41 research outputs found
Nonclassical radiation from diamond nanocrystals
The quantum properties of the fluorescence light emitted by diamond
nanocrystals containing a single nitrogen-vacancy (NV) colored center is
investigated. We have observed photon antibunching with very low background
light. This system is therefore a very good candidate for the production of
single photon on demand. In addition, we have measured larger NV center
lifetime in nanocrystals than in the bulk, in good agreement with a simple
quantum electrodynamical model.Comment: 8 pages, 5 figures, revised version, to appear in PR
Bell inequalities and density matrix for polarization entangled photons out of a two-photon cascade in a single quantum dot
We theoretically investigate the joint photodetection probabilities of the
biexciton-exciton cascade in single semiconductor quantum dots and analytically
derive the density matrix and the Bell's inequalities of the entangled state.
Our model includes different mechanisms that may spoil or even destroy
entanglement such as dephasing, energy splitting of the relay excitonic states
and incoherent population exchange between these relay levels. We explicitly
relate the fidelity of entanglement to the dynamics of these processes and
derive a threshold for violation of Bell's inequalities. Applied to standard
InAs/GaAs self-assembled quantum dots, our model indicates that spontaneous
emission enhancement of the excitonic states by cavity effects increases the
fidelity of entanglement to a value allowing for violation of Bell's
inequalities.Comment: Accepted Phys. Rev.
High quality asynchronous heralded single photon source at telecom wavelength
We report on the experimental realization and characterization of an
asynchronous heralded single photon source based on spontaneous parametric down
conversion. Photons at 1550nm are heralded as being inside a single-mode fiber
with more than 60% probability, and the multi-photon emission probability is
reduced by up to a factor 600 compared to poissonian light sources. These
figures of merit, together with the choice of telecom wavelength for the
heralded photons are compatible with practical applications needing very
efficient and robust single photon sources.Comment: 7 pages, 8 figure
Single photon quantum cryptography
We report the full implementation of a quantum cryptography protocol using a
stream of single photon pulses generated by a stable and efficient source
operating at room temperature. The single photon pulses are emitted on demand
by a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. The
quantum bit error rate is less that 4.6% and the secure bit rate is 9500
bits/s. The overall performances of our system reaches a domain where single
photons have a measurable advantage over an equivalent system based on
attenuated light pulses.Comment: 4 pages, 3 figure
Resolution of the mystery of counter-intuitive photon correlations in far off-resonance emission from a quantum dot-cavity system
Cavity quantum-electrodynamics experiments using an atom coupled to a single
radiation-field mode have played a central role in testing foundations of
quantum mechanics, thus motivating solid-state implementations using single
quantum dots coupled to monolithic nano-cavities. In stark contrast to their
atom based counterparts, the latter experiments revealed strong cavity
emission, even when the quantum dot is far off resonance. Here we present
experimental and theoretical results demonstrating that this effect arises from
the mesoscopic nature of quantum dot confinement, ensuring the presence of a
quasi-continuum of transitions between excited quantum dot states that are
enhanced by the cavity mode. Our model fully explains photon correlation
measurements demonstrating that photons emitted at the cavity frequency are
essentially uncorrelated with each other even though they are generated by a
single quantum dot.Comment: 5 pages, 4 figure
Photon antibunching in the fluorescence of individual color centers in diamond
We have observed photon antibunching in the fluorescence light emitted from a
single N-V center in diamond at room temperature. The possibility of generating
triggerable single photons with such a solide state system is discussedComment: 4 pages, 4 figure
Efficient photonic mirrors for semiconductor nanowires
International audienceUsing a fully vectorial frequency-domain aperiodic Fourier modal method, we study nanowire metallic mirrors and their photonic performance. We show that the performance of standard quarter-wave Bragg mirrors at subwavelength diameters is surprisingly poor, while engineered metallic mirrors that incorporate a thin dielectric adlayer may offer reflectance larger than 90% even for diameters as small as lambda/5
Metal-coated nano-cylinder cavity for broadband nonclassical light emission
A novel metal-coated nanocylinder-cavity architecture fully compatible with
III-V GaInAs technology and benefiting from a broad spectral range enhancement
of the localdensity- of-states is proposed as an integrated source of
non-classical light. Due to a judicious selection of the mode volume, the
cavity combines good collection efficiency (\gg 45%), large Purcell factors
(\gg 15) over a 80-nm spectral range, and a low sensitivity to inevitable
spatial mismatches between the single emitter and the cavity mode. This
represents a decisive step towards the implementation of reliable solid-state
devices for the generation of entangled photon pairs at infrared wavelengths