21 research outputs found
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
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
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.
Characterization of the non-classical nature of conditionally prepared single photons
A reliable single photon source is a prerequisite for linear optical quantum
computation and for secure quantum key distribution. A criterion yielding a
conclusive test of the single photon character of a given source, attainable
with realistic detectors, is therefore highly desirable. In the context of
heralded single photon sources, such a criterion should be sensitive to the
effects of higher photon number contributions, and to vacuum introduced through
optical losses, which tend to degrade source performance. In this paper we
present, theoretically and experimentally, a criterion meeting the above
requirements.Comment: 4 pages; 3 figure
Temperature-controlled entangled-photon absorption spectroscopy
Entangled two-photon absorption spectroscopy (TPA) has been widely recognized as a powerful tool for revealing relevant information about the structure of complex molecular systems. However, to date, the experimental implementation of this technique has remained elusive, mainly because of two major difficulties: first, the need to perform multiple experiments with two-photon states bearing different temporal correlations, which translates into the necessity to have at the experimenter’s disposal tens, if not hundreds, of sources of entangled photons; second, the need to have a priori knowledge of the absorbing medium’s lowest-lying intermediate energy level. In this work, we put forward a simple experimental scheme that successfully overcomes these two limitations. By making use of a temperature-controlled entangled-photon source, which allows the tuning of the central frequencies of the absorbed photons, we show that the TPA signal, measured as a function of the temperature of the nonlinear crystal that generates the paired photons, and a controllable delay between them, carries all information about the electronic level structure of the absorbing medium, which can be revealed by a simple Fourier transformation.Peer ReviewedPostprint (author's final draft
Generation of correlated photons in controlled spatial modes by down-conversion in nonlinear waveguides
We report the observation of correlated photon pairs generated by spontaneous
parametric down-conversion in a quasi-phase matched KTiOPO4 nonlinear
waveguide. The highest ratio of coincidence to single photon count rates
observed in the 830 nm wavelength region exceeds 18%. This makes nonlinear
waveguides a promising source of correlated photons for metrology and quantum
information processing applications. We also discuss possibilities of
controlling the spatial characteristics of the down-converted photons produced
in multimode waveguide structures.Comment: 4 pages, REVTe