108 research outputs found
Seeing bulk topological properties of band insulators in small photonic lattices
We present a general scheme for measuring the bulk properties of
non-interacting tight-binding models realized in arrays of coupled photonic
cavities. Specifically, we propose to implement a single unit cell of the
targeted model with tunable twisted boundary conditions in order to simulate
large systems and, most importantly, to access bulk topological properties
experimentally. We illustrate our method by demonstrating how to measure
topological invariants in a two-dimensional quantum Hall-like model.Comment: 5 pages, 2 figures; with Supplemental Material (2 pages
Forensic data hiding optimized for JPEG 2000
This paper presents a novel image adaptive data hiding system using properties of the discrete wavelet transform and which is ready to use in combination with JPEG 2000. Image adaptive watermarking schemes determine the embedding samples and strength from the image statistics. We propose to use the energy of wavelet coefficients at high frequencies to measure the amount of distortion that can be tolerated by a lower frequency coefficient. The watermark decoder in image adaptive data hiding needs to estimate the same parameters used for encoding from a modified source and hence is vulnerable to desynchronization. We present a novel way to resolve these synchronization issues by employing specialized insertion, deletion and substitution codes. Given the low complexity and reduced perceptual impact of the embedding technique, it is suitable for inserting camera and/or projector information to facilitate image forensics
Quantum networks reveal quantum nonlocality
The results of local measurements on some composite quantum systems cannot be
reproduced classically. This impossibility, known as quantum nonlocality,
represents a milestone in the foundations of quantum theory. Quantum
nonlocality is also a valuable resource for information processing tasks, e.g.
quantum communication, quantum key distribution, quantum state estimation, or
randomness extraction. Still, deciding if a quantum state is nonlocal remains a
challenging problem. Here we introduce a novel approach to this question: we
study the nonlocal properties of quantum states when distributed and measured
in networks. Using our framework, we show how any one-way entanglement
distillable state leads to nonlocal correlations. Then, we prove that
nonlocality is a non-additive resource, which can be activated. There exist
states, local at the single-copy level, that become nonlocal when taking
several copies of it. Our results imply that the nonlocality of quantum states
strongly depends on the measurement context.Comment: 4 + 3 pages, 4 figure
Efficient algorithm to compute the Berry conductivity
We propose and construct a numerical algorithm to calculate the Berry conductivityin topological band insulators. The method is applicable to cold atomsystems as well as solid state setups, both for the insulating case where the Fermienergy lies in the gap between two bulk bands as well as in the metallic regime.This method interpolates smoothly between both regimes. The algorithm isgauge-invariant by construction, efficient, and yields the Berry conductivity withknown and controllable statistical error bars. We apply the algorithm to severalparadigmatic models in the field of topological insulators, including Haldaneʼsmodel on the honeycomb lattice, the multi-band Hofstadter model, and the BHZmodel, which describes the 2D spin Hall effect observed in CdTe/HgTe/CdTequantum well heterostructures
Out-of-equilibrium physics in driven dissipative coupled resonator arrays
Coupled resonator arrays have been shown to exhibit interesting many- body
physics including Mott and Fractional Hall states of photons. One of the main
differences between these photonic quantum simulators and their cold atoms
coun- terparts is in the dissipative nature of their photonic excitations. The
natural equi- librium state is where there are no photons left in the cavity.
Pumping the system with external drives is therefore necessary to compensate
for the losses and realise non-trivial states. The external driving here can
easily be tuned to be incoherent, coherent or fully quantum, opening the road
for exploration of many body regimes beyond the reach of other approaches. In
this chapter, we review some of the physics arising in driven dissipative
coupled resonator arrays including photon fermionisa- tion, crystallisation, as
well as photonic quantum Hall physics out of equilibrium. We start by briefly
describing possible experimental candidates to realise coupled resonator arrays
along with the two theoretical models that capture their physics, the
Jaynes-Cummings-Hubbard and Bose-Hubbard Hamiltonians. A brief review of the
analytical and sophisticated numerical methods required to tackle these systems
is included.Comment: Chapter that appeared in "Quantum Simulations with Photons and
Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by
D.G.Angelakis, Quantum Science and Technology Series, Springer 201
Realistic loophole-free Bell test with atom-photon entanglement
The establishment of nonlocal correlations, obtained through the violation of
a Bell inequality, is not only important from a fundamental point of view, but
constitutes the basis for device-independent quantum information technologies.
