39 research outputs found
Independent high-purity photons created in domain-engineered crystals
Advanced photonic quantum technology relies on multi-photon interference
which requires bright sources of high-purity single photons. Here, we implement
a novel domain-engineering technique for tailoring the nonlinearity of a
parametric down-conversion crystal. We create pairs of independently-heralded
telecom-wavelength photons and achieve high heralding, brightness and spectral
purities without filtering.Comment: 8 pages, 5 figures Imprecise comparison with the experimental results
in [28] has been remove
Pure down-conversion photons through sub-coherence length domain engineering
Photonic quantum technology relies on efficient sources of coherent single
photons, the ideal carriers of quantum information. Heralded single photons
from parametric down-conversion can approximate on-demand single photons to a
desired degree, with high spectral purities achieved through group-velocity
matching and tailored crystal nonlinearities.
Here we propose crystal nonlinearity engineering techniques with
sub-coherence-length domains. We first introduce a combination of two existing
methods: a deterministic approach with coherence-length domains and
probabilistic domain-width annealing. We then show how the same deterministic
domain-flip approach can be implemented with sub-coherence length domains. Both
of these complementary techniques create highly pure photons, outperforming
previous methods, in particular for short nonlinear crystals matched to
femtosecond lasers.Comment: 12 pages, 4 figures. Minor update to Fig.
Enhanced Multi-Qubit Phase Estimation in Noisy Environments by Local Encoding
The first generation of multi-qubit quantum technologies will consist of
noisy, intermediate-scale devices for which active error correction remains out
of reach. To exploit such devices, it is thus imperative to use passive error
protection that meets a careful trade-off between noise protection and resource
overhead. Here, we experimentally demonstrate that single-qubit encoding can
significantly enhance the robustness of entanglement and coherence of
four-qubit graph states against local noise with a preferred direction. In
particular, we explicitly show that local encoding provides a significant
practical advantage for phase estimation in noisy environments. This
demonstrates the efficacy of local unitary encoding under realistic conditions,
with potential applications in multi-qubit quantum technologies for metrology,
multi-partite secrecy and error correction.Comment: 7 figure
Experimental test of local observer-independence
The scientific method relies on facts, established through repeated
measurements and agreed upon universally, independently of who observed them.
In quantum mechanics, the objectivity of observations is not so clear, most
dramatically exposed in Eugene Wigner's eponymous thought experiment where two
observers can experience seemingly different realities. The question whether
these realities can be reconciled in an observer-independent way has long
remained inaccessible to empirical investigation, until recent no-go-theorems
constructed an extended Wigner's friend scenario with four observers that
allows us to put it to the test. In a state-of-the-art 6-photon experiment, we
realise this extended Wigner's friend scenario, experimentally violating the
associated Bell-type inequality by 5 standard deviations. If one holds fast to
the assumptions of locality and free-choice, this result implies that quantum
theory should be interpreted in an observer-dependent way.Comment: 5+5 pages, 6 figure
Quantum teleportation on a photonic chip
Quantum teleportation is a fundamental concept in quantum physics which now
finds important applications at the heart of quantum technology including
quantum relays, quantum repeaters and linear optics quantum computing (LOQC).
Photonic implementations have largely focussed on achieving long distance
teleportation due to its suitability for decoherence-free communication.
Teleportation also plays a vital role in the scalability of photonic quantum
computing, for which large linear optical networks will likely require an
integrated architecture. Here we report the first demonstration of quantum
teleportation in which all key parts - entanglement preparation, Bell-state
analysis and quantum state tomography - are performed on a reconfigurable
integrated photonic chip. We also show that a novel element-wise
characterisation method is critical to mitigate component errors, a key
technique which will become increasingly important as integrated circuits reach
higher complexities necessary for quantum enhanced operation.Comment: Originally submitted version - refer to online journal for accepted
manuscript; Nature Photonics (2014
Nonlinear spectroscopy of semiconductor nanostructures
EThOS - Electronic Theses Online ServiceGBUnited Kingdo