293,648 research outputs found
Demonstration of a programmable source of two-photon multiqubit entangled states
We suggest and demonstrate a novel source of two-photon multipartite
entangled states which exploits the transverse spatial structure of spontaneous
parametric downconversion together with a programmable spatial light modulator
(SLM). The 1D SLM is used to perform polarization entanglement purification and
to realize arbitrary phase-gates between polarization and momentum degrees of
freedom of photons. We experimentally demonstrate our scheme by generating
two-photon three qubit linear cluster states with high fidelity using a diode
laser pump with a limited coherence time and power on the crystal as low as
2.5$mW.Comment: 5 pages, 4 figures, to appear on PR
Enhancing quantum entropy in vacuum-based quantum random number generator
Information-theoretically provable unique true random numbers, which cannot
be correlated or controlled by an attacker, can be generated based on quantum
measurement of vacuum state and universal-hashing randomness extraction.
Quantum entropy in the measurements decides the quality and security of the
random number generator. At the same time, it directly determine the extraction
ratio of true randomness from the raw data, in other words, it affects quantum
random numbers generating rate obviously. In this work, considering the effects
of classical noise, the best way to enhance quantum entropy in the vacuum-based
quantum random number generator is explored in the optimum dynamical
analog-digital converter (ADC) range scenario. The influence of classical noise
excursion, which may be intrinsic to a system or deliberately induced by an
eavesdropper, on the quantum entropy is derived. We propose enhancing local
oscillator intensity rather than electrical gain for noise-independent
amplification of quadrature fluctuation of vacuum state. Abundant quantum
entropy is extractable from the raw data even when classical noise excursion is
large. Experimentally, an extraction ratio of true randomness of 85.3% is
achieved by finite enhancement of the local oscillator power when classical
noise excursions of the raw data is obvious.Comment: 12 pages,8 figure
Digital phase conjugation of second harmonic radiation emitted by nanoparticles in turbid media
We demonstrate focusing coherent light on a nanoparticle through turbid media based on digital optical phase conjugation of second harmonic generation (SHG) field from the nanoparticle. A SHG active nanoparticle inside a turbid medium was excited at the fundamental frequency and emitted SHG field as a point source. The SHG emission was scattered by the turbid medium, and the scattered field was recorded by off-axis digital holography. A phase-conjugated beam was then generated by using a phase-only spatial light modulator and sent back through the turbid medium, which formed a nearly ideal focus on the nanoparticle
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Solving the Jitter Problem in Microwave Compressed Ultrafast Electron Diffraction Instruments: Robust Sub-50 fs Cavity-Laser Phase Stabilization
We demonstrate the compression of electron pulses in a high-brightness
ultrafast electron diffraction (UED) instrument using phase-locked microwave
signals directly generated from a mode-locked femtosecond oscillator.
Additionally, a continuous-wave phase stabilization system that accurately
corrects for phase fluctuations arising in the compression cavity from both
power amplification and thermal drift induced detuning was designed and
implemented. An improvement in the microwave timing stability from 100 fs to 5
fs RMS is measured electronically and the long-term arrival time stability
(10 hours) of the electron pulses improves to below our measurement
resolution of 50 fs. These results demonstrate sub-relativistic ultrafast
electron diffraction with compressed pulses that is no longer limited by
laser-microwave synchronization.Comment: Accepted for publication in Structural Dynamic
Producing high fidelity single photons with optimal brightness via waveguided parametric down-conversion
Parametric down-conversion (PDC) offers the possibility to control the
fabrication of non-Gaussian states such as Fock states. However, in
conventional PDC sources energy and momentum conservation introduce strict
frequency and photon number correlations, which impact the fidelity of the
prepared state. In our work we optimize the preparation of single-photon Fock
states from the emission of waveguided PDC via spectral filtering. We study the
effect of correlations via photon number resolving detection and quantum
interference. Our measurements show how the reduction of mixedness due to
filtering can be evaluated. Interfering the prepared photon with a coherent
state we establish an experimentally measured fidelity of the produced target
state of 78%.Comment: 15 pages, 10 Figures, published versio
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