84 research outputs found
Proof-of-Concept Experiments for Quantum Physics in Space
Quantum physics experiments in space using entangled photons and satellites
are within reach of current technology. We propose a series of fundamental
quantum physics experiments that make advantageous use of the space
infrastructure with specific emphasis on the satellite-based distribution of
entangled photon pairs. The experiments are feasible already today and will
eventually lead to a Bell-experiment over thousands of kilometers, thus
demonstrating quantum correlations over distances which cannot be achieved by
purely earth-bound experiments.Comment: 15 pages, 10 figures, to appear in: SPIE Proceedings on Quantum
Communications and Quantum Imaging (2003
Large Quantum Superpositions and Interference of Massive Nanometer-Sized Objects
We propose a method to prepare and verify spatial quantum superpositions of a
nanometer-sized object separated by distances of the order of its size. This
method provides unprecedented bounds for objective collapse models of the wave
function by merging techniques and insights from cavity quantum optomechanics
and matter wave interferometry. An analysis and simulation of the experiment is
performed taking into account standard sources of decoherence. We provide an
operational parameter regime using present day and planned technology.Comment: 4 pages, 2 figures, to appear in PR
Talbot-Lau effect beyond the point-particle approximation
Recent progress in matter-wave interferometry aims to directly probe the quantum properties of matter on ever increasing scales. However, in order to perform interferometric experiments with massive mesoscopic objects, taking into account the constraints on the experimental setups, the pointlike-particle approximation needs to be cast aside. In this work, we consider near-field interferometry based on the Talbot effects with a single optical grating for large spherical particles beyond the point-particle approximation. We account for the suppression of the coherent grating effect and, at the same time, the enhancement of the decoherence effects due to scattering and absorption of grating photons
Testing the foundation of quantum physics in space via Interferometric and non-interferometric experiments with mesoscopic nanoparticles
Quantum technologies are opening novel avenues for applied and fundamental science at an impressive pace. In this perspective article, we focus on the promises coming from the combination of quantum technologies and space science to test the very foundations of quantum physics and, possibly, new physics. In particular, we survey the field of mesoscopic superpositions of nanoparticles and the potential of interferometric and non-interferometric experiments in space for the investigation of the superposition principle of quantum mechanics and the quantum-to-classical transition. We delve into the possibilities offered by the state-of-the-art of nanoparticle physics projected in the space environment and discuss the numerous challenges, and the corresponding potential advancements, that the space environment presents. In doing this, we also offer an ab-initio estimate of the potential of space-based interferometry with some of the largest systems ever considered and show that there is room for tests of quantum mechanics at an unprecedented level of detail
Low-dimensional quite noisy bound entanglement with cryptographic key
We provide a class of bound entangled states that have positive distillable
secure key rate. The smallest state of this kind is 4 \bigotimes 4. Our class
is a generalization of the class presented in [1] (IEEE Trans. Inf. Theory 54,
2621 (2008); arXiv:quant-ph/0506203). It is much wider, containing, in
particular, states from the boundary of PPT entangled states (all of the states
in the class in [1] were of this kind) but also states inside the set of PPT
entangled states, even, approaching the separable states. This generalization
comes with a price: for the wider class a positive key rate requires, in
general, apart from the one-way Devetak-Winter protocol (used in [1]) also the
recurrence preprocessing and thus effectively is a two-way protocol. We also
analyze the amount of noise that can be admixtured to the states of our class
without losing key distillability property which may be crucial for
experimental realization. The wider class contains key-distillable states with
higher entropy (up to 3.524, as opposed to 2.564 for the class in [1]).Comment: 10 pages, final version for J. Phys. A: Math. Theo
Optical implementation of a unitarily correctable code
Noise poses a challenge for any real-world implementation in quantum
information science. The theory of quantum error correction deals with this
problem via methods to encode and recover quantum information in a way that is
resilient against that noise. Unitarily correctable codes are an error
correction technique wherein a single unitary recovery operation is applied
without the need for an ancilla Hilbert space. Here, we present the first
optical implementation of a non-trivial unitarily correctable code for a noisy
quantum channel with no decoherence-free subspaces or noiseless subsystems. We
show that recovery of our initial states is achieved with high fidelity
(>=0.97), quantitatively proving the efficacy of this unitarily correctable
code.Comment: 6 pages, 3 figure
Tunable Indistinguishable Photons From Remote Quantum Dots
Single semiconductor quantum dots have been widely studied within devices
that can apply an electric field. In the most common system, the low energy
offset between the InGaAs quantum dot and the surrounding GaAs material limits
the magnitude of field that can be applied to tens of kVcm^-1, before carriers
tunnel out of the dot. The Stark shift experienced by the emission line is
typically 1 meV. We report that by embedding the quantum dots in a quantum well
heterostructure the vertical field that can be applied is increased by over an
order of magnitude whilst preserving the narrow linewidths, high internal
quantum efficiencies and familiar emission spectra. Individual dots can then be
continuously tuned to the same energy allowing for two-photon interference
between remote, independent, quantum dots
Optical one-way quantum computing with a simulated valence-bond solid
One-way quantum computation proceeds by sequentially measuring individual
spins (qubits) in an entangled many-spin resource state. It remains a
challenge, however, to efficiently produce such resource states. Is it possible
to reduce the task of generating these states to simply cooling a quantum
many-body system to its ground state? Cluster states, the canonical resource
for one-way quantum computing, do not naturally occur as ground states of
physical systems. This led to a significant effort to identify alternative
resource states that appear as ground states in spin lattices. An appealing
candidate is a valence-bond-solid state described by Affleck, Kennedy, Lieb,
and Tasaki (AKLT). It is the unique, gapped ground state for a two-body
Hamiltonian on a spin-1 chain, and can be used as a resource for one-way
quantum computing. Here, we experimentally generate a photonic AKLT state and
use it to implement single-qubit quantum logic gates.Comment: 11 pages, 4 figures, 8 tables - added one referenc
Experimental violation of Svetlichny's inequality
It is well known that quantum mechanics is incompatible with local realistic
theories. Svetlichny showed, through the development of a Bell-like inequality,
that quantum mechanics is also incompatible with a restricted class of nonlocal
realistic theories for three particles where any two-body nonlocal correlations
are allowed [Phys. Rev. D 35, 3066 (1987)]. In the present work, we
experimentally generate three-photon GHZ states to test Svetlichny's
inequality. Our states are fully characterized by quantum state tomography
using an overcomplete set of measurements and have a fidelity of (84+/-1)% with
the target state. We measure a convincing, 3.6 std., violation of Svetlichny's
inequality and rule out this class of restricted nonlocal realistic models.Comment: 10 pages, 3 figures, 1 tabl
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