7 research outputs found
Single spin measurement using spin-orbital entanglement
Single spin measurement represents a major challenge for spin-based quantum
computation. In this article we propose a new method for measuring the spin of
a single electron confined in a quantum dot (QD). Our strategy is based on
entangling (using unitary gates) the spin and orbital degrees of freedom. An
{\em orbital qubit}, defined by a second, empty QD, is used as an ancilla and
is prepared in a known initial state. Measuring the orbital qubit will reveal
the state of the (unknown) initial spin qubit, hence reducing the problem to
the easier task of single charge measurement. Since spin-charge conversion is
done with unit probability, single-shot measurement of an electronic spin can
be, in principle, achieved. We evaluate the robustness of our method against
various sources of error and discuss briefly possible implementations.Comment: RevTeX4, 4 pages, some figs; updated to the published versio
Photochromism in single nitrogen-vacancy defect in diamond
Photochromism in single nitrogen-vacancy optical centers in diamond is
demonstrated. Time-resolved optical spectroscopy shows that intense irradiation
at 514 nm switches the nitrogen-vacancy defects to the negative form. This
defect state relaxes back to the neutral form under dark conditions. Temporal
anticorrelation of photons emitted by the different charge states of the
optical center unambiguously indicates that the nitrogen-vacancy defect
accounts for both 575 nm and 638 nm emission bands. Possible mechanism of
photochromism involving nitrogen donors is discussed.Comment: 11 pages, 3 figures, submitted to Applied Physics B: Lasers and
Optic
Experimental open air quantum key distribution with a single photon source
We present a full implementation of a quantum key distribution (QKD) system
with a single photon source, operating at night in open air. The single photon
source at the heart of the functional and reliable setup relies on the pulsed
excitation of a single nitrogen-vacancy color center in diamond nanocrystal. We
tested the effect of attenuation on the polarized encoded photons for inferring
longer distance performance of our system. For strong attenuation, the use of
pure single photon states gives measurable advantage over systems relying on
weak attenuated laser pulses. The results are in good agreement with
theoretical models developed to assess QKD security