125 research outputs found
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 optical quantum state engineering
We discuss a novel method of efficiently producing multi-photon states using
repeated spontaneous parametric downconversion. Specifically, by attempting
downconversion several times, we can pseudo-deterministically add photons to a
mode, producing various several-photon states. We discuss both expected
performance and experimental limitations.Comment: 4 pages, 4 figure
Entanglement and purity of single- and two-photon states
Whereas single- and two-photon wave packets are usually treated as pure
states, in practice they will be mixed. We study how entanglement created with
mixed photon wave packets is degraded. We find in particular that the
entanglement of a delocalized single-photon state of the electro-magnetic field
is determined simply by its purity. We also discuss entanglement for two-photon
mixed states, as well as the influence of a vacuum component.Comment: 11 pages, 10 figures, 1 debuting autho
A bright, pulsed two-mode squeezer
We report the realization of a bright ultrafast two-mode squeezer based on
type II parametric downconversion (PDC) in periodically poled
(PP-KTP) waveguides. It produces a pulsed two-mode squeezed
vacuum state: a photon-number entangled pair of truly single-mode pulses or, in
terms of continuous variables quantum optics, a pulsed, single mode
Einstein-Podolsky-Rosen (EPR) state in the telecom regime. We prove the single
mode character of our source by measuring its correlation function
and demonstrate a mean photon number of up to 2.5 per pulse, equivalent to 11dB
of two-mode squeezing.Comment: 4 pages, 3 figure
Spectral Effects of Strong Chi-2 Non-Linearity for Quantum Processing
Optical non-linearity can be used for parametric amplification
and producing down-converted entangled photon pairs that have broad
applications. It is known that weak non-linear media exhibit dispersion and
produce a frequency response. It is therefore of interest to know how spectral
effects of a strong crystal affect the performance. Here we model
the spectral effects of the dispersion of a strong crystal and
illustrate how this affects its ability to perform Bell measurements and
influence the performance of a quantum gates that employ such a Bell
measurement. We show that a Dyson series expansion of the unitary operator is
necessary in general, leading to unwanted spectral entanglement. We identify a
limiting situation employing periodic poling, in which a Taylor series
expansion is a good approximation and this entanglement can be removed.Comment: Will be submitted to PR
Bright source of spectrally uncorrelated polarization-entangled photons with nearly single-mode emission
We present results of a bright polarization-entangled photon source operating
at 1552 nm via type-II collinear degenerate spontaneous parametric
down-conversion in a periodically poled potassium titanyl phosphate crystal. We
report a conservative inferred pair generation rate of 123,000 pairs/s/mW into
collection modes. Minimization of spectral and spatial entanglement was
achieved by group velocity matching the pump, signal and idler modes and
through properly focusing the pump beam. By utilizing a pair of calcite beam
displacers, we are able to overlap photons from adjacent down-conversion
processes to obtain polarization-entanglement visibility of 94.7 +/- 1.1% with
accidentals subtracted.Comment: 4 pages, 7 color figures. Revised manuscript includes the following
changes: corrected pair generation rate from 44,000/s/mW pump to 123,000/s/mW
pump; replaced Fig. 1b to enhance clarity; minor alterations to the title,
abstract and introduction; grammatical correction
Indistinguishability of independent single photons
The indistinguishability of independent single photons is presented by
decomposing the single photon pulse into the mixed state of different transform
limited pulses. The entanglement between single photons and outer environment
or other photons induces the distribution of the center frequencies of those
transform limited pulses and makes photons distinguishable. Only the single
photons with the same transform limited form are indistinguishable. In details,
the indistinguishability of single photons from the solid-state quantum emitter
and spontaneous parametric down conversion is examined with two-photon
Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the
indistinguishability are discussed, where the usage of spectral filter is
highlighted.Comment: 6 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
Tailored photon-pair generation in optical fibers
We experimentally control the spectral structure of photon pairs created via
spontaneous four-wave mixing in microstructured fibers. By fabricating fibers
with designed dispersion, one can manipulate the photons' wavelengths, joint
spectrum, and, thus, entanglement. As an example, we produce photon-pairs with
no spectral correlations, allowing direct heralding of single photons in
pure-state wave packets without filtering. We achieve an experimental purity of
, while theoretical analysis and preliminary tests suggest 94.5%
purity is possible with a much longer fiber
Optimal photons for quantum-information processing
Photonic quantum-information processing schemes, such as linear optics quantum computing, and other experiments relying on single-photon interference, inherently require complete photon indistinguishability to enable the desired photonic interactions to take place. Mode-mismatch is the dominant cause of photon distinguishability in optical circuits. Here we study the effects of photon wave-packet shape on tolerance against the effects of mode mismatch in linear optical circuits, and show that Gaussian distributed photons with large bandwidth are optimal. The result is general and holds for arbitrary linear optical circuits, including ones which allow for postselection and classical feed forward. Our findings indicate that some single photon sources, frequently cited for their potential application to quantum-information processing, may in fact be suboptimal for such applications
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