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Author Usmani, Imam; Clausen, Christoph; Bussières, Félix; Sangouard, Nicolas; Afzelius, Mikael; Gisin, Nicolas
Title Heralded quantum entanglement between two crystals Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue 4 Pages 234-237
Keywords fromIPMRAS
Abstract (up) Quantum networks must have the crucial ability to entangle quantum nodes. A prominent example is the quantum repeater, which allows the distance barrier of direct transmission of single photons to be overcome, provided remote quantum memories can be entangled in a heralded fashion. Here, we report the observation of heralded entanglement between two ensembles of rare-earth ions doped into separate crystals. A heralded single photon is sent through a 50/50 beamsplitter, creating a single-photon entangled state delocalized between two spatial modes. The quantum state of each mode is subsequently mapped onto a crystal, leading to an entangled state consisting of a single collective excitation delocalized between two crystals. This entanglement is revealed by mapping it back to optical modes and by estimating the concurrence of the retrieved light state. Our results highlight the potential of crystals doped with rare-earth ions for entangled quantum nodes and bring quantum networks based on solid-state resources one step closer.
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Call Number RPLAB @ gujma @ Serial 793
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Author Pile, David
Title How many bits can a photon carry Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue 1 Pages 14-15
Keywords fromIPMRAS
Abstract (up) Quantum physics offers a way to enhance the amount of information a photon can carry, with potential applications in optical communication, lithography, metrology and imaging.
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Notes View from... OSA Frontiers in Optics 2011: How many bits can a photon carry? Approved no
Call Number RPLAB @ gujma @ Serial 780
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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 Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 5 Pages 399-405
Keywords fromIPMRAS
Abstract (up) 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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Call Number RPLAB @ gujma @ Serial 842
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Author Smith, Devin H.; Gillett, Geoff; de Almeida, Marcelo P.; Branciard, Cyril; Fedrizzi, Alessandro; Weinhold, Till J.; Lita, Adriana; Calkins, Brice; Gerrits, Thomas; Wiseman, Howard M.; Nam, Sae Woo; White, Andrew G.
Title Conclusive quantum steering with superconducting transition-edge sensors Type Journal Article
Year 2012 Publication Nature Communications Abbreviated Journal Nat. Comm.
Volume 3 Issue 625 Pages 6
Keywords fromIPMRAS
Abstract (up) Quantum steering allows two parties to verify shared entanglement even if one measurement device is untrusted. A conclusive demonstration of steering through the violation of a steering inequality is of considerable fundamental interest and opens up applications in quantum communication. To date, all experimental tests with single-photon states have relied on post selection, allowing untrusted devices to cheat by hiding unfavourable events in losses. Here we close this 'detection loophole' by combining a highly efficient source of entangled photon pairs with superconducting transition-edge sensors. We achieve an unprecedented ~62% conditional detection efficiency of entangled photons and violate a steering inequality with the minimal number of measurement settings by 48 s.d.s. Our results provide a clear path to practical applications of steering and to a photonic loophole-free Bell test.
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Call Number RPLAB @ gujma @ Serial 768
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Author Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei
Title Experimental quantum teleportation of a two-qubit composite system Type Journal Article
Year 2006 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 2 Issue 10 Pages 678-682
Keywords fromIPMRAS; quantum teleportation
Abstract (up) Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols
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Call Number RPLAB @ gujma @ Serial 795
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Author Tassin, Philippe; Koschny, Thomas; Kafesaki, Maria; Soukoulis, Costas M.
Title A comparison of graphene, superconductors and metals as conductors for metamaterials and plasmonics Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue 4 Pages 259-264
Keywords fromIPMRAS
Abstract (up) Recent advancements in metamaterials and plasmonics have promised a number of exciting applications, in particular at terahertz and optical frequencies. Unfortunately, the noble metals used in these photonic structures are not particularly good conductors at high frequencies, resulting in significant dissipative loss. Here, we address the question of what is a good conductor for metamaterials and plasmonics. For resonant metamaterials, we develop a figure-of-merit for conductors that allows for a straightforward classification of conducting materials according to the resulting dissipative loss in the metamaterial. Application of our method predicts that graphene and high-Tc superconductors are not viable alternatives for metals in metamaterials. We also provide an overview of a number of transition metals, alkali metals and transparent conducting oxides. For plasmonic systems, we predict that graphene and high-Tc superconductors cannot outperform gold as a platform for surface plasmon polaritons, because graphene has a smaller propagation length-to-wavelength ratio.
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Call Number RPLAB @ gujma @ Serial 790
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Author Xu, XinAn; Wong, Chee Wei
Title Quantum optics: Correlations on a chip Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue Pages 75-76
Keywords fromIPMRAS
Abstract (up) Researchers have developed a semiconductor structure capable of supporting quantum correlations between photons and strong single-photon nonlinearities, thus paving the way for the development of chip-based devices for quantum secure communications and quantum information processing.
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Call Number RPLAB @ gujma @ Serial 782
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Author Gao, Jie; McMillan, James F.; Wong, Chee Wei
Title Nanophotonics: Remote on-chip coupling Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue 1 Pages 7-8
Keywords fromIPMRAS
Abstract (up) Scientists have demonstrated strongly coupled photon states between two distant high-Q photonic crystal cavities connected by a photonic crystal waveguide. Remote dynamic control over the coupled states could aid the development of delay lines, optical buffers and qubit operations in both classical and quantum information processing.
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Call Number RPLAB @ gujma @ Serial 779
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Author Ghali, Mohsen; Ohtani1, Keita; Ohno, Yuzo; Ohno, Hideo
Title Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field Type Journal Article
Year 2012 Publication Nature Communications Abbreviated Journal Nat. Comm.
Volume 3 Issue 661 Pages 6
Keywords fromIPMRAS
Abstract (up) Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.
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Call Number RPLAB @ gujma @ Serial 769
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Author Kumar, Sushil; Wang I. Chan, Chun; Hu, Qing; Reno, John L.
Title A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue Pages
Keywords fromIPMRAS
Abstract (up) Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~ω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9ω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser.
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Call Number RPLAB @ gujma @ Serial 836
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