with the exact numerical solutions and discuss the results for a case of BBO crystals.Comment: 15 pages, 4 figure

Ultra-broadband photon pair preparation by spontaneous four wave mixing in dispersion-engineered optical fiber

We present a study of the spectral properties of photon pairs generated through the process of spontaneous four wave mixing (SFWM) in single mode fiber. Our analysis assumes narrowband pumps, which are allowed to be frequency-degenerate or non-degenerate. Based on this analysis, we derive conditions on the pump frequencies and on the fiber dispersion parameters which guarantee the generation of ultra-broadband photon pairs. Such photon pairs are characterized by: i) a very large degree of entanglement, and ii) a very high degree of temporal synchronization between the signal and idler photons. Through a numerical exercise, we find that the use of photonic crystal fiber (PCF) facilitates the fulfilment of the conditions for ultra-broadband photon pair generation; in particular, the spectral region in which emission occurs can be adjusted to particular needs through an appropriate choice of the PCF parameters. In addition, we present a novel quantum interference effect, resulting from indistinguishable pathways to the same outcome, which can occur when pumping a SFWM source with multiple spectral lines.Comment: 15 pages, 10 figures. To be published in Phys. Rev.