68 research outputs found
Chirped-pulse interferometry with finite frequency correlations
Chirped-pulse interferometry is a new interferometric technique encapsulating
the advantages of the quantum Hong-Ou-Mandel interferometer without the
drawbacks of using entangled photons. Both interferometers can exhibit
even-order dispersion cancellation which allows high resolution optical delay
measurements even in thick optical samples. In the present work, we show that
finite frequency correlations in chirped-pulse interferometry and
Hong-Ou-Mandel interferometry limit the degree of dispersion cancellation. Our
results are important considerations in designing practical devices based on
these technologies.Comment: 10 pages, 2 figure
Discriminating single-photon states unambiguously in high dimensions
The ability to uniquely identify a quantum state is integral to quantum
science, but for non-orthogonal states, quantum mechanics precludes
deterministic, error-free discrimination. However, using the non-deterministic
protocol of unambiguous state discrimination (USD) enables error-free
differentiation of states, at the cost of a lower frequency of success. We
discriminate experimentally between non-orthogonal, high-dimensional states
encoded in single photons; our results range from dimension to . We
quantify the performance of our method by comparing the total measured error
rate to the theoretical rate predicted by minimum-error state discrimination.
For the chosen states, we find a lower error rate by more than one standard
deviation for dimensions up to . This method will find immediate
application in high-dimensional implementations of quantum information
protocols, such as quantum cryptography.Comment: 4 pages + 3 pages supplementary, 4 figure
Experimental bound entanglement in a four-photon state
Entanglement [1, 2] enables powerful new quantum technologies [3-8], but in
real-world implementations, entangled states are often subject to decoherence
and preparation errors. Entanglement distillation [9, 10] can often counteract
these effects by converting imperfectly entangled states into a smaller number
of maximally entangled states. States that are entangled but cannot be
distilled are called bound entangled [11]. Bound entanglement is central to
many exciting theoretical results in quantum information processing [12-14],
but has thus far not been experimentally realized. A recent claim for
experimental bound entanglement is not supported by their data [15]. Here, we
consider a family of four-qubit Smolin states [16], focusing on a regime where
the bound entanglement is experimentally robust. We encode the state into the
polarization of four photons and show that our state exhibits both entanglement
and undistillability, the two defining properties of bound entanglement. We
then use our state to implement entanglement unlocking, a key feature of Smolin
states [16].Comment: 10 pages, 6 figures. For a simultaneously submitted related work see
arXiv:1005.196
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