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Author |
Ma, Xiao-Song; Dakic, Borivoje; Naylor, William; Zeilinger, Anton; Walther, Philip |
Title |
Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems |
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Journal Article |
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2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
5 |
Pages |
399-405 |
Keywords |
fromIPMRAS |
Abstract |
Quantum simulators are controllable quantum systems that can reproduce the dynamics of the system of interest in situations that are not amenable to classical computers. Recent developments in quantum technology enable the precise control of individual quantum particles as required for studying complex quantum systems. In particular, quantum simulators capable of simulating frustrated Heisenberg spin systems provide platforms for understanding exotic matter such as high-temperature superconductors. Here we report the analogue quantum simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type interactions among four spin-1/2 particles. Depending on the interaction strength, frustration within the system emerges such that the ground state evolves from a localized to a resonating-valence-bond state. This spin-1/2 tetramer is created using the polarization states of four photons. The single-particle addressability and tunable measurement-induced interactions provide us with insights into entanglement dynamics among individual particles. We directly extract ground-state energies and pairwise quantum correlations to observe the monogamy of entanglement. |
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RPLAB @ gujma @ |
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842 |
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Author |
Lydersen, Lars; Wiechers, Carlos; Wittmann, Christoffer; Elser, Dominique; Skaar, Johannes; Makarov, Vadim |
Title |
Hacking commercial quantum cryptography systems by tailored bright illumination |
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Journal Article |
Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2010 |
Publication |
Nature Photonics |
Abbreviated Journal |
Nat. Photon. |
Volume |
4 |
Issue |
10 |
Pages |
686 - 689 |
Keywords |
quantum cryptography, hacking, QKD, APD |
Abstract |
The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built of off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies. |
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657 |
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Author |
Bonifas, Andrew P.; McCreery, Richard L. |
Title |
‘Soft’ Au, Pt and Cu contacts for molecular junctions through surface-diffusion-mediated deposition |
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Journal Article |
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2010 |
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Nature Nanotechnology |
Abbreviated Journal |
Nat. Nanotech. |
Volume |
5 |
Issue |
8 |
Pages |
612–617 |
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Virtually all types of molecular electronic devices depend on electronically addressing a molecule or molecular layer through the formation of a metallic contact. The introduction of molecular devices into integrated circuits will probably depend on the formation of contacts using a vapour deposition technique, but this approach frequently results in the metal atoms penetrating or damaging the molecular layer. Here, we report a method of forming 'soft' metallic contacts on molecular layers through surface-diffusion-mediated deposition, in which the metal atoms are deposited remotely and then diffuse onto the molecular layer, thus eliminating the problems of penetration and damage. Molecular junctions fabricated by this method exhibit excellent yield (typically >90%) and reproducibility, and allow examination of the effects of molecular-layer structure, thickness and contact work function. |
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682 |
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Freer, Erik M.; Grachev, Oleg; Duan, Xiangfeng; Martin, Samuel; Stumbo, David P. |
Title |
High-yield self-limiting single-nanowire assembly with dielectrophoresis |
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Journal Article |
Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2010 |
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Nature Nanotechnology |
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Nat. Nanotech. |
Volume |
5 |
Issue |
7 |
Pages |
525–530 |
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Single-crystal nanowire transistors and other nanowire-based devices could have applications in large-area and flexible electronics if conventional top-down fabrication techniques can be integrated with high-precision bottom-up nanowire assembly. Here, we extend dielectrophoretic nanowire assembly to achieve a 98.5% yield of single nanowires assembled over 16,000 patterned electrode sites with submicrometre alignment precision. The balancing of surface, hydrodynamic and dielectrophoretic forces makes the self-assembly process controllable, and a hydrodynamic force component makes it self-limiting. Our approach represents a methodology to quantify nanowire assembly, and makes single nanowire assembly possible over an area limited only by the ability to reproduce process conditions uniformly. |
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RPLAB @ gujma @ |
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683 |
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Author |
Konstantatos, Gerasimos; Sargent, Edward H. |
Title |
Nanostructured materials for photon detection |
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Journal Article |
Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2010 |
Publication |
Nature Nanotechnology |
Abbreviated Journal |
Nat. Nanotech. |
Volume |
5 |
Issue |
6 |
Pages |
391–400 |
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The detection of photons underpins imaging, spectroscopy, fibre-optic communications and time-gated distance measurements. Nanostructured materials are attractive for detection applications because they can be integrated with conventional silicon electronics and flexible, large-area substrates, and can be processed from the solution phase using established techniques such as spin casting, spray coating and layer-by-layer deposition. In addition, their performance has improved rapidly in recent years. Here we review progress in light sensing using nanostructured materials, focusing on solution-processed materials such as colloidal quantum dots and metal nanoparticles. These devices exhibit phenomena such as absorption of ultraviolet light, plasmonic enhancement of absorption, size-based spectral tuning, multiexciton generation, and charge carrier storage in surface and interface traps. |
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RPLAB @ gujma @ |
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684 |
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