Although several nonlocality tests have been performed so far, all of them
suffered from either the locality or the detection loopholes. Recent studies
have suggested that the use of atom-photon entanglement can lead to Bell
inequality violations with moderate transmission and detection efficiencies. In
this paper we propose an experimental setup realizing a simple atom-photon
entangled state that, under realistic experimental parameters available to
date, achieves a significant violation of the Clauser-Horn-Shimony-Holt
inequality. Most importantly, the violation remains when considering typical
detection efficiencies and losses due to required propagation distances.Comment: 21 pages, 5 figures, 3 table, to appear in Nature Com
Experimental estimation of the dimension of classical and quantum systems
An overwhelming majority of experiments in classical and quantum physics make
a priori assumptions about the dimension of the system under consideration.
However, would it be possible to assess the dimension of a completely unknown
system only from the results of measurements performed on it, without any extra
assumption? The concept of a dimension witness answers this question, as it
allows one to bound the dimension of an unknown classical or quantum system in
a device-independent manner, that is, only from the statistics of measurements
performed on it. Here, we report on the experimental demonstration of dimension
witnesses in a prepare and measure scenario. We use pairs of photons entangled
in both polarization and orbital angular momentum to generate ensembles of
classical and quantum states of dimensions up to 4. We then use a dimension
witness to certify their dimensionality as well as their quantum nature. Our
results open new avenues for the device-independent estimation of unknown
quantum systems and for applications in quantum information science.Comment: See also similar, independent and jointly submitted work of J. Ahrens
et al., quant-ph/1111.127
Sampling interplanetary dust from Antarctic air
We built a collector to filter interplanetary dust particles (IDPs) larger than 5 μm from the clean air at the Amundsen Scott South Pole station. Our sampling strategy used long duration, continuous dry filtering of near‐surface air in place of short duration, high‐speed impact collection on flags flown in the stratosphere. We filtered ~10 m of clean Antarctic air through 20 cm diameter, 3 µm filters coupled to a suction blower of modest power consumption (5–6 kW). Our collector ran continuously for 2 years and yielded 41 filters for analyses. Based on stratospheric concentrations, we predicted that each month’s collection would provide 300–900 IDPs for analysis. We identified 19 extraterrestrial (ET) particles on the 66 cm of filter examined, which represented ~0.5% of the exposed filter surfaces. The 11 ET particles larger than 5 µm yield about a fifth of the expected flux based on >5 µm stratospheric ET particle flux. Of the 19 ET particles identified, four were chondritic porous IDPs, seven were FeNiS beads, two were FeNi grains, and six were chondritic material with FeNiS components. Most were <10 µm in diameter and none were cluster particles. Additionally, a carbon‐rich candidate particle was found to have a small N isotopic enrichment, supporting an ET origin. Many other candidate grains, including chondritic glasses and C‐rich particles with Mg and Si and FeS grains, require further analysis to determine if they are ET. The vast majority of exposed filter surfaces remain to be examined
Subwavelength vacuum lattices and atom–atom interactions in two-dimensional photonic crystals
Quantum simulation with cold atoms in optical lattices is an attractive avenue for explorations of quantum many-body physics. A principal challenge in the field is to increase the energy and length scales in current set-ups, thereby reducing temperature and coherence-time requirements. Here, we present a new paradigm for high-density, two-dimensional optical lattices in photonic crystal waveguides. Specially engineered two-dimensional photonic crystals provide a practical platform to trap atoms and engineer their interactions in ways that surpass the limitations of current technologies and enable investigations of novel quantum many-body matter. Our schemes remove the constraint on the lattice constant set by the free-space optical wavelength in favour of deeply sub-wavelength atomic arrays. We further describe possibilities for atom–atom interactions mediated by photons in two-dimensional photonic crystal waveguides with energy scales several orders of magnitude larger than for exchange interactions in free-space lattices and with the capability to engineer strongly long-range interactions
On the origin and evolution of the material in 67P/Churyumov-Gerasimenko
International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects
